TRANSVERSE BONE TRANSPORT OSTEOGENESIS: A NEW LIMB SALVAGE

TECHNIQUE FOR THE TREATMENT OF DISTAL RADIAL OSTEOSARCOMA IN DOGS

By

CARL T. JEHN

A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT

OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE

UNIVERSITY OF FLORIDA

2006

Copyright 2006

by

Carl T. Jehn

To Walter for his courage, spirit, and the sacrifice he made for the greater good.

ACKNOWLEDGMENTS

In addition to my supervisory committee, I would like to thank Gary Sinkus

(Precision Tool & Engineering) for his ideas and contributions to this project. I thank

Wendy Conley for all of her hard work and help with development and data collection. I

thank Hall Griffin for his input on developing the hardware used. I thank Kristin Kirkby

for helping with the logistics of writing my thesis. I thank Nelly Amador for all of her

help and continued support.

iv

TABLE OF CONTENTS page

ACKNOWLEDGMENTS ................................................................................................. iv

LIST OF TABLES............................................................................................................ vii

LIST OF FIGURES ......................................................................................................... viii

ABSTRACT....................................................................................................................... ix

CHAPTER

1 CURRENT TREATMENT OPTIONS FOR DOGS AFFECTED WITH APPENDICULAR OSTEOSARCOMA ......................................................................1

Canine Osteosarcoma ...................................................................................................1 Amputation ...................................................................................................................3 Limb Salvage Procedures .............................................................................................3

Cortical Bone Allograft Implantation....................................................................5 Pasteurized Bone Autografting..............................................................................7 Distraction Osteogenesis and Bone Transport ......................................................8 Endoprostheses ....................................................................................................10

Radiation.....................................................................................................................10 Chemotherapy.............................................................................................................13 Conclusion ..................................................................................................................15

2 TRANSVERSE BONE TRANSPORT OSTEOGENESIS: A MORPHOLOGIC COMPARISON FOR TWO TECHNIQUES FOR LIMB SALVAGE FOR THE TREATMENT OF DISTAL RADIAL OSTEOSARCOMA IN DOGS....................20

Limb Salvage ..............................................................................................................20 Bone Transport Osteogenesis ..............................................................................20 Longitudinal Bone Transport Osteogenesis ........................................................21 Transverse Ulnar Bone Transport Osteogenesis .................................................22 Objectives and Hypothesis ..................................................................................23

Materials and Methods ...............................................................................................23 Angle and Direction of Deviation .......................................................................29 Distraction Distance ............................................................................................29 Fill Ratio..............................................................................................................30

v

Statistical Analysis of Parameters .......................................................................30 Comparison of the mean angles of deviation using an unpaired t-test.........30 Comparison of the directions of deviation using a chi-squared test ............30 Comparison of the mean distraction distances using unpaired t-test ...........31 Comparison of the mean fill ratios using unpaired t-test .............................31

Results.........................................................................................................................31 Measured Parameters...........................................................................................31 Fixator Construction, Application, and Distraction ............................................33

Discussion...................................................................................................................35 Conclusion ..................................................................................................................43

3 TRANSVERSE BONE TRANSPORT OSTEOGENESIS: A LIVE DOG MODEL FOR THE TREATMENT OF DISTAL RADIAL OSTEOSARCOMA IN DOGS ....................................................................................................................50

Bone Transport Osteogenesis .....................................................................................50 Transverse Ulnar Bone Transport Osteogenesis .................................................50 Objectives ............................................................................................................51 Hypotheses ..........................................................................................................51

Materials and Methods ...............................................................................................51 Surgical Technique, Fixator Construction, and Distraction ................................52 Subjective and Objective Assessment .................................................................53

Results.........................................................................................................................53 Daily Subjective Assessment ..............................................................................53 Radiographic and CT Analysis............................................................................54 Houndsfield Units................................................................................................55 Cross-sectional Area of Regenerate Bone ...........................................................56

Discussion...................................................................................................................56 Conclusion ..................................................................................................................60

LIST OF REFERENCES...................................................................................................62

BIOGRAPHICAL SKETCH .............................................................................................69

vi

LIST OF TABLES

Table page 1-1. Median survival times in dogs with appendicular osteosarcoma ...............................19

2-1. Angle and direction of deviation ................................................................................47

2-2. Distraction distance ....................................................................................................48

2-3. Fill ratio ......................................................................................................................48

2-4. Cross-sectional area of intact and regenerate bone ....................................................49

3-1. Houndsfield unit assessment ......................................................................................61

3-2. Day-45 fill ratio ..........................................................................................................61

3-3. Day-94 fill ratio ..........................................................................................................61

vii

LIST OF FIGURES

Figure page 1-1. Lateral radiograph of a dog’s distal forelimb ...........................................................16

1-2. Serial radiographs of a dog with a distal radial osteosarcoma .................................17

1-3. Longitudinal radial bone transport osteogenesis ......................................................17

1-4. Radial endoprosthesis ...............................................................................................18

1-5. Computed tomography image of an osteosarcoma...................................................18

2-1. The LM and RM constructs placed on each limb.....................................................44

2-2. The positioning trough afforded duplicate limb position .........................................44

2-3. The reeling motors....................................................................................................45

2-4. Each loop of distraction suture is anchored to its respective reeling motor. ............45

2-5. UPOR point marks the ulnar point of reference .......................................................46

2-6. The blue shaded area outlined in black denotes the extrapolated cross-sectional area of the regenerate bone once distraction is completed.......................................46

viii

Abstract of Thesis Presented to the Graduate School

of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Science

TRANSVERSE BONE TRANSPORT OSTEOGENESIS: A NEW LIMB SALVAGE TECHNIQUE FOR THE TREATMENT OF DISTAL RADIAL OSTEOSACROMA IN

DOGS

By

Carl T. Jehn

May 2006

Chair: Dan Lewis Major Department: Veterinary Medicine

Appendicular osteosarcoma occurs in more than 6,000 dogs per year in the United

States alone. Although amputation has traditionally been the treatment of choice, limb

salvage procedures are gaining popularity. Several methods of limb salvage have been

described for dogs including bone transport osteogenesis (BTO), a specific application of

distraction osteogenesis in which a segment of bone is slowly moved across an osseous

defect, forming new regenerate bone in its wake. Although this technique circumvents

many of the complications encountered with other limb salvage procedures, current

methods of BTO involve prolonged convalescence. The purpose of our study was to

develop a novel means of performing BTO that would dramatically reduce recovery time

and be feasible in a clinical setting.

Once the necessary instrumentation and surgical techniques for the procedure were

developed, the antibrachii and manus were harvested from ten healthy, skeletally mature

canine cadavers. Transverse BTO was performed on each limb using one of two surgical

ix

techniques: RM and LM. Once the procedure was complete, CT images of each limb

were analyzed to assess accuracy of bone transport and to determine any statistical

differences in results of the two techniques. Parameters used for assessing outcome were

angle of deviation, direction of deviation, distance of distraction, and fill ratio.

Of the four parameters measured, only direction of deviation differed significantly

for RM versus LM. There was a tendency for the RM group to position the transport

segment caudally, and for the LM group to do so cranially. None of the remaining

parameters differed significantly between the two groups. Quantitatively, both techniques

proved effective at completing the bone transport process. However, considerable

qualitative differences were noted as the RM group showed many advantages over the

LM group. Both surgical techniques provided an effective means of performing

transverse BTO; however, the RM group was more versatile and more suitable in a

clinical setting. Transverse BTO offers many of the benefits of conventional BTO, but

would allow faster resolution of subtotal radial defects. This is particularly important in

performing limb salvage in dogs with osteosarcoma, where minimizing convalescence

and maximizing quality of life is a priority.

x

CHAPTER 1 CURRENT TREATMENT OPTIONS FOR DOGS AFFECTED WITH

APPENDICULAR OSTEOSARCOMA

Canine Osteosarcoma

Osteosarcoma is estimated to occur in more than 8,000 dogs per year in the United

States.1 Although amputation has traditionally been used as a palliative treatment for

affected dogs, treatment modalities including chemotherapy, radiation, and limb salvage

are constantly evolving. Osteosarcoma is the most-common primary bone neoplasia

affecting dogs and accounts for nearly 6% of all canine malignancies.2 Large and giant

breeds dogs are more commonly affected, and males are more commonly affected than

females, by a ratio of 1.5:1.3-6 Although osteosarcoma has been reported in dogs as young

as 6 months,7 there is a bimodal age peak incidence at 3 and 8 years.8 If left untreated,

most dogs are euthanatized within 3 months of diagnosis.5,8

Osteosarcomas are classified as simple (bone formed in collagenous matrix),

compound (both bone and cartilage are present), or pleomorphic (anaplastic, with only

small islands of osteoid present).9 Classification has also been based on cell type and

activity (osteoblastic, chondroblastic, or fibroblastic); radiographic appearance (lytic,

sclerotic, or mixed); or origin (central, juxtacortical, or periosteal).9 Clinically,

osteosarcoma is characterized by aggressive local bone destruction with invasion into the

surrounding soft tissues.9 With the exception of those arising in bones of the skull,

osteosarcomas rapidly metastasize to the lung.9 Seventy-five percent of the tumors arise

in the metaphyseal region of the long bones.5,8,9 The remaining 25% occur in the axial

1

2

skeleton or soft tissues.5,8,10 The distal radius is the most common site of occurrence in

dogs.5,8,9 Other less-common appendicular sites of occurrence include the proximal

humerus, distal ulna, proximal or distal femur, and the proximal or distal tibia.

Osteosarcomas are typically rapidly growing, painful tumors.9 Grossly, central or

interosseous osteosarcomas have a gray-white appearance and contain variable amounts

of mineralized bone.9 Large, pale areas surrounded by zones of hemorrhage (areas of

infarction) and irregular areas of hemorrhage are common in rapidly growing

intramedullary neoplasms.9 Neoplastic tissue tends to fill the medullary cavity of the

metaphysis and can extend proximally and distally. Typically, however, this extension

does not penetrate metaphyseal growth plates or articular cartilage to enter the joint

space.9 Cortical bone is destroyed with varying amounts of new reactive bone

surrounding the area, while neoplastic cells penetrate and undermine the periosteum.9

New bone formation may be abundant and widespread or minimal.9

Usually there is a lack of radiographic evidence of metastasis at the time of initial

diagnosis.1 Common sites of metastasis are the lungs and other skeletal tissues.

Metastasis has also been reported in the visceral organs, brain, and subcutaneous tissues.1

Although, fewer than 10% of affected dogs have radiographically detectible metastasis at

the time of presentation, 90% of dogs die of metastatic disease within 1 year of diagnosis

if not treated with chemotherapy and surgery.5,8 This suggests that micrometastatic

disease is usually present in the lungs at the time of diagnosis, possibly in a dormant

state.5,8 Depending on the location and stage of the disease, surgery, chemotherapy, and

radiation therapy can be used in a variety of treatment protocols for palliative therapy or

to increase survival time.

3

Amputation

Amputation is the most-common surgical treatment for appendicular osteosarcoma,

and is recommended for most dogs affected with osteosarcoma. Limb amputation

provides palliation of pain, relatively short anesthesia times, low risk of surgical and

post-operative complications, short convalescence, lower costs than limb salvage, and

limited risk of tissue contamination or local recurrence due to incomplete margins.11

Some owners, however, are reluctant to pursue amputation.12,13 This is unfortunate, since

most dogs (including the larger breeds) function well after amputation; and owners who

elect amputation are typically satisfied with their pet’s quality of life after the

procedure.11,14 Body size, age, and fore versus hind limb do not reportedly influence rate

of recovery, owner satisfaction, or ability of a dog to adapt following amputation.12 Poor

candidates for amputation are those afflicted with concurrent orthopedic or neurologic

problems, or severe obesity.15

Limb Salvage Procedures

Limb salvage procedures attempt to resect the primary lesion and preserve a

functional, pain-free limb.16 These procedures are often considered when adverse

circumstances preclude amputation or owners refuse. Limb salvage procedures described

for treating appendicular osteosarcoma in dogs include implantation of frozen cortical

bone allografts,17 pasteurized cortical bone autografts,18,19 endoprosthesis,20 and bone

transport osteogenesis.21,22 Most limb salvage procedures performed to treat

osteosarcoma in dogs involve lesions affecting the distal radius.16 Although local tumor

recurrence after resection ranges from 20 to 40% in dogs undergoing limb salvage

procedures,14,16,17 this does not appear to decrease survival rates.11,17 Previous studies

show that, with adjunctive chemotherapy, survival rates do not differ significantly for

4

dogs undergoing amputation versus dogs undergoing limb salvage procedures.11,17

Methods to prevent local recurrence include systemic, regional or local pre- and post-

surgical chemotherapy, and/or pre-operative radiation therapy.1

Proper biopsy techniques should be used when considering limb salvage

procedures. Techniques include open incisional biopsy, closed (hypodermic or Jamshidi)

biopsy, and trephine (Michelle) biopsy.23-25 A closed-needle technique using a Jamshidi

biopsy instrument can help minimize the risk of complications such as hematoma

formation, infection, and pathologic fractures.25 Biopsy site selection should be based on

evaluation of radiographs and consideration of subsequent treatments. Biopsy site

selection is critical for lesions of the distal radius. Failure to place the biopsy tract in the

correct location can compromise successful limb salvage. Biopsies of distal radial lesions

should be performed at the craniolateral aspect of the distal antebrachium and should not

include biopsy of the distal ulna unless the primary tumor is in the ulna. If owners

express interest in limb salvage, the veterinarian should consider referral for the biopsy

procedure. Ideally, the biopsy should be performed by the same surgeon who will

perform the limb salvage surgery.

The clinician should review the radiographs before the biopsy, and have the

radiographs available for reference during the procedure. The center of the radiographic

lesion should be targeted as the site most likely to yield a diagnosis.25 Areas of dense

reactive bone should be avoided.25 The skin incision should be as small as possible and

positioned in a location where the biopsy tract and any potentially seeded tumor cells can

be easily resected en bloc with the tumor at the time of surgery.25

5

Proper case selection for limb salvage is essential for a favorable outcome. Case

eligibility for limb salvage surgery is determined by several criteria. Tumors that

radiographically involve greater than 50% of the bone’s length are not amenable to

adequate resection and leaving sufficient tissue for reconstruction.26 Extensive invasion

into adjacent soft tissues (especially the palmar nerves, vessels and tendons) will not

allow adequate resection with concurrent preservation of essential neurovascular bundles

to the paw.11,26 Unstable or catastrophic pathologic fractures result in local tumor

dissemination and seeding of tumor cells, making it difficult to achieve complete excision

of tumor-contaminated tissue.27 Small pathologic fractures or telescoping collapse of lytic

bone are commonly observed on preoperative radiographs however, these minor

pathologic fractures do not preclude limb salvage. Local infection and radiographic

evidence of metastasis are also circumstances under which limb sparing is not

recommended.7,11,26 When in doubt, it is best to seek the opinion of a specialist who

regularly performs limb salvage surgery to ensure appropriate case eligibility.

Cortical Bone Allograft Implantation

The most-common limb salvage procedure used to treat distal radial osteosarcoma

is cortical-bone allograft implantation.16,17 In this procedure a fresh-frozen (not

preserved) cortical bone segment is cut to match the length of the excised-tumor segment,

and is affixed to the host bone using a bone plate and screws.17,26 Cortical bone allografts

have been used to salvage the limbs of dogs affected with osteosarcoma of the distal

radius, proximal humerus, ulna, and scapula; however, only the distal radius location has

been widely successful.16 Dogs usually attempt to bear weight on the affected limb within

24 hours of surgery, and gradually regain normal limb function within one to two months

following surgery.11,16,17,26 Reported median survival times for this procedure range from

6

240-487 days depending on the presence of local infection. Non-tumor related

complications associated with cortical bone allograft limb sparing procedures include

infection, fracture of the host bone, rejection of the allograft, non-union, or implant

loosening or failure.16,28

Infection is the most common of these complications.16,28 Approximately half the dogs

undergoing cortical bone allograft implantation develop an infection at some time

following surgery.16 Factors contributing to the high rate of infection include extensive

surgical resection, use of a nonviable cortical bone allograft and large metallic implants,

infusion of the allograft marrow cavity with bone cement to improve screw purchase,

paucity of adjacent soft tissues to supply sufficient vasculature in the distal extremity,

self-trauma and the administration of adjunctive chemotherapy.16,28,29 Complete

resolution of infection is extremely difficult due to bacteria residing in the allograft and

bone cement as well as incorporation into the implant biofilm.16 Although 75% of

infections can be managed with basic wound management, bandaging and antibiotic

therapy, the remaining 25% require additional surgery. Resolution of the clinical signs

relating to the infection is sometimes achieved by removal of the allograft or by

placement of antibiotic-impregnated cement beads.30 For dogs that do not respond to

these approaches, limb amputation may be the only remaining option.16 It has been noted

that dogs that develop infection at the surgical site have significantly longer survival

times and higher local control rates than dogs that do not develop infections.16,31,32 The

reason for this difference in survival and local tumor control is believed to have an

immunologic basis.16 Post-operative infection is not, however, desirable as the quality of

life for dogs with infected allografts are generally compromised by periods of pain,

7

lameness and drainage and the necessity for continual bandage changes and wound care.

Amputation is elected in some dogs to resolve the adverse sequels associated with

infection.31

Pasteurized Bone Autografting

Pasteurized tumoral autografting involves the temporary removal (ostectomy) and

pasteurization of the affected bone segment. The treated bone segment is then replaced as

an orthotopic autograft and stabilized with a bone plate and screws.18,19 The

pasteurization process requires placing the bone segment into a sealed container filled

with sterile saline preheated to 65o C.19 The container is kept in a thermostat controlled

water bath and maintained at 65o C for 40 minutes.19 Pasteurization is advantageous in

that all the cellular constituents of the excised bone segment are killed, but unlike

autoclaving which is pressurized and done at a higher temperature, important proteins,

such as bone morphogenic proteins, are not damaged. Dogs undergoing pasteurized

autograft limb salvage have survival times and complication rates comparable to dogs

undergoing cortical bone allograft and bone transport osteogenesis limb salvages.18 When

used in conjunction with adjuvant chemotherapy, mean and median survival times in a

small cohort of patients in which this technique was used were 531 and 324 days,

respectively with overall survival rates of 100%, 50% and 44% at 6, 12, and 18 months,

respectively.18 While this technique eliminates the need for establishing and maintaining

a bone bank and has the advantage of proper fit to the recipient site, pasteurization

increases the duration of surgery and screw placement in the pasteurized bone segment

can be limited by tumor erosion.18

8

Distraction Osteogenesis and Bone Transport

The techniques for performing distraction osteogenesis and bone transport

osteogenesis were originally developed by Professor Ilizarov.33 Ilizarov found that

gradual traction creates stresses that can stimulate and maintain the regeneration of active

growth of certain tissues. Persistent traction causes tissues to become metabolically

activated, resulting in an increase in the proliferative and biosynthetic functions. These

processes are dependent upon adequate blood supply to the tissues being elongated and

the stimulating effect of functional weight-bearing.33 Ilizarov described how to use this

biologic phenomenon to control healing and shape forming of bone and soft tissue in

order to treat traumatic and pathologic musculoskeletal abonrmalities.33

Bone transport osteogenesis is a specific application of distraction osteogenesis.

Bone transport osteogenesis is used to replace large segmental bone defects and has been

utilized clinically in both animals and humans.21,22,29,34-38 This technique involves slowly

moving an intercalary segment of healthy normal bone into an adjacent defect. As the

transport segment is moved, new regenerate bone forms in the trailing distraction

pathway. Optimal bone formation is obtained using a distraction rate of approximately 1

mm per day.29,36 The regenerate bone acts as a highly vascularized autogenous graft

which remodels into lamellar bone. In addition to being successfully used in dogs and

humans for repairing defects related to trauma and infection,37,38 this technique has been

successfully used to resolve subtotal defects of the distal radius and tibia of dogs after

tumor resection.21,22

Many of the complications associated with the use of cortical bone allografts can be

avoided when bone transport osteogenesis is used to replace the resultant bone defect.

With autogenous bone, concerns regarding failure or loosening of internal implant

9

components, graft rejection, transmission of infectious disease, and harbored bacterial

infections are either decreased or eliminated.21 Previous research has shown that there

were fewer complications (such as fracture and infection) associated with the use of bone

transport osteogenesis (33%) than with traditional segmental defect replacement (60%).38

The well-vascularized regenerate bone is highly resistant to infection.39 The costs and

inconvenience of establishing and maintaining a bone bank is also eliminated.21

Local recurrence of the tumor is still a concern; however, proper case selection,

administration of adjuvant chemotherapy, and adherence to sound surgical oncologic

technique helps to minimize this potential risk.11,16,21,23,40 While necrosis of the regenerate

bone has been reported, this complication may have been related to the administration of

pre-operative radiation.21 A recent study has shown that the administration of cisplatin

during the distraction and docking process does not adversely affect regenerate bone

formation.41

The major disadvantage of utilizing bone transport osteogenesis for limb sparing is

the relatively long period of time that the fixator must be maintained. This is particularly

true when dealing with longer segmental defects. Previously reported applications of

bone transport osteogenesis for limb salvage in dogs diagnosed with osteosarcoma

utilized a rate of 1 mm/day and a rhythm of 0.25 mm/6 hours.21 Therefore, a large defect

may require a substantial amount of time for adequate distraction and consolidation; 100

to147 days of distraction was reported in cases without local recurrence.21 A technique

known as double bone transport has been recently reported as a treatment for tibial

osteosarcoma in dogs.22 This technique involves the simultaneous distraction of two

10

transport segments allowing a defect to be filled more quickly than with a single transport

segment.

Endoprostheses

A radial endoprosthesis (Veterinary Orthopedic Implants, Buffalo Grove, Illinois)

has been developed as an alternative to cortical bone allografting. This prosthesis couples

a specially designed limb-sparing bone plate with a metal spacer that spans the defect

between the radial osteotomy site and the radiocarpal bone. Advantages of this technique

include lack of the need for a bone bank, less technical difficulty, and shorter operative

time.20 Preliminary results of this technique also indicate that endoprosthesis may be

associated with a lower infection rate and that the infections may be more superficial and

easier to resolve.20 A theoretical disadvantage is that the host bone is not incorporated

into the endoprosthesis. This disadvantage maybe negated, however, by the relatively

short survival times typical of most dogs affected with osteosarcoma. In addition, such

concerns are not unique to endoprosthesis as there is also some question as to whether or

not cortical allografts are effectively incorporated and replaced by recipient bone as well.

Radiation

Radiation therapy has been used extensively in the treatment of appendicular

osteosarcoma.31,42 Radiation therapy administered prior to surgery, when given in

moderate doses (32 Gy) , has been shown to significantly reduce local tumor recurrence

rate following cortical allograft limb-sparing.42 Previous studies, however, have shown

that pre-operative radiotherapy at higher doses (36-52 Gy) causes unacceptable rates of

fixation device failure and graft complications.31 As survival is often limited by distant

metastasis rather than local recurrence, pre-operative radiation has not been shown to

increase long-term survival.42

11

Palliative radiation therapy is another alternative to amputation and limb salvage

procedures. This treatment can effectively palliate the pain associated with appendicular

osteosarcoma.43-45 Previously described palliative protocols involve three fractions of 10

Gy given at 0, 7, and 21 days.43,44 A more effective protocol has recently been described

which employs four 8 Gy fractions with one fraction given every seventh day.45 This new

protocol eliminates the two week gap between the seventh and twenty-first day which has

been shown to provide a higher response rate and longer survival times.45 Using the four

fraction protocol resulted in a 92%45 response rate versus 74%44 or 80%43 reported using

the three fraction protocol. The median duration of response using the four fraction

protocol is 95 days with a median survival time 313 days,45 much higher than that

observed using the previously described protocols.43,44

Recently, stereotactic radiosurgery (SRS) has been utilized to treat dogs with

appendicular osteosarcoma.46 Unlike fractional therapy, SRS delivers the entire radiation

treatment (approximately 30 Gy) via a single, large dose in a highly targeted manner.

The precise nature of SRS allows the delivery of a volume of radiation dose that is

conformed to the shape of the tumor target and damage to the normal surrounding tissues

is minimized by a steep dose gradient.47 Advantages of administering a single, large

fraction include fewer anesthetic episodes and possibly a greater biologic effect on tumor

tissue when compared to an equivalent total dose delivered in multiple (e.g. three 10 cGy)

fractions.48 Preliminary results with SRS in lower extremity tumors (radius and tibia)

have shown the ability to provide long-term local control (> 2 years), especially when it

is possible to surround the entire tumor with the 30 Gy isodose line during treatment

planning and when combined with chemotherapy.46 Currently, carboplatin (300 mg/m2)

12

is given intravenously just prior to SRS as a radiation sensitizer and carboplatin alone, or

in combination with doxorubicin, is given adjunctively during the convalescent period.

Upper extremity tumors (humerus and femur) have also been treated (unpublished data,

currently being evaluated for response) and may become the ideal application of SRS

since surgical limb sparing is not performed routinely in these tumor locations. The

prominent muscle mass present between the tumor and the skin in upper extremity

locations enables even larger radiation doses to be used without causing significant

radiation skin injury.

As with conventional radiation therapy, pathologic fracture may occur after

treatment since the quality of the bone structure is often compromised by tumor

associated osteolysis. The limiting factors of SRS therapy for appendicular osteosarcoma

are the size of the tumor and the condition of the bone at the time of therapy, as adequate

coverage of large tumors with the 30 Gy isodose line is not always possible and the risk

of pathologic fracture remains after treatment. Thus, SRS should ideally be used to treat

appendicular osteosarcomas that are relatively small and have caused minimal bone

destruction.

An additional limb sparing technique utilizing intra-operative extracorporeal

irradiation has been utilized in a small number of dogs with osteosarcoma located at sites

other than the distal radius or ulna.1 Following surgical isolation of the tumor from the

surrounding soft tissues, an osteotomy is performed through an unaffected portion of the

bone proximal or distal to the tumor site. While maintaining joint capsule attachments,

the neoplastic bone segment is rotated out of the surgical field and a single dose of 70 Gy

13

is delivered. The irradiated bone segment is replaced in situ and the osteotomy stabilized

with internal fixation.1

Chemotherapy

Chemotherapy has been used primarily as an adjunct to surgery to help control

metastasis. Previous reports have shown that survival time in dogs with appendicular

osteosarcoma can be improved by adjuvant chemotherapy. Protocols and reported median

survival times are outlined in Table 1-1.8,16,32,40,49-58

Cisplatin has been shown to prolong the disease free interval in dogs and remains a

commonly utilized chemotherapeutic agent for treating dogs with osteosarcoma.41

Myelosupression and nephrotoxicity are the most common side effects noted with

cisplatin therapy.59 Using cisplatin or doxorubicin as a single agent as adjunctive

treatment to amputation has yielded median survival times ranging from 262 days50 to

366 days51, one year survival rates ranging from 3750,54 to 46%,41 and two year survival

rates ranging from 1650 to 26%.54 These results are a significant improvement in survival

over amputation alone which has been reported to yield a median survival time of 102-

175 days, a one year survival rate of 12% and a two year survival rate of 2%.8,49,54

Carboplatin is an alternative chemotherapeutic agent that has shown to be at least as

efficacious as cisplatin.56 Carboplatin is a second-generation platinum compound that,

unlike cisplatin, does not induce nephrotoxicity and is easier to administer. Although

initially some combination protocols (e.g., cisplatin and doxorubicin) appeared to offer

survival benefit over single agent therapy,60 recent evidence indicates that combination

protocols do not increase survival.55,57,58

Other chemotherapeutic agents that have been evaluated include cisplatin-

impregnated open cell polylactic acid polymer (OPLA-Pt) and liposome-encapsulated

14

muramyl tripeptide-phosphatidylethanolamine (liposome/MTP-PE).61,62 Cisplatin-

OPLA-Pt has also been placed in the wound bed adjacent to allografts in limb salvage

cases to reduce local tumor recurrence and has been reported to reduce local recurrence

by 10%.61 Liposome/MTP-PE has also been shown to be effective at treating dogs with

osteosarcoma.62 In a study by MacEwen et al.,62 dogs treated by amputation and

intravenous liposome/MTP-PE had a median survival time of 222 days while those

treated with empty liposomes had a median survival time of only 77 days. Aside from

mild elevations in body temperature (1-2oC) for 2-6 hours post injection, treatment with

liposome/MTP-PE was well tolerated.

Use of chemotheraputic agents in dogs with measurable pulmonary metastatic

osteosarcoma has also been evaluated. 63 Findings indicated that single-agent therapy

with either cisplatin, doxorubicin, or mitoxantrone was ineffective for the treatment of

measurable metastatic disease, providing a median survival time of only 61 days (range,

14 to 192 days).63

Although surgical management of the primary tumor is often elected, many owners

of affected dogs do not perceive the outcome of surgery (with or without chemotherapy)

to be worthwhile. In these instances, medical management of the primary tumor may be

elected. Medical management typically consists of daily treatment with a non-steroidal

anti-inflammatory drug (NSAID) to alleviate the associated bone pain. When lameness

worsens and is refractory to treatment with NSAID, oral formulations of various opioids

may provide more effective pain control. In human patients, osteolytic bone diseases (eg.

bone metastases and hypercalcemia of malignancy) are often treated with a class of drugs

called bisphosphonates. 64 Bisphosphonates reduce bone resorption by inhibiting

15

osteoclast function.64 There is only one clinical report of the use of bisphosphonates in

dogs with spontaneously occurring osteosarcomas.65 In this report, alendronate was used

in efforts to palliate two cases of primary canine osteosarcoma, one affecting the tibia and

the other affecting the maxilla. According to the report, both dogs remained comfortable

surviving for 12 and 10 months, respectively. However, since there were only two dogs

studied, there was no control group and since survival was the only parameter measured,

it is difficult to conclude what benefit alendronate provided. This case report along with

evidence for efficacy in the treatment of various malignant bone diseases in humans has

prompted veterinary clinicians to treat some dogs affected by osteosarcoma with

bisphosphonates. Recently, the bisphosphonates alendronate, pamidronate and

zoledronate have been shown to inhibit canine osteosarcoma cell growth in vitro, raising

the possibility that bisphosphonates may also be helpful as adjunctive chemotherapeutic

agents.66-68

Conclusion

Amputation in conjunction with chemotherapy continues to be the most common

and effective form of treatment available for dogs affected with appendicular

osteosarcoma;5,41 however, new approaches are continuing to be developed which

should prolong survival times and decrease morbidity. As the efficacy of treatment

modalities such as limb salvage techniques, chemotherapy, and radiation are established,

the level of practitioner and owner interest will grow.

16

Figure 1-1. Lateral radiograph of a dog’s distal forelimb following cortical bone allograft implantation for the treatment of a distal radial osteosarcoma.

17

Figure 1-2. Serial radiographs of a dog with a distal radial osteosarcoma undergoing bone transport osteogenesis in order to replace a radial defect with regenerate bone. The radiographs were obtained at A) 14, B) 21, C) 28, and D) 35 days following surgery. Note the movement of the transport segment distally and the subsequent regenerate bone formation.

Figure 1-3. Longitudinal radial bone transport osteogenesis. A) Post-operative. B) Corresponding radiograph of a forelimb undergoing longitudinal radial bone transport osteogenesis.

18

Figure 1-4. Radial endoprosthesis. A) Intraoperative photograph of a radial endoprosthesis being implanted during a limb salvage procedure. B) The corresponding lateral post-operative radiograph following this limb sparing procedure.

Figure 1-5. Computed tomography image of an osteosarcoma of the distal tibia of a dog. The 75% isodose line (30 Gy) is shown in blue, the 50% isodose line (20 Gy) in red and the 25% isodose line (10 Gy) in green. The isodose lines represent three-dimensional dose shells surrounding the target.

19

Table 1-1. Median survival times in dogs with appendicular osteosarcoma Survival (days) Chemotheraputic agent Reference 102 119 134 134 165 168 175

Amputation alone

49 50 8 51 52 53 54

262/282 275 290 300

Amputation and chemotherapy Cisplatin Carboplatin alone or with doxorubicin Cisplatin Cisplatin and doxorubicin

50 32 53 54

300 301 321 330/345 366

Cisplatin and doxorubicin Cisplatin Carboplatin Cisplatin and doxorubicin Doxorubicin

55 49 56 52 51

Amputation or limb-sparing and chemo 235 320 322 223 274 480

Carboplatin and doxorubicin Carboplatin and doxorubicin Cisplatin Non-infected limb-sparing and chemo Carboplatin or carboplatin and doxorubicin Cisplatin Infected limb-sparing and chemo Carboplatin or carboplatin and doxorubicin

57 58 40 32 16 32

487 Cisplatin 16

CHAPTER 2 TRANSVERSE BONE TRANSPORT OSTEOGENESIS: A MORPHOLOGIC COMPARISON FOR TWO TECHNIQUES FOR LIMB SALVAGE FOR THE

TREATMENT OF DISTAL RADIAL OSTEOSARCOMA IN DOGS

Limb Salvage

Although amputation is the most common method of treatment for appendicular

osteosarcoma, limb salvage procedures also provide an effective alternative means for

primary tumor removal.5,11 Limb salvage procedures may be considered when

circumstances preclude, or owners decline, amputation. Local tumor recurrence after

resection ranges from 20-40% in dogs undergoing limb salvage;14,16,17 however, studies

have shown that when performed in conjunction with chemotherapy, there is no

significant difference in survival rates between dogs undergoing limb salvage and dogs

undergoing amputation.11,17 Limb salvage procedures described for the treatment of dogs

with appendicular osteosarcoma utilize implantation of frozen cortical allografts,17

pasteurized autografts,18,19 endoprostheses,20 and bone transport osteogenesis.21,22

Bone Transport Osteogenesis

Bone transport osteogenesis is a specific application of distraction osteogenesis

which has been successfully used in dogs as a technique for the replacement of large sub-

total distal radial and tibial defects resulting from tumor resection.21,22 Bone transport

osteogenesis is a process in which a healthy, intercalary bone segment is sequentially

moved across an adjacent defect forming new regenerate bone in its wake, filling the

defect.21,69 The regenerate bone behaves similarly to a highly vascularized autogenous

graft as it remodels into lamellar bone.21 Because bone transport osteogenesis utilizes

20

21

autogenous bone, the trepidations associated with traditional limb salvage techniques,

such as implant failure, implant loosening, graft rejection, and disease transmission are

diminished or eliminated.21 Regenerate bone is highly vascular and highly resistant to

infection.39 Bone transport osteogenesis has a nearly 30% lower complication rate in

comparison to traditional means of segmental defect repair.38 Complications of bone

transport osteogenesis include local tumor recurrence and necrosis of the regenerate

bone.21,22 Fortunately the risk of local recurrence can be kept to a minimum with proper

case selection, chemotherapy, and sound surgical oncologic technique and regenerate

bone necrosis is primarily associated with the administration of preoperative

radiation.11,16,21,23,40,69 The primary disadvantage of utilizing bone transport osteogenesis

for limb salvage is the relatively long period of time required to complete the process.

Longitudinal Bone Transport Osteogenesis

Previously reported applications of bone transport osteogenesis for dogs with distal

radial osteosarcoma utilized longitudinal transport of a proximal radial segment

(transportation in a proximal to distal direction) at a rate of 1 mm/day and a rhythm of

0.25 mm/6 hours.21,69 Consequently, large segmental defects required a substantial

amount of time to complete the distraction and consolidation process. A case series

evaluating dogs with distal radial osteosarcoma undergoing longitudinal bone transport

osteogenesis investigated by Tommasini et al reported 120 to147 days of distraction for

successful cases.21 A second case series done by Ehrhart et al reported a mean time of

123 days (range: 66-150 days) of distraction until docking and a mean time of 205 days

(range: 90-350 days) until frame removal.69 The time until frame removal accounts for

the time necessary for consolidation of the regenerate bone after docking.

22

A modification of this procedure, known as double bone transport has also been

reported for use in dogs affected with osteosarcoma of the tibia and involves the

simultaneous longitudinal transport of two bone segments at different rates allowing the

defect to be filled in less time than with a single transport segment.22 A case report

written by Rovesti et al., reported a time of 92 days of distraction and 162 days until

frame removal using this technique to produce 11 cm of regenerate bone in the distal

tibia.22 The proximal bone segment was distracted at a rate of 0.75 mm/day and the distal

bone segment was transported at 1.50 mm/day.22

Transverse Ulnar Bone Transport Osteogenesis

Transverse bone transport is a form of distraction osteogenesis in which the

transport segment is moved in a transverse plane relative to the dominant axis of the

bone. Transverse distraction osteogenesis was first described by Ilizarov when he applied

this technique to increase the transverse diameter of narrow bones and treat patients with

disorders resulting from chronic ischemia.33 Reports of using this technique by anyone

other than Ilizarov since that time are extremely limited however. A case report by

Aronson described the successful treatment of a subtotal defect in the proximal tibia

using transverse transport of the fibula.34 A technique similar to transverse transport

osteogenesis, known as multidimensional distraction, has also been applied in the field of

human craniofacial surgery and reconstruction.70,71 Like transverse bone transport,

multidimensional distraction transports segments of membranous bones of the

craniofacial skeleton in various directions in order to reconstruct or regenerate defects

within the human face and cranium.70,71 More recently, an experimental canine tibia

model was reported which quantitatively evaluated regenerating bone during transverse

transport.72 The findings of this study supported those originally reported by Ilizarov, that

23

osteogenesis and angiogenesis can occur when bone is transported in the transverse plane

and that the direction of osteogenesis is parallel to that of the distraction axis.72

Transverse bone transport osteogenesis is advantageous in that it may serve to

decrease convalescence when attempting to resolve large segmental bone defects in

locations with paired long bones.21,34,35,72 A detailed description regarding the clinical use

of transverse bone transport osteogenesis, outside of that which has been described by

Ilizarov, has not been reported in the human or veterinary litterature.72 The question of

how the devices should be applied when using transverse transport osteogenesis

remains.72 Consequently, there is a need for the development of appropriate, safe, and

functional devices that can be easily maintained for the time necessary to complete the

distraction process.72

Objectives and Hypothesis

The objectives of this chapter of the thesis were to develop the instrumentation and

surgical technique necessary to successfully perform transverse ulnar bone transport

osteogenesis, compare the accuracy and ease of two potential methods of transverse ulnar

bone transport osteogenesis (reeling motor construct vs. linear motor construct), and

evaluate each method’s potential as a viable treatment modality for limb salvage in dogs

with distal radial osteosarcoma. The hypothesis is that the ulnar transport segment will be

distracted into a more anatomic position with the reeling motor construct than with the

linear motor construct.

Materials and Methods

Both distal forelimbs were harvested, via transection at the distal humeral

metaphysis, from ten skeletally mature, large breed dogs (numbered 1-10) previously

euthanatized for reasons unrelated to this study. Radiographs were obtained to confirm

24

that the limbs had no musculoskeletal abnormalities prior to their inclusion into the study.

Each limb was labeled as right or left and designated a number corresponding to the

donor number (L1-L10, R1-R10). Limbs L1-L5 and R6-R10 were assigned to the reeling-

motor (RM) group and limbs R1-R5 and L6-L10 were assigned to the linear-motor (LM)

group.

Each limb was placed into a circular fixator (IMEX Veterinary, Inc. Longview,

TX) constructed from 84 mm diameter rings. The RM group was fitted with a four

complete ring construct. The LM group was fitted with a six ring construct consisting of

four complete and two 5/8th rings. The rings of both the RM and LM groups were each

supported with three 6 mm x 255 mm threaded connecting rods. The connecting rods

were spaced to provide an opening 3/8th of the ring’s circumference along the

craniomedial aspect of each limb. The proximal and distal rings of the frame were

secured to the limb with 1.6 mm Kirschner wires (IMEX Veterinary, Inc. Longview, TX)

which were placed using a battery operated drill (Makita, La Mirada, CA). The

intermediate rings were not secured to the limb at this time. A 1 cm incision was made

over the distal ulna and a 1.0 mm Kirschner wire was placed obliquely (proximal-to-

distal) through the styloid process, securing it to the carpal bones. The wire was cut short,

close to the styloid process, and bent 90o at the bone-pin interface. The opposite end of

the wire, exiting from the medial aspect of the carpus, was secured to the distal ring of

the frame.

Computed tomography (CT) scans were performed on each limb. The limbs were

scanned using a third generation single detector CT scanner (Philips Tomoscan

M/EG/EG Compact, Shelton, CT). Standardized positioning of the limbs for CT was

25

accomplished by fastening a radiolucent, 250 mm long, 9.5 mm diameter SK carbon fiber

rod (IMEX Veterinary, Inc. Longview, TX) along the longitudinal axis of the fixator

frame. Two 150 mm connecting rods were also fixed at the proximal and distal ends of

the construct, perpendicular to the carbon fiber rod which allowed the frame to be

secured squarely inside a Plexiglass® positioning trough. Two 6.0 mm diameter holes

were drilled through the positioning trough to receive the proximal connecting rod and

hold the frame in place. Using the CT laser guides, the carbon fiber rod served as a

marker for aligning the limb in the sagittal (Y) and dorsal (Z) planes. The distal 150 mm

connecting rod served as a marker for aligning the limb in the transverse (X) plane. A

scanogram image was obtained using a lateral tube position with a technique of 10 mA

and 120 kVp. A survey plan of each cadaver limb specimen was then created using the

scanogram image. The survey plane was set to include the entire length of the

antebrachium and manus between the most proximal and distal rings of the ring

construct. Two mm contiguous transverse images were obtained of each limb at 40 mA,

120 kVp, a sharp extremity filter (EXTREM SF9) and a field of view size of 130 mm.

This same protocol was used to acquire images of the limbs on subsequent evaluations.

After obtaining the initial CT images, a medial approach was made to the distal

radius. The surrounding soft tissues were bluntly dissected exposing the distal two-thirds

of the radius and proximal portion of the radiocarpal joint. A pneumatic oscillating bone

saw (Synthes-Stratec, Inc. Oberdorf, Switzerland) was used to perform a transverse

osteotomy of the radius at its mid-point. The entire distal half of the radius was removed.

Dissection of the soft tissue was continued to expose the ulna adjacent to the radial

defect. Starting proximally and progressing distally, a longitudinal, dorsal-to-ventral

26

osteotomy was made in the ulna, bisecting the ulna lengthwise from the level of the

proximal radial osteotomy through the styloid process to the carpus. A partial thickness,

medial, transverse, ulnar osteotomy was made adjacent to the radial osteotomy, freeing

the medial ulnar segment from the proximal and lateral portions of the ulna. The resultant

free ulnar segment was equal in length to the radial defect.

Constructs for the RM group were fitted with reeling distraction motors consisting

of modified 3 x 3 enclosed-gear, locking, guitar tuning machines, (model #P2644, Ping®,

Taiwan). Modifications necessary to fashion the reeling distraction motors included

mounting the guitar tuning machines onto aluminum plates which could be secured to the

frame, drilling two holes in the wind-shaft to receive the distraction sutures, cutting off

the finger grip, drilling a hole in the drive-shaft to receive a turn key, and adding an end-

plate wire-guide to the wind-shaft to prevent the distraction sutures from sliding off the

wind-shaft. Two reeling distraction motors were mounted onto the construct’s connecting

rods as shown in pictures A and B of Figure 2-1. A proximal reeling distraction motor

was placed along the cranial surface of the construct allowing transport of the proximal

portion of the ulnar transport segment in an oblique caudal-to-cranial direction. The

second reeling distraction motor was placed along the medial surface of the frame

allowing transport of the distal portion of the ulnar transport segment in a more lateral-to-

medial direction. Two pairs of 1.6 mm holes were drilled through the cortex of the ulnar

transport segment: each of the holes was positioned at the longitudinal location of the

reeling distraction motor. Thirty-seven kg test monofilament nylon distraction sutures

(Mason Tackle Co, Otisville, MI) were threaded through each reeling motor’s wind-shaft

and the corresponding pair of drill holes in the ulnar transport segment. The ends of each

27

distraction suture were tied together at the level of the wind-shaft providing two

continuous loops, one proximal and one distal, between the motors and the ulnar

transport segment.

Constructs for the LM group were fitted with two outrigger plates mounted on four

50 mm linear motors as shown in pictures C and D of Figure 2-1. One-hole posts were

used to mount the four linear motors at 90o angles to the surface of the central two rings

such that the drive bushings were directed in a transverse plane, tangential to the outer

circumference of the rings. Each pair of motors was positioned 180o from each other

(cranial and caudal) along the circumference of the rings. A 28-hole plate was secured to

the threaded rod of both the dorsally and ventrally positioned motors. One-hole posts

with an articulating threaded rod were placed both proximally and distally on each plate.

The result was a four-motor outrigger designed to move lateral-to-medial in the

transverse plane. A length of monofilament nylon distraction suture was threaded through

the paired proximal and distal drill holes in the ulnar transport segment in a similar

fashion to the RM group with the exception that the ends of the leader material were

captured between two nuts and a lock-washer placed along the outrigger’s horizontal

connecting rods. This design allowed medial distraction of the ulnar transport segment

into the radial defect.

The ulnar segments for each group were transported into the radial defect as shown

above in Figure 2-4. The proximal end of the transport segment was visually aligned with

the outer circumference of the radius proximal to the defect. The distal end of the

transport segment was visually aligned with the outer circumference of the radial carpal

bone. The entire distraction gap was then filled with silicone sealant (GE, Waterford,

28

NY), the skin was sutured closed, and the limb was frozen to maintain the position of the

transport segment.

Post-distraction CT imaging was performed for all limbs using the same protocol

described for the pre-distraction CT imaging. All of the CT scans were reviewed on a

dedicated diagnostic workstation (Phillips Easy Vision, Netherlands, BV). Pre-selected

cross-sectional locations of the antebrachium were acquired for image analysis of bone

position and cross-sectional area. Cross-sectional views through the distal 1, 33, 66, and

99% of the ulnar transport segment were chosen. The corresponding pre- and post-

distraction cross-sectional locations were matched for each cadaver limb, providing a

comparable image set for each selected cross-sectional location of the antebrachium.

The cross-sectional locations were optimized to a bone window technique (WW

2500; WL 500) on a dedicated diagnostic workstation. The images were then exported in

a digital format (TIFF) to be aligned and superimposed using an imaging software

package (Adobe Photoshop: Professional Editing Software, Adobe, San Jose, CA).

Aligning and superimposing the corresponding cross-sectional locations required

removing the background of each post-distraction image and then selecting and layering

that post-distraction image over the corresponding pre-distraction image as shown in

Figure 2-5. The frame’s connecting rods were used as reference points to align and

superimpose the corresponding pre- and post-distraction cross-sectional locations. The

resultant pre- and post-distraction superimposed image was then exported in digital

format (TIFF) for the purpose of making the necessary measurements using an image

analysis software package (SCION-Imaging analysis software, Scion Corporation,

Fredrick, MD).

29

Angle and Direction of Deviation

The distraction axis of the transport segment was determined by locating the two

points along the outer circumference of the radial defect and the remaining intact ulna

furthest apart from each other as seen in the cross-sectional location. These two points

provided radial and ulnar points of reference (POR). The line drawn between the radial

and ulnar POR defined the ideal distraction axis as transport along this axis should result

in the most anatomical regenerate bone formation in the distraction gap of a live dog.The

point at which the ideal distraction axis intersected with the trans-cortex of the pre-

distraction ulna provided an initial transport segment POR. The initial transport POR

became the final transport segment POR after distraction was complete. The initial and

final transport segment POR mark the same point on the trans-cortex of the ulna, but

obviously are not in the same location spatially. The line drawn between the ulnar and

final transport segment POR defined the observed distraction axis. If the observed

distraction axis deviated from the ideal distraction axis, the angle between the two axes

was measured and it was noted if the observed distraction axis was cranial or caudal to

the ideal distraction axis.

Distraction Distance

The length of the ideal distraction axis was compared to the length of the

observed to determine whether the transport segment had been distracted the appropriate

distance. Defining the extent to which over or under distraction occurred was done by

providing the length of the observed distraction axis as a percentage over or under the

ideal. The points used to calculate this measurement are shown above in Figure 2-5.

30

Fill Ratio

The outer circumference of the split ulnar segment and the lines drawn between the

cranial and caudal margins of the split ulnar segment were used to extrapolate the area of

existing cortical and regenerate bone that would potentially result from transverse bone

transport osteogenesis in a live dog. The extrapolated area was then compared to the

cross-sectional area (mm2) of the intact radius, ulna, and the radius and ulna combined at

each of the cross-sectional locations. This provided three sets of ratios between the cross-

sectional area of the pre-distraction bone and potential regenerate bone, referred to as fill

ratios.

Statistical Analysis of Parameters

The data was recorded and formatted onto a spreadsheet using Microsoft Excel

software (Microsoft Corp, Redmond, WA). The data was then statistically analyzed using

Sigma Stat software (Systat Software Inc, Point Richmond, CA).

Comparison of the mean angles of deviation using an unpaired t-test

The mean angle of deviation for each cross-sectional location and the four cross-

sectional locations combined were determined for both the RM and LM groups. An

unpaired t-test was then performed in order to compare mean angle of deviation between

the RM and LM groups (significance was set at p <0.05).

Comparison of the directions of deviation using a chi-squared test

The number of cranially, caudally and neutrally distracted transport segments for

all of the cross-sectional locations was determined for each group. A comparison was

then made to determine if one of the two groups deviated in a particular direction

significantly more or less often than the other (significance was set at p <0.05, 1 degree

of freedom).

31

Comparison of the mean distraction distances using unpaired t-test

The number of neutral, over, and under distracted transport segments at each cross-

sectional location and all cross-sectional locations combined was recorded for both the

RM and LM groups. The mean percent over and under distraction was then determined

for each cross-sectional location for each group. The mean distraction distances for the

RM group were then compared to those of the LM group using an unpaired t-test to

determine if there were any significant differences between the two groups (significance

was set at p <0.05).

Comparison of the mean fill ratios using unpaired t-test

The mean regenerate to radius fill ratio for each cross-sectional location and the

four cross-sectional locations combined were determined for the RM group. This was

then repeated to obtain the mean regenerate to ulna fill ratio and the mean regenerate to

radius and ulna fill ratio. The same values were similarly calculated for the LM group.

An unpaired t-test was then performed in order to make a comparison between the RM

and LM groups’ mean fill ratios. The standard deviation and range were also calculated

for each cross sectional location and all cross-sectional locations combined.

Results

Limbs were obtained from five male and five female mixed breed dogs ranging in

weight from 23-32 kg (mean ± SD: 26 kg ± 3 kg). All were skeletally mature adult dogs

and their forelimbs were verified radiographically to be free of any musculoskeletal

abnormalities.

Measured Parameters

The mean angles of deviation along with the standard deviations and ranges at

each cross-sectional location and the four cross-sectional locations combined for the RM

32

and LM groups are listed in Table 2-1. The mean values for the angle of deviation at each

of the cross-sectional locations ranged from two to ten degrees. The angles of deviation

did not differ significantly between the RM and the LM groups at any of the cross-

sectional locations (1% cross-section: t=-0.0565, 18 degrees of freedom, P=0.956; 33%

cross-section: t=-1.142, 17 degrees of freedom, P=0.269; 66% cross-section: t=1.152, 18

degrees of freedom, P=0.264; 99% cross-section: t=0.511, 18 degrees of freedom,

P=0.615). The number of RM and LM transport segments found to deviate cranially or

caudally are also listed in Table 2-1 for each cross-sectional location and the cross-

sectional locations combined. Only 13% of the LM and 10% of the RM group had no

deviation and were positioned neutrally along the ideal distraction axis. While the

direction of deviation was variable, the statistical analysis revealed that there was a

tendency for the LM constructs to result in cranial deviation more frequently than the RM

constructs and the RM constructs to result in caudal deviation more frequently than the

LM constructs (1 degree of freedom, P=0.0474).

The extent of over and under distraction observed in the RM and LM groups did

not differ significantly at any of the cross-sectional locations (1%: t=0.178, 18 degrees of

freedom, P=0.861; 33%: t=0.505, 17 degrees of freedom, P=0.620; 66%: t=0.421, 18

degrees of freedom, P=0.679; 99%: t=1.394, 18 degrees of freedom, P=0.180). The

number of transport segments found to be over and under distracted are listed in Table 2-

2 along with the mean percentage that the over or under distraction occurred. The values

were calculated for each cross-sectional location and the four cross-sectional locations

combined for both the RM and LM group.

33

The fill ratio compares the area of the intact radius, intact ulna and intact radius and ulna

combined to that of the potential regenerate bone. The unpaired t-test performed on the

fill ratios for each cross-sectional location did not reveal any significant differences

between the RM group and LM group in any of the four cross-sections (radius:regenerate

1%: t=-0.533, 18 degrees of freedom, P=0.600; 33%: t=-0.386, 18 degrees of freedom,

P=0.704; 66%: t=0.401, 18 degrees of freedom, P=0.693; 99%: t=0.987, 18 degrees of

freedom, P=0.337; ulna:regenerate 1%: t=-1.074, 18 degrees of freedom, P=0.297; 33%:

t=0.695, 18 degrees of freedom, P=0.496; 66%: t=0.644, 18 degrees of freedom,

P=0.528; 99%: t=1.254, 18 degrees of freedom, P=0.226; radius/ulna:regenerate 1%: t=-

0.610, 18 degrees of freedom, P=0.550; 33%: t=-0.180, 18 degrees of freedom, P=0.859;

66%: t=0.479, 18 degrees of freedom, P=0.638; 99%: t=1.131, 18 degrees of freedom,

P=0.273). The RM and LM mean, standard deviation, and range for these fill ratios at

each cross-sectional location are listed in Table 2-3. The data shown in Table 2-4

provides the cross-sectional area of the regenerate, radius and ulna (mm2) for each of the

cross-sectional locations for the RM and the LM groups. These values were used to

calculate the fill ratios listed above; however, this data was not analyzed statistically.

Fixator Construction, Application, and Distraction

The hypothesis of this study could not be proven. The reeling motor constructs

did not distract the transport segment into a more anatomic position than the linear motor

construct; however, several subjective differences were noted. The RM frames required

fewer components, were simpler to assemble and apply, and the frames were more

compact and lighter weight. The reeling-motors functioned as small pre-assembled units

that could quickly and easily be secured to any location on the frame. During application

of the frame onto the limb, the reeling-motors were readily repositioned, and doing so did

34

not necessitate disassembling a major portion of the frame. Predicting the distraction axis

prior to assembly was also easier with the reeling-motors as the direction of distraction

could more readily be appreciated prior to their application to the construct. The compact

reeling-motors provided convenient spaces in the construct frame which allowed better

access to the limb during the procedure and it also afforded better visualization of the

surgical site radiographically.

The plate outrigger could not be accurately pre-assembled and had to be assembled

one component at a time in order to obtain the most accurate distraction axis for the

transport segment. That is to say a pre-assembled plate outrigger would have been much

easier to apply to the frame of the construct; however, assembling the LM construct in

this manner usually resulted in a considerably obscured distraction axis when the

distraction process was subsequently carried out. The plate outrigger was heavier and

more cumbersome and lacked the inherent stability of the compact reeling-motors.

Jarring forces applied to the plate outrigger misaligned its position, altering the course of

the distraction axis. Since the plate outrigger moved as a functional unit, sequential

distraction of the proximally and distally located linear motors often resulted in binding

and distortion of the plate outrigger device. It was therefore necessary to sequentially turn

each individual linear motor in small increments no greater than a single revolution in

order to mitigate any distortion of the outrigger frame. Unfortunately, in a live dog, the

proximal and distal ends of the transport segment must be distracted at different rates due

to the differences in size between the proximal and distal distraction axis. Consequently,

the outrigger device may frequently bind if used in the live dog and not function

adequately in this capacity.

35

Discussion

Ulnar bone transport osteogenesis would appear to be a feasible means for

performing limb salvage procedures. It is a technique that affords a combination of

advantages for the treatment of osteosarcoma that no other single technique can offer.

Development of a construct that would provide an accurate and effective means of

performing transverse bone transport osteogenesis would be a key innovation in the

treatment of osteosarcoma. Both of the constructs developed in this study were effective

at performing this task; however, the RM constructs afforded several advantages over the

LM construct.

The angle of deviation was considered to be an appropriate means of assessing the

position of the ulnar transport segment. This parameter compared the actual position of

the transport segment to a position that would provide the most anatomical regenerate

bone. In theory, an anatomically positioned regenerate should correlate with the

functionality of the limb following the bone transport procedure. As such, deviation from

that position may provide an indicator as to the quality of the end result. Unfortunately,

with no previous reports of this application it is difficult to assess the clinical significance

of the values obtained for the angles of deviation. Once further in vivo studies are

complete, it may possible to better evaluate the importance of this parameter.

There was no statistical difference found between the RM and LM group’s angle of

deviation, although it is important to note that the distraction process was carried out in

this study with the benefit of direct visualization of the transport segment during

distraction. If the transport segment was observed to deviate from its intended path during

distraction, adjustments were made to the construct in order to improve its position.

Adjustments were cosequently necessary when using the LM constructs, but were

36

infrequent when using the RM constructs. Making these adjustments to the construct

would be more difficult in a live dog, particularly if serial computed tomography imaging

were not available. From a clinical standpoint, the ease of maintaining a small angle of

deviation without the need for repeated adjustments may give the reeling motors a major

advantage over the linear motors.

Although the angle of deviation described the net difference between the observed

and ideal, it did not take into account the direction in which the error occurred. The

direction of deviation was assessed to determine if the constructs tested had a propensity

to position the transport segment in a particular position relative to the ideal distraction

axis. The data revealed that the RM construct was more likely than the LM construct to

deviate the transport segment in a caudal direction and the LM construct was more likely

than the RM construct to do so in a cranial direction. It is difficult to speculate as to why

this occurred. It may simply be a function of how the constructs were assembled or it

may be that the variation in visualization afforded by each construct created some bias

during the distraction process. Regardless, the significance of this observation is currently

unknown.

Over and under distraction described how far along the distraction axis the

transport segment was moved. Like the angle of deviation, this parameter,has an impact

on final anatomic configuration of the regenerate bone. Unlike the angle of deviation,

however, over or under distraction is easier to control, particularly if CT were used to

monitor the distraction process. In this study the distraction was carried out until the

transport segment was visually aligned with the proximal and distal docking sites. If there

was 10% over or under distraction, this was somewhat difficult to appreciate given that

37

this often translated to a discrepancy of only a few millimeters, viewed through a surgical

incision. In the clinical setting radiography could be used in conjunction with CT to

assess distraction distance. Once the proximal and distal cortices matched with the

cortices of the docking sites, distraction could be discontinued.

Fill ratio is a means of quantifying the potential volume of bone that could be

expected following bone transport relative to the amount of bone present in the in tact

antebrachium. This ratio was determined by comparing the cross-sectional areas

measured on the pre- and post-distraction CT scans. Calculating ratios allows

comparisons to be made between different sized specimens and in effect normalizes the

data. There was no significant differences found between the RM and LM groups’ fill

ratios, but what was shown was that overall, the amount of regenerate bone expected to

form is comparable to the amount of bone present in a normal dog’s antebrachium.

Proximally, the projected cross-sectional area of the regenerate bone approached or

exceeded that of the cross-sectional area of the intact radius and ulna combined. It is

reasonable to assume then that the proximal portion of the regenerate will provide

adequate bone to support weight-bearing. At the distal aspect of the radial defect (1%

cross-sectional location) fill ratios for the radius and the radius and ulna combined were

all less than 100%. This observation is primarily a function of the dog’s anatomy. The

distal radius widens in the region of the distal metaphysis and epiphysis. Conversely, the

ulna is relatively narrow in this region. As a result, distraction of the small ulnar transport

segment across this wider radial defect provided relatively less potential regenerate bone

to fill the defect and may have adverse consequences with respect to weight-bearing in a

live dog. Distally the radius supports nearly all of the limb’s weight.73 The projected

38

mean cross-sectional area of the regenerate bone at that location was found to be 75-78%

that of the intact radius and the most important question that must be answered is whether

or not this amount of bone would be sufficient to comfortably support weight on that

limb. It should be noted that the projected mean regenerate:radius fill ratio of 75-78%

distally may under estimate the actual cross-sectional area of regenerate bone that would

develop over time due to remodeling and circumferential bone growth. Circumferential

bone osteogenesis was reported by Aronson in a human patient utilizing transverse bone

transport of the fibula to replace bone in a subtotal defect of the proximal tibia.34 Aronson

observed that distraction osteogenesis not only occurred at the trailing end of the

transport segment but from the outer surfaces adjacent to the transport segment as well.34

Whether or not circumferential bone osteogenesis is a phenomenon that can be

consistently relied upon to provide a meaningful quantity of regenerate bone however has

not yet been determined. Experimental work recently published by Matsuyama et al

reported that the direction of osteogenesis during cranial transverse transport of a

segment of the tibia was parallel to the direction of distraction and independent of the

direction of the weight-bearing forces applied to the limb.72 This study did not, however,

assess osteogenesis beyond 28 days post-distraction. Furthermore, the study by

Matsuyama et al72 was different from the clinical case reported by Aronson34 in that the

transport segment used was not transported into a defect toward the weight bearing axis

but rather away from it. A transport segment distracted into a bone defect may respond

differently to the forces placed upon it. This may be of even more significance if the

transport segment and subsequent regenerate bone was smaller in cross-sectional area

than the defect into which it was distracted. Unfortunately, many questions are left that

39

can not be answered until further studies have been done using live dogs in clinically

applicable cases.

Concern regarding adequate bone volume, strength or consolidation following

transverse ulnar transport also raises questions regarding the use of pharmaceutical agents

to augment bone formation during this process. Bisphosphonates have been used

successfully in dogs and humans as supplemental treatment for both osteosarcoma and

distraction osteogenesis.64-68,74-76 Bisphosphonates have been shown to inhibit bone

resorption and cancer cell proliferation, as well as reduce osteoporosis while increasing

osteoblastic proliferation, new bone formation, and bone strength. 64-68,74-76 There are

other drugs that have been used in these circumstances as well. Bone morphogenic

protein (BMP) is a class of drug that has been shown to enhance bone consolidation

during distraction osteogenesis and induce rapid healing of segmental bone defects.77,78

Thrombin-related peptide TP508, is yet another drug that has recently been employed for

its ability to enhance bone formation and consolidation during distraction osteogenesis.79

Treatment options that provide benefits such as these are likely to play a pivotal roll as

adjunctive therapy when performing transverse ulnar transport osteogenesis for the

treatment of osteosarcoma.

The values for over and under distraction were found not to differ between the RM

and LM groups. In general, the two groups over and under distracted the transport

segments a similar distance with similar frequency. It is noteworthy, however, that over

or under distraction also impacts the fill ratio. Over distraction of a transport segment

will result in an increased cross-sectional area, where as under-distraction of a transport

segment will produce a decreased cross-sectional area. The resultant fill ratio may

40

thereby misrepresent the regenerate bone’s capacity to withstand the forces generated

across the radial defect. Fortunately, the data revealed that 90% of both the RM and LM

group transport segments were 13% under-distracted at the distal aspect of the transport

segment (the primary location of concern). This would indicate that if anything, the fill

ratios at the distal docking site would be greater than those projected values reported in

the results of this study. This again raises the question as to what values are clinically

significant when considering fill ratio and the function of the spared limb. As for the

remaining more proximal cross-sections, there were no trends towards over or under

distraction and the impact on fill ratio is not likely significant.

While there were only minor statistical differences found between the RM and the

LM groups, several advantageous attributes of the RM constructs were obvious during

their construction and application. Independent function of the two reeling motors allows

uncomplicated transport of the segment at different rates and along different axes. This

attribute is likely to be an important element in ultimately providing more anatomic,

functional regenerate bone. There were circumstances which required the outrigger plates

of the LM constructs to become bent or distorted in order to adequately transport the

bone as the design necessitated moving the outrigger entirely as one unit. Proximally

where the ulna is positioned relatively caudal to the radius, making accurate simultaneous

distraction of both ends of the transport segment was difficult with the LM construct

outrigger which functioned as a single transportation device. Independent motor function

would be more efficient in dogs that require more proximal radial osteotomies to obtain

adequate margins of resection. This is due primarily to the fact that the distraction axis at

41

the proximal antebrachium is nearly perpendicular to the distraction axis at the level of

the carpus.

Subjectively, the RM constructs utilized fewer components, were less complicated

and faster to assemble than the LM constructs. The reeling-motor was also more

adaptable to the diverse antebrachial anatomy encountered among the various breeds. The

placement of the motor was more adaptable to variations in bone segment alignment and

the distraction axes because they operated independently from one another. Achieving

comparable alignment with the LM construct took longer to achieve and often required

deformation of the outrigger plates to attain distraction of the ulnar transport segment in

the appropriate planes. The LM construct was also considerably heavier, larger, and more

awkward. The LM construct would likely pose substantial practical problems if utilized

on a live dog.

The guitar tuning machines used for the drive component of the reeling-motors are

ideal for performing bone distraction osteogenesis. The gear ratios required to fine tune

guitar wire allow bone transport to be carried out in the minute increments necessary for

effective regenerate bone formation. The gears are self-locking and can withstand large

tensile forces; they are therefore very effective at applying the tension necessary to

transport the ulnar bone segments and maintain them in that position. In addition, the

guitar tuning machines can readily withstand gas and steam sterilization allowing them to

be safely used intra-operatively.

The cadavers selected for this study were considerably varied in body-weight and

anatomic conformation. Making the longitudinal ulnar osteotomy was easier in larger

specimens. The size of the ulna is an important parameter that needs to be carefully

42

considered during case selection. Adequate healthy bone must be present on both the

medial and lateral cortex of the ulna. An insufficiently sized transport segment or an

insufficient amount ulna left in tact may not provide a large enough volume of bone to

allow for effective osteogenesis. The minimal amount of bone required is unknown

although equal longitudinal division of the distal ulna would provide the maximum

amount of bone on both sides and theoretically would provide the most favorable

conditions for osteogenesis. An off-center ulnar osteotomy in very large dog, although

less than ideal, would be more likely to still provide sufficient bone for osteogensis than

an off-center osteotomy through a smaller ulna. Including body weight in the selection

criteria was important primarily for this reason.

In addition to size of the ulna, the condition of the bone and surrounding tissue is

obviously an important factor when selecting clinical cases for this procedure. All of the

cadavers utilized in this study were large breed, skeletally normal dogs. As such,

pathological fractures and surgical margins were not an issue of concern but are clearly

relevant factors clinically. In a live dog, any ulnar involvement, microscopic or

otherwise, is a cause for trepidation. In such cases, ulnar preservation may result in an

increased incidence of local recurrence. Careful case selection in this regard will be

essential.

In a live dog the soft tissue alone may not be capable of providing sufficient tension

to hold the distraction segment in place. For this study, counter-traction was provided by

rubber bands placed within the surgical site. If performed in a clinical case,

circumferential elastic restraints (vessel loops) could be placed around the ulna or

43

additional reeling motors on the opposite side of the construct may be added to provide

counter-traction and maintain the transport segment in proper alignment.

Conclusion

It is difficult to predict the efficacy of transverse ulnar transport osteogenesis for

the treatment of subtotal radial defects following tumor resection. Without evaluating

living tissue and its response within a segmental bone defect along the weight bearing

axis, one cannot determine how the tissue will heal or what the function of the limb will

be once the process is complete. Moreover, adjunctive therapies such as bisphosphonates,

BMP, and thrombin related peptide TP508 will likely impact the outcome of procedures

such as transverse bone transport rather significantly. What can be concluded from this

study is that using the techniques developed here, both transport motor designs will

effectively distract the ulnar transport segment into the radial defect. The reeling

transport motors appear to be a more practical means of performing transverse bone

transport osteogenesis and further studies using a live animal model will be helpful in

determining the practicality of using this technique in vivo.

Transverse bone transport would afford many of the benefits of longitudinal bone

transport osteogenesis, but may provide resolution of sub-total radial defects in

substantially less time. With disease processes such as osteosarcoma, it is important to

minimize convalescence and maximize the quality and quantity of life. Transverse bone

transport osteogenesis may be an effective means of achieving these goals.

44

Figure 2-1. The LM and RM constructs placed on each limb. A) Cranial view of the RM construct. B) Lateral view of the RM construct. C) Cranial view of the LM construct. D) Lateral view of the LM construct.

Figure 2-2. The positioning trough afforded duplicate limb position for the pre- and post-distraction CT scan. A) In the dorsovental view, the carbon fiber rod provided sagital plane alignment (Y axis) and the distal 150 mm connecting rod provided transverse plane alignment (X axis). B) In the lateral view the carbon fiber rod provided dorsal plane alignment (Z axis).

45

Figure 2-3. The reeling motors could be mounted at any position along the outer circumference of the RM construct. The drive-shaft, mounting plate, wind-shaft, and wire-guide are labeled accordingly.

Figure 2-4. Each loop of distraction suture is anchored to its respective reeling motor. Rubber bands are placed around the intact ulna and transport segment at the level of each distraction suture to provide counter traction as distraction is carried out. In vivo, the function of the rubber bands could be achieved via sterilized elastic vessel loops along with the surrounding soft tissue.

46

Figure 2-5. UPOR point marks the ulnar point of reference, the RPOR point marks the radial point of reference, the ITPOR point marks the initial transport segment point of reference, the FTPOR point reperesents the final transport segment point of reference, the solid line marks the ideal distraction axis, the dashed line marks the observed distraction axis, the angle between the two lines is the angle of deviation, the difference in length between the two lines is the distance over or under distraction took place.

Figure 2-6. The blue shaded area outlined in black denotes the extrapolated cross-sectional area of the regenerate bone once distraction is completed.

47

Table 2-1. Angle and direction of deviation

*The RM group deviated caudally significantly more often than the LM group and the LM group deviated cranially significantly more often than the RM group.

Cross-sectional location

Angle of deviation (degrees) RM LM

Direction of deviation RM LM

1% Mean Std dev Range

7.9 7.8 7.8 6.7 0-26.2 1.6-24.1

Cranial Caudal Neutral

1/10 4/10 8/10 6/10 1/10 0/10

33% Mean Std dev Range

7.2 9.6 Cranial Caudal Neutral

1/10 2/9 9/10 7/9 0/10 0/9

4.9 4.3 0.7-14.2 1.3-14.9

66% Mean Std dev Range

2.1 3.9 1.7 4.7 0.2-4.9 0-12.8

Cranial Caudal Neutral

0/10 3/10 10/10 4/10 0/10 3/10

99% Mean Std dev Range

4.6 6.0 5/10 5/10 Cranial Caudal Neutral

6.9 4.7 0-22.5 0-13.9

2/10 3/10 3/10 2/10

All locations

Mean Std dev Range

5.5 6.8 2.7 2.4 0-26.2 0-24.1

Cranial Caudal Neutral

7/40 14/39* 29/40* 20/39 4/40 5/39

48

Table 2-2. Distraction distance Cross-sectional location

Distraction Position

RM – extent over or under

LM – extent over or under

1% Over Under Neutral

1/10 + 10% 9/10 – 13% 0/10 N/A

1/10 + 15% 9/10 – 13% 0/10 N/A

33% Over Under Neutral

6/10 + 12% 4/10 – 10% 0/10 N/A

6/9 + 14% 2/9 – 16% 1/9 0%

66% Over Under

5/10 + 11% 4/10 – 13% 1/10 0%

6/10 + 13% 3/10 – 15%

Neutral 1/10 0% 99% Over

Under Neutral

5/10 + 7% 7/10 + 14% 5/10 – 13% 3/10 – 15% 0/10 N/A 0/10 N/A

All cross-sections

Over Under Neutral

17/40 + 10% 22/40 – 13% 1/40 0%

20/39 + 14% 17/39 – 13% 2/39 0%

The extent over or under distraction is the length of the observed distraction axis represented as the average percentage it was over- or under-distracted relative to the ideal distraction axis. The number of observed distraction axes included in each category is also listed for each cross-sectional location. Table 2-3. Fill ratio

Cross-sectional

Regenerate:radius RM LM

Regenerate:ulna RM LM location

Regenerate:rad+ulna RM LM

1%

Mean Std dev Range

78% 75% 459% 427% 12% 15% 65% 69% 64%-96% 45%-99%

395%-596% 301-521%

66% 63% 10% 12% 55%-80% 39%-83%

33% Mean Std dev Range

122% 117% 23% 30% 93%-166% 84%-177%

315% 332% 39% 63% 238%-376% 238%-463%

88% 86% 15% 20% 67%-115% 62%-128%

66% Mean Std dev Range

127% 132% 25% 29% 85%-166% 91%-191%

322% 339% 46% 69% 252%-400% 253%-466%

91% 95% 16% 20% 65%-116% 67%-133%

99% Mean Std dev Range

140% 152% 30% 26% 92%-200% 105%-195%

274% 306% 92% 101% 39% 69% 17% 19%

66%-126% 73%-132% 213%-344% 236%-449%

All locations

Mean Std dev Range

117% 119% 27% 33% 64%-200% 45%-195%

343% 351% 81% 53% 213%-596% 236%-521%

84% 86% 12% 17% 55%-126% 39%-133%

49

Table 2-4. Cross-sectional area of intact and regenerate bone Cross-sectional

Mean regenerate cross-sectional area (mm2)

Mean radial cross- sectional area (mm2)

Mean ulnar cross-sectional area (mm2)

location RM LM RM LM RM LM 1% 180.9 165.6 232.1 222.3 39.5 38.8 33% 142.2 132.7 118.7 114.4 45.2 40.1

126.1 128.9 101.7 99.3 39.5 38.6 66% 135.6 149.4 100.1 99.1 49.9 50.2 99%

CHAPTER 3 TRANSVERSE BONE TRANSPORT OSTEOGENESIS: A LIVE DOG MODEL FOR

THE TREATMENT OF DISTAL RADIAL OSTEOSARCOMA IN DOGS

Bone Transport Osteogenesis

Limb salvage for the treatment of appendicular osteosarcoma is becoming an

increasingly common procedure in dogs. Several surgical methods have been described

for performing limb salvage. The most widely used technique is the implantation of

frozen cortical bone allograft.17 Other procedures such as endoprostheses, vascularized

ulnar transposition graft, and linear bone transport osteogenesis (BTO) have also been

described.20-22,69 The latter technique, linear BTO, utilizes the phenomenon of distraction

osteogenesis to replace bone defects created by tumor removal.21,22,69 Bone transport

osteogenesis avoids many of the complications encountered with other limb salvage

procedures; however, since BTO involves the transport of a proximal radial bone

segment longitudinally along a substantially large radial defect, the distraction time is

often considerably long.21,69

Transverse Ulnar Bone Transport Osteogenesis

The previous chapter describes the development of the methodology to perform

transverse ulnar bone transport osteogenesis. This technique uses a circular external

fixator and newly designed instrumentation to transport the medial half of the ulna

transversely into an adjacent radial defect which should allow distraction to be completed

over a two to three week period. The study described in this chapter details the

application of transverse ulnar BTO using a single live adult dog. The dog’s progress was

50

51

monitored regularly for 180 days post-operatively using various subjective and objective

techniques to assess the quality and pattern of regenerate bone formation and to

document the distraction process. Complications associated with the clinical application

of transverse ulnar BTO procedure as well as the final clinical outcome were

documented.

Objectives

The objectives of the study outlined in this chapter were to validate the procedure

described in Chapter 2 using a live dog, document the gradual distraction of the ulnar

bone segment transversely across a segmental distal radial defect, quantify regenerate

bone formation and compare the cross-sectional measurements in this dog to the

predicted values obtained from the cadaveric model described in Chapter 2. This study

also aimed to quantify the number of days necessary to perform the distraction and

quantify the number of days necessary for consolidation of the regenerate bone to occur.

These times were compared to the predicted times reported in chapter two as well as

previously reported times from dogs undergoing radial longitudinal BTO.

Hypotheses

The hypotheses tested were: transverse ulnar BTO can produce viable regenerate

bone; the amount of regenerate produced is comparable to the regenerate predicted in the

cadaveric model described in chapter two; the regenerate is sufficient to support weight-

bearing; and the transport time and time in external fixation is substantially shorter with

transverse ulnar BTO than with linear radial BTO.

Materials and Methods

The dog used in this study was an approximately 2 ½ year old, male Walker hound.

A complete physical examination revealed that the dog was healthy and did not have any

52

appreciable systemic abnormalities. An orthopedic examination, radiographs, and CT

scans performed prior to inclusion in the study confirmed that the subject was free of any

musculoskeletal abnormalities.

Surgical Technique, Fixator Construction, and Distraction

Surgical removal of the distal 50% the right radius was conducted similarly to the

technique described for removal of distal radial osteosarcoma tumors during standard

limb salvage surgery.17 The underlying extensor muscles were exposed and access to the

craniolateral aspect of the mid-distal ulna was achieved by careful subperiosteal

elevation. The attachments of the surrounding musculature and the caudal interosseous

artery were carefully preserved. A longitudinal osteotomy was made along the length of

the ulna using a 545 Dremel® diamond cutting wheel with a 22.2 mm bit diameter, 3.2

mm shank diameter, and 0.6 mm kerf (Dremel®, Racine, WI). A partial transverse

osteotomy was then performed at the proximal most extent of the bisected portion of the

ulna to free the medial ulnar transport segment from the remaining ulna. Two 1.6 mm

diameter Kirschner wires were placed from medial-to-lateral through the transport

segment and lateral ulna to function as guide wires. The proximal surface of the radial

carpal and ulnar carpal bones were osteotomized transversely to remove all articular

cartilage. The limb was placed into a circular fixator (IMEX Veterinary, Inc. Longview,

TX) constructed from four 84 mm diameter rings and three 6 x 255 mm threaded

connecting rods. Two reeling distraction motors were fitted onto the construct and

secured to the ulnar transport segment using 28 kg test fluorocarbon distraction sutures

(Kreha Corporation of America, New York, NY) in a manner similar to that described in

chapter two. After a latency period of 4 days, the distraction process was initiated. The

distraction rate of the proximal motor was 0.75 mm/day with a rhythm of twice per day

53

(0.25 mm AM, 0.5 mm PM). The distraction rate of the distal motor was 1 mm/day, also

with a rhythm of twice per day (0.5 mm AM, 0.5 mm PM). Distraction was carried out

for 19 days.

Subjective and Objective Assessment

Post-operatively, subjective evaluation of gait and visual inspection of the surgical

site was performed daily and the observations were recorded. Radiographs and CT scans

were performed once weekly for the first two months and then every three to four weeks

for four months thereafter. The radiographs and CT scans were used to subjectively

assess the status of the surgical implants, transport segment position, bone density, bone

volume, distraction axis and distraction distance. The radiographs and CT scans were also

used to help confirm that the distraction and consolidation processes were complete.

Regenerate bone density was determined by measuring the number of Houndsfield units

(HU) observed within a 10 mm2 area adjacent to the medial aspect of the lateral ulnar

segment 50 mm proximal to the accessory carpal bone on CT scans acquired 10, 17, 23, 45,

and 59 days post-operatively. Measurements of cross-sectional area acquired pre-

operatively for the same four cross-sectional locations used in Chapter 2 (1, 33, 66, and

99%) were compared to the corresponding measurements of cross-sectional area obtained

from post-operative CT images acquired on day 45 and day 94.

Results

Daily Subjective Assessment

The surgical procedure took approximately 7 hours, with 8.5 hours of total

anesthesia time. There were no complications encountered intra-operatively and recovery

was uneventful. A subjective visual assessment of the surgical site and the limb itself

revealed substantial swelling and bruising initially; however, this resolved almost entirely

54

by day 9. The dog began placing minimal weight on the limb intermittently on the second

day after surgery. Gradual subjective improvement was observed in the gait over the

subsequent 12 days to the point the dog was consistently partially weight-bearing. On day

14 the dog became acutely lame and non-weight-bearing. At bandage change the

proximal most wire through the radius was found to be broken at the wire-bone interface.

The broken wire was replaced and subjectively the lameness improved but only slightly.

On day 23, all the proximal wires of the frame were found to be broken and surgical

intervention was performed the following day to provide additional support. The dog’s

gait began to steadily improve each day thereafter. By day 28 the patient subjectively

appeared to be bearing substantial weight on the limb, a mild lameness was apparent but

limb function appeared satisfactory.

Radiographic and CT Analysis

Radiographs and CT performed immediately post-operatively (day 0) revealed

what initially appeared to be adequate stabilization. Subjectively, the cut made through

the ulna appeared to be well placed and the transport segment was situated in proper

alignment with the desired distraction axis. By day 7, distraction was underway but had

only been carried out for two days. As such, the only observable changes were 1-2 mm of

transverse distraction and a mild to moderate increase in soft tissue swelling since day 0.

Radiographs and CT taken on day 14 appeared satisfactory, distraction was

approximately 50% complete. No complications were noted at that time. On day 23 the

distraction process was completed. Faint mineralization could be observed in the wake of

the transport segment indicating early regenerate bone formation. As was mentioned

above, it was also observed at this time that all of the olive wires secured to the proximal

two rings had broken and the remaining portion of intact ulna had fractured at the

55

proximal aspect of the osteotomy. The pre-existing ulna and regenerate bone

radiographically appeared slightly askew but not in anyway that was thought to be

significant. The olive wires were replaced and half-pins were drilled into the proximal

radius to provide additional support. Post-operative radiographs performed on day 24

revealed that revision of the external fixator resulted in a moderate amount of shifting of

the ulna and regenerate bone within the frame although the shift was not considered

severe enough to warrant further surgery. The reinforcement appeared to provide

adequate stabilization of the antebrachium. By day 31 the regenerate bone appeared to be

increased in radiodensity in comparison to that observed in the earlier images. The

subsequent radiographs and CT scans performed over the following two months revealed

continued and steady increases in regenerate bone radiodensity. No further radiographic

evidence of complications were observed for the remainder of the consolidation period.

Consolidation was complete by day 94, at which time radiographic osseous union had

been achieved and the external fixator was removed. On day 108, two weeks following

frame removal, radiographs revealed that the regenerate bone failed to maintain union at

the distal docking site. A splint was subsequently applied to the antebrachium for an

additional 27 days to provide supplementary stabilization and expedite the docking

process. On day 146 a 16-hole, 3.5 bone plate was applied from the proximal third of the

radius across the carpus to the distal half of the metacarpal bones in order to provide a

more definitive means of resolution. The plate appeared to be affective as the dog quickly

began using limb well following the procedure.

Houndsfield Units

Houndsfield units are computed tomography image voxel values indicating the

degree of x-ray attenuation relative to water and provide one with the ability to determine

56

the density of the tissue being observed. Houndsfield units were measured from a 10 mm2

area adjacent to the medial aspect of the lateral ulnar segment, 50 mm proximal to the

accessory carpal bone on days 10, 17, 23, 45, and 59. The results showed that the

regenerate bone reached the density of normal bone (≥ +500 HU) at some point between

day 23 and day 45.

Cross-sectional Area of Regenerate Bone

The cross-sectional area at each of the 4 cross-sectional locations was obtained

from the pre-operative CT scan and compared to the cross-sectional areas of both the 45-

and 94-day post-operative CT scans. Using the methods described in Chapter 2, the fill

ratios were calculated for the radius, the ulna and the radius and ulna combined. The fill

ratio values are listed in Tables 3-2 and 3-3.

Discussion

Transverse ulnar BTO was successful in this live dog model. Subjectively the dog

maintained good limb function and experienced minimal morbidity (with the exception of

fixation-wire complications) over the duration of the procedure. Bone formation occurred

as expected and did so in a relatively timely manner.

Breakage of the fixation wires occurred in this dog as a result of improper wire

placement through the proximal radius. Unfortunately this error was not appreciated until

after the breakage had occurred. The broken wires lead to insufficient support of the

surgical site and resulted in fracture of the intact lateral ulnar segment. Fortunately, the

problem was quickly resolved with minor modifications and minimal surgical

intervention. The complications encountered with the distal docking site of this dog were

a bit more complicated. Failure or delayed docking of regenerate bone with the existing

bone found proximally and distally is a potential complication of BTO.69 This process

57

does not always occur readily and may require surgical intervention in order to be

successful.69 Such intervention typically involves placement of autogenous cancellous

bone graft, allogenic demineralized bone matrix or a combination of the two into the

docking site. Given the short duration of the distraction process when utilizing transverse

ulnar BTO, it may be possible to perform this grafting procedure at the time of the initial

surgery, eliminating the need for additional surgery weeks later. In this dog, insufficient

regenerate bone volume also may have contributed to the problems in maintaining osseus

union at the distal docking sight. To ensure adequate regenerate bone formation, it is

important to preserve soft tissue attachments to the distal ulna including the periosteum,

surrounding musculature, and the caudal interosseous artery. Pharmaceuticals such as

bisphosphonates, bone morphogenic proteins, and thrombin related protein have also

demonstrated significant enhancement of bone formation during bone distraction

osteogenesis. These drugs were not used in this study however they clearly have the

potential to play a major role in the future of limb salvage and bone transport

osteogenesis. Another contributing factor to the poor docking observed distally may have

been the increased distance left between the ulnar transport segment and the radial carpal

bone following distraction. As the transport segment reached its final position, it became

obliqued given that the distal end was transported farther medially than the proximal end.

As a result, the obliqued segment of ulna did not span the entire distance of the radial

defect, creating a gap approximately 10 mm in length at the medial distal docking site.

Compression across the radial defect using the external fixator may have helped to avoid

this complication. A plate was eventually placed to resolve the docking site difficulties;

however, this obviously required additional surgery and prolonged convalescence.

58

Failure to accurately distract the medial ulnar transport segment into the proper

location is another potential complication of transverse ulnar BTO. Given the necessity

for the newly formed bone to be in alignment with the remaining proximal radius and the

carpus distally, accurate transport of the ulnar fragment into the radial defect is essential.

The pre-operative CT scan of the antebrachium obtained in this study did not provide any

static external points of reference, such as those provided by the connecting rods of the

external fixators used in the cadaveric model. When comparing pre and post-operative

CT images, external points of reference are necessary in order to correct for variation in

limb position between the CT scans. As a result, assessment of the distraction axis and

distance in this study had to be made subjectively rather than using the parameters

described in chapter two. Serial CT and radiographic examinations provided an early

indication of the distraction axis. Although it was not necessary in this study, these

images can aid in adjusting the direction of distraction. Adjustments can easily be made

by sliding the reeling motors to a more appropriate location around the circumference of

the fixator rings. Guide wires placed through the intact ulna and transport segment prior

to distraction can also help insure that the transport segment remains on course.

It required 19 days to distract the ulnar transport segment into the radial defect and

as a result, the distraction process was completed by day 23. Linear radial BTO requires

an average of 123 days to complete the distraction process.21,69 The total time the dog

spent in the external fixator in this study was 94 days. Dogs undergoing linear radial

transport spend an average of 205 days in external fixation.21,69 The regenerate produced

by the dog in this study reached a density equivalent to that of normal bone (≥ +500 HU)

before day 45. These numbers match closely with the times predicted in chapter two.

59

The cross-sectional locations selected (1, 33, 66, and 99%) were the same as those

used for the cadaveric model. Unlike the cadaveric model however, the cross-sectional

areas of the regenerate bone were not estimates but a true measure of regenerate bone

quantity. As was discussed in chapter two, the fill ratio of most interest was that of the

distal radius. On day 45 the dog in this study only generated a regenerate:radius fill ratio

of 36% but by day 94 the fill ratio had increased to 96%. This was an improvement over

the expected fill ratio of 78% predicted by the cadaveric model. Proximally, the cross-

sectional area was also larger than expected. The cadaveric model predicted a

regenerate:radius fill ratio of 140% at the 99% cross-sectional location. The fill ratio

observed in this study was 176% by day 94. It is also interesting to note that the more

central cross-sectional locations actually decreased in bone production between day 45

and 94. On day 45 the regenerate:radius fill ratio for the 33% and 66% cross-sectional

locations were 89% and 102% respectively but by day 94, theses values dropped to 83%

and 93%. These two values are slightly less than the average values predicted in the

cadaveric model, 122% and 127% respectively.

It is likely that extensive remodeling of the bone during this time resulted in

substantial changes in bone callus thickness at each of the cross-sectional locations.

Presuming that the proximal and distal ends of the transport segment have a higher

degree of micro-motion during the healing process, an increase in cross-sectional area

which approaches or surpasses that of the normal bone could result at these locations.

This would suggest that under physiologic stress, the bone may be able to remodel in

such a way that it forms more regenerate bone where needed; more bone than the

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cadaveric model suggests. If this is true it may even produce sufficient regenerate bone

for a limb salvage patient to bear weight.

Conclusion

Several methods have be described for performing limb salvage including

implantation of cortical bone allografts, endoprotheses, and the use of BTO osteogenesis.

Each of these procedures has been shown to be reasonably effective; however, each

method has inherent disadvantages. Bone transport osteogenesis effectively avoids many

of the complications encountered with other limb sparing procedures; unfortunately

transport of a proximal radial segment can take a substantial amount of time. This long

convalescence period is of particular concern as it may adversely impact the quality life

for both owners and their pets undergoing this procedure. The live dog model described

in this chapter validates the findings of chapter two and demonstrates that transverse bone

transport osteogenesis is a feasible means of addressing large sub-total defects in the

distal radius of the dog. Transverse ulnar BTO can provide a patient with viable

regenerate bone resulting in a functional weight-bearing limb and can do so in

substantially less time than longitudinal transport of a proximal radial segment.

Further studies looking at regenerate bone formation following transverse BTO of

undersized transport segments should be performed. These studies should consider how

the bone behaves under physiologic loads and consider the benefit of supplemental

treatment with bone grafting procedures and pharmaceuticals shown to enhance

regenerate bone formation.

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Table 3-1. Houndsfield unit assessment Day HU 10 17 23 45 59

60 110 240 600 650

Table 3-2. Day-45 fill ratio Cross-sectional location

Regenerate:radius Regenerate:ulna Regenerate:radius+ulna

1% 33% 66% 99%

36% 89%

102% 176%

186% 198% 209% 306%

30% 61% 68%

112%

Table 3-3. Day-94 fill ratio

Cross-sectional Regenerate:radius Regenerate:ulna Regenerate:radius+ulna location

80% 358% 1% 96% 33% 57% 185% 83%

62% 191% 93% 66% 128% 351% 201% 99%

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BIOGRAPHICAL SKETCH

Carl T. Jehn was born in Burlington, Iowa in April 1975. Soon afterward, he and

his family moved to Elkhart Lake, Wisconsin where he grew up and graduated high

school. After graduating high school in 1993, Carl attended the University of Wisconsin-

Madison, where he earned his Bachelor of Science degree in 1998, majoring in wildlife

ecology. The next year, Carl went on to pursue his Doctor of Veterinary Medicine

degree, also at the University of Wisconsin-Madison. After earning his DVM in 2002,

Carl moved to Athens, Georgia, where he completed an internship in small animal

medicine and surgery at the University of Georgia-Athens. He completed his internship

training in 2003; at which time he moved to Gainesville, Florida to pursue his graduate

training and begin his residency in small animal surgery at the University of Florida. Carl

is currently a small animal surgery resident at the University of Florida Veterinary

Medical Center. His areas of interest include circular ring fixation, osteosarcoma

research, and canine rehabilitation physical therapy.

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