25 review of endoprosthetic reconstruction in limb-sparing...

25

Review of EndoprostheticReconstruction in Limb-sparingSurgery

Robert Henshaw and Martin Malawer

OVERVIEW

Endoprosthetic replacement of segmental skeletal defects is the preferred technique of reconstruction after resectionof bone sarcomas. Today, all of the major anatomic joints with their adjacent segmental bone can be reconstructedsafely and reliabily with a modular endoprosthetic replacement. Prosthetic reconstruction is routinely performed forthe proximal femur, distal femur, total femur, proximal tibia, proximal humerus, and scapula. Allografts are rarely used.

A major advantage of a modular endoprosthetic system is intraoperative flexibility; it enables the surgeon toreconstruct defects of any size with minimal preoperative planning. Instead of performing a resection to match aprosthesis customized on the basis of imaging studies that are 4–8 weeks old, the surgeon can concentrate onperforming the best possible resection indicated for the patient at the time of surgery. Overall survival analyss of largesegmental replacements is approximately 90% at 10 years (reported at 98% for the proximal humerus and 90% forthe distal femur).

This chapter reviews the indications and techniques for performing endoprosthetic replacements for bone tumors.Many of the described surgical techniques were developed by the senior author, placing emphasis on techniques forreconstructing the soft tissues after implantation of a modular endoprosthesis to optimize the functional outcome.

Malawer Chapter 25 22/02/2001 08:50 Page 381

INTRODUCTION

The concept of limb-sparing surgery, or limb salvage,has gradually evolved over the past 25 years. Prior tothis the basic principles of surgical oncology for theextremities consisted solely of determining the correctlevel at which to perform an amputation. With theintroduction of effective Adriamycin- and methotrexate-based chemotherapy protocols in the early 1970s atcenters such as Memorial–Sloan Kettering, New YorkUniversity, and the Children’s Hospital of Philadelphia,surgeons such as Ralph Marcove, Kenneth Francis, andHugh Watts developed techniques of limb-sparingsurgery. Today, 90–95% of patients with extremitysarcomas who are treated at major centers specializingin musculoskeletal oncology can undergo successfullimb-sparing procedures.

This dramatic alteration in patient care is the result ofsignificant advances along many fronts, including:

1. improved understanding of tumor biology;2. effective induction chemotherapy;3. technical advances in surgical techniques;4. better characterization of the biomechanics of the

human skeleton;5. advanced material engineering and manufacturing

techniques;6. the development of a reliable, stable modular

prosthesis for reconstruction of the hip, shoulder,and knee.

This book focuses primarily on techniques of oncologicresection that have been developed by the authors overthe past 20 years. Emphasis is placed on several prin-ciples that are key to the success of this technique. Thefirst is identification and preservation of key neurologicand vascular structures in the limbs and pelvis. Second,the importance of achieving an appropriate oncologicmargin cannot be overstated, for preservation of thelimb should rarely, if ever, take precedence over thesurvival of the patient. Achieving safe margins requiresmeticulous surgical technique. Resection, however, isonly the first stage of a limb-sparing procedure.Reconstruction of the axial skeleton and restoration ofsoft-tissue coverage for optimal function are alsoperformed.

The purpose of Chapter 25 is to review the majormedical and surgical considerations in selecting apatient for limb salvage and to discuss the optionsavailable for reconstructing the defect remaining afteran oncologic resection. An overview of the surgicaltechniques for reconstruction of each major joint, asdeveloped and currently practiced by the authors, ispresented.

PATIENT SELECTION

Appropriate patient selection for limb-sparing proce-dures is essential to ensure good, consistent results.Although the introduction of chemotherapy forosteosarcoma was a major impetus for the developmentof techniques for limb-sparing surgery, increasinglyhigh long-term survival rates have placed greateremphasis on the functional outcome and longevity ofthe reconstruction. Today’s patient expects a solutionthat addresses his or her functional, cosmetic, andpsychological needs.

The location and involvement of critical anatomicstructures are often the determining factors in selectingpatients for limb salvage versus a primary amputation.With the use of modern neoadjuvant (i.e. preoperative,induction) chemotherapy, many patients who areinitially not suited for a limb-sparing procedure mayultimately become candidates for such surgery.Therefore, the final surgical decision is often not madeuntil a patient has been re-evaluated following thecompletion of neoadjuvant treatment. Improvementsin chemotherapy have increased the pool of patientsamenable to limb-sparing procedures.

Limb-sparing procedures, moreover, are not neces-sarily limited to patients who respond to treatment.Patients with very poor prognostic factors, such asthose with metastatic disease upon initial presentationand those who fail to respond to chemotherapy, oftenrequire significant palliative surgery in order tomaintain an acceptable quality of life. Because theseindividuals have a limited life expectancy, amputationshould be avoided in all but the extreme cases whorequire emergency palliation. Radical or mutilatingprocedures are not appropriate for patients if there isno hope of prolonging their survival. The surgicalintervention selected is dependent on where a givenpatient falls within the spectrum of potential oncologicoutcomes.

ROLE OF IMAGING STUDIES AND PATIENTSTAGING

Advanced imaging modalities have vastly improvedour ability to accurately determine the extent of tumorprior to surgical exploration. High-resolution axial andmultiplanar images from computerized tomography(CT) or magnetic resonance imaging (MRI) scans candetermine the extent of the tumor and its relationshipto the surrounding anatomic compartments. CTimaging of the chest is performed to detect pulmonarymetastases, and technetium bone scanning of the entireskeleton is performed to detect the presence ofmetastatic disease. For bone sarcomas, and most soft-

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tissue sarcomas, the lungs and skeleton account for thevast majority of all sites for metastases. High-qualityimaging studies, combined with detailed histologicgrading of a biopsy (preferably done by a core needle),allows for accurate staging.

Early attempts to stratify patients on the basis oftumor size failed to account for the biologic behavior ofa given tumor. A more reliable approach is a stagingscheme that accommodates the fact that the aggressivenature of a tumor can be graded by the histologicappearance of the cells and their nuclei. WilliamEnneking1 added to this the concept of an anatomiccompartment, which acts as a relative barrier to tumorspread. His staging system combined tumor grade andanatomic extent in a simple, yet easily reproducible andprognostically significant format. The MusculoskeletalTumor Society has adopted this system as its preferredmethod for staging extremity sarcomas.

Limb salvage for Stage I (low-grade) and Stage IIA(high-grade, intracompartmental) lesions is nowroutinely performed, because these tumors are easilyresectable. A majority of the surrounding soft tissue canroutinely be preserved. For these patients, recon-struction is typically limited to restoration of skeletalstability. Stage IIB tumors, which can involve multiplecompartments, may be unresectable at presentation.Neoadjuvant chemotherapy can have a dramatic role inconverting patients with tumors that are initiallythought to be unresectable into candidates for limb-sparing surgery. Such a conversion may occur whenchemotherapy causes the tumor to shrink, therebyfreeing critical neurovascular structures. Finally,patients with Stage III disease may be considered forpalliative resections in lieu of amputation, providedthat prolonged immobilization or delayed woundhealing does not interfere with their medical treatment.In patients with Stage IIB and III tumors, skeletal andsoft-tissue reconstruction must be performed.

STAGES OF LIMB-SPARING SURGERY

A successful limb-sparing procedure can be dividedinto three stages, each of which directly affects patientoutcome and survival. First and foremost, tumorresection must spare significant structures. Second, astable, painless skeletal reconstruction must beaccomplished. Third, the surrounding and supportingsoft tissue is required to restore function and skeletalreconstruction.

As the techniques of surgical resection have beenrefined, the number of patients that fulfill these cate-gories has increased. For example, involvement of amajor vascular bundle formerly mandated anamputation. Today, major vessels are routinely resected

en-bloc with the tumor; this is followed by vascularreconstruction utilizing an artificial graft or reversedvein graft. Likewise, use of local rotational pedicle flapsor microvascular free flaps allows for reconstruction ofpatients whose tumor resection necessitated removal ofsignificant portions of the surrounding soft tissue. Suchflaps provide the muscle and skin coverage necessaryto restore limb function and prevent postoperativeperiprosthetic infections.

RECONSTRUCTIVE OPTIONS FOR SKELETALDEFECTS

There are four major methods of reconstructing askeletal defect. These are as follows:

1. Resection arthrodesis. Prior to the routine use ofchemotherapy in the 1970s, resection of a sarcomaentailed the loss of significant amounts of muscle.Little tissue was left for functional reconstruction. Inthese early days of limb salvage, resection arthrodesiswas the main method of reconstruction. (Figure 25.1)Its primary advantages were to restore skeletalstability and produce a long-term, durable recon-struction. No attempt was made to restore motion atthe resected joint, however, and many patientsexpressed dissatisfaction with their loss of function.Today, effective chemotherapy allows for thepreservation of significant functional muscle groups,and the use of rotational flaps can restore functionwhen muscle is lost. As a result, resection arthrodesisis rarely recommended as the primary method ofreconstruction today; in fact, a number of long-termsurvivors originally treated with arthrodeses aroundthe knee have undergone conversion to endo-prosthetic reconstruction to restore their ability topassively flex and extend the knee.

2. Osteoarticular or massive allografts. Allograft recon-struction was championed in the 1970s as a biologicsolution to the problem of restoring a segmentaldefect of the skeleton. Despite technical improve-ments in the method of fixation, and in theprocessing of the allograft to preserve cartilage cellsand reduce contaminants, this method ofreconstruction has significant complications. Theseinclude early complications, such as infection,nonunion and joint instability, and late compli-cations such as instability and allograft fracture.Overall complication rates can exceed 50%,including an infection rate of 30%, even whenperformed at a major center.2 As a result, allograftprocedures are preferred at only a few centers today.Many surgeons avoid them entirely in patientsundergoing chemotherapy for high-grade sarcomas.

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Currently, we perform allograft reconstruction forthe rare patient with a diaphyseal lesion that can bereconstructed with an intercalary allograft or forvery young patients who might be expected todevelop substantial leg-length discrepancies as theygrow. For the latter patients an allograft can preserveadditional growth plates and reduce the expectedleg-length discrepancy. Ultimately, such patientsoften require conversion to an endoprosthesis becausetheir functional demands result in fracture of theallograft.

3. Endoprosthesis. Endoprosthetic reconstruction is ahighly successful and durable method for therestoration of skeletal integrity and joint function.Use of a cemented stem provides immediate fixation,which allows for early mobilization and rehabilita-tion. Extensive experience in joint replacement hasled to the development of materials suited for long-term prosthetic survival; at the same time, advancesin the use of local rotational flaps have improvedjoint stability and simultaneously reduced the risk ofinfection. Since the mid-1980s custom-manufacturedendoprostheses have been replaced by modularsystems with standard instrumentation that vastlyexpands the reconstruction options (Figure 25.2).This is the authors’ preferred method of recon-struction and this chapter will expand on the topic,below.

4. Allograft–prosthetic composite (APC). APCs can beviewed as a transitional step between allografts andendoprostheses. This procedure became popular

when surgeons began to abandon pure osteo-articular allografts. APCs were thought to providethe benefits of a biologic reconstruction along withthe immediate stability achieved by a cementedendoprosthesis. Experience has shown that thismethod has the same high rate of early complica-tions (i.e. infection and nonunion) as does standardallograft reconstruction. Accordingly, this method isbetter suited for a patient undergoing revision of afailed allograft, rather than a patient undergoingchemotherapy for a sarcoma.3

HISTORY OF ENDOPROSTHETICRECONSTRUCTION

The earliest published example of an endoprostheticreconstruction following treatment of a bone tumordates to 1940, when Austin Moore and Harold Bohlmanimplanted a vitallium proximal femur in a patient witha giant-cell tumor. In the early 1970s Kenneth Francisand Ralph Marcove ushered in the current age of endo-prosthetic reconstruction following radical resection ofosteosarcomas by developing a distal femoral and atotal femoral replacement, respectively (Figure 25.3).4

This new concept of limb-sparing surgery forsarcoma patients was based on the hope thatAdriamycin and methotrexate, newly introduced forosteosarcoma in the early 1970s, would permit a safelimb-sparing resection in lieu of primary amputation.However, it was soon recognized that the 6–8 week lagtime between diagnosis and the creation of a custom


Figure 25.1 Resection arthrodesis (per Enneking). (A) Intraoperative photograph demonstrating the dual fibular reconstructionwith an intramedullary rod fixation following resection of the distal femur. This technique of reconstruction was popularizedduring the 1970s by Dr William F. Enneking prior to the development of reliable reconstruction prostheses. Note the medialgastrocnemius flap (gm) has been mobilized for rotation closure of the defect. (B) Gross specimen following an extra-articularresection of the distal femur. Note the biopsy tract was removed with the specimen. The arrows indicate the level of the joint.This was the standard technique for resection during the 1970s and early 1980s. Today this technique is rarely performed.

A B


endoprosthesis for a given patient could have a negativeimpact on survival. As a result, Gerry Rosen and RalphMarcove invented the concept of induction (i.e. pre-operative or neoadjuvant) chemotherapy, according towhich patients with osteosarcomas received chemo-therapy during the interval from time of diagnosis ofthe tumor to the delivery of that patient’s customimplant.4 Induction chemotherapy is now administeredto patients with a wide variety of cancers.

Specific examples of endoprosthetic reconstructions,that will be discussed in detail in this chapter, includethe following:

Hip (Proximal Femur, Saddle)

Tumors involving the proximal femur, which includeboth primary sarcomas and metastatic carcinomas, areextremely common. Following resection of a primarytumor or fracture through a subtrochanteric metastaticlesion, the proximal femur can be readily replaced.Typically, a bipolar hemiarthroplasty is used for the hipjoint with reconstruction of the hip capsule to prevent

complications related to postoperative dislocation. Hipabductors can be reconstructed by attaching themdirectly to the prosthesis via a laterally placed metalloop. Much less common are resections of the entire hipjoint (type II pelvic resection and its modifications).This defect can be reconstructed with a saddle pros-thesis, a device that derives its name from the U-shapedcomponent that articulates with the remaining iliacwing. Stability is achieved by balancing the muscletension between the medial iliopsoas and the lateralhip abductors.

Knee (Distal Femur) (Figure 25.4)

The distal femur is the most common site for primarybone sarcomas. Prosthetic reconstruction requires aunique combination of flexibility and stability, becausethe knee capsule and the cruciate and collateral liga-ments are removed during the resection. The rotatinghinge design permits both flexion and extension, aswell as rotation through the knee, while maintainingstability in varus/valgus and anterior/posterior planes.


Figure 25.2 Types of distal femoral replacements. (A) Anterior–posterior view. (B) Lateral view. A = initial custom prosthesisused between 1981 and 1985; B = similar prosthesis with porous coating adjacent to the stem (arrow) to permit intracorticalbone fixation: this prosthesis was first used in 1985; C = Modular prosthesis (Howmedica, Inc., Allendale, NJ) initially used in1988 (see text). The modular design is presently used for most anatomic sites.

A B



Figure 25.3 Photographs of the first distal femoral replace-ment performed in the United States by Dr Kenneth Francisat New York University in 1973. (A) Plain radiograph of a largeStage IIB osteosarcoma. This patient was treated withAdriamycin alone, which was the only available active sarcomadrug at that time. (B) Anterior–posterior photograph of thedistal femoral replacement utilized. Note the long femoraland tibial stems. Polymethylmethacrylate was utilized forfixation. The knee component was a modified Walldius fixedknee hinge. (C) Lateral photograph of the same prosthesis.Note the long tibial stem and spikes for fixation.

A B

C


Reconstruction of the extensor mechanism is rarelyrequired since the patella can usually be saved duringthe resection.

Total Femur

Patients presenting with the rare sarcoma that has anextensive intramedullary extent, as well as patientswith multiply failed total joints and little remainingbone stock, can be treated with a total femoralreplacement. A natural combination of the distal

femoral rotating hinge and the proximal femoralreplacement with a bipolar head, this type of recon-struction has proven to be extremely durable as a resultof the degrees of freedom that are afforded by the twoseparate, but related, joints.

Proximal Tibia

The tibia is unique given its subcutaneous border alongthe anterior leg. Any form of reconstruction can bejeopardized by even minimal amounts of skin necrosis.Routine use of a gastrocnemius rotation flap hasdramatically reduced the incidence of postoperativecomplications. Joint stability at the knee is assured byusing the same rotating hinge design used for distalfemoral replacements.

Shoulder (Proximal Humerus)

High-grade sarcomas of the proximal humerus requireextra-articular resection, that includes the entire rotatorcuff and deltoid muscles. The functional outcome of aproximal humeral replacement following this type ofresection is therefore greatly restricted by lack offunctional muscle. A combination of static and dynamicsuspension, including transfer of the pectoralis muscle,stabilizes the proximal humerus to the scapula, andpermits painless and functional use of the elbow, wrist,and hand.

Scapula (Scapulohumeral)

Following total resection of the scapula, a scapularprosthesis helps lateralize the humerus and stabilizethe shoulder joint. Resurfacing the humeral head andreconstruction of the capsule with a Dacron graft isnecessary for optimal stability. Functional outcomedepends on the amount of muscle preserved duringresection.

Elbow

The elbow joint is rarely involved by sarcomas or meta-static disease. Customized, hinged implants with small-caliber stems to fit the ulna and distal humeral canalsmay be used, provided that sufficient soft tissueremains to cover the prosthesis.

Total Humerus

This implant is a combination of a proximal humeralimplant and an elbow replacement. The indications forthis procedure are rare, but a sensate, functional handremains preferable to an amputation.


Figure 25.4 Custom distal femoral prostheses used between1982 and 2000. (Knee component not shown) (A) Originalcustom prosthesis (1982). (B) Custom prosthesis (1984–1988)with porous collar (solid arrow) to permit extracortical bonefixation and soft tissue attachments (1984–1988). (C) Modularsegmental prosthesis. This was the original segmentaldesign (1988) which is currently in use today with somemodifications (Courtesy Howmedica Inc., Rutherford, NJ).


Calcaneus

There has been one reported case of a total calcanealprosthesis implanted in lieu of a below-knee amputa-tion in a patient with osteosarcoma. Five years aftersurgery this patient is fully ambulatory and does notdepend on assistive devices.

Expandable Implants for the Skeletally ImmaturePatient

Reconstruction of the axial skeleton in immaturepatients is problematic. Children over the age of 10–12years can often be treated as adults, using smallerversions of the modular prostheses, occasionally incombination with contralateral epiphyseodesis toequalize leg length at skeletal maturity. Below the ageof 6, primary amputation remains the preferred methodof tumor resection, given the extraordinary difficulty inobtaining a proper oncologic margin around the criticalneurovascular bundles. In children between the ages of6 and 10–12 reconstruction is feasible, but limb-lengthinequality becomes functionally disabling as the childgrows. Implants that can be expanded multiple timesduring growth permit prosthetic reconstruction forthese children. These custom-created implants havebeen used both in the upper and lower extremities withmixed results. Mechanical failures of the expansionmechanism are not uncommon (see Figure 25.10,arrows). Many patients must undergo as many as 10operative procedures to ensure limb equalizationduring the period of active growth.

As experience with prosthetic design and implanta-tion grew, a wide variety of custom implants becameavailable (Figure 25.2). All of the early prostheses,however, were individually designed and manu-factured on a one-off basis. Prosthetic failures related todesign flaws and errors in manufacturing were common.Improved design concepts and manufacturing tech-niques developed during the production of standardtotal hip and total knee prostheses were eventuallyapplied to these “mega” prostheses (Figure 25.4).However, design improvements requiring increasinglycomplex mechanical geometry, and the increasing useof difficult-to-process alloys such as titanium and cobaltchrome, have lengthened the manufacturing time.These considerations offset the gains associated with longexperience in handling custom implants and the reducedtime needed to design the actual implant. As a resultthe minimum time between design and delivery of asterilized custom endoprosthesis remains 6–12 weeks.

Endoprosthetic reconstruction is associated bothwith mechanical failures (e.g. stem fracture, erosion andfailure of polyethylene components) and nonmechanical

failures (e.g. infection and aseptic loosening). Advancesin design and surgical techniques have reduced theseproblems substantially. However, the problem uniqueto custom endoprosthetic implants that cannot becontrolled for is that the planned resection may need tobe revised at the time of surgery. This is particularlytrue when the tumor grows significantly during thetime that the prosthesis is being manufactured, orwhen there is a difference in the preoperative imagingmeasurements and the actual dimensions of thepatient's bony anatomy or size of the tumor. Attemptsto use a component that is not the appropriate size cansignificantly jeopardize the oncologic result, thefunctional result, or both.

Flexibility at the time of surgical reconstruction canbe increased by incorporating modular features into theprosthesis (Figure 25.5). Although modularity increasesthe complexity of the mechanical construct, and carrieswith it risk of failure associated with the sum of all ofthe components, it has several significant benefits. Theprimary advantage is flexibility: the surgeon can con-centrate on performing the best-possible oncologicresection knowing that any changes in the pre-operative plan can be accommodated by having athand the components needed to reconstruct the actualskeletal defect. The use of standard components alsoallows the surgeon to articulate trial components duringthe procedure, and to repeatedly modify and test areconstruction before selecting and assembling thefinal prosthesis. Standardization of components alsopermits the implant manufacturer to greatly increasethe level of quality control while reducing the cost ofmanufacturing through economies of scale. Modularsystems can also reduce the overall inventory neededto provide a large choice of prosthetic shapes and sizes.Finally, a modular system lends itself to reconstructivesituations outside of oncologic resections immediatelyavailable as a backup option for selected patients, suchas those undergoing difficult joint revision surgery.

The Howmedica Modular Replacement System(HMRS, Howmedica International) designed andmanufactured in Europe, was a first-generationmodular endoprosthetic system. It featured intra-medullary, cementless, press-fit stems supported byexternal flanges and cortical transfixation screws. Theknee mechanism consisted of a simple hinge design.Significant problems encountered with this deviceincluded aseptic stem loosening (osteolysis), substantialstress shielding with bone resorption, screw fractureand migration, and a greater than 40% polyethylenefailure rate for the knee mechanism.5 As a result thissystem has rarely been used in the United States.

A second-generation limited modular system fromEurope currently available in the United States is the



modular saddle endoprosthesis (Link America,Denville, New Jersey). This prosthesis, designed for thetreatment of infected, failed total hip replacements, hasbeen modified to allow for reconstruction of the hipfollowing resection of the pelvis. The unique feature of

this system is the saddle, which is a U-shapedcomponent that straddles the ilium, allowing motion inflexion/extension, and abduction/adduction by rockingin the AP and lateral planes against the bone. Anadditional ring containing polyethylene permits


Figure 25.5 (see also following page) Modular replacement system (Howmedica, Inc.). (A) A distal femoral Modular ReplacementSystem showing the stem, body, and condyles with the tibial insert (polyethylene) in which a tibial bearing plug (metal) is inserted.(B) Anterior-posterior photograph showing a distal femoral Modular Replacement System prosthesis in place. (C) Multi-phasephotograph of the distal femur and proximal tibial component that demonstrates the range of flexion that is permitted with thekinematic rotating hinge knee component. (D) Multi-phase photograph of the distal femoral modular replacement showing therotation that is permitted within the tibial bearing component. Note, there is almost a complete freedom of rotation. In order tocontrol this rotation, good muscle reconstruction is essential.

A B


rotation, and increases the degree of freedom for thejoint. The saddle component connects to a series ofinterchangeable modular bodies that, in turn, connectto a standard cemented hip component. This devicepreserves limb length following resection of theperiacetabulum (type 2 pelvic resection, modifiedinternal hemipelvectomy) while functioning like a totalhip prosthesis. The clinical and functional resultsfollowing saddle reconstruction of the pelvis with thissystem have been extremely good.6

CURRENT DESIGNS – THE MODULARREPLACEMENT SYSTEM (MRS)

A second-generation universal system, originally calledthe modular segmental replacement system (MSRS)and recently renamed the modular replacement system(MRS), was introduced in 1988 (Howmedica Inc.,Rutherford, NJ). This system was designed to providemodular replacements for the proximal humerus,proximal femur, total femur, distal femur, and proximal


C D

Figure 25.5 C,D


tibia. Careful failure analysis of custom endoprosthesesguided the design of the new modular system.Significant design features are the following:

1. Cemented stems. The use of bone cement (methyl-methacrylate) has a substantial track record in jointreplacement. Long-term outcome studies now covernearly 25 years. Cement is well tolerated biologicallyand functions as a grout that compensates for anymismatch between the geometry of the medullarycanal and the prosthetic stem. Additionally, asepticloosening, which was once believed to be associatedwith the bone cement and even termed “cementdisease”, has now been attributed to the biologicresponse to wear debris, particularly polyethylene.Cemented stems ensure immediate fixation, avoidthe need for postoperative bracing or prolongednon-weight-bearing, and permit early rehabilitation.

2. Multiple stem diameters. Experience with customendoprostheses demonstrated a substantial risk ofstem fracture secondary to fatigue failure when small-diameter stems were used. The modular systempermits the use of the largest stem diameter possiblefor a given patient, thereby minimizing this risk. Inaddition, the use of a facing reamer that matches theouter radius of the stem/body junction allows for aperfect seat for the prosthesis, and protects the stemfrom bending stresses.

3. Circumferential porous coating. A porous surfacecomposed of two layers of sintered beads around thebody of the prosthesis was originally designed topermit the ingrowth of bone graft placed at the bone/prosthesis junction (extraskeletal fixation) (Figure 25.6).This bone graft can protect the prosthetic stem bysharing all bending and loading stresses on theimplant. A potentially more significant benefit of thisfeature is that it supports the ingrowth of soft tissue,which produces a seal between the debris-ladenarticular and periprosthetic fluid and the vulnerablebone–cement–stem interface. Termed the “biologicnoose”, this seal has been shown by Ward et al.7 toessentially eliminate the risk of osteolysis when usedin endoprosthetic reconstructions.8

4. Rotating hinge knee (Figure 25.5C). The Kinematicrotating hinge knee, originally designed as a semi-constrained total knee replacement, was adopted forthis system because it not only provides stability butalso offers a high degree of freedom of motion. Thisis critical for reconstructing the knee when all of thecruciates and collateral ligaments have been resectedor are otherwise incompetent.

Other important new features of this system includefull instrumentation to assist in preparing the canal forimplantation, and a series of assembly modules that

hold and impact the modular components together.Metal loops and porous coated surfaces exist at theimportant insertion points of significant functionaltendons (e.g. extensor mechanism for a proximal tibialreplacement) to permit dependable soft-tissue reattach-ment and fibrous ingrowth into the prosthesis.

BIOMECHANICAL CONSIDERATIONS FORENDOPROSTHETIC RECONSTRUCTION

Prosthetic Design

Careful observation of modes of failure over time iscritical to understanding the mechanical and materiallimitations of any manufactured device. Reports oflong-term clinical experience with various customendoprosthetic systems served as a basis for many ofthe design features of the current MRS. The process ofobservation and redesign should not, however, beviewed as a one-off activity. Continued analysis of theresults of each modification to the system is required toensure that corrections of existing problems do not inthemselves lead to unforeseen new difficulties.

For the early devices a major mode of catastrophicmechanical failure was fracture of the intramedullarystem. This problem was caused by a number ofunrelated factors. Errors in the mixture of the alloysused in the manufacturing process, as well as inprocesses used in creating the device (e.g. casting,forging, machining, tempering) can leave microscopicstructural defects within the stem that can besusceptible to fatigue failure over time. The bio-mechanical loads carried by an endoprosthesis can bestaggering. Experiments with instrumented hipreplacements have documented a joint reaction force of2.3–3.3 times body weight during routine weight-bearing and 0.86–2.19 times body weight during single-leg stance.8 Much greater loads occur with impactactivities. An average person has a stride length ofaround 0.6 m when walking at a normal pace9 of1.2 m/s. This translates to two steps (heel strike to heelstrike) every second. If one assumes that an average of15 min of every waking hour are spent walking, thisequates to over 10 million cycles of loading each year.What is impressive is not that some stems fail over timebut that many stems survive.

The most important determinant of the strength of astem is its cross-sectional diameter. Resistance tobending in a given plane is proportional to the radius inthat plane raised to the fourth power. Consequently,small increases in the diameter of the stem lead tosignificant gains in rigidity and resistance to bending.This is supported by the fact that the stems thattypically fracture in custom implants are typically verysmall (≤ 9 mm in diameter).10 The MRS system enables



the surgeon to implant the largest-diameter stem thatcan fit within the intramedullary canal. This factoralone can dramatically reduce the risk of stem failure.

Modular systems, however, require a dependablemethod of assembly. The Morse taper, and its manyproprietary modifications, enables the surgeon toassemble a prosthesis simply by the impacting of itscomponents (Figure 25.6A). Long-term results of

modular hip replacements have made orthopedicsurgeons familiar with this method of fixation. Whileisolated examples of component dissociation have beenreported for various modular implants of all designs,our experience with over 100 MRS implants has failedto reveal any problems with this taper. A crucial step inthe assembly is to ensure that the taper is completelydry and free of debris that may interfere with complete


Figure 25.6 Extracortical fixation of a distal femoral prosthesis.(A) Close-up of the taper of the Modular ReplacementSystem (Howmedica, Inc., Rutherford NJ). Note the porouscoating of the body of the stem (arrow). (B) Autopsyretrieval of distal femoral prosthesis. The bone graft (arrow)is well fixed to the porous coating. Note the beads are hardlyvisible. The Dacron (3 mm) tape is intact and is utilized to fixthe autogenous bone graft to the porous-coated segment ofthe prosthesis. Note there is no evidence of corrosion of thetaper. This prosthesis was in for 5 years. (C) Typicalradiographic view of extracortical bone fixation (arrow) fromthe host bone to the porous-coated segment of a customprosthesis. This is approximately 4 years since implantation.Extracortical bone fixation was first developed as a practicalconcept following the introduction of porous coating byHowmedica (Rutherford , NJ) during the early 1980s.

A

B

C


seating of the taper. Failure to do this can result in aloose fit. The ability to create a loose fit has actually beenused to advantage clinically in patients requiring atemporary prosthesis (such as a spacer for treating aninfection) that can be easily disassembled to permitrevision surgery.

A second method of protecting a stem from failuretakes advantage of the biologic properties of bone. Abone bridge, termed “extracortical bone fixation”, iscreated between the outer diameter of the prostheticbody and the outer bone cortex, bypassing the relativelyvulnerable transition zone between the prostheticbody, prosthetic stem, cement, and diaphyseal bone(Figure 25.6).11 The bone bridge protects the stem byincreasing the diameter of the composite mechanicalstructure that resists bending moment, therebyreducing the overall stress applied to the actual stem.This method of biologic fixation, however, requires thatthe bone graft adheres or attaches to the prosthesis.Early attempts at simple onlay bone graft weredisappointing because the graft was often resorbed.Fixation of the onlay graft with a circumferentialDacron tape, however, has been shown to provideenough compression so that the bone graft not onlyadheres to but also hypertrophies around the pros-thesis. This outcome was the original impetus forplacing porous-coated surfaces on the prosthetic bodyadjacent to the stem. Clinical experience has shownthat this effect is readily reproducible. Additionalapplication of demineralized bone matrix containingbone morphogenic protein (BMP) is a promisingmethod of further improving this method of fixation.

A nonbiologic method of protecting the stem is anexternal flange, which is utilized in the Europeanmodular system. Biomechanically, the flange increasesthe diameter of the composite mechanical structure.Unfortunately, the clinical results of flanges have beendisappointing. Significant stress shielding and resultingbone loss of the cortex located between the stem andthe external flange occur. This destabilizes the interfacebetween the stem and the bone, resulting in increasedmicromotion that produces rapid fatigue failure of thetransfixation screws placed through the flange intocortical bone. The wear debris associated with the failedscrews, combined with prosthetic micromotion, resultsin a spiral of increasing loosening. Eventually, the stemfixation fails. Despite extensive modification of theflange positioning and the number of transfixationscrews, this design remains inferior to the MRSproduced in the United States.

An unexpected benefit of extracortical bone fixationhas been the clinical observation that osteolysis sur-rounding the cemented stem does not appear inregions immediately adjacent to the porous coating on

the body. This effect, termed the “biologic pursestring”,is believed to occur because tissue that has adhered tothe porous coating isolates the stem–cement–bonecomplex from the wear-debris-laden fluid thatsurrounds the joint and prosthetic body. In addition tosupporting laboratory and clinical data implicatingpolyethylene wear-debris in the genesis of osteolysis,this observation indicates that a circumferential porouscoating is a necessary feature for any prosthetic boneimplant. Accordingly, the MRS features circumferentialbeads, that permit bone grafting for extracorticalfixation and stress reduction of the cemented stem, aswell as ingrowth of fibrous tissue to prevent osteolysisand loosening of the cemented stem.

Selection of an appropriate joint mechanism is criticalboth to the functional outcome and the long-term dura-bility of an endoprosthesis. A prosthetic joint mustprovide stability, particularly in situations with signifi-cant resection of soft-tissue constraints (ligaments,capsules). Reconstruction of the hip joint is readilyaccomplished by means of a bipolar hemiarthroplasty,given the inherent stability of a ball-and-socket joint.Dislocation can be prevented through meticulousreconstruction and/or augmentation of the hip capsule.Because the majority of these patients are young, thereare few indications for total hip replacement. Tumorsrequiring resection of the acetabulum may bereconstructed with a saddle endoprosthesis.

Replacement of the knee is more difficult, largelybecause of the unique anatomical and biomechanicalfeatures of this joint. Early prosthetic designs consistedof a simple hinge mechanism (Walldius, Guepar) or aconstrained ball-and-socket design (Spherocentric).However, highly constrained systems such as the earlytotal knee designs, have a high incidence of failurerelated to loosening or breakage. The most probablereason is that normal knee biomechanics includegliding translations and rotations that cannot beduplicated by a simple hinge (Figure 25.5). The originalHMRS prosthesis used a simple hinge joint supportedby polyethylene bushings. The high incidence ofbushing failure noted in clinical series supports thisassumption. Accordingly, the current MRS relies uponthe Kinematic rotating hinge design. This semicon-strained mechanism permits three major degrees offreedom (superior/inferior translation, internal/ externalrotation, and flexion/extension), one minor degree offreedom (five degrees of varus/valgus rotation or tilt),and constraints on medial/lateral and anterior/posterior translation. This mechanism reproduces therestraints provided by the cruciate and collateralligaments, and creates a very stable knee, even whenthese primary restraints of the knee have been totallyresected. Preservation of the four degrees of freedom



helps protect the polyethylene bushings that supportthe primary axle and reduce torques transmitted to theprosthetic/bone junctions.

FUNCTIONAL RECONSTRUCTION ANDANATOMIC CONSIDERATIONS

The functional outcome of an endoprosthetic replace-ment is directly related to the amount of functionalmuscle preserved at the time of surgical resection. Thissimple observation can be used to project an outcomefor an individual patient prior to surgery. For example,a large high-grade sarcoma of the proximal humerusrequires an extra-articular resection of the shoulder,sacrificing the entire rotator cuff, in conjunction withsacrifice of the axillary nerve to achieve a true oncologicwide resection. Given the magnitude of this resectionthe optimal outcome is a stable painless shoulder thatpermits functional use of the elbow, forearm, wrist, andhand. This is accomplished by combining a staticsuspension of the prosthesis from the remainingscapula and clavicle, with a dynamic suspensioncomposed of local muscle transfers that stabilize theshoulder and facilitate internal rotation (i.e. transfer ofthe pectoralis major). In contrast, the resection of rarelow-grade sarcoma or a palliative resection for meta-static disease can be safely accomplished by performinga marginal resection, preserving many of the criticalfunctional elements around the shoulder. Shoulderfunction will be much greater if the means of poweringthe shoulder are preserved.

These same principles hold true for endoprostheticreplacement of any portion of the skeleton, and areindependent of the design of the prosthesis. However,prosthetic design can help facilitate the overall outcomein several key aspects. First, exact duplication of theskeletal anatomy being reconstructed is not necessaryto achieve an excellent outcome. On the contrary, it ispreferable to minimize prosthetic protuberances (suchas a faux greater trochanter for a proximal femoralreplacement) so that a better closure can be achievedwith the remaining soft tissues following resection.Minimization of the medial/lateral diameter of thecomponents around the knee can also greatly facilitatesoft tissue closure of the knee mechanism. Second,functional groups have traditionally been reattached bymaking drill holes to pass sutures through the pros-thesis. The loops allow the surgeon to pass sutures ifdesired, but also permit a tendon to be passed thoughthe loop so that it may be sewn directly to itself. Thepositioning of these loops is therefore a critical designfeature. Again, exact mimicry of the skeletal anatomyfails to account for tissue loss during the resectionprocess; this must be considered in the placement of

the attachment sites. The soft-tissue attachment may befurther reinforced by adding bone graft to the site,where a porous coating can permit ingrowth of tissue.Other methods of soft-tissue attachment, such asspiked screw plates designed to firmly hold a tendon,are under investigation.

The use of a polished smooth stem inserted withbone cement using “third-generation” cement tech-niques (i.e. vacuum mixing to reduce porosity, pressureinjection into a prepared canal with an inserted cementrestrictor, and centralization of the stem during theinsertion process), remains the gold standard forfixation of an endoprosthesis. This is particularly true inpatients undergoing adjuvant treatments such assystemic chemotherapy or radiation that can inhibitbone growth. The major advantage of cementation foroncologic patients is that it produces the immediaterigid and painless fixation, which reduces the need forpostoperative protected weight-bearing or bracing andpermits early functional rehabilitation. This has atremendous positive physical and mental impact on thepatient. Cement also conforms to the biologic and stemgeometry, maximizing the contact between the stemand bone. In addition, the injection of cement canstrengthen and compensate for the reduced mechanicalproperties of bone, which may be significantly weak-ened. Osteoporosis from disuse and osteopenia frompoor nutritional intake, increased metabolic wasting,and an altered hormonal milieu, frequently occur inpatients with chronic disease as well as in those receivingchemotherapy. Certain patients may, however, be candi-dates for “biologic fixation”, such as a porous-coatedpress-fit stem.11 For example, a young, active patientwith excellent bone stock undergoing revision surgeryor resection of a low-grade tumor for which adjuvanttreatment is not indicated may benefit from the long-term fixation that a press-fit stem may offer. Oneadvantage of a system such as the MRS is that a simple,customized stem that matches a patient’s unique anatomymay be readily manufactured and used in conjunctionwith the other modular parts of the system.

STAGES OF LIMB-SPARING SURGERY

The three stages of a limb-sparing procedure are asfollows:

1. tumor resection;2. skeletal reconstruction; and 3. soft-tissue coverage and muscle transfers to restore

function.

The majority of this textbook deals with the surgicaltechniques required to perform a safe oncologic resec-tion of a primary bone sarcoma. Successful functional



reconstruction of the resulting defect consists of twoseparate but dependent stages. The first is the implan-tation of an endoprosthesis, which restores the lengthand stability of the skeleton. The second is the soft-tissue reconstruction that is required to cover theprosthesis and restore function to the joint.

The endoprosthesis is implanted in a systematicfashion. By rigorously following the same steps thesurgeon can achieve a reliable, long-lasting reconstruc-tion. Meticulous attention to soft-tissue reconstructionis vital to reducing the incidence of wound breakdownand secondary prosthetic infection.

GUIDELINES FOR SKELETAL RECONSTRUCTION(STAGE 2)

Endoprosthetic Selection and Implantation

Following resection of a segment of bone, the specimenis carefully measured in order to select the best-fittingprosthetic components. Trial components are providedto enable a rapid comparison with the specimen, aswell as to perform trial reductions prior to selection andassembly of the final prosthesis. The following steps arenecessary to prepare the intramedullary canal for steminsertion. Note that the selection of the stem diameteris dependent upon the anatomy of the canal, which issequentially reamed in order to accommodate thelargest-diameter stem possible.

1. Frozen section evaluation of the marrow contents bya skilled musculoskeletal pathologist is required toensure that no tumor cells are present within the bonemarrow prior to the preparation of the intramedul-lary canal. After insertion of a guidewire the canal issized and enlarged with a flexible intramedullaryreamer.

2. After the stem diameter has been selected, a facingreamer is inserted into the canal to machine a curvedradius in the free end of the bone. This radius isdesigned to match the radius of curvature at thestem/body junction of the prosthesis, and therebymaximizes the fit between the prosthetic body andthe bone.

3. The reamed canal is cleaned. A pulsatile lavage andan intramedullary brush helps remove clots andbone debris. A plastic cement restrictor is inserted toassist in pressurization of the cement at the time ofimplantation. The canal is packed to minimize bleedingduring the remaining preparatory steps.

4. The adjacent joint surface is then prepared to acceptthe prosthesis. The steps required vary by anatomicsite and are outlined in the following section.

5. A trial prosthesis is assembled and inserted. Thesurgeon checks for implant position, joint stability,

limb length, and range of motion. Length discrep-ancies are corrected by removing additional boneusing the facing reamer (for small adjustments),varying the size of the polyethylene component inthe proximal tibia (for distal femoral replacements),or changing the body segment selected.

6. The final prosthesis is assembled on a back table usingthe assembly holders and impactors provided withthe system. All Morse tapers must be completely cleanand dry to ensure a mechanically sound interferencefit.

7. Cementation of the canal and insertion of the assem-bled endoprosthesis is performed using third-gener-ation techniques.

8. The final step prior to the soft-tissue reconstructionis the application of onlay bone graft for extracorticalfixation. Autogenous bone graft (often taken fromthe adjacent joint surface) is positioned across theprosthetic bone junction and tied in place using alarge-diameter dacron tape.

Preparation of the Adjacent Joint by Anatomic Site

The adjacent joint surface must be prepared to acceptthe endoprosthesis prior to assembly of the finalcomponent. The preparation process varies with theanatomic location, as described below.

Shoulder (Proximal Humerus)

The majority of patients treated for tumors of theproximal humerus undergo an extra-articular resectionof the shoulder in order to ensure an adequate surgicalmargin.12 A combination of static and dynamic restraintsaround a unipolar prosthetic head provides stability forthe joint. Selection of the head diameter is based on thelocal anatomy. Large-diameter Dacron tapes are used tosuspend the prosthesis from the remaining scapulaand/or clavicle (static restraint). Multiple muscle transfers,including the pectoralis major muscle, are performed toachieve prosthetic coverage and joint stability.

Proximal Femur (and Total Femur) (Figure 25.7)

Bipolar hemiarthoplasty is the preferred method ofreconstruction for the hip. Resection of the surround-ing tissue of the acetabulum significantly denervatesthe acetabulum, and creates a painless hip, even inyoung, very active, patients. Conversion to a total hip ispossible, but rarely indicated. The bipolar head size ischosen after measurement of the acetabulum (eitherwith sized acetabular trials by direct measurement of



the diameter or of the excised femoral head). Followingimplantation of the prosthesis, joint stability is enhancedby transfer and myotenodesis of the psoas and theexternal rotators. Dacron tapes are placed around theprosthetic neck, where they act as static restraints. Thismethod virtually eliminates the risk of dislocation inthe postoperative period.

Distal Femur (and Total Femur) (Figure 25.8)

The top 1 cm of the tibial plateau is removed with anoscillating saw (a neutral cut without posterior slope)and saved for the extracortical onlay bone graft. Trialcomponents are used to select the largest tibialcomponent that fits on the proximal tibia with minimalmedial–lateral overlap. (Overlap must be avoided tofacilitate the soft-tissue closure over the prosthesis.)The tibial canal is prepared with a guide placed overthe plateau to create a distal bone plug and proximalbox to accommodate the stemmed polyethylene tibial-bearing component. Following trial reduction of theselected components the tibial insert is cemented intoplace using third-generation cement techniques.

Proximal Tibia (Figure 25.9)

The femoral condyles are resurfaced using a techniquesimilar to that used for a total knee replacement. Thefemoral canal is opened with a reamer to allow forinsertion of an intramedullary guide. A distal femoralcut is performed to remove 8 mm of the condyles.Anterior and posterior chamfers are created with anoscillating saw or a high-speed burr to accommodatethe standard-sized femoral component. After trialreduction this component is cemented into place usingthird-generation cement techniques.

GUIDELINES FOR SOFT-TISSUERECONSTRUCTION (STAGE 3)

The basic goals of the soft-tissue reconstruction are toprovide adequate coverage of the prosthesis and restoremuscle power and joint stability. A variety of local andregional muscular rotation flaps must be performed tomaximize functional outcome and ensure adequatecoverage of the prosthesis. Meticulous attention to han-dling the soft tissues and preserving the regional bloodsupply is essential at this step. Complete muscularcoverage of the prosthesis minimizes the risk of peri-prosthetic infection related to superficial woundbreakdown (marginal necrosis) that occasionally occursfollowing the creation of large flaps during an oncologicresection. Muscle transfers also improve stability of thereconstructed joint, and restore useful joint function.Aggressive mobilization of the remaining musclescrossing a given joint, as well as specific muscularrotational flaps, permits the surgeon to achieve all ofthese goals without creating free flaps.

To provide functional power to the limb, soft tissuemust be attached to the prosthesis. This entails attach-ing the major tendons to the prosthesis (using theprovided metal loops) and creating a musculotendinouscuff around the body of the prosthesis. In addition,


Figure 25.7 Radiograph of a large total femoral customprosthesis with a bipolar hip component and a Kinematicrotating hinge prior to the use of the modular design (1988).


restoration of proper limb length helps ensure stabilityof the reconstruction. As noted previously, the prosthesishas a beaded porous coating at sites of important tissueattachments. The porosity allows both for bone andfibrous ingrowth: a new tendon–bone junction is createdby adding bone graft between the porous surface of theprosthesis and the tendon which is held firm to theprosthesis with Dacron sutures.

Details of common muscle transfers are providedelsewhere in this textbook. These routine muscletransfers include the following:

1. Shoulder: transfer of the pectoralis major and latis-simus dorsi muscles covers and dynamically stabilizes

a proximal humeral prosthesis. Dacron tapes areused to statically suspend the prosthesis from thescapula.

2. Hip: the psoas and external rotators are transferredto create a pseudocapsule around the prosthetichead. This capsule is reinforced with circumferentialDacron tapes to prevent dislocation. Reattachmentof the abductor muscles is necessary to minimize theTrendelenberg lurch in the postoperative phase. Thislimp improves over time with strengthening of theabductors.

3. Knee: 25% of distal femoral replacements and allproximal tibial replacements require rotation of agastrocnemius muscle (typically the medial head) to


Figure 25.8 Intraoperative photographs of a distal femoral replacement. (A) A completely assembled distal femoral prosthesis(Modular Replacement System, Stryker Howmedica Osteonics, Inc., Allendale, NJ). (B) Trial prosthesis to determine theappropriate length and tension. Note a trial prosthesis of the Modular Replacement System has large holes in the body and stemto avoid mistaken implantation. (C) Distal femoral replacement without the use of a body. This is utilized for small segmentalresections and is required for some Stage III giant cell tumors and small (Stage I) intra-osseous sarcomas. (D) Intraoperativephotograph of a custom prosthesis used prior to 1988 with a large area of the body being porous coated. Note the attached bonegraft to the porous coating with Dacron tape (arrow) is to permit extracortical fixation. New bone formation is usually visualizedradiographically between 8 and 16 weeks postoperatively.

A B

C D


repair the soft-tissue defect following resection of atumor around the knee. This local flap is incorporatedinto the reconstruction of the patellar tendon inpatients undergoing proximal tibial replacements.13

Final closure of the wound may be jeopardized by skinloss following resection of a biopsy tract. Patients withvery large tumors generally have extra skin because thegrowing tumor acts as an internal skin stretcher. This

extra skin can be rotated to facilitate the wound closure.Excess skin along the incision should be excised toavoid marginal wound necrosis related to regionaldevascularization during the creation of large flaps. Toavoid pressure-induced ischemia, patients with tightskin closures are best served by leaving the skin openand performing a primary or secondary split-thicknessskin graft. Patients must be maximally elevated in thepostoperative phase to reduce swelling that can


Figure 25.9 Custom segmental prosthesis with a spherocentric knee component utilized prior to the early 1980s for theproximal tibia. (A) The anterior–posterior view. (B) Lateral view. Note that this is a spherocentric knee design and not a rotatinghinge. This was the original design utilized for knee replacements during the 1970s. A rotating hinge knee became availableduring the early 1980s.

A B


jeopardize the wound closure. Use of large-bore closedsuction drains and correction of any postoperativecoagulopathies is necessary to prevent hematomas.Patients who develop hematomas or wound break-down require aggressive treatment in the operatingroom to prevent secondary infection of the endopros-thesis.

CLINICAL RESULTS FOLLOWINGENDOPROSTHETIC REPLACEMENT

Prosthetic survival has improved dramatically since thedevelopment of advanced surgical techniques, betterprosthetic designs, and modern manufacturing tech-niques. Results of some early custom prostheses weredisappointing, leading many surgeons to use allograftsor other methods of reconstruction. More recently, ashigh rates of allograft complications have beenreported, there has been increasing interest in the newgeneration of endoprostheses.

Complications are not uncommon with any type oflimb-sparing procedure. The majority of these patientshave altered immune systems from chronic disease,chemotherapy, and malnutrition. Many patients areanemic and have clotting abnormalities, includingthrombocytopenia. Long-term indwelling catheters,used for the administration of chemotherapy, maycause a high incidence of line infections, that canjeopardize an endoprosthetic replacement throughhematogenous spread of bacteria. The local anatomiclocation of a tumor may disrupt the venous andlymphatic drainage of the extremity during resection,leading to venous stasis, swelling, and lymphedema.This can quickly result in flap necrosis during thepostoperative period. Secondary infection and eventualamputation may be the result. Finally, oncologiccomplications, including local recurrence of tumor ortissue necrosis from radiation, may result in failure of alimb-sparing procedure.

Complications specific to endoprosthetic reconstruc-tion may be related to mechanical or biologic factors.Prosthetic fracture, dissociation of modular compo-nents, fatigue failure, and polyethylene wear may beencountered. Improved designs and metallurgy cansignificantly reduce the incidence of these problems(Figure 25.10). Our experience with more than 150 MRSimplants over the past 12 years has revealed no stemfractures, body fractures, or taper dissociation.Polyethylene wear does occur, but less than 5% ofpatients with bushings in the rotating hinge mechanismhave required exchange of these components.

Nonmechanical (biologic), failure of an endo-prosthsis may occur as a result of aseptic loosening, orfracture of bone around the prosthesis. Joint stability is

no longer a problem. Moreover, the use ofcircumferential porous coating has dramaticallyreduced the incidence of aseptic loosening in ourpatients. Surgical technique, as well as the use ofcemented stems, has prevented periprosthetic fracturesduring surgery. The few patients who have developedfractures as a result of blunt trauma (falls, autoaccidents) have been treated successfully with castingand protected weight-bearing.

ENDOPROSTHETIC SURVIVAL

The majority of published United States series lookingat the survival of endoprosthetic reconstructions arebased on small series of custom components implantedin the late 1970s and early 1980s. These include thefollowing:


Figure 25.10 Composite photograph showing failures ofseveral different prosthetic devices utilized during the 1980sand the various modes of failure. The most common modeof failure was either stem breakage or bending. Today, stemsare heavily forged, have a curved transition at the junctionwith the prosthesis and are rarely less than 9 mm in diameter.


1. Chicago: 66% 10-year survival for distal femoralreplacements (DFRs).14

2. England: 64% 7-year survival rate for DFRs.15

3. New York: 89% proximal femur, 59% distal femur,54% proximal tibia.16

4. Washington: 83% 5-year and 67% 10-year survivalfor tumors at all sites.17

A more modern series was based upon experience withthe HMRS system in Europe. Long-term data for thedistal femoral replacement have been disappointing;an overall complication rate of 55%, a mechanical failurerate of 6% for stem breakage, and 42% polyethylenefailure after a follow-up of 64 months18. As a result thisparticular system was never approved for use in theUnited States.

Our experience with the current-generation MRS hasbeen very gratifying. Since its introduction in the 1980s,over 150 implants have been used at our center. Resultsof the first 100 prostheses, which have been followedfor a minimum of 2 years, are summarized in Table 25.1.

For this series, “failure” was defined as removal of theprosthesis for any reason. Most notably there havebeen no mechanical failures to date involving the stems,bodies or tapers. All the prostheses that failed were theresult of periprosthetic infection, at a 7% rate. Althoughthis is significantly higher than the infection rateassociated with total joint replacement, the majority ofthese patients were immunocompromised as the resultof chemotherapy treatments. The rate of polyethylenebushing failure has been approximately 5%.

FUTURE DIRECTIONS FOR ENDOPROSTHETICRECONSTRUCTION

The current MRS prosthesis has greatly facilitated limb-sparing surgery following resection of bone sarcomas.

Its success has expanded the indications for endo-prosthetic reconstruction to include bone defects fornononcologic problems. Increasing experience withthis system for salvage of failed total joint replacements,chronic nonunions of fractures, and reconstructionfollowing radical resection of osteomyelitis has shownthat the proven concepts of limb- sparing surgery canbe easily applied to many other clinical situations.

Current research to improve the performance of theMRS prosthesis is focusing on improved work onadvanced bioactive coatings, alternative methods ofstem fixation, and improved methods of attaching softtissue. Continued work on improved metallurgy andpolymers, particularly with the introduction of cross-linked polyethylene, is expected to improve thedurability of the MRS. Although future advances intissue engineering hold the promise of artificiallyengineered bones, we expect that endoprostheticreconstruction will remain the implant of choice oforthopedists for many years to come.


Table 25.1 Results of the first 100 MRS

Site of prosthesis Survival at Kaplan–Meier(no.) median Survival at

follow-up 10 years

Distal femur (48) 90.7% at 63.0 months 90%Proximal humerus (22) 98% at 77.7 months 98%Proximal femur (15) 100% at 58.8 months 100%Proximal tibia (13) 78% at 61.7 months 78%Total femur (2) 100% at 25.4 months

All sites (100) 88.2% at 64.4 months 88%

1. Enneking WF. Clinical Musculoskeletal Pathology.Gainsville: University Press of Florida; 1977.

2. Gebhardt MC, Flugstad DI, Springfield DS, Mankin HJ. The use of bone allografts for limb salvage in high-grade extremity sarcomas. Clin Orthop. 1991;270:181–96.

3. Hejna MJ, Gitelis S. Allograft prosthetic compositereconstruction for bone tumors. Sem Surg Oncol. 1997;13:18–24.

4. Marcove RC, Lewis MM, Rosen G et al. Total femur andtotal knee replacement. A preliminary report. ClinOrthop. 1977;126:147–52.

5. Capanna R, Morris HG, Campanacci D et al. Modularuncemented prosthetic reconstruction after resection oftumours of the distal femur. J Bone Joint Surg. 1994;76B:178–86.

6. Aboulafia AJ, Buch R, Mathews J, Li W, Malawer MM.Reconstruction using the saddle prosthesis followingexcision of primary and metastatic periacetabular tumors.Clin Orthop. 1995;314:203–13.

7. Ward WG, Johnson KS, Dorey FJ, Eckardt JJ. Extra-medullary porous coating to prevent diaphyseal osteolysisand radiolucent lines around proximal tibial replace-ments. J Bone Joint Surg. 1993;75A:976–87.

References


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9. Andriacchi TP, Natarajan RN, Hurwitz DE. Musculo-skeletal dynamics, locomotion and clinical applications.In: Mow VC, Hayes WC, editors. Basic OrthopaedicBiomechanics, 2nd edn. New York: Lippincott Raven;1997:000–00.

10. Henshaw RM, Malawer MM. Survival of modular versuscustom endoprostheses for limb salvage: are we actuallydoing better? Presented at American Academy ofOrthopaedic Surgeons 1998 Annual Meeting – ScientificProgram; Paper No. 157, 20 March, 1998.

11. Malawer MM, Canfield D, Meller I. Porous-coated seg-mental prosthesis for large tumor defects. A prosthesisbased upon immediate fixation (PMMA) and extracorticalbone fixation. In: Yamamuro T, editor. New Develop-ments for Limb Salvage in Musculoskeletal Tumors. NewYork: Springer; 1989:247–55.

12. Malawer MM. Tumors of the shoulder girdle. Techniqueof resection and description of a surgical classification.Orthop Clin N Am. 1991;22:7–35.

13. Malawer MM, Price WM. Gastrocnemius transpositionflap in conjunction with limb-sparing surgery for primarybone sarcomas around the knee. Plast Reconstr Surg.1984;73:741.

14. Rougraff BT, Simon MA, Kneisl JS, Greenberg DB, MankinHJ. Limb salvage compared with amputation forosteosarcoma of the distal end of the femur: a long-termoncological, functional, and quality of life study. J BoneJoint Surg. 1994;76:649.

15. Roberts P, Chan D, Gimer RJ, Sneath RS, Scales JT.Prosthetic replacement of the distal femur for primarybone tumours. J Bone Joint Surg. 1991;73B:762.

16. Horowitz S, Glasser D, Lane J, Healey J. Prosthetic andextremity survivorship in limb salvage: how long do thereconstructions last? Clin Orthop. 1993;293:280.

17. Malawer MM, Chou LB. Prosthetic survival and clinicalresults with use of large-segment replacements in thetreatment of high-grade bone sarcomas. J Bone Joint Surg.1995;77A:1154–65.

18. Capanna R, Morris HG, Campanacci D et al. Modularuncemented prosthetic reconstruction after resection oftumours of the distal femur. J Bone Joint Surg. 1994;76B:178–86.

19. Henshaw RM, Jones V, Malawer MM. Endoprostheticreconstruction with the modular replacement system.Survival analysis of the first 100 implants with aminimum 2 year follow-up. Proceedings, Fourth AnnualCombined Meeting of the American and EuropeanMusculoskeletal Tumor Societies, Washington, DC;1998:90.



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