Microangiographic Comparison of the Effects of Three-Loop Pulley and Six-Strand

Savage Tenorrhaphy Techniques on the Equine Superficial Digital Flexor Tendon

Kendra D. Freeman

Thesis submitted to the faculty of the Virginia Polytechnic Institute and State University

in partial fulfillment of the requirements for the degree of

Master of Science In

Biomedical and Veterinary Sciences

Jennifer G. Barrett

Nathaniel A. White II

Kenneth E. Sullins

February 13, 2014

Keywords: equine, tenorrhaphy, vasculature, tendon

 

Microangiographic Comparison of the Effects of Three-Loop Pulley and Six-Strand

Savage Tenorrhaphy Techniques on the Equine Superficial Digital Flexor Tendon

Kendra D. Freeman

Abstract

Injuries to the equine distal limb are common and often involve synovial,

tendinous and/or ligamentous structures. Historically, lacerations involving the equine

digital flexor tendons carried a poor prognosis for return to athletic function due to

contamination of the site at presentation, involvement of multiple anatomic structures and

the need for immediate weight bearing after surgery. The need for weight bearing after

surgery places strain on the tenorrhaphy site that exceeds the strength of the repair itself.

Extrapolation of complex, stronger tenorrhaphy patterns from human literature and

applying them to equine patients has been challenging.

Human tenorrhaphy techniques initially focused on strong repairs, which are able

to match or exceed the strength of tendon itself. Adhesion formation is problematic in

human flexor tenorrhaphies, as most injuries occur to tendons surrounded by synovial

structures. Human literature now focuses on using repairs that provide initial strength,

minimal damage to intrinsic tendon architecture, and allow for early mobilization. This

treatment protocol has greatly improved the functional outcome of human tenorrhaphies.

Recent studies have evaluated the strength of complex tenorrhaphy patterns in

equine superficial digital flexor tendons, using modifications of the Savage technique.

The newly evaluated patterns are stronger than previously tested and commonly used

techniques, such as the three-loop pulley (3LP). A review of tendon vasculature across

species and healing characteristics of tendons highlights the importance of intrinsic

 

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tendon vasculature in the healing process. Using tenorrhaphy techniques that preserve

this vasculature may improve the clinical outcome in these cases. Only one study has

previously evaluated the effect of tenorrhaphy patterns on intrinsic tendon vasculature in

equine superficial digital flexor tendon.

This study compared perfusion of intrinsic tendon vasculature of equine

superficial digital flexor tendon (SDFT) after 3LP and six-strand Savage (SSS)

tenorrhaphies. We hypothesized that the SSS technique would significantly decrease

vascular perfusion compared to the 3LP technique.

Under general anesthesia, eight pairs of forelimb SDFTs were transected and

either SSS or 3LP tenorrhaphy was performed on each forelimb. The horses were

heparinized, euthanatized, and forelimbs perfused with barium sulfate solution then fixed

with formalin under tension. The tendons were transected every 5mm and

microangiographic images were obtained using a Faxitron X-ray cabinet with computed

radiography imaging. Microvascular analysis of sections proximal to the tenorrhaphy,

throughout the tenorrhaphy and distal to the tenorrhaphy was completed using Image J

software and a custom macro.

A significant reduction in the number of perfused vessels was seen in the SSS

compared to the 3LP at two locations within the tenorrhaphy (p=0.004 and 0.039). The

SSS technique took on average 4.7 ± 0.9 times longer to place.

The SSS technique causes a reduction in tendon perfusion compared to the 3LP,

which may limit its clinical use. Further research is required to elucidate the clinical

significance of this difference.

 

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Acknowledgements

I would like to thank and acknowledge the members of my graduate committee,

Dr. Jennifer G. Barrett, Dr. Nathaniel A. White II, and Dr. Kenneth E. Sullins for their

support and guidance over the course of this project. I would also like to thank Daniel W.

Youngstrom for assistance with perfusion, statistical analysis, and figure development. I

am grateful for the hard work of Dr. Elaine Meilahn, coordinating donation horses for

this study. Additionally, I would like to thank the American College of Veterinary

Surgeons for the funding of this project via the ACVS Diplomate Clinical Research Grant

Program.

 

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Attributions

The committee members were involved in the project and contributed to the

conceptualization, execution of the research and production of the thesis.

Jennifer G. Barrett – DVM, PhD, Diplomate ACVS, Diplomate ACVSMR (Marion

duPont Scott Equine Medical Center, Virginia-Maryland Regional College of Veterinary

Medicine) is the primary advisor and committee chair. Dr. Barrett’s primary research

interest is tissue engineering and regenerative medicine. Dr. Barrett has earned a PhD in

molecular biology and has extensive research experience. She played a vital role in the

overall project design and execution as well as the writing of the thesis.

Nathaniel A. White II – DVM, MS, Diplomate ACVS (Marion duPont Scott Equine

Medical Center, Virginia-Maryland Regional College of Veterinary Medicine) is a

committee member. Dr. White has extensive clinical experience in the treatment of

equine tendon and ligament injury. He contributed significantly to project design and

thesis review.

Kenneth. E. Sullins – DVM, MS, Diplomate ACVS ) Marion duPont Scott Equine

Medical Center, Virginia-Maryland Regional College of Veterinary Medicine) is a

committee member. Dr. Sullins has extensive clinical experience in the treatment of

equine lameness and emergency case management. He contributed significantly to the

review of the thesis.

 

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Table of Contents Abstract ii Acknowledgements iv Attributions v Table of Contents vi List of Figures vii Thesis Organization viii Chapter 1 Introduction Clinical Relevance of Tendon Injury 1 Tendon Structure and Organization 2 Tendon Anatomy 5

Techniques to Determine Normal Vasculature 6 Tendon Vasculature 8 Tendon Healing 9

Tenorrhaphy Techniques in Human Literature 12 Human Postoperative Rehabilitation Techniques 13 Tenorrhaphy Techniques in Veterinary Medicine 14 Small animal 14 Equine Implant Materials 15 Equine Suture Patterns 17 Equine Non-Surgical Management 19 Equine Distal Limb Immobilization 19 Conclusions 20 References 22 Chapter 2

Microangiographic comparison of the effects of three-loop pulley and six strand Savage tenorrhaphy techniques on the equine superficial digital flexor tendon Abstract 33 Introduction 35 Materials and Methods 37 Results 43 Discussion 45 References 49 Chapter 3 Conclusions 55

 

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List of Figures

Chapter One Figure 1: Hierarchal organization of tendon. (Dowling 2000) 4

Used under fair use guidelines. Figure 2: Diagram of the three-loop pulley and six-strand Savage patterns. 18

Adapted from Everett et al 2011. Chapter Two Figure 1: Perfused limb with tensioning device. 40

Figure 2: Tenorrhaphy regions for microangiographic analysis. 42

Figure 3: Vascular count data by region. 44

Figure 4: Box and whisker plot of surgery times. 44

 

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Thesis Organization

This thesis is organized into three chapters. The first chapter provides a review of

literature pertaining to tendon repair and healing. The second chapter contains a journal

publication entitled “Microangiographic comparison of the effects of three-loop pulley

and six strand Savage tenorrhaphy techniques on the equine superficial digital flexor

tendon” and contains its own introduction, materials and methods, results, discussion and

references. The final chapter contains thoughts on future research directions.

 

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Chapter One

Clinical Relevance of Tendon Injury

Traumatic injuries to the equine distal limb are common and often occur due to

kicks, wire or overreach injuries. Because of the complexity and lack of extensive soft

tissue protection of the equine distal limb anatomy, many support structures can be

affected by trauma, including the extensor and flexor tendons, suspensory ligament, distal

sesamoidean ligaments, neurovascular structures and well as joints and tendon sheaths. 1,2

Injuries to the tendons and ligaments that support the limb can be challenging to treat and

generally carry a poor to guarded prognosis for return to full athletic function. Extensor

tendon lacerations carry a better prognosis with 80% of horses returning to some level of

riding soundness. 3 Flexor tendons lacerations have guarded prognosis with 55-58% of

horses returning to riding soundness. 3,1,2,4 Injuries to the tendons of the equine distal limb

are often complicated by involvement of synovial compartments, wound contamination,

and the involvement of multiple structures. A study by Jordana et al 1 found the prognosis

for distal limb lacerations was related to the number of structures involved.

  Clinical presentation of these injuries varies with some horses presenting with

small, seemingly insignificant skin wounds to large palmar metacarpal lacerations with

transected tendon fibers visible through the wound. Palpation and ultrasonographic

examination of the area can assist in making the diagnosis of a flexor tendon laceration,

especially in the case of partial transection. Horses with complete transection of the

superficial digital flexor tendon will often present in hyperextension of the

metacarpo/metatarsophalangeal joints. Disruption of the superficial and deep digital

flexor tendons will cause hyperextension of the metacarpo/metarsophalangeal joint as

 

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well as elevation of the toe during weight bearing. 5,6 Often, close examination of the site

under general anesthesia is required to fully evaluate the extent of the injuries and

determine the number of structures involved.

Tendon Structure and Organization

The structural and material properties of a tendon are determined by the three

dimensional structure and organization of the fibrils. Tenocytes and non-collagenous

proteins aid in fibril organization. 6,7 One of the most studied non-collagenous proteins in

tendon is cartilage oligomeric matrix protein (COMP). This molecule is most active in

young, growing animals, appears to be involved in the organization of collagen fibrils

during growth 6, and has been shown to accelerate collagen fibrillogenesis in vitro. 8

Increased concentration of COMP has been identified in areas of equine tendon under

tension, peaking during the first two years of life. The more COMP that is synthesized

during growth phase, the stronger the resulting tendon.8

Tendon extracellular matrix is a gel-like substance with varying composition

along the length of a tendon and serves to provide the gliding functions of tendons 9,10

Large proteoglycans such as aggrecan and versican are present in highest concentrations

in areas of compression along the tendon, (i.e. deep digital flexor tendon over the

proximal sesamoid bones). These proteoglycans have a large water holding capacity due

to their high numbers of highly sulfated glycosaminoglycan side chains, allowing them

the resist compression.8 Smaller proteoglycans such as decorin, fibromodulin, and

lumican predominate in areas of tension7,8 and are involved in the regulation of collagen

fibril diameter.11

 

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Tendons are composed of highly organized collagen fibers, collected into bundles,

and surrounded by a gel-like extracellular matrix. 9,12 Tendon has low cellularity and

vascularity with abundant extracellular matrix. The extracellular matrix is composed of

collagens, proteoglycans, glycoproteins, and glycosaminoglycans. The predominant

fibrillar collagen in tendon is type I collagen. The smallest unit of in the tendon structure

is the tropocollagen, a triple helical structure, followed by sequentially larger

microfibrils, subfibrils and fibrils (Fig 1). Fibrils together with fibroblasts form tendon

fascicles. Fascicles measure 0.8-1.2mm in diameter and form a characteristic wave form

or crimp when viewed microscopically. 7 This crimp pattern contributes to tendon

elasticity allowing the tendon to elongate during early loading. 7 The larger diameter

fascicles provide strength and smaller diameter fibers contributing to elasticity. 13

Fascicles and associated connective tissue form the functional tendon unit. 6,8 8 The

tendon fibers are often described as longitudinal structures. While this is mostly true, in

some tendon regions the fibers are arranged in a spiral or helical pattern.14,15 This allows

for more even distribution of load during increased tension while changing direction

around a joint (i.e. sesamoid bones at the fetlock joint). This arrangement decreases

tendon distortion during range of motion, lessens friction between tendon fibers and

causes less interference with intrinsic blood vessels. 14

 

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Figure 1: Hierarchal organization of tendon. (Dowling 2000) Used under fair use

guidelines.

The functional tendon unit is surrounded by the epitenon. This structure is

connected to the paratenon, a connective tissue layer present in non-synovial regions.6

The paratenon connects the epitenon to the connective tissue surrounding the tendon and

decreases the frictional forces placed on the tendon by surrounding structures as well as

the provides vascular suport and cellular elements necessary for repair of the damaged

tendon.6 The epitenon is continuous with the connective tissue that surrounds fascicles

called the endotenon. The endotenon is important as blood vessels and nerves course

within the endotendon to reach the fascicles throughout the tendon.6 Type I collagen

predominates within the tendon while type III collagen predominates in the endotenon

and epitenon.10

strain). Crimp angles and lengths were found to be 19–20° and17–19 µm respectively in the midmetacarpal region of the youngSDFT(Wilmink et al. 1992), reducing to 12–17° and 11–15µ mwith ageing. The elimination of the crimp with age is thought tocontribute partly to the increased stiffness of tendon with age.

The noncollagenous substance is composed of tenocytes andglycoproteins. Three distinct cell types ( I, II and III), have beenidentified on light microscopy within the fascicles of normalequine tendon, based on the morphology of their nuclei. Thedistribution of cell types varies with age, between tendons andwithin tendons (Webbon 1978; Goodship et al. 1994; Smith andWebbon 1996). The functions of these different cell types areunclear but it is postulated that Type II and III cells have highermetabolic activity because their nuclei are larger and containnucleoli. These cells may be concerned primarily withextracellular matrix synthesis (Smith and Webbon 1996) butconsiderably more information is needed on the nature of thesed i fferent cell types and their function. There is a furtherpopulation of cells resident within the endotenon septa of thetendon whose function are largely unknown.

Of the glycoproteins, cartilage oligomeric matrix protein(COMP) is one of the most abundant (Smith et al. 1997a). T h epresence of a phenotype associated with a mutation of the humanC O M P gene (pseudoachondroplasia), characterised by tendonand ligament laxity (Hecht et al. 1995; Briggs et al. 1995), lendscredence to the hypothesis that COMP plays a structural role intendon. Its accumulation in tendons under high loads (such as theweightbearing equine digital flexor tendons) in comparison tolower load-bearing tendons (e.g. the equine digital extensortendons) is intriguing but not understood, especially as thispattern appears to be also present in human tendons.

Proteoglycans consist of glycosaminoglycan side-chain(s)attached to a protein core. Various glycosaminoglycans have beendemonstrated within the equine SDFT including chondroitinsulphate, dermatan sulphate, keratan sulphate, heparin, heparinsulphate and hyaluronic acid (Smith and Webbon 1996), but thisknowledge is only of limited benefit as this does not indicate thenature of the proteins to which they are attached. T h e

metacarpophalangeal regions of normal SDFT contain more of thel a rg e r, cartilage-like, proteoglycans, and experience higher rates ofproteoglycan synthesis compared to the midmetacarpal region.These differences probably reflect functional and metabolicvariance that exists between regions of tension and compression(Smith and Webbon 1996; Perez-Castro and Vogel 1999; L.Micklethwaite et al., unpublished data). The small proteoglycansdecorin, fibromodulin and biglycan have been shown to occurthroughout the SDFT (Smith and Webbon 1996) and are thought toinfluence tenocyte functions, collagen fibrillogenesis, and thespatial organisation of fibres, thereby influencing tendon strength(Hedbom and Heinegard 1993; Svensson et al. 1995; Gu and Wa d a1996). The advent of gene knock-outs has demonstrated that acomplete lack of decorin results in large irregular collagen fibrilswith poor mechanical strength in skin (Danielson et al. 1 9 9 7 ) ;h o w e v e r, little is known about the small proteoglycans’precise rolein modulating biomechanical properties in tendons (Cribb andScott 1995). In addition, the small proteoglycans have becomeincreasingly recognised as potentially having a metabolic role suchas the sequestration of growth factors in the matrix (Yamaguchi et al. 1 9 9 0 ) .

370 Superficial digital flexor tendonitis in the horse

Fig 1: Schematic representation of the collagen arrangement in superficial digital flexor tendon (adapted from Kastelic et al. 1978).

Tropocollagen

Microfibril

Subfibril Fibre/Fibril

Fascicle(CSA =

0.8–1.2 mm2 Tendon

64 nmperiodicity

TenocytesCrimp (angle

= 12–20°length =

11–19 µm)Endotenon

Epitenon/Paratenon

1.5 nm 10–20 nm 40–500 nm 50–300 µm3.5 nm

Stress

StrainFig 2: Simplified stress-strain curve for the superficial digital flexortendon (from Goodship et al. 1994). Key: 1 = ‘toe’ region; 2 = lineardeformation; 3 = yield; 4 = rupture.

1

2

3

4

 

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Tendon Anatomy

Movement of the equine distal limb is made possible, in part, by groups of flexor

and extensor muscles. The forelimb extensor group contains the m. extensor carpi

radialis, m. extensor digitorum communis, m. extensor digitorum lateralis and m. ulnaris

lateralis, all innervated by the radial nerve, while the hind limb extensor group is

composed of m. tibialis cranialis, m. extensor digitorum longus, m. peroneus tertius and

m. extensor digitorum lateralis innervated by the fibular nerve.16,17 The forelimb flexor

group is composed of the m. flexor carpi radialis, m. flexor carpi ulnaris, m. flexor

digitorum superficialis, m. flexor digitorum profundus and interossei innervated by the

median and ulnar nerves. The hindlimb caudal muscle group consists of the

gastrocnemius, flexor digitorum superficialis, flexor digitorum profundus, popliteus, and

interosseous and muscles innervated by the tibial nerve. 16,17

The most clinically relevant musculotendinous units of the equine distal forelimb

are the m. flexor digitorum superficialis and m. flexor digitorum profundus. The m. flexor

digitorum superficialis originates from the medial epicondyle of the humerus as well as

the caudal radius. The musculotendinous unit travels distad on the caudal aspect of the

limb, joining with its accessory ligament (proximal check ligament) at the level of the

distal radius. The superficial digital flexor tendon continues through the carpal canal,

coursing distad just deep to the skin and superficial to the deep digital flexor tendon

along the palmar metacarpal region. The tendon divides into two branches at the level of

the proximal phalanx and coursing on either side of the deep digital flexor tendon to

insert on the distal aspect of the proximal phalanx and the proximal aspect of the middle

phalanx. The m. flexor digitorum profundus originates on the humerus, olecranon and

 

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radius. It courses in a similar manner along the caudal aspect of the antebrachium and

through the carpal canal. It joins its accessory ligament (distal check ligament) in the

proximal metacarpal region, and continues distad along the palmer metacarpal region

deep to the superficial digital flexor tendon and superficial to the interosseous ligament.

The tendon ultimately inserts on the distal phalanx. 16

The forelimb flexor group travels through two synovial structures: the common

carpal sheath of the flexor tendons and the digital flexor tendon sheath. The purposes of

these synovial structures are to protect the flexor tendons and provide lubrication in

regions of joint movement. The proximal extent of the carpal sheath is located 8-10 cm

proximal to the carpus, and extends distad to the level of the mid-metacarpus. The flexor

tendons are located within a component of the common sheath called the carpal canal.

The borders of the carpal canal include the carpal flexor retinaculum, accessory carpal

bone and the carpal ligament. Within this structure the superficial digital flexor tendon

has a close association with the medial palmar vein and nerve. 18

The digital synovial sheath begins in the distal metacarpal region, above the

metacarpophalangeal joint and extends distad to the level of the mid-second phalanx and

navicular bone. The T ligament separates the digital synovial sheath from the

podotrochlear (navicular) bursa.16,18 Within the digital synovial sheath, the proximal

portion of the deep digital flexor tendon is encircled by a thin sleeve of the superficial

digital flexor tendon called the manica flexoria.18

Techniques to Determine Normal Vasculature

Identification of tissue vasculature can be performed using several methods. The

method used depends on the invasiveness of the procedure, ease of use and the use of

 

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patients vs. postmortem samples. In living tissue the use of ultrasonography, computed

tomography, and magnetic resonance imaging are commonly used. Doppler

ultrasonography analyzes frequency shifts of echoes scattered by red blood cells to

measure velocity of blood flow.19,20 Color flow Doppler has been used to identify

neovascularization in chronic tendinopathy patients.21 Power Doppler used the amplitude

of signals received from tissue to quantify the number of moving red blood cells in a

region of interest.20 Power Doppler ultrasonography can detect vessels as small as 0.3mm

in diameter and is superior than color flow Doppler in low flow regions.22,20 Power

Doppler has been shown to be more sensitive at detecting microvasculature in human

Achilles tendon compared to color Doppler. This is because power Doppler is not as

dependent on alignment of the probe with flow as color Doppler.23

Three dimensional microvascular imaging can be accomplished with three-

dimensional computed tomographic angiography. This has been used to determine three

dimensional anatomy and structure of vessels for neurovascular and abdominal vascular

surgery as well as reconstructive surgery.24-31 This technique uses a narrow x-ray beam

and multiple detectors that rotate 360 degrees to generate cross-sectional data for a region

of interest. Computer reconstruction of the region is used to create the three dimensional

image.31 Magnetic resonance imaging techniques have been used to evaluate cardiac

perfusion in myocardial infarction patients.32 A more sensitive method of this type of

imaging is dynamic contrast enhanced magnetic resonance imaging. This technique uses

sequential images obtained before, during and after injection of contrast agents. With this

technique differences in blood volume and vascular permeability can be identified. This

 

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has proved useful in the detection and diagnosis of neoplastic conditions in humans. In

addition, it can be used to detect response to anti-angiogenic oncology treatments.33-36

In postmortem tissues, the use of radiopaque substances, dyes, silicone mixtures

and radioisotopes have been used to determine the vascular anatomy of tissues.37-42 Many

anatomical studies of equine tendon vasculature have been performed using barium

perfusion studies.37,38,43 Different barium products and solutions have been used, with

smaller particle sizes providing better vascular filling than larger particle sizes.41

Radiographic angiography can provide detailed images of microvasculature; however,

limitations include the inability to differentiate between vessels in different tissue planes,

locations of vessel anastomoses, and differentiation of vessels traversing tissue planes.31

Tendon Vasculature

Tendons receive their blood supply from several sources including the

musculotendinous or osteotendinous junctions, vessels derived from the tendon sheath

and the paratenon.42,44-46 Using barium perfusion studies Kraus- Hansen et al described

the vascular supply of the equine superficial digital flexor tendon (SDFT) as a network of

anastomosing vessels within the tendon body with large parallel vessels coursing

longitudinally at the medial and lateral aspects of the tendon.37,47 Additionally, a branch

of the median artery was consistently present within the accessory ligament of the

SDFT.37 Work by Stromberg identified a decreased number of intrinsic vessels in equine

flexor tendons in middle and distal portions of tendons compared to proximal regions.41

In regions of flexor tendons outside of a synovial structure, the paratenon is

involved in vascular support of the tendon. The vessels in the paratenon have a transverse

orientation. These vessels traverse through the epitenon. At this level the vessels branch

 

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into arcades and enter the tendon. Each arcade has limited anastomotic connections with

other adjacent arcades. Even with the anastomotic connections the arcades are only able

to supply vascular supply to a limited, regional area.42 In human flexor tendons the

segmental arcades supply areas of no more than one centimeter in length.42

Within synovial structures, flexor tendons receive their blood supply from

mesotendinous attachments to the sheath. Within this common carpal canal the flexor

tendons receive their blood supply from the common mesotendon that exits from the

caudomedial aspect of the tendons, attaching to the caudal aspect of the sheath.

Additionally the superficial digital flexor tendon receives vascular support from its

accessory ligament and the medial and lateral vessels entering at the distal reflection of

the sheath. The deep digital flexor tendon receives vascular support from its radial

head.18,41 Mesotendinous attachments in the digital flexor sheath are located at the palmar

aspect of the superficial digital flexor tendon and the proximolateral and proximomedial

margins of the deep digital flexor tendon.18 Synovial sheaths have an increased number of

transverse vessels at locations where tendons traverse over changes in limb angles at

joints (i.e. sesamoid bones). Intrinsic vasculature is decreased at these locations and the

sheaths and mesotendinous attachments at these locations provide additional

vasculature.42

Tendon Healing

Healing of an injured tendon can be divided into three general stages:

Inflammatory, Fibroblastic and Remodeling. During the exudative stage inflammatory

mediators such as leukocytes, macrophages and erythrocytes move from the vasculature

to the site of injury. This phase lasts 48-72 hours and during this time, the tenorrhaphy

 

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provides all strength to the repair, as the clot at the site of injury provides little strength.

During this stage the migrating cells work to remove necrotic tissue, initiate

angiogenesis, promote tenocyte proliferation and recruit additional inflammatory

mediators.48

During the fibroblastic stage, tenocytes and fibroblasts proliferate and synthesize

new extracellular matrix and fibroblasts fill the damaged area, leading to an increase in

tendon size.49,50 The fibroblasts produce pro-collagen molecules. These alpha-helical

collagen molecules are cleaved by collagenases and three of the helices combine to form

the triple helical collagen fibril.6 These triple helical collagen fibrils form a three-

dimensional collagen structure. Type III collagen production predominates at this stage.7

The fibroblasts identified in scar tissue of equine superficial digital flexor tendons have

different morphology than typical fibroblasts. They have a larger and more rounded

nucleus with prominent basophilic cytoplasm, and are larger than tenocytes. It has been

postulated that these cells are myofibroblasts. Smooth muscle cells from local blood

vessels are recruited to the site of injury and supply these cells to the area.50,51 Intrinsic

tenocytes and regional myofibroblasts are important at this phase of healing.

The final stage of healing is the remodeling stage, which starts about six weeks

after injury. The remodeling phase is important as it determines the final functional

properties of the healed tendon. During this stage small, immature collagen fibers

coalesce to form bundles of predominately type III collagen fibers, which realign along

the long axis of the tendon and provide increased strength to the site. 7,52 During this

process it is important to have the majority of the healing at the damaged tendon ends,

with less cell proliferation adjacent to the tendon and surrounding tissues to decrease the

 

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formation of adhesions.8 In human flexor tendon injury management, controlled early

motion exercises are used to limit adhesion formation and to apply stress to the scar to

help stimulate tissue remodeling.53-56

Two major mechanisms are thought to contribute to the ultimate healing of a

tendon. The extrinsic mechanism involves the movement of inflammatory cells from the

periphery to the site of injury to initiate the exudative phase of healing. This process

appears to promote adhesion formation during healing.10 The intrinsic mechanism

involves migration and proliferation of cells from the endotenon and epitenon. These

cells establish an extracellular matrix at the site of injury as well as an internal

neovascular network.10 This process is responsible for the reorganization of collagen

fibers during the final phase of healing. It is likely that a balance of both mechanisms is

necessary for tendon healing, making it important to minimize further trauma to the

tendon, epitenon, and paratenon as well as the surrounding environment during treatment

of a tendon laceration.

The metabolic activity of tendons has been identified to be 7.5 times less than

skeletal muscle.57 In addition, intrinsic tendon vasculature is compromised at sites of

friction and compression.58 Because of the decreased metabolic activity and relative

hypovascular regions within tendons, they have a natural ability to function in anaerobic

environments. This allows tendons to tolerate loads and tension without development of

ischemia.58

Both the intrinsic and extrinsic tendon blood supplies are important in the healing

process. Diminished blood supply has been demonstrated to impair tendon healing.59,60

Following injury, equine tendons heal from both intrinsic or extrinsic mechanisms.

 

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Extrinsic healing involves the ingrowth of cells from the paratenon and is especially

active in the repair of damaged tendons within a synovial compartment, often leading to

the formation of fibrous adhesions. Intrinsic healing occurs via activation of

macrophage-like cells from the epitendon and endotendon.46,61,62 Damage to the intrinsic

tendon vasculature has been proposed to promote adhesion formation in human

tenorrhaphies although the exact mechanism has yet to be elucidated.59,61,63 A balance

between intrinsic and extrinsic healing mechanisms is necessary for healing of the

damaged tendon with minimal adhesions.

Tenorrhaphy Techniques in Human Literature

Primary repair of damaged flexor tendons is advised when more than 60% of the

tendon cross sectional area has been transected.64-66 Although primarily repaired flexor

tendons have been shown to have a better functional outcome compared to either delayed

repair or tendon grafting67,68 there is no consensus on the best tenorrhaphy pattern to use.

Strickland et al69 stated that the ideal repair should have minimal gapping, minimal

interference with the vasculature, secure suture knots, smooth junction of the tendon ends

and provide sufficient strength. One of the first tenorrhaphy techniques widely used was

the Bunnell.70 This pattern consists of multiple diagonal passes of the suture across the

tendon, creating multiple figure-of-eights in the tendon. Studies have since found that

pattern produces severe constriction of the tendon and focal ischemia.71,8,72

Methods to increase tenorrhaphy strength include increasing the number of suture

passes across the tenorrhaphy, increasing suture size and the addition of peripheral

sutures.73,74 In an effort to increase the strength of the repair, more complex suture

patterns consisting of increased number of suture passes across the tenorrhaphy site were

 

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developed including the modified Kessler, Tsuge, and Savage suture patterns.48,74,75

Patterns such as the Savage technique are advantageous due to multiple suture strands

crossing the tenorrhaphy site with minimal exposed suture. This leads to a strong repair

with satisfactory gliding function.74,76,77

Placement of a suture peripheral to the tendon has been advocated to have several

benefits. Peripheral patterns have the advantages of providing additional strength to the

tenorrhaphy and decreasing gliding friction at the site.78-83 The combination of core and

peripheral repairs are not only stronger than core repairs alone, they are also more

resistant to early gap formation.79,84 The Lin-locking peripheral suture has been found to

be the strongest peripheral suture, increasing the tensile strength of a core repair by 3.7

fold.81,83 The disadvantage of this pattern is its technical difficulty.83 Currently, the

placement of both a multi-strand core suture with a continuous peripheral pattern is

recommended; however, pre-operative planning is necessary as circumferential access to

the tendon is necessary for any continuous peripheral suture pattern.48,79,81-85

Human Postoperative Rehabilitation Techniques

Adhesion formation following human flexor tendon repair is common and

troublesome, especially for repairs of tendons located within synovial cavities.61,52,86,87

Prolonged immobilization can lead to development of weaker fascicles, decreased

proteoglycan content and overall tendon atrophy.58,88 Controlled mobilization is currently

recommended in the early postoperative phase to limit formation of adhesions as well as

strengthen the healed tendon tissue.89,55,85, 86,90-92 Three general methods used to achieve

early controlled motion include active extension-passive flexion using rubber bands,

passive motion provided by a physical therapist and controlled passive motion with the

 

  14  

patient actively flexing the affected digit. 48 These techniques rely on the strength of the

tenorrhaphy to prevent gap formation in the early healing phase. The human digital flexor

tendons in the hand need to withstand 10-17 N force during mild to moderate resistance

to flexion.93 Commonly used tenorrhaphy techniques for these injuries provide strength

of up to 67 N before ultimate failure94, easily overcoming the force placed on the flexor

tendons during normal movement. Further studies have identified the exact excursion

flexor tendons undergo during range of motion of the joints in the digit.95 For example,

passive motion exercises often involve 3-5mm of tendon excursion by flexing the digits

by 10 degrees.55,56 Although various braces and splints have been designed to stabilize,

support and control the tenorrhaphy site, consequences of overzealous motion or poor

patient compliance include separation, elongation or rupture of the repair.96

Tenorrhaphy Techniques in Veterinary Medicine

Small Animal

Canine tendon and ligament lacerations that are treated with primary repair

include stifle collateral ligaments and Achilles tendon injuries. The most commonly

reported suture patterns used in repair of these injuries are the locking loop and three-

loop pulley patterns.97,98 The three-loop pulley has been found to be stronger in single

load to failure than both the locking-loop pattern97 and a double locking-loop pattern.98

These suture patterns are often modified to re-attach the Achilles tendon to the calcaneus,

including addition of a mesh to strengthen the repair.99,98

The strength of repair achieved in canine soft tendon and ligament repairs vary,

but are less than those achieved in equine repairs. Biomechanical testing has determined

 

  15  

the strength of the three-loop pulley to be between eight and 145 N, depending on the soft

tissue tested.97-99 When directly compared to the three-loop pulley, the locking loop

pattern has been found to be significantly weaker with a single load to failure of 35 N.

97,98

Equine Implant Material

Carbon fiber sutures were evaluated in equine flexor tendon repair due to the

strength of the implant. The carbon fiber material has been reported to be successful in

both clinical and experimental cases; however, outcome variables are different between

studies and follow up information was as short as 24 weeks in some of the studies.100-103

Although the carbon fiber sutures have been used successfully in other species 103-106they

have been found to cause a progressive, granulomatous foreign body reaction in equine

flexor tendons.45 This reaction makes repair with this material weaker than repairs with

nylon suture by eight weeks after the repair.102

Bioabsorbable tendon plates have also been used in equine flexor tendon repair.

The goal of these implants, made of absorbable poly-L-lactic acid, is to provide a scaffold

for fibroblast ingrowth, and a stronger repair.107,108 The plates have demonstrated

significant strength with a mean load to failure of 1507.08 +- 184.34 N compared to the

mean strength of the three-loop pulley technique, 460.86 +-60.93N. 109 These implants

are bulky, present substantial foreign material into a potentially infected or contaminated

wound and require extensive dissection around the tendon for placement, limiting their

clinical use.

Although many different implant materials have been tested, suture, both

absorbable and non-absorbable, is the most common material used for the repair of

 

  16  

tendon lacerations. In general, absorbable suture material is recommended as non-

absorbable suture material is thought to decrease the strength of the repair, increase the

risk of tissue reaction and have increased adhesion formation.48 Non-absorbable suture

materials such as nylon and polypropylene do have the advantage of maintaining their

tensile strength while the tendon heals. It is possible for any suture material to harbor

infection if placed in a contaminated environment, and equine tendon lacerations are

often contaminated, if not infected, at the time of treatment. This potential to harbor

infection with non-absorbable suture is the major advantage offered by using a

monofilament, absorbable suture material such as polydioxanone.

In general absorbable suture material is recommended as non-absorbable suture

material is thought to decrease the strength of the repair, increase the risk of tissue

reaction and have increased adhesion formation.48. 48,85 The most commonly reported

suture materials reported in equine flexor tendon tenorrhaphy are polygalactin 910,

polypropylene, polydioxanone and nylon.1,2,4,109-112 Polyglactin 910 is a braided

monofilament, absorbable suture that loses 100% of its tensile strength by day 35.

Polypropylene, a synthetic monofilament material that does not appear to lose any

significant tensile strength. It is contraindicated for use in infected tissue and has poor

knot security, making it undesirable in equine flexor tenorrhaphies. Polydioxanone, an

absorbable, synthetic monofilament suture, loses 50% of its tensile strength by day

42.113,114 Nylon is a non-absorbable material available as either a mono- or multifilament.

It loses 30% of its tensile strength after two years.

Increasing the diameter of the suture material has been used as a way the further

strengthen the repair. Merely increasing the suture caliber from 4-0 to 3-0 was shown to

 

  17  

increase the strength of the repair 2-3 fold. 115 Taras et al evaluated 5-0 and 2-0 suture

material in both the Kessler and double-grasping patterns. The 2-0 suture material was

167% stronger for the Kessler repair and 391% stronger for the double-grasping pattern

compared to the 5-0 suture material. 116 The disadvantage of larger suture material is the

potential negative effect on the tendon itself. Hatanaka et al showed that tendon healing

was negatively affected by suture material of 3-0 or greater. 117

Equine Suture Patterns

In an effort to strengthen equine tenorrhaphies many suture patterns have been

attempted, although the three-loop pulley pattern remains the mainstay of equine flexor

tendon laceration repair. The pattern is easy to place, moderate in strength, resists gap

formation, and has less negative effect on intrinsic tendon vasculature compared to the

locking loop pattern.43,118,1,112,119 The three-loop pulley pattern involves placement of

three suture loops oriented 120 degrees from each other. Numerous equine studies have

evaluated this pattern biomechanically with the strength of the pattern at failure ranging

from 245 N to 461 N.109-111,112 The strength of this pattern, regardless of the suture

material used, does not come close to the load of 3559 N placed on the equine superficial

digital flexor tendon during weight bearing without external coaptation.120

Recent equine veterinary literature has evaluated several complex tenorrhaphy

patterns in equine superficial digital flexor tendons. Everett et al 111 evaluated the six-

strand Savage pattern, compared to the three-loop pulley pattern. The six-strand Savage

pattern was first reported in for use in human tenorrhaphies.74 This pattern contains

grasping and locking sutures, better engaging the tendon fascicles than the three-loop

pulley technique. Using #2 polydioxanone suture the six-strand Savage pattern was

 

  18  

consistently stronger than the three-loop pulley technique. The mean load to failure of the

three-loop pulley technique was 193 N compared to 421 N for the six-strand Savage

technique. Importantly, the three-loop pulley consistently failed by suture pulling out

through the tendon, because this pattern fails to engage tendon fascicles. Alternatively the

six-strand Savage technique always failed by breakage of the suture.111

Smith et al evaluated a modification of the Savage technique in 2011. The pattern

was modified to include more passes of suture across the tenorrhaphy site, making the

pattern a ten-strand technique. This was significantly stronger than the three-loop pulley

technique, using both polyglactin 910 and polydioxanone, with ultimate load to failure

978 N and 965 N, respectively.110 A Lin-locking epitenon suture pattern in conjunction

with the ten-strand Savage pattern was proven to be stronger than the ten-strand Savage

pattern alone, achieving strength of 1105 N when placed with #2 polyglactin 910.110

Figure two: Diagram of the three-loop pulley tenorrhaphy (A) and the six-strand Savage

pattern. Adapted from Everett et al 2011.

Equine Nonsurgical Management

Biomechanical Testing of Suture Patterns for Equine Tendon Repair Everett et al.

Figure 1 (A) Region of tendon specimen used in testing. (B) Graphicalrepresentation of tenorrhaphy pattern used in 3-loop pulley (3LP) repair.Bracket indicates core purchase length that was uniform at 20 mm.(C) Graphical representation of tenorrhaphy pattern used in 6-strandSavage (SSS) repair.

favorably to other patterns, such as the compound-lockingloop (CLP), and has been recommended for primary ten-orrhaphy in the horse.25 In particular, the 3LP resisted gapformation better than the CLP; however, the low ultimatefailure load of the 3LP pattern (31.5 ± 4.0 kg) and failureby pulling through the tendon rather than suture failuresuggest that tenorrhaphy in equine FTs can be improved.

The 6-strand Savage (SSS) technique (Fig 1C) is rou-tinely used in human hand surgery for tendon repair,and has compared well biomechanically with other su-ture patterns.26–28 The SSS uses a grasping mechanism toengage tendon fibrils in the longitudinal axis for greaterstrength. In contrast, the 3LP pattern relies on collagencross-linking and other interfibril connections to resist su-ture pull through, as it is neither a grasping nor lockingpattern. Ideally, the suture patterns should be comparedcontrolling for the variables of core purchase length, suturematerial size, and strand number between the 2 patterns,

focusing the investigation on the intrinsic qualities of thetenorrhaphy under load.

Our purpose was to compare a novel tenorrhaphy pat-tern for equine tendon repair, the SSS technique, with thecurrently recommended pattern, the 3LP, in an in vitromodel. We hypothesized that the SSS will provide a strongerrepair that is more resistant to gap formation than the 3LPpattern in an in vitro model. Additionally, we hypothesizedthat failure mode for the SSS will occur by suture breakage,and the 3LP will fail primarily by suture pulling throughthe tendon tissue.

MATERIALS AND METHODS

Experimental Design

The SSS and 3LP suture techniques were applied in anin vitro model of tenorrhaphy and their biomechanical qual-ities compared in a randomized, paired design; the 3LP wasperformed on 1 forelimb, and the SSS on the contralaterallimb. The same surgeon (EE) performed all tenotomies andtenorrhaphies to ensure consistency. The same suture (2polydioxanone) was used, in a 6-strand continuous patternfor each, meaning that the strand crossed the tenotomy site6 times. Identical 5-mm bites were made from transectionsite, and identical core purchase lengths were used (the dis-tance from tenotomy to most distant suture placement, seeFig 1B). The ultimate failure load, stiffness, mode of failure,and the load required to create a 3-mm gap were computedby performing tensile tests.

Sample Preparation

Pairs of forelimb SDFTs were collected from 12 adult horseseuthanatized for reasons other than musculoskeletal in-jury. The horses were 5 Thoroughbreds, 2 Warmbloods,1 Warmblood cross, 1 Thoroughbred cross, 1 Arabian, 1Quarter Horse cross, and 1 Draft cross. Mean age was 12years (range, 2–25 years old) and there were 7 geldings and5 mares.

The FT specimens were isolated in the metacarpal re-gion from a point immediately distal to the carpal canal tothe proximal aspect of the proximal sesamoid bones. TheFTs were dissected free from any other soft tissue and theparatenon removed. The specimens were then wrapped ina towel moistened with saline (0.9% NaCl) solution andsealed in plastic before freezing. Tendon specimens werepreserved at !70"C until they were transported frozen ondry ice to the testing laboratory.

After thawing to 30"C, each SDFT was transectedtransversely at the same location: 50% of the distance be-tween the carpometacarpal joint and the proximal sesamoidbones for each paired tendon specimen, to ensure similarcross-sectional area between repair methods in each pair oftendons. Next, the 3LP or SSS was used to repair the tran-sected tendon ends of the randomized, paired SDFT using 2

2 Veterinary Surgery 00 (2011) 1–7 C# Copyright 2011 by The American College of Veterinary Surgeons

Biomechanical Testing of Suture Patterns for Equine Tendon Repair Everett et al.

Figure 1 (A) Region of tendon specimen used in testing. (B) Graphicalrepresentation of tenorrhaphy pattern used in 3-loop pulley (3LP) repair.Bracket indicates core purchase length that was uniform at 20 mm.(C) Graphical representation of tenorrhaphy pattern used in 6-strandSavage (SSS) repair.

favorably to other patterns, such as the compound-lockingloop (CLP), and has been recommended for primary ten-orrhaphy in the horse.25 In particular, the 3LP resisted gapformation better than the CLP; however, the low ultimatefailure load of the 3LP pattern (31.5 ± 4.0 kg) and failureby pulling through the tendon rather than suture failuresuggest that tenorrhaphy in equine FTs can be improved.

The 6-strand Savage (SSS) technique (Fig 1C) is rou-tinely used in human hand surgery for tendon repair,and has compared well biomechanically with other su-ture patterns.26–28 The SSS uses a grasping mechanism toengage tendon fibrils in the longitudinal axis for greaterstrength. In contrast, the 3LP pattern relies on collagencross-linking and other interfibril connections to resist su-ture pull through, as it is neither a grasping nor lockingpattern. Ideally, the suture patterns should be comparedcontrolling for the variables of core purchase length, suturematerial size, and strand number between the 2 patterns,

focusing the investigation on the intrinsic qualities of thetenorrhaphy under load.

Our purpose was to compare a novel tenorrhaphy pat-tern for equine tendon repair, the SSS technique, with thecurrently recommended pattern, the 3LP, in an in vitromodel. We hypothesized that the SSS will provide a strongerrepair that is more resistant to gap formation than the 3LPpattern in an in vitro model. Additionally, we hypothesizedthat failure mode for the SSS will occur by suture breakage,and the 3LP will fail primarily by suture pulling throughthe tendon tissue.

MATERIALS AND METHODS

Experimental Design

The SSS and 3LP suture techniques were applied in anin vitro model of tenorrhaphy and their biomechanical qual-ities compared in a randomized, paired design; the 3LP wasperformed on 1 forelimb, and the SSS on the contralaterallimb. The same surgeon (EE) performed all tenotomies andtenorrhaphies to ensure consistency. The same suture (2polydioxanone) was used, in a 6-strand continuous patternfor each, meaning that the strand crossed the tenotomy site6 times. Identical 5-mm bites were made from transectionsite, and identical core purchase lengths were used (the dis-tance from tenotomy to most distant suture placement, seeFig 1B). The ultimate failure load, stiffness, mode of failure,and the load required to create a 3-mm gap were computedby performing tensile tests.

Sample Preparation

Pairs of forelimb SDFTs were collected from 12 adult horseseuthanatized for reasons other than musculoskeletal in-jury. The horses were 5 Thoroughbreds, 2 Warmbloods,1 Warmblood cross, 1 Thoroughbred cross, 1 Arabian, 1Quarter Horse cross, and 1 Draft cross. Mean age was 12years (range, 2–25 years old) and there were 7 geldings and5 mares.

The FT specimens were isolated in the metacarpal re-gion from a point immediately distal to the carpal canal tothe proximal aspect of the proximal sesamoid bones. TheFTs were dissected free from any other soft tissue and theparatenon removed. The specimens were then wrapped ina towel moistened with saline (0.9% NaCl) solution andsealed in plastic before freezing. Tendon specimens werepreserved at !70"C until they were transported frozen ondry ice to the testing laboratory.

After thawing to 30"C, each SDFT was transectedtransversely at the same location: 50% of the distance be-tween the carpometacarpal joint and the proximal sesamoidbones for each paired tendon specimen, to ensure similarcross-sectional area between repair methods in each pair oftendons. Next, the 3LP or SSS was used to repair the tran-sected tendon ends of the randomized, paired SDFT using 2

2 Veterinary Surgery 00 (2011) 1–7 C# Copyright 2011 by The American College of Veterinary Surgeons

A B

 

  19  

Some horses with equine flexor tendon lacerations can be treated without

tenorrhaphy. These cases are often treated with debridement of the damaged tendon ends

and surrounding non-viable or contaminated tissue, aggressive antimicrobial therapy and

distal limb immobilization in the form of a splint or cast.3,6,121,122 This form of treatment

is reserved for horses with less than 50% of the tendon being injured.6 Conservative

management of these injuries often carries a worse prognosis compared to surgical

intervention, with fewer horses returning to their intended level of work and inferior

cosmetic outcome.45,102,119 The most catastrophic long-term complication of non-surgical

management of flexor tendon lacerations is breakdown of the palmar support apparatus,

with excessive hyperextension of the metacarpo/metatarsophalangeal joint(s). This is

especially concerning with conservative management of completely transected flexor

tendons.

Equine Distal Limb Immobilization

Distal limb immobilization is recommended as part of the treatment of equine

flexor tendon lacerations, for both surgically and non-surgically treated cases. A

fiberglass cast extending from the proximal metacarpal region to the hoof is often placed

at the time of initial treatment. Recommendations are to maintain the horse in the cast for

at least six weeks following the injury.3,6,122 This requires a prolonged hospital stay for

cast management and the potential for several cast changes depending on the individual

horse. Horses can then be transitioned to a splint of splint/bandage combination as the

injury heals. Potential complications of prolonged distal limb immobilization include the

development of cast sores, client cost, and osteopenia.123

 

  20  

A custom-made, fetlock support brace has been reported as an alternative to distal

limb casts in the management of equine flexor tendon lacerations.121 The advantage of

this coaptation is ease of bandage changes, allowing long-term management of these

cases outside of the hospital, potentially decreasing the cost of treatment to the client. In

this series of 15 cases, 80% of horses treated with this coaptation were reported to return

to some level of soundness. Although this success rate seems promising, the performance

level following treatment was minimal, with the majority of the horses being used for

pleasure riding and breeding purposes.

Although external coaptation is recommended to ease some of the tension placed

on flexor tenorrhaphy sites, the amount of tension relieved is unknown. The force placed

on the equine superficial digital flexor tendon is reported to be 3559 N.120 This coupled

with 3634-4560 limb loading events per day for a horse confined to a stall124 places large

strain on the tenorrhaphy. It would be helpful to know the amount of this load that is

shared by external coaptation, but this data is lacking.

Conclusions

Treatment of traumatic lacerations of equine flexor tendons remains difficult, with

50-55% of horses returning to athletic function.1-4 Lacerations involving more than 50%

of the width of the tendon are best treated with primary repair and distal limb

immobilization. Human literature initially focused on development a strong repair that

could adequately oppose the transected tendon ends.70 With greater understanding of how

damaged tendons heal, the focus shifted to development of tenorrhaphy patterns that were

not only strong, but also promoted healing of the tendon with minimal adhesion

formation. This led to the development of tenorrhaphy patterns utilizing both core and

 

  21  

peripheral sutures followed controlled physical therapy programs starting shortly after

repair.54,74,84,90,115,125,126,77,82,117,127 Data is lacking on the effect of these techniques on

intrinsic tendon vasculature.

Equine tenorrhaphy research has focused on the development of a repair using

material and patterns that are strong in an attempt to withstand forces placed on the

tendons during normal weight bearing. 100,109-111 Recent evaluation of complex patterns

such as the six- and ten-strand Savage as well as addition of epitenon sutures have shown

that these patterns are much stronger than the commonly used three-loop pulley pattern.

110,111 Both of these studies were performed ex vivo and the effects that these patterns may

have on tendon healing have yet to be elucidated.

 

  22  

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58. Sharma P, Maffulli N: Biology of tendon injury: healing, modeling and remodeling J

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59. Matthews JP: Vascular changes in flexor tendons after injury and repair: an

experimental study Injury 8:227-233, 1977.

60. Fenwick SA, Hazleman BL, Riley GP: The vasculature and its role in the damaged

and healing tendon. Arthritis Res 4:252-260, 2002.

61. Matthews P, Richards H: Factors in the adherence of flexor tendon after repair J

Bone and Joint Surgery 58B:230-236, 1976.

62. Russell JE, Manske PR: Collagen synthesis during primate flexor tendon repair in

vitro J Orthop Res 8:13-20, 1990.

 

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63. Richards HJ: Repair and healing of the divided digital flexor tendon. Injury 12:1-12,

1980.

64. Chow SP, Yu OD: An experimental study on incompletly cut chicken tendons- A

comparison of two methods of management J Hand Surg 9B:121-125, 1984.

65. McGeorge DD, Stilwell JH: Partial flexor tendon injuries: To repair or not J Hand

Surg 17B:176-177, 1992.

66. Bishop AT, Cooney WP, Wood MB: Treatment of partial flexor tendon lacerations:

The effect of tenorrhaphy and early protected mobilization. Journal of Trauma

26:301-312, 1986.

67. Tang JB: Tendon injuries across the world: treatment. Injury 37:1036-1042, 2006.

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Journal of Hand Therapy 18:80-85, 2005.

69. Strickland JW: Flexor tendon injuries: II. Operative technique. J Am Acad Orthop

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70. Bunnell S: Repair of nerves and tendons of the hand J Bone and Joint Surgery 10:1-

26, 1928.

71. Stein LE, Pijanowski GJ, Johnson AL: A histological evaluation of rabbit tendons

sutured using the Bunnell pattern Veterinary Surgery 14:145-148, 1985.

72. Pijanowski GJ, Stein LE, Turner TA: Strength characteristics and failure modes of

suture patterns in severed goat tendons Veterinary Surgery 18:335-339, 1989.

73. Barrie KA, Wolfe SW: The relationship of suture design to biomechanical strength

of flexor tendon repairs Hand Surgery 6:89-97, 2001.

74. Savage R: In vitro studies of a new method of flexor tendon repair J Hand Surg

10B:135-141, 1985.

75. Tsuge K, Ikuta Y, Matshishi Y: Intra-tendinous tendon suture in the hand- a new

technique. The Hand 7:250-255, 1975.

76. Noguchi M, Seiler JG, Gelberman RH, et al: In vitro biomechanical analysis of

suture methods for flexor tendon repair J Orthop Res 11:603-611, 1993.

77. Savage R, Risitano G: Flexor tendon repair using a "six strand" method of repair and

early active mobilisation. J Hand Surg 14B:396-399, 1989.

 

  28  

78. Lotz JC, Hariharan JS, Diao E: Analytic model to predict the strength of tendon

repairs J Orthop Res 16:399-405, 1998.

79. Wade PJF, Muir IFK, Hutcheon LL: Primary flexor tendon repair: The mechanical

limitations of the modified Kessler technique J Hand Surg 11B:71-76, 1986.

80. Diao E, Hariharan JS, Soejima O, et al: Effect of peripheral suture depth on strength

of tendon repairs J Hand Surg 21A:234-239, 1996.

81. Lin G-T, An K-N, Amadio PC, et al: Biomechanical studies of running suture for

flexor tendon repair in dogs J Hand Surg 13A:553-558, 1988.

82. Wade PJF, Wetherell RG, Amis AA: Flexor tendon repair: significant gain in

strength from the halsted peripheral suture technique. J Hand Surg 14B:232-235,

1989.

83. Kubota H, Aoki M, Pruitt DL, et al: The tensile strength of various peripheral

circumferential repair techniques in canin flexor tendons J Orthop Sci 1:136-139,

1996.

84. Al-Qattan MM, Al-Rakan MA, Al-Hassan TS: A biomechanical study of flexor

tendon repair in zone II: comparing a combined grasping and locking core suture

technique to its grasping and locking components. Injury 42:1300-1302, 2011.

85. Kleinert HE, Spokevicus S, Papas NH: History of flexor tendon repair J Hand Surg

20A:546-552, 1995.

86. Tang JB: Indications, methods, postoperative motions and outcome evaluation of

primary flexor tendon reparis in zone 2. J Hand Surg 32:118-129, 2007.

87. Strickland JW: The Scientific Basis for Advances in Flexor Tendon Surgery. Journal

of Hand Therapy 18:94-110, 2005.

88. Yamamoto E HK, Yamamoto N: Mechanical properties of collagen fascicles from

stress-shielded patellar tendons in the rabit Clinical Biomechanics 14:418-425, 1999.

89. Cooney WP, Lin GT, An K-N: Improved tendon excursion following flexor tendon

repair. Journal of Hand Therapy 2:102-106, 1989.

90. Gelberman RH, Amifl D, Gonsalves M, et al: The influence of protected passive

mobilization on the healing of flexor tendons: A biochemical and microangiographic

study. The Hand 13:120-128, 1981.

 

  29  

91. Gelberman RH, Menon J, Gonsalves M, et al: The effects of mobilization on the

vascularization of healing flexor tendons in dogs. 153:283-289, 1980.

92. Gelberman RH, Manske PR, Akeson WH, et al: Flexor tendon repair. J Orthop Res

4:119-128, 1986.

93. Schuind F, Garcia-Elias M, Cooney WP, et al: Flexor tendon forces: In vivo

measurements. J Hand Surg 17A:291-298, 1992.

94. Zatiti SCA, Mazzer N, Barbieri CH: Mechanical strengths of tendon sutures J Hand

Surg 23:228-233, 1998.

95. Silfverskiold KL, May EJ, Tornvall AH: Flexor digitorum profundus tendon

excursions during controlled motion after flexor tendon repari in zone II: A

prospective clinical study. J Hand Surg 17!:122-131, 1992.

96. JW S: Flexor tendon surgery part 1: Primary flexor tendon repair. J Hand Surg

15:261-272, 1989.

97. Berg RJ, Egger EL: In vitro comparison of the three loop pulley and locking loop

suture patterns for repari of canine weightbearing tendons and collateral ligaments.

Veterianry Surgery 15:197-110, 1986.

98. Moores AP, Owen MR, Tarlton JF: The three-loop pulley suture versus two locking-

loop sutures for the repair of canine achilles tendons. Vet Surg 33:131-137, 2004.

99. Gall TT, Santoni BG, Egger EL, et al: In vitro biomechanical comparison of

polypropylene mesh, modified three-loop pulley suture pattern, and a combination for

repair of distal canine achilles' tendon injuries. Vet Surg 38:845-851, 2009.

100. Valdez H, Clark RG, Hanselka DV: Repair of digital flexor tendon lacerations in

the horse, using carbon fiber implants J Am Vet Med Assoc 77:427-435, 1980.

101. Vaughan LC, Edwards GB, Gerring EL: Tendon injuries in horses treated with

carbon fibre implants Equine Vet J 17:45-50, 1985.

102. Nixon AJ, Stashak TS, Smith FW, et al: Comparison of carbon fibre and nylon

suture for repair of transected flexor tendons in the horse. Equine Vet J 16:93-102,

1984.

103. Brown MP, Pool RR: Experimental and clinical investigations of the use of carbon

fiber sutures in equine tendon repair J Am Vet Med Assoc 182:956-966, 1983.

 

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104. Johnson-Nurse C JD: The use of flexible carbon fibre in the repair of experimental

large ambdominal incisional hernias Br J Surg 67:135-137, 1980.

105. Jenkins D, McKibbin, B: The role of flexible carbon-fibre implants as tendon and

ligament substitutes in clinical practice: a preliminary report Journal of Bone and

Joint Surgery 62B:497-499, 1980.

106. Strover AE FP: The use of carbon fiber implants in anterior cruciate ligament

surgery Clin orthop 196:88-98, 1985.

107. Eliashar E, Schramme MC, Schumacher J, et al: Use of a bioabsorbable implant for

the repair of severed deigital flexor tendons in four horses Veterinary Record

148:506-509, 2001.

108. Goodship AE, Brown PN, Yeats JJ, et al: An assessment of filamentous carbon

fibre for the treatment of tendon injury in the horse Veterinary Record 106:217-221,

1980.

109. Jenson PW, Lillich JD, Roush JK, et al: Ex vivo strength comparison of

bioabsorbable tendon plates and bioabsorbable suture in a 3-loop pulley pattern for

repair of transected flexor tendons from horse cadavers. Vet Surg 34:565-570, 2005.

110. Smith RL, Murphy DJ, Day RE, et al: An ex vivo biomechanical study comparing

strength characteristics of a new technique with the three-loop pulley for equine

tenorrhaphy. Vet Surg 40:768-773, 2011.

111. Everett E, Barrett JG, Morelli J, et al: Biomechanical testing of a novel suture

pattern for repair of equine tendon lacerations. Vet Surg 41:278-285, 2012.

112. Adair HS, Gobel DO, Rhorback BW: In vitro comparison of the locking loop and

the three loop pulley suture techniques in the repair of equine flexor tendons Equine

Veterinary Science 9:186-190, 1989.

113. Kümmerle JM: Suture Materials and Patterns, in Auer JA, Stick JA (eds): Equine

Surgery (ed 4), Vol. St. Louis, Missouri Elsevier Saunders 2012, pp 181-202.

114. Tan RHH BR, Dowling BA, Dart AJ: Suture materials: composition and

applications in veterinary wound repair Aust vet J 81:140-145, 2003.

115. Barrie KA, Tomak SL, Cholewicki J, et al: Effect of suture locking and suture

caliber on fatigue strength of flexor tendon repairs. J Hand Surg Am 26:340-346,

2001.

 

  31  

116. Taras JS, Raphael JS, Marczyk SC, et al: Evaluation of suture caliber in flexor

tendon repair. J Hand Surg Am 26:1100-1104, 2001.

117. Hatanaka H, Manske PR: Effect of the cross-sectional area of locking loops in

flexor tendon repair J Hand Surg 24A:751-760, 1999.

118. Easley KJ, Stashak TS, Smith FW, et al: Mechanical properties of four suture

patterns for transected equine tendon repair Veternary Surgery 19:102-106, 1990.

119. Jann HW, Good JK, Morgan SJ, et al: Healing of transected equine supeficial

digital flexor tendons with and without tenorrhaphy. Veterinary Surgery 21:254-265,

1992.

120. Lochner FK, Milne DW, Mills EJ, et al: In vivo and in vitro measurement of tendon

strain in the horse Am J Vet Res 41:1929-1937, 1980.

121. Whitfield-Cargile C, Dabareiner RM, Sustaire D: Use of a fetlock support brace to

manage lacerations of equine flexor tendons. Equine Veterinary Education 23:46-52,

2011.

122. Spurlock GH: Management of traumatic tendon lacerations Vet Clin North Am

equine Pract 5:575-590, 1989.

123. Auer JA: Principles of Fracture Treatment, in Auer JA SJ (ed): Equine Surgery Vol.

St. Louis, Missouri, Elsevier, 2012, pp 1047-1081.

124. McDuffee LA, Stover SM, Coleman K: Limb loading activity of adult horses

confined to box stalls in an equine hospital barn. Am J Vet Res 61:234-237, 2000.

125. Lin TW, Cardenas L, Soslowsky LJ: Biomechanics of tendon injury and repair. J

Biomech 37:865-877, 2004.

126. Chow JA, Thomes LJ, Dovelle S, et al: Controlled motion rehabilitation after flexor

tendon repair and grafting Journal of Bone and Joint Surgery 70B:591-595, 1988.

127. Winters SC, Gelberman RH, Woo S, et al: The effects of multiple-strand suture

methods on the strength and excursion of repaired intrasynovial flexor tendons: A

biomechanical study in dogs. J Hand Surg 23A:97-104, 1988.

   

 

  32  

Chapter Two

Microangiographic comparison of the effects of three-loop pulley and six-strand Savage

tenorrhaphy techniques on the equine superficial digital flexor tendon

Kendra D. Freeman, DVM, Jennifer G. Barrett, PhD, DVM, Diplomate ACVS,

Diplomate ACVSMR, Daniel W. Youngstrom, BS, Nathaniel A. White, MS, DVM,

Diplomate ACVS

Marion duPont Scott Equine Medical Center, Virginia-Maryland Regional College of

Veterinary Medicine, Virginia Tech, Leesburg, VA

 

  33  

Abstract

Objective: Equine flexor tendon lacerations can be severe and life threatening. The six-

strand Savage (SSS) tenorrhaphy pattern is biomechanically superior to the commonly

employed three-loop pulley (3LP); however, its effects on intrinsic tendon vasculature

remain unknown. The objective of this study was to compare perfusion of intrinsic

vasculature of equine superficial digital flexor tendon (SDFT) after 3LP and SSS

tenorrhaphies. We hypothesized that the SSS technique would significantly decrease

vascular perfusion compared to the 3LP technique.

Study Design: Ex vivo, randomized, paired design.

Animals: Eight mature horses.

Methods: Under general anesthesia, eight pairs of forelimb SDFTs were transected and

either SSS or 3LP tenorrhaphy was performed on each forelimb. The horses were

heparinized, euthanatized, and forelimbs perfused with barium sulfate solution then fixed

with formalin under tension. The tendons were transected every 5mm and

microangiographic images were obtained using a Faxitron X-ray cabinet with computed

radiography imaging. Microvascular analysis of sections proximal to the tenorrhaphy,

throughout the tenorrhaphy and distal to the tenorrhaphy was completed using Image J

software and a custom macro.

Results: A significant reduction in the number of perfused vessels was seen in the SSS

compared to the 3LP at two locations within the tenorrhaphy (p=0.004 and 0.039). The

SSS technique took on average 4.7 ± 0.9 times longer to place.

 

  34  

Conclusions: The SSS technique causes a reduction in tendon perfusion compared to the

3LP, which may limit its clinical use. Further research is required to elucidate the clinical

significance of this difference.

 

  35  

Introduction

Injuries to the equine distal limb are common and often involve the extensor or

flexor tendons.1-4 These injuries can be challenging to treat and generally carry a guarded

to poor prognosis for return to full athletic function. Extensor tendon lacerations carry a

better prognosis with 80% of horses returning to some level of riding soundness.1 Flexor

tendons have a more guarded prognosis with 55-58% of horses returning to riding

soundness.1,5 Injuries to the tendons of the equine distal limb are often complicated by

involvement of synovial compartments, wound contamination, and the involvement of

multiple structures. The prognosis for return to soundness decreases with an increase in

the number of associated structures affected.2

Primary repair of tendon lacerations can be challenging; however, superior

healing has been shown following tenorrhaphy.6,7 The goals of tendon repair are to limit

gap formation, minimize damage to the intrinsic tendon vasculature and prevent or

reduce the incidence of adhesion formation. For a number of years, the most common and

often most recommended repair technique used in equine flexor tenorrhaphies is the 3LP

pattern. Compared to the locking loop pattern, the 3LP technique is easy to place,

moderate in strength, and reduced perfusion less.8-12 The 3LP pattern does not contain

locking or grasping sutures to engage the tendon fascicles and consistently fails by suture

pull through along the tendon parenchyma.9,13-15 There has been testing and application of

more complex patterns. These patterns have an increased number of suture passes

crossing the tenorrhaphy site, which is correlated with increased strength of the suture

pattern. 9,13,16-19 Biomechanical studies have shown that either a six-strand Savage or ten-

strand Savage repair technique in the equine SDFT is stronger than the 3LP.9,13 These

 

  36  

studies tested the strength and failure mechanism of the suture patterns but not the effect

of these techniques on intrinsic tendon vasculature or healing.

Tendons receive their blood supply from several sources including the

musculotendinous junctions and vessels derived from the tendon sheath and the

paratenon.20, 21 Barium perfusion studies have been used to further characterize the

vascular supply of the equine flexor tendons.22-24 Kraus- Hansen et al described the

vascular supply of the equine superficial digital flexor tendon (SDFT) as a network of

anastomosing vessels within the tendon body with large parallel vessels present

longitudinally at the medial and lateral aspects of the tendon. 23 Additionally, a branch of

the median artery was consistently present within the accessory ligament of the SDFT.23

This intratendinous blood supply to the tendon is potentially more important than the

paratendinous supply to facilitate healing.25 A decrease in vascular filling has been found

following tenotomy, with a more drastic decrease following repair with a modified

Bunnell-type suture pattern. Tendons that underwent this repair also had increased

adhesion formation. The authors proposed that ischemia caused by damage to the

intrinsic vasculature may have contributed to adhesion formation.26 The compound

locking loop and 3LP patterns have both been shown to negatively affect the vasculature

in the equine superficial digital flexor tendon.12 Though the strength of the repair is

important to decrease any gap formation after the tenorrhaphy, this must be balanced with

the potential detrimental effect on intrinsic tendon vasculature.

The purpose of this study was to compare the effects of the SSS and 3LP

techniques on equine intrinsic tendon vasculature. We hypothesized that the SSS

technique will reduce the number of perfused vessels in comparison to the 3LP technique.

 

  37  

Specifically, we hypothesized that the region of the SSS pattern containing locking

cruciates will have less perfused vessels than the 3LP. However, because the locking

cruciate bites are >5mm distant from the tendon transection, we hypothesized that within

5mm adjacent to the transection, there will be no difference in the number of perfused

vessels.

Materials and Methods

Experimental Design

Eight horses had one forelimb of each pair randomly assigned to 3LP, and the

contralateral to SSS. Two surgeons (JGB and KDF) performed tenorrhaphies

simultaneously, as determined by random assignment. Surgery was performed on live

horses under general anesthesia, horses were then heparinized and euthanatized.

Forelimbs were perfused with barium and fixed with formalin for microangiography with

a tensioning device to standardize positioning. Microangiography was performed with

identical settings on every limb; the deep digital flexor tendon (DDFT) and non-sutured

SDFT were used as internal controls for each limb to verify perfusion.

Microangiographic images were objectively analyzed using a custom macro in Image J

and statistical analysis was performed with JMP 10.

Sample population

Eight mature horses with clinically normal tendons were selected for inclusion in

the study. The horses were euthanized at the owner’s request for reasons other than

lameness or injury associated with the flexor tendons. The study was approved by the

Virginia Tech Institutional Animal Care and Use Committee.

Surgical procedure

 

  38  

An intravenous catheter was placed, horses were sedated and induction and

maintenance of general anesthesia was maintained with ketamine, guaifenesin and

xylazine. Horses were positioned in dorsal recumbency with the forelimbs suspended in

full extension. The hair over the palmar aspect of the metacarpal region of each forelimb

was clipped and prepared for aseptic surgery.

The SDFTs were randomly assigned to one of the treatment groups. Eight tendons

were assigned to the 3LP group and SSS group respectively. All tenorrhaphies were

performed simultaneously by one of two individuals (JGB and KDF). Random

assignment was used to determine the pattern performed by each surgeon. Tenotomies

were completed using a palmar approach through a 12cm longitudinal skin incision

centered over the SDFT, 15cm proximal to the ergot. Blunt and sharp dissection was used

to expose the SDFT. A 5cm incision was made in the paratenon to isolate it from the

SDFT using blunt and sharp dissection. At 15 cm distal to the accessory carpal bone, the

SDFT was sharply transected and one of the two tenorrhaphy techniques was performed

with 2 polydioxanone on a preswaged CP (cutting point) 0.5 x 40mm reverse cutting

needle (Ethicon Inc., Somerville, NJ). Both patterns were started 5mm from the

transected tendon ends and completed within 2 cm of the tenorrhaphy. For all

tenorrhaphies a surgeons knot and four throws were used to secure the suture. Time of

tenorrhaphy placement was recorded and commenced once suture placement started and

ended after the tightening of the final throw of the knot. At completion of the

tenorrhaphy, heparin sodium (200 U/kg, IV) was administered to each horse. Fifteen

minutes after administering heparin the horses were euthanized.

Tensioning Device

 

  39  

The forelimbs were amputated at the level of the mid-radius. In order to apply

load to the tenorrhaphy, similar to Crowson et al., a tensioning device was applied to

standardize tension and place the metacarpophalangeal joint in a slightly hyperextended

position (Fig 1). This device was not intended to mimic the tension during full weight

bearing, since splinting or external coaptation is most common after tenorrhaphy. In

brief, holes were drilled in the toe of the hoof and in the proximal radius using a 15.9mm

drill bit. A 12.7mm diameter eyebolt with washers was secured into each hole. A

ratcheting tie strap (Erickson MFG LTD, Cottrellville, MI) in line with a digital tension

gage (American Weigh Scales Inc., Norcross, GA) were placed dorsal to the limb from

one eyebolt to the other. The ratcheting tie strap was tightened until the digital tension

gage showed 200N of force was being applied between the two eyebolts. Each pair of

forelimbs was prepared in precisely the same manner in tandem to avoid confounding

variables.

 

  40  

Fig 1: Perfused limb with tensioning device. The eyebolts are secured to the distal radius

as well as the hoof. The tension strap and gauge are spanning the eyebolts, on the dorsal

aspect of the limb, with the gauge tensioned to 200N.

Perfusion technique

A 4.7mm red rubber catheter (Tyco, Mansfield, MA)i was placed into the median

artery proximal to the musculotendinous junction of the SDFT, and secured with a purse-

string suture. A suspension of 600mL barium sulfate (EZ-EM, Lake Success, New York)

and 800mL water was perfused the limb via the red rubber catheter at a constant pressure

of 250mmHg using an Arthro-Flo (C.R. Bard, Inc., Warwick, RI). Eighty milliliters of

10% buffered formalin (Fisher Scientific, Baltimore, MD) was added to the final 150mL

of the barium suspension and the limbs were fixed at 4oC for 18 hours with 200N of

tension. Each SDFT and DDFT was dissected from the limbs. The tendons were

 

  41  

transected proximally at the level of the accessory carpal bone and distally at the level of

the metacarpalphalangeal joint. The DDFT, which was neither transected nor sutured,

served as an internal control for perfusion of the flexor tendons.

Microangiographic protocol

The SDFTs were manually transected with a #10 scalpel blade into 5mm sections

along the length of the tendon. The cuts started at the tenorrhaphy site and extended

proximad to the level of the accessory carpal bone and distad to the metacarpophalangeal

joint. The DDFTs were manually transected into 5mm sections and used to verify

perfusion of each limb.

The 5mm sections were transferred to a high detail radiographic cassette for soft

tissue radiography. Each SDFT was divided into six regions (Fig 2) in order to determine

if the different regions of the SSS pattern have different effects on vessel perfusion.

Specifically, the SSS pattern has locking cruciate bites at the proximal and distal extent

of the pattern, but adjacent to the transection or laceration, the suture pattern does not

grasp the tendon fascicles. The regions spanned from proximal to distal, starting with

region A, which was proximal to any suture placement. For the SSS pattern, Region B

contained the locking cruciate sutures. Region C contained sutures parallel to the tendon

fibrils. Region D contained sutures parallel to the tendon fibrils, but distal to the

transection. Region E contained the locking cruciate sutures distal to the transection zone.

Region F was tendon distal to any suture placement. For the 3LP pattern Region B and C

contained suture proximal to the transection. Regions D and E contained sutures distal to

the transection and Region F contained tendon distal to any suture placement (Fig 2).

Tenorrhaphy sutures were removed from the sections prior to imaging. A cabinet x-ray

 

  42  

system (Faxitron Series, Hewlett-Packard, Palo Alto, CA) was used at 30 kVp and 5mAs.

Tendons from each forelimb were radiographed separately along with the sectioned

DDFTs to control for perfusion of the limb. The cassettes were processed using a

computed radiography processor (Fujifilm Corporation USA, Valhalia, New York) No

contrast or brightness changes were made to the images.

Figure 2: Tenorrhaphy regions for microangiographic analysis from proximal (A) to

distal (F). Regions A and F are unsutured regions of the tendon (proximal and distal,

respectively). In the six-strand Savage pattern (left) regions B and E contain the cruciate

suture regions a d regions C and D contain the linear suture patterns. In the three loop

pulley pattern (right) regions B, C, D and E contain sutured tendon.

Image Analysis

Digital radiographic images of the SDFT sections were quantitatively interpreted

using a custom semi-automated analysis macro in Image J (National Institutes of Health,

Bethesda, MD). Briefly, isolated points of radio-opacity representing vascular cross-

 

  43  

sections were demarcated using a thresholding procedure and counted with a standard

particle analyzer. Raw vascular count data was obtained and organized by region for

comparison.

Data Analysis

Vascular perfusion is presented as mean ± standard error of the total vascular

count registering as radiopaque per tissue section. Differences between contralateral

treatment groups were assessed by implementing a one-way paired Student’s t-test,

signified with an asterisk. Within-subject effects comparing tenorrhaphy perfusion

(regions B-E) to non-sutured segments of SDFT (regions A and F) were analyzed with a

one-way repeated measures multivariate analysis of variance (MANOVA). Times to

complete tenorrhaphy were not normally distributed. Non-parametric data were assessed

for significant differences using the Wilcoxon signed rank test, The threshold for

determining statistical significance was set at p≤0.05. Calculations were conducted in

JMP 10 (SAS Institute Inc., Rockville, MD) and Excel 12 (Microsoft Inc., Redmond,

WA).

Results

Perfusion of all pairs of limbs was apparent during the experiment, as barium was

seen exiting the transected tendon ends. Minimal gap formation (<3mm) occurred after

application of the tensioning device, and all metacarpophalangeal joints were in slight

hyperextension. Average surgery times varied between techniques – 3LP: median 3.5

minutes (range 2-5), SSS: median 16.0 minutes (range 9-39). The SSS technique took on

average 4.7 ± 0.9 times longer than 3LP, and differential surgery times were positively

 

  44  

skewed (γ1=1.16) (Fig 4). This difference was statistically significant as determined via

the Wilcoxon signed rank test (p=0.0013).

Figure 3: A) Vascular count for each tenorrhaphy pattern by region. Significant

differences between the patterns in regions B and C for the six-strand Savage compared

to the three loop pulley technique. B) Vascular counts of the deep digital flexor tendons

used to evaluate adequacy of perfusion. No difference was present between deep digital

flexor tendons on the limbs of sutured tendons. C) Diagram of the two tenorrhaphy

patterns and their associated regions for the regions compared with figure A.

Figure 4: Box and whisker plot of surgery times (minutes) for the two tenorrhaphy

patterns. The three-loop pulley pattern was quicker to place than the six-strand Savage

technique. This difference was statistically significant (p= 0.0013).

 

  45  

A significant acute reduction in vascular count was identified in the SSS

compared to the 3LP at two regions within the tenorrhaphy. In region B, the raw vascular

count of SSS was an average of 31% lower than 3LP. This difference was statistically

significant (p=0.0390, power 0.72). At point C, there was a significant difference in the

raw vascular count of SSS, which was an average of 27% lower than 3LP (p=0.0044,

power 0.86) (Fig 3A). All perfusions were completed successfully and no significant

differences in vascular count were observed DDFTs between untreated limbs (Fig 3B).

For within-group comparison of the SSS pattern, regions B (p=0.003), C

(p=0.001), D (p=0.009) and E (p=0.019) were significantly lower than region A

(proximal SDFT outside of tenorrhaphy). Regions B and C were significantly lower than

region F (distal SDFT outside of tenorrhaphy) (p=0.010 and p=0.007, respectively). For

within-group comparisons of the 3LP pattern, regions D and E were significantly lower

than region F (distal SDFT outside of tenorrhaphy) (p=0.012 and p=0.035, respectively).

Discussion

Primary repair of tendon lacerations has been validated as superior to second

intention healing in multiple studies. Jann et al 7 identified stronger healing of sutured

tendons at five and nine weeks after repair versus non-sutured tendon. Second intention

healing of tendons resulted in hyperextension of the fetlock and increased proliferation of

soft tissues leading to a weaker musculotendious unit, and cosmetic blemish.6 Because

primary repair results in superior healing, many studies have focused on maximizing the

strength of repair to overcome the high forces placed on equine flexor tendons.

 

  46  

Following repair to human flexor tendon injuries, early controlled movement is

advocated27,28 and associated with rapid recovery of tensile strength, improved tendon

excursion, decreased adhesion formation and better overall clinical outcome.29-33 Multiple

studies have determined the normal amount of flexor tendon excursion and the amount of

excursion with various splints and range of motion exercises in normal tendons. This

allows for very rigid, controlled treatment protocols.29, 34 Several limitations currently

prevent these types of rehabilitation programs in equine patients.

Equine tenorrhaphies require significantly more strength than human

tenorrhaphies. Human flexor tendons must withstand 34-50N35,36 while equine tendons

must withstand 3559N in the absence of splinting or coaptation.37 Equine patients with

flexor tendon lacerations are typically placed in partial flexion of the

metacarpo/tarsophalangeal joint through splinting or casting to reduce the tension on the

healing tendon. The load applied to the SDFT when the metacarpo/tarsophalangeal joint

is in partial flexion in a cast is unknown. Even so, the cyclic loading horses experience

(3624-4560 limb loading events per day) when standing in a stall and the tension applied

from the muscle can cause gap formation. 38,39

Tenorrhaphy patterns either contain locking loops, which tighten around tendon

bundles, or grasping loops, which pull through the tendon fibrils when tightened. The

3LP pattern does not contain locking nor grasping sutures. Locking loops are proven to

increase the ultimate strength and decrease gap formation at the repair site.17,40-43 Suture

patterns such as the SSS and its modifications have been advocated due to the presence of

locking loop suture compared to the 3LP pattern that only contains longitudinally

oriented loops. Although stronger, locking loops can have a negative effect on intrinsic

 

  47  

vasculature compared to grasping loops.12 It is interesting that in our study only one

region of decreased perfusion was located in the locking portion of the SSS pattern. The

3LP also had decreased perfusion in regions of suture placement, compared to regions

without sutures, and this pattern contains neither locking nor grasping sutures. Decreased

perfusion in only two sections may have little clinical significance if healing is facilitated

by the strength of the repair pattern. Ischemia has been proposed to promote adhesion

formation in tendon repair 44, although it is possible that the minor decrease in vascular

filling identified in this study would have minimal effect on healing and adhesion

development in clinical cases of flexor tendon lacerations.

To date in the veterinary literature modifications of the SSS technique have only

been reported in ex vivo studies of equine flexor tendons. This is the first report of

placement of the SSS pattern in the superficial flexor tendon using a routine surgical

approach. The pattern requires circumferential access to the tendon. The ability to place

sutures at exact, predetermined and equal locations, as in done in ex vivo biomechanical

studies, is limited in the clinical setting The SSS pattern took significantly longer to place

than the 3LP. The surgery time in a clinical setting would be prolonged further by the

need to clean and debride the affected tissue prior to suture placement. In human

literature, the SSS technique has had limited use due to its difficulty in placement. 29,45,46

Although complex patterns such as the Savage techniques are mechanically superior,

their clinical utility may be limited.

Limitations of this study include the ex vivo experimental design, absence of

control SDFT for baseline perfusion, and the possibility that transection alone would

cause significant reduction of perfusion. Problems with ex vivo experimental design of

 

  48  

tendon repair studies include incomplete understanding of the role of reduced perfusion

on tendon healing. Our goal was to investigate one aspect of SSS biological effects prior

to conducting a live animal study. Since we were primarily interested in comparison of

the commonly used 3LP to the SSS, and since a pilot control horse (data not shown) had

excellent perfusion in a control SDFT and DDFT, we opted to use the DDFT and regions

of SDFT outside of suture pattern placement as internal controls for tendon perfusion.

Other studies looking at the effect of transection on intrinsic vascular perfusion has

shown either normal perfusion or a minimal region of reduced perfusion at transection

site.44,47 Our experimental approach reduced the number of horses needed for this

terminal study, and allowed comparison of vascular perfusion in a controlled

environment between the commonly used technique (3LP) and a newer reported

technique for tendon repair in horses (SSS).

The SSS technique is technically challenging and causes a higher reduction in

tendon perfusion than the 3LP technique. Although the negative effect on the intrinsic

vasculature was more pronounced with the SSS pattern compared to the 3LP, the clinical

significance is unknown. The tradeoff between strength of repair and vascular perfusion

is one that needs to be carefully considered. Further research is needed to elucidate the

effects of these differences on equine tendon healing in vivo.

 

  49  

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Chapter Three

Equine flexor tendon lacerations remain challenging to treat successfully. The

need for immediate weight bearing following surgery, even with the support of external

coaptation, puts stress on the newly placed tenorrhaphy. Although complex patterns such

as the six- and ten-strand Savage patterns are much stronger than the three-loop pulley

pattern, they are not nearly strong enough to overcome the forces placed on the

superficial digital flexor tendon during weight bearing in the unsupported limb. These

complex patterns, especially those involving the placement of a peripheral suture pattern

require circumferential access to the tendon.

Adhesion formation is common in human flexor tendon repair and is often

detrimental to the overall outcome of a case. The majority of human flexor tendon

lacerations occur in regions of tendons surrounded by synovial structures. These regions

are prone to adhesion formation in the healing process. In early human tenorrhaphy repair

these locations were considered “no man’s land” and repair was avoided. The

development of early mobilization protocols has limited the formation of adhesions in

these regions. Because of the need for early mobilization to limit adhesion formation,

many human studies have focused on the strength of the repair. Several patterns are

strong enough to overcome the strain of early mobilization. Although the Savage pattern

and its modifications are biomechanically superior, they are not the tenorrhaphy patterns

used. Surgeons use a combination of core and peripheral sutures to limit gap formation

and increase initial strength, allowing for early mobilization to decrease adhesion

formation.

 

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Preservation of the vascular supply to lacerated tendons is commonly cited as one

of the main goals of treatment of these injuries. It has been proposed that damage to this

vasculature can contribute to adhesion formation, although the mechanism of this

phenomenon is not known. Adhesion formation is more of a concern in treatment of

human tendon lacerations compared to equine lacerations. In humans the goal is to

achieve a healed tendon that functions mechanically similar to an undamaged tendon. In

equine lacerations the goals are to first save the life of the animal and secondly, obtain a

healed tendon that can tolerate at least partial return to work.

Research scenarios used to test biomechanical strength of a repair pattern are

often much different than what is seen in clinical settings. The clinical case rarely

presents with a completely transected superficial digital flexor tendon, in the mid

metacarpal or metatarsal region. Clinical cases often involve multiple structures and

tendon ends usually require debridement to remove necrotic, contaminated or damaged

tissue. It is likely that cases of equine flexor tendon laceration would best benefit from a

combination of treatments including debridement, tenorrhaphy and distal limb

immobilization, followed by transition to a fetlock support brace or shoe. Even with this

combination of therapy, it is important to optimize each step of the treatment to ensure

the best cosmetic and functional case outcome.