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ontributions of the different rabbit models tour understanding of rotator cuff pathology

anjan Gupta, MD, and Thay Q Lee, PhD, Long Beach, CA

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nimal models designed to investigate the biologicspects of rotator cuff pathology are being used andeing developed in the rat, rabbit, dog, and otherammals. The current models have provided valuable

nformation regarding the etiology, pathogenesis, andealing potential of the tendon, as well as effectiveurgical repair techniques for rotator cuff tears. Rabbitodels have primarily been used to describe the mus-ular changes, rotator cuff enthesis formation, androwth factor expression after rotator cuff injury. Thisrticle will serve to review the data obtained from pre-iously described rabbit models and a newly devel-ped rabbit model for studying rotator cuff pathology.J Shoulder Elbow Surg 2007;16:149S-157S.)

NTRODUCTION

The development of animal models is an importantool in the advancement of orthopaedic research.nimal models provide the ability to increase ournderstanding of the natural history of diseases, tovaluate the effects of clinical treatments, and toevelop new and improved surgical techniques. These of animals in orthopaedic research is an impor-ant bridge between in vitro cadaveric studies anduman clinical trials. There are many well-establishednimal models in orthopaedic research for the inves-

igation of topics including fractures, articular carti-age degeneration, joint replacement, spinal cordnjury, and arthritis. There remain many areas ofrthopaedic research including rotator cuff pathology

hat lack a well-accepted animal model.The search for an animal model for rotator cuff

athology has been under way for the past decade withixed results. Although the nonhuman primate woulde the closest model of the human shoulder, ethical

rom the Orthopaedic Biomechanics Laboratory, VA Long BeachHealthcare System and University of California, Irvine, and Depart-ment of Orthopaedic Surgery, University of California, Irvine.

eprint requests: Thay Q Lee, PhD, Orthopaedic BiomechanicsLaboratory, VA Long Beach Healthcare System (09/151), 5901E 7th St, Long Beach, CA 90822 (E-mail: [email protected]).opyright © 2007 by Journal of Shoulder and Elbow SurgeryBoard of Trustees.

058-2746/2007/$32.00
toi:10.1016/j.jse.2007.05.002
ssues coupled with the lack of availability and high costave prohibited its use. Animals that have been usedange from lower vertebrates to larger more complexertebrates including the rat, rabbit, dog, sheep, andoat.11,28 As expected, there are inherent strengths and

imitations to each model, with different models beingetter suited to answer certain questions. The rabbit is arequently used animal in orthopaedic research. Recentublications involving rabbit models include articularartilage repair,4,9,14 ligament reconstruction,1 and ten-on repair.25,26 Whereas the rabbit medial collateral

igament has served as the foundation for many extra-rticular ligament and musculoskeletal soft-tissue stud-

es,5 the application of the rabbit model to shouldernjury research has been rather limited. To date, theajority of rabbit shoulder studies have looked at theistologic and mechanical changes that result from de-achment of the supraspinatus tendon (Table I). We shallrovide a critical review of the data obtained fromurrent and newly developed rabbit models for rotatoruff pathology.

USCLE RESPONSE TO TENDON INJURY

The earliest studies that used rabbit models toetter understand rotator cuff pathology focused on

he secondary response of the affected muscle afterendon injury. Specifically, investigators have de-ached the rotator cuff tendon and analyzed muscletrophy, twitch tension, fatigue index, and dischargef the mechanosensitive afferent units.2,7,8,33 Bjorken-eim2 removed the tendinous portion of the supraspi-atus in 12 rabbits to simulate a major rotator cuffear. He evaluated the contractile properties and de-ree of atrophy of the muscle at different time pointsfter tendon injury and determined that the changes

n contractile response and development of atrophyere significant. Of note, the fatty degeneration of

he interspace and supraspinatus muscle atrophyere most prominent at 6 weeks after injury andiminished at subsequent time points. It is possible

hat the limited functional improvements observed af-er repair of massive rotator cuff repairs may be aesult of residual muscle pathologic changes. In sub-equent experiments, Bjorkenheim et al3 used a novelxperimental design to demonstrate that monitoring
he intra-articular hydrodynamic pressure may be a
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eliable method of determining the strength of theealing supraspinatus tendon.

Fabis et al8 detached the supraspinatus tendonrom the greater tubercle and evaluated the muscle upo 6 months after injury. They demonstrated not only aeduction in power and fatigue index of the muscleut also development of fatty muscle degeneration in

he distal one third of the muscle. In a follow-up studyrom the same group, the investigators showed thathe decrease in twitch tension and fatigue index ac-ually occurred within the first 6 weeks after injury.7he development of fatty degeneration within theuscle did not progress significantly beyond the-month time point. It is possible that these changesid not progress because of the spontaneous healingnd scar formation at 6 weeks. Importantly, thesetudies independently confirmed data from Bjorken-eim et al3 so as to establish that there are mostertainly changes to supraspinatus muscle contractil-ty and development of fatty degeneration after su-raspinatus tendon injury in a rabbit model.

As these muscular changes after rotator cuff tendonnjury are likely clinically relevant to functional out-omes, attempts have been made to determine

able I Summary showing recent research on rabbit models used fo

First author Intervention

jorkenheim2,3 A healing model of a standardized defectin the supraspinatus tendon wasmonitored with arthrography andsimultaneous determination of the intra-articular hydrodynamic pressure of theglenohumeral joint.

In jointsleakaevideto hydprovedetermof the

hthoff32 A rotator cuff healing model was createdby supraspinatus detachment withreattachment.

The undbursacontrimediajudicitissue

hthoff31 A rotator cuff healing model was createdby supraspinatus detachment withreattachment after 6 or 12 weeks.

Reattachreversaccumreattafat acdiffer

hoi6 A transverse, full-thickness tear of thesupraspinatus tendon was created toexamine molecular changes associatedwith tenotomy.

These reexprehealintendorole i

abis7,8 The supraspinatus tendon was detachedfrom the greater tubercle in rabbits. Invivo evaluation of the twitch tensionand fatigue index was done.

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hether reattachment of the tendon to bone might re- r

erse the pathology. In one of their earlier studies,hthoff and colleagues22 created a tendon injury and

epaired the tendon to bone 12 weeks after injury. Asreviously reported,2,7,8 muscle atrophy and fatty de-eneration between muscle fascicles developed after

endon injury. Surprisingly, these changes did not re-erse after tendon reattachment, but rather actually pro-ressed. Moreover, the authors discussed the possibility

hat fatty muscle degeneration may not actually occurut, rather, that there is an extramuscular and intramus-ular fat accumulation. In a follow-up study from theame group,31 the investigators reattached the su-raspinatus tendon to bone 6 weeks after injuryith the hypothesis that earlier reattachment might

everse the pathologic changes. Yet the data did notupport the hypothesis. Whereas earlier reattachmentid prevent further increase in fat accumulation, theuscle atrophy and fatty accumulation did not reverse

o control levels. These findings do lend support for earlyeattachment of acute rotator cuff tendon tears.

ENDON-TO-BONE ENTHESIS

Another area of rotator cuff pathology that war-

ying rotator cuff pathology

Findings Advantages

supraspinatus tendon defects,the contrast medium wasto the sixth week. Resistancenamic intra-articular pressuree a reliable method ofthe strength of the healingspinatus defects.

Healing properties of severed rotatorcuff tendons examined in therabbit were found to be similar tothose in clinical rotator cuff injury.

g bone and the subacromialot the stump of the tendonto the process of repair. Thep should be debridedbut cutting back to bleeding

t necessary.

The rotator cuff repair modelreproducibly created.

of the supraspinatusither muscle atrophy nor fatn. However, earlier

nt prevented an increase inlation, but there was non muscle atrophy.

The rotator cuff repair model wasestablished to evaluate the healingresponse.

suggest that MMP-2 isand activated during thecess of acute supraspinatusand can play an important

remodeling process.

Molecular biology techniquesavailable in the rabbit can beused in evaluating rotator cuffhealing.

arked reduction in powerindex. The computed

y examination showed fattyeneration.

Postoperative fatigue correlation withtwitch tension was modeled.

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J Shoulder Elbow Surg Gupta and Lee 151SVolume 16, Number 5S

ion of the rotator cuff enthesis. The enthesis is apecialized region where the tendon meets the bone,nd this transitional area is organized into 4 specialones: the tendon proper, nonmineralized fibrocarti-age, mineralized fibrocartilage, and the bone. Forore than 60 years, the standard surgical treatmentas been to place the tendon into a bony trough of thereater tuberosity.23,24,27 It is of critical importance to

earn about how the enthesis re-forms after this pro-edure. One of the earlier healing studies that fo-used on the enthesis histologically evaluated theendon-to-bone interface 2 weeks after surgical re-air.32 After evaluating for the presence of bloodessels, type II collagen, and metachromasia, theuthors concluded that both the underlying bone and

he subacromial bursa, but not the stump of the ten-on, play an important role in the healing process.herefore, extensive decortication of the anatomicootprint may not be necessary, and great carehould be taken to preserve the subacromial bursa.32

The next significant study that explored the forma-ion of the supraspinatus enthesis focused on quanti-ying some of the cellular changes after surgical re-air.17 The authors not only performed cellular countsf chondrocytes and non-chondrocytic cells but alsoeasured extracellular matrix restoration by deter-ining proteoglycan content and spatial collagenber alignment. Proteoglycan content was evaluatedy determining the area of metachromasia on tolu-

dine blue–stained sections, and the area of diffractedolarized light served to indicate the spatial align-ent of the collagen fibers. Whereas both chondro-ytic and non-chondrocytic cells increased as early asweeks after repair, the spatial organization of the

ells continued for the duration of the study (ie, 24eeks). Importantly, although proteoglycan contentnd collagen orientation continued to improve

hroughout the study, the extracellular matrix was stillot restored to baseline levels by 24 weeks afternjury. The authors cautioned that early and aggres-ive rehabilitation programs after surgical repair maye detrimental to rotator cuff enthesis formation. Theyepeated this study with the same method but delayedepair to either 6 or 12 weeks after rotator cuffnjury.16 They showed that although this delay inepair did not have an effect on enthesis formation,he formation of this fibrocartilaginous structure wasependent on the time elapsed after repair. Thesetudies on the normal enthesis formation after surgicalepair of the rotator cuff are critical as we moveorward to determine better ways to improve healing.

ROWTH FACTOR EXPRESSION AND ROTATORUFF HEALING

With the advancement of orthopaedic molecular
edicine, it stands to reason that a better understand- r
ng of the growth factors and genes involved withotator cuff healing is required. Molecular tools holdhe potential for increasingly sophisticated analysis ofendon healing and improvement in functional out-omes. Although the rabbit genome is not as com-letely described as the rat and mouse genomes, theabbit does have immunohistochemical and molecu-ar markers available, as rabbit models are wellstablished in dermatology and ophthalmology re-earch.

One of the first studies to evaluate these markersescribed the temporal expression of matrix metallo-roteinase (MMP) 2 and tissue inhibitors of metallo-roteinases (TIMPs) during the spontaneous healingrocess of rabbit rotator cuff tears.6 MMPs are aamily of zinc-dependent endopeptidases that haveeen shown to be critical for remodeling, as they canegrade the extracellular matrix. MMP-2 is particu-

arly important for the degradation of several colla-en isoforms including type I and type III collagen. As

hese proteins comprise significant portions of theotator cuff, this description of the spatial and tempo-al pattern of MMP-2 and TIMP expression expandsur understanding of rotator cuff remodeling. Theame group of investigators performed immunohisto-hemical analysis of transverse full-thickness supraspi-atus tears for type I and type III collagen expressionithin the reparative tissue and tendon edges.12 On

he basis of their data, they concluded that the ep-tenon from the bursal side of the rotator cuff tendon ishe primary source of reparative tissue.

Other investigators have focused their explora-ion on better understanding the source of shoulderain after rotator cuff injury by evaluating proin-ammatory markers such as interleukin 1� (IL-1�),rostaglandin E2 (PGE2), and cyclooxygenase 2COX-2).18 After creation of the supraspinatus tear,he tendon was harvested at various postinjury timeoints and placed in tissue culture media. Expres-ion of IL-1� and PGE2 within the supernatant vianzyme-linked immunosorbent assay testing andeverse transcriptase–polymerase chain reactionnalysis of IL-1� and COX-2 within the tendon dem-nstrated early upregulation of IL-1� with subsequentpregulation of PGE2. Immunohistochemistry de-ailed that IL-1� and COX-2 were upregulated in bothendon cells and articular chondrocytes remote fromhe site of injury.

Most recently, some investigators have attempted toefine the spatial and temporal expression patterns ofpregulation of wound-healing growth factors withinhe supraspinatus tendon after an acute injury.15 Asartial-thickness rotator cuff tears often progress toull-thickness tears, there is currently no interventionhat reproducibly prevents the progression of thisathology. As such, identifying the growth factors
esponsible for promoting tissue regeneration and

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ealing may prove beneficial. The investigators iden-ified 4 growth factors that they believed critical forendon healing: basic fibroblast growth factorbFGF), insulin-like growth factor (IGF) 1, platelet-erived growth factor (PDGF), and transformingrowth factor (TGF) �.15 They performed immunohis-

ochemical analysis of paraffin-embedded rotator cuffendon at various time points and determined thatpontaneous healing after tenotomy occurs in a pre-ictable manner. After creation of the defect, a bloodlot filled this space, followed by creation of a synovium-ike tissue that eventually had the appearance of tendon-ike tissue. bFGF was expressed in the fibroblast-likeells and the vascular endothelial cells within the defect.GF-1 was found in blood cells and vascular endothelialells, whereas PDGF was localized to endothelial cellsnd TGF-� in the blood cells. This growth factor expres-ion was primarily localized to bursal-sided synovialissue and provides further evidence as to the impor-ance of the subacromial bursa for tendon healing.

HERAPEUTIC VIABILITY

With the explosion of interest in orthobiologicgents, there remains much work and experimenta-

ion required to demonstrate the efficacy of suchherapeutic agents. Although clinical trials can andill certainly be performed, they are inherently limited

n their ability to determine whether the therapeuticdjunct was successfully incorporated into the hostotator cuff. Recently, a rabbit model of rotator cuffnjury was used to test regeneration after placement of

chitin fabric as an acellular matrix graft.10 A 10 �0–mm defect was created within the rabbit infraspi-atus tendons with a chitin patch graft placed withinhis defect in the experimental group. Tissue wasarvested at various post-intervention time points formmunohistochemical and biomechanical testing. The

Figure 1 The anterior aspect of the glenohumeral jobeing the tuberculum supraglenoidale laterally, the coinferiorly, and the coracobrachialis muscle medially. Thsupraglenoidale and inserts on the lesser tuberclesupraspinatus tendon passing under the acromion to t

issue within this acellular matrix showed not only an b

ncreased cell number, improved collagen alignment,nd significant type III collagen, but also superiorechanical properties relative to the control. More

mportantly, this study provided invaluable in vivoata to support further exploration of this orthobio-

ogic agent as a potential therapeutic agent for rota-or cuff defects.

EW NOVEL RABBIT SUBSCAPULARIS MODELOR STUDYING ROTATOR CUFF PATHOLOGY

Almost all animal models of rotator cuff injuryimulate the acute condition by creating a tenotomy ofhe rotator cuff tendon and then evaluating the subse-uent response.28-30 Although this is certainly a validethod as different models are being developed, it is

mportant to remember that skeletal muscle responseo similar injuries is variable not only between speciesut also within different muscles of the same ani-al.13 As such, it is important to recognize thatlmost all rabbit rotator cuff studies have been per-ormed on supraspinatus tendon. Although this is theendon that certainly is most often the source of pa-hology in human beings, this may not be the bestabbit rotator cuff muscle to simulate the human con-ition, as the acromion of the rabbit scapula is aelatively rudimentary structure that creates an archhat the infraspinatus and teres minor pass under-eath. At the point where the infraspinatus passesnder the acromion, it is muscular rather than tendi-ous as with the human rotator cuff. Therefore, bothhe anatomic and biomechanical characteristics ofhe supraspinatus and infraspinatus tendons are sig-ificantly different between rabbits and humans.

ABBIT SUBSCAPULARIS ANATOMY

Anatomic investigation showed that there exists a

ntains an additional bony tunnel with its boundariesid process superiorly, the tuberculum infraglenoidalebit subscapularis tendon passes under the tuberculum

e humerus in an analogous manner to the humaneater tuberosity.

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ony prominence or a tunnel on the anterior aspect of

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he rabbit glenohumeral joint through which the sub-capularis tendon and muscle travel (Figure 1). Theateral wall of this structure consists of the tuberculumupraglenoidale, the roof is the coracoid process, theoor is the tuberculum infraglenoidale, and finally,he medial wall is the coracobrachialis muscle.

ithin this bony tunnel travels the tendon of theubscapularis muscle as it inserts onto the lesser tu-ercle of the humerus. This is a distinct similarity innatomic and biomechanical characteristics between

he rabbit subscapularis tendon complex and humanupraspinatus tendon complex. It is these anatomicnd biomechanical characteristics that suggest that

he rabbit subscapularis tendon complex is a reliableodel for studying rotator cuff pathology and subse-uently affords the opportunity to explore extrinsicechanisms involved with rotator cuff healing. Func-

ionally, the rabbit subscapularis muscle, given itsrigin, insertion, and direction of fibers, appears tounction as an internal rotator of the shoulder as wells aiding the additional muscles of the rotator cuffith concavity compression of the glenohumeral joint.reliminary video analysis of forward locomotion ofhe forelimb demonstrates that excursion of the sub-capularis tendon does occur within the bony tunnelFigure 2). Furthermore, the rabbit subscapularis foot-rint has length and width dimensions that are almostxactly one fourth those of the human supraspinatusootprint (which has a length of 25.2 � 2.41 mm andidth of 12.1 � 1.25 mm). The rabbit supraspinatus

ootprint measured 10.28 mm (SD, 0.62 mm) by.74 mm (SD, 0.62 mm). The infraspinatus footprintas 4.80 mm (SD, 0.46) by 2.44 mm (SD, 0.13). The

abbit subscapularis tendon footprint area of the bonynsertion (6.84 mm [SD, 0.29] by 2.51 mm [SD,.17]) provides a similar aspect ratio to the humanupraspinatus tendon, which further supports the an-

Figure 2 Gross dissections in conjunction with videostance, and liftoff) were used to confirm the angle bsubscapularis within the bony canal.

tomic similarity.19,20 w

NTRINSIC RESPONSE TO RABBITUBSCAPULARIS INJURY

To validate the rabbit subscapularis model fortudying rotator cuff pathology, we simulated ancute rotator cuff injury by creating a tonotomy of theubscapularis muscle in rabbits. We randomized 48ale New Zealand white rabbits, weighing betweenand 4 kg, into 3 groups: (1) partial rotator cuff tear,

2) complete rotator cuff tear, and (3) nerve transec-ion (Figure 3). The left subscapularis tendon fromach rabbit served as the experimental rotator cuff,hereas the right shoulder served as the control.abbits were randomly killed at 2 or 6 weeks from theperation after harvesting of the bilateral subscapu-

aris muscle, tendon, neuromuscular junction, sub-capular nerve, and C5/C6 dorsal root ganglion.

The wet mass from each subscapularis muscle andendon was calculated via a digital scale. Muscle crossections from the midsubstance of the harvested sub-capularis muscle were fixed and stained with hematox-lin-eosin or oil red O to determine cross-sectional areand fatty infiltration, respectively. The cross-sectionalrea of 50 random subscapular muscle fibers per mus-le was measured by use of ImageJ v1.32 image anal-sis software (NIH, Bethesda, Maryland). The ratio of fatrea over subscapularis muscle area was used to calcu-

ate the percentage of intramuscular fat on 2 randommages. Statistical analysis was performed by use of thetest assuming unequal variances, and statistical signif-cance was set at P � .05.

Rabbits in the groups with complete tendon injurynd nerve transection had a statistically significantecrease in wet mass, with losses of 10.2% (P � .05)nd 15.9% (P � .018), respectively, at 6 weeks whenompared with controls. Muscle cross-sectional areaFigure 4) also decreased significantly in the groups

ysis at each phase of the gait cycle (paw strike, miden the scapular spine and the tendinous portion of

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hen compared with controls (P � .05) at 2 weeksnd 6 weeks. Animals with partial-thickness tears didot show a significant change in cross-sectional arearom controls at 2 or 6 weeks. Fatty infiltration of theubscapularis muscle (Figure 5) was significantlyreater in the groups with complete tendon injury anderve transection when compared with controls at 6eeks. There was no significant change in fatty infil-

ration of the muscle in all 3 groups at 2 weeks or inhe group with partial tendon injury at 6 weeks. In thisabbit model, the muscle mass decreased and fattynfiltration of the muscle increased significantly at the-week time point in a manner analogous to theuman condition. The data support the idea that aomplete rotator cuff tendon injury has many charac-eristics similar to that of an isolated neural injury.

It has been theorized that the progression of fattynfiltration of the supraspinatus muscle in humans afterhronically torn rotator cuffs is attributed to the loss ofistal attachment, drop in muscle tension, and de-rease in muscle function. It is possible, however, thatome of these changes are secondary responsesather than the actual cause of the fatty infiltration.ecent clinical reports have also suggested that theetraction of the muscle belly (ie, supraspinatus inumans) places excessive tension on the suprascapu-ar nerve and subsequently creates changes in theerve.21 Although it is known that neural injury in-uces muscle pathology secondarily, this reciprocalelationship may be maintained after rotator cuff in-

Figure 3 Flow chart showing exp

ury where the initiating event is the retraction of the c

yotendinous unit that secondarily causes neural in-ury. As a result of the pathologic changes in nerveunction, there are ensuing muscular changes seenith complete rotator cuff injury—that is, the decrease

n muscle mass and the development of fatty infiltra-ion. There remains much to be investigated to explorehis novel hypothesis detailing the pathogenesis ofotator cuff injuries.

ONCLUSIONS

Our biologic understanding of rotator cuff pathol-gy will be advanced by the progression of reproduc-ble animal models that will allow investigation intohe natural history of tears and the healing response tourgical repair techniques. The selection of an animalill be determined by many factors, including the ap-ropriateness of the model to the human condition, thevailability of background studies using the animal,ousing requirements, cost, and the ease of experimen-al manipulation of the animal. As animal models muste appropriate for the condition being studied, no sin-le model can be expected to be superior in all situa-

ions. Rabbit models of rotator cuff injury have primarilysed the supraspinatus muscle tendon unit. These studiesave provided invaluable data about muscle changes,otator cuff enthesis formation, and growth factor ex-ression after rotator cuff injury.

As we move forward to better understand theathogenesis of rotator cuff injuries, the guiding prin-

ntal design for rabbit groupings.

iple that determines the appropriateness of the

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odel is whether the animal model closely mimics theroperty or aspect of the human condition that isnder investigation. In terms of rotator cuff pathology,here are 3 important considerations. First, the modelhould resemble the biomechanics of the humanhoulder in structure and function. Ideally, the bonyrchitecture of the subacromial region would model

he extrinsic impingement seen in humans. Second,he soft tissues of the model’s glenohumeral jointhould be histologically similar to the human condi-ion and undergo the characteristic rotator cuff muscle

Figure 4 a, Photomicrograph showing muscle cross-hematoxylin-eosin, and 50 random fibers were used fcomplete tonotomy, 2 weeks; (C) nerve, 2 weeks; (D) c6 weeks. b, Histograms showing muscle cross-sectiocomplete rotator cuff tear (Comp), and nerve transecti

etachment changes of fatty infiltration and atrophy. t

hird, the model should be large enough to alloweproducible surgical technique studies. An applica-ion of a proper animal model will guide the future ofotator cuff disease research and unlock the door tomproved clinical management and surgical repairechnique.

The search for an animal model for rotator cuffathology has yielded mixed results. Animals thatave been used range from lower vertebrates toarger more complex vertebrates including the rat,abbit, dog, sheep, and goat.11,28 Of these, the rat is

nal area. The sections were frozen and stained withoss-sectional area analysis. (A) Control, 2 weeks; (B)l, 6 weeks; (E) complete tonotomy, 6 weeks; (F) nerve,rea in 3 groups: partial rotator cuff tear (Partial ),erve).

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he most extensively studied model. The rat has a

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nique geometric construct of its subacromial region.he rat rotator cuff muscles and tendons pass undern arch composed of the coracoid, acromion, andoracoacromial ligament. However, no significantatty infiltration is observed in this model. Other ani-al models do not possess anatomic similarities toumans. Therefore, we believe that this new rabbitubscapularis model for studying rotator cuff pathol-gy may serve to address many of these consider-

Figure 5 a, Photomicrograph showing muscle fat cohematoxylin counterstain. (A) Control, 2 weeks; (B)control, 6 weeks; (E) complete tonotomy, 6 weeks;content in 3 groups: partial rotator cuff tear (Partial ),(Nerve).

tions and warrants further exploration.

EFERENCES

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2. Bjorkenheim JM. Structure and function of the rabbit’s supraspi-natus muscle after resection of its tendon. Acta Orthop Scand1989;60:461-3.

3. Bjorkenheim JM, Paavolainen P, Ahovuo J, Slatis P. Resistance ofa defect of the supraspinatus tendon to intraarticular hydrody-namic pressure: an experimental study on rabbits. J Orthop Res1990;8:175-9.

. The sections were stained with oil red O stain andplete tonotomy, 2 weeks; (C) nerve, 2 weeks; (D)erve, 6 weeks. b, Histograms showing muscle fatplete rotator cuff tear (Comp), and nerve transection

ntentcom(F) n

4. Brittberg M, Nilsson A, Lindahl A, Ohlsson C, Peterson L. Rabbit

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7. Fabis J, Kordek P, Bogucki A, Mazanowska-Gajdowicz J. Func-tion of the rabbit supraspinatus muscle after large detachment ofits tendon: 6-week, 3-month, and 6-month observation. J ShoulderElbow Surg 2000;9:211-6.

8. Fabis J, Kordek P, Bogucki A, Synder M, Kolczynska H. Functionof the rabbit supraspinatus muscle after detachment of its tendonfrom the greater tubercle. Observations up to 6 months. ActaOrthop Scand 1998;69:570-4.

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Documents

Contributions of the different rabbit models to our understanding of rotator cuff pathology