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Chronic Rotator Cuff Injury and Repair Model in Sheep
Struan H. Coleman, MD, PhD1; Stephen Fealy, MD1; John R. Ehteshami, MD1; John D. MacGillivray, MD1; David W. Altchek, MD1; Russell F. Warren, MD1; A. Simon Turner, BVSc, MS, Dipl ACVS2
1 Department of Sports Medicine and Shoulder Service, The Hospital for Special Surgery, 535 East 70th Street, New York, NY 10021. E-mail address for S.H. Coleman: colemans@hss.edu
2 Department of Clinical Sciences, Colorado State University, 300 West Drake Road, Fort Collins, CO 80523
View Disclosures and Other Information
In support of their research or preparation of this manuscript, one or more of the authors received grants or outside funding from the Institute for Sports Medicine Research, Smith and Nephew Endoscopy, Musculoskeletal Transplant Foundation, and W.L. Gore and Associates. None of the authors received payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, educational institution, or other charitable or nonprofit organization with which the authors are affiliated or associated.
Investigation performed at the Department of Sports Medicine and Shoulder Service, The Hospital for Special Surgery, New York, NY, and the Department of Clinical Sciences, Colorado State University, Fort Collins, Colorado

The Journal of Bone and Joint Surgery, Incorporated
J Bone Joint Surg Am, 2003 Dec 01;85(12):2391-2402
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Background: Most rotator cuff surgery is performed on chronic tears. As there is no animal model in which to examine the physiology of muscle and tendon injury and repair in this setting, we developed a chronic rotator cuff injury model in sheep.

Methods: The infraspinatus tendon was released in thirty-six female sheep. Biopsy specimens were obtained from the muscle and were analyzed for fat content. The force generated by the muscle with supramaximal stimulation was recorded intraoperatively. A control group (twelve sheep) underwent an immediate tendon repair. In the remaining twenty-four sheep, the tendon was wrapped in a dura substitute to prevent scarring and was repaired at six weeks (eight sheep) and eighteen weeks (sixteen sheep) after release. In the immediate repair group, four animals were killed at six weeks; four, at twelve weeks; and four, at twenty weeks. In the six-week delayed repair group, four animals were killed at twelve weeks and four were killed at twenty weeks after the repair. In the eighteen-week delayed repair group, eight animals were killed at twelve weeks; four, at twenty weeks; and four, at thirty weeks after the repair. Muscle biopsies and testing were repeated prior to killing of the animals.

Results: The average force of muscle contraction decreased 3.6 lb (1.6 kg) by six weeks after the injury and 3.9 lb (1.8 kg) by eighteen weeks after the injury. After the repair, the force of contraction in the six-week group improved by 0.8 lb (0.4 kg) at twelve weeks postoperatively and by 1.3 lb (0.6 kg) at twenty weeks postoperatively. In contrast, no improvement occurred in the eighteen-week group until thirty weeks after the repair, at which time a 0.9-lb (0.4-kg) improvement was noted. There was a twelvefold increase in intramuscular fat concentration; this lipid infiltration was partially reversed after the tendon repair. Isolated tendon samples demonstrated an increase in the modulus of elasticity after chronic detachment that partially corrected after the tendon repair in the earlier (six-week) repair group.

Conclusions: We found that earlier repair of the tendon results in a more rapid recovery of both muscle function and tendon elasticity compared with a more delayed repair. We concluded that there may be a "point of no return" in rotator cuff injury after which the elasticity of the muscle-tendon unit does not return to normal.

Clinical Relevance: Injury and subsequent healing of the rotator cuff is a complex process that is poorly understood. We established a chronic rotator cuff injury and repair model in sheep. The model is reproducible and can be used to analyze both a direct repair of tendon to bone (chronic group) and an indirect repair requiring augmentation with a degradable patch (irreparable group).

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    Accreditation Statement
    These activities have been planned and implemented in accordance with the Essential Areas and policies of the Accreditation Council for Continuing Medical Education (ACCME) through the joint sponsorship of the American Academy of Orthopaedic Surgeons and The Journal of Bone and Joint Surgery, Inc. The American Academy of Orthopaedic Surgeons is accredited by the ACCME to provide continuing medical education for physicians.
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    Hans K. Uhthoff
    Posted on March 21, 2004
    Chronic Rotator Cuff Injury and Repair Model in Sheep
    University of Ottawa

    To the Editor:

    We enjoyed reading “Chronic Rotator Cuff Injury and Repair Model in Sheep” (2003;85:2391-1402) and would like to congratulate the authors of this interesting study. We must take issue, however, with their statements that “As there is no animal model in which to examine the physiology of muscle and tendon injury and repair in this setting, we developed a chronic rotator cuff injury model”; and, “the purpose of our study was to develop a chronic cuff repair model in sheep that allows differentiation between released tendon edge and surrounding scar at the time of repair”.

    We would like to point out that such a model has already been developed and tested. (1,2). In those studies we found that in rabbits, delayed reinsertion of the supraspinatus tendon by wrapping the tendon stump in a Durapore® membrane prevented adhesions. Our results were supported by precise measurements of extra- and intramuscular fat and by the description of enthesis reformation. They were presented at the closed meeting of the American Shoulder and Elbows in Austin Texas on October 20, 20001 and published in J Orthop.Research (2).

    Research in this field will undoubtedly benefit from the addition of a sheep model to investigate the problems associated with delayed tendon healing.

    Hans K. Uhthoff MD FRCSC Guy Trudel MD FRCPC Bone and Joint Research Laboratory University of Ottawa 451 Smyth Road #1319 Ottawa ON Canada K1H 8M5

    1. Uhthoff HK, Matsumoto F, Trudel G: Irreversibility of muscle atrophy and fatty infiltration after delayed reattachment of the supraspinatus tendon. Closed meeting of American Shoulder and Elbow Surgeons, Austin TX October 20, 2000. Abstract #1, page 20. 2. Matsumoto F, Uhthoff HK, Trudel G, Loehr JF Delayed tendon reattachment does not reverse atrophy and fat accumulation of the supraspinatus. J Orthop Res. 2002;20:357-363

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