Effect of Tendon Release and Delayed Repair on the Structure of the Muscles of the Rotator Cuff: An Experimental Study in Sheep

• Published in: Journal of bone and joint surgery. American volume 2004-09, Vol.86 (9), p.1973-1982
• Main Authors: Gerber, C, Meyer, D.C, Schneeberger, A.G, Hoppeler, H, von Rechenberg, B
• Format: Article
• Language: English
• Subjects: Adipose Tissue - pathology; Animals; Biological and medical sciences; Disease Models, Animal; Diseases of the osteoarticular system; Medical sciences; Rotator Cuff - pathology; Rotator Cuff - surgery; Rotator Cuff Injuries; Sheep; Time Factors
• ISSN: 0021-9355; 1535-1386
• DOI: 10.2106/00004623-200409000-00016

BackgroundRuptures of the tendons of the rotator cuff lead to profound and possibly irreversible changes in the structure and physiological properties of the rotator cuff muscles. Muscle atrophy and fatty infiltration are important prognostic factors that affect the natural history and outcome of treatment. The purpose of this study was to examine the amount of muscle atrophy and fatty infiltration in an animal model and to determine whether the repair of a long-standing tendon tear can reverse these changes.MethodsThe infraspinatus tendon in six sheep was released and encased in a silicone tube to prevent spontaneous healing. The musculotendinous unit was allowed to retract for forty weeks. Throughout this period, the muscular changes were studied with use of computed tomography, histological analysis, and electron microscopy. At forty weeks, the elasticity, intramuscular pressure, and perfusion were measured intraoperatively and a tendon repair was carried out. The structural changes of the muscle were studied for thirty-five weeks after the repair. The animals were then killed, and the musculotendinous units were examined macroscopically and by computed tomography, histological analysis, and electron microscopy.ResultsAt the time of the tendon release, the infraspinatus showed no fatty changes. The force needed to cause a tendon excursion of 1 cm was a mean (and standard deviation) of 6.8 ± 1 N. The application of tension on the tendon did not alter the perfusion and decreased the intramuscular pressure. After the tendon release, muscular atrophy developed and there was a significant increase (p < 0.001) in interfascicular and intrafascicular fat, representing fatty infiltration rather than fatty degeneration. Furthermore, there was an increase of interstitial connective tissue. At the time of the tendon repair, between forty and forty-two weeks after the release, there was a sevenfold poorer elasticity of the musculotendinous unit but preserved muscle perfusion. The structural changes increased six weeks after the repair and then recovered partially at twelve and thirty-five weeks thereafter but only to the amount demonstrated before the repair.ConclusionsMusculotendinous retraction induced by tendon release is associated with profound changes in the structure and function of the affected muscle. Vascularization, intramuscular pressure, and individual fiber composition are not markedly affected, and muscle fibers do not appear to degenerate. However, m