Muscle regeneration following repair of the rotator cuff.

AIMS: The aim of this study was to analyse human muscle tissue before and after rotator cuff repair to look for evidence of regeneration, and to characterise the changes seen in the type of muscle fibre. PATIENTS AND METHODS: Patients were assessed pre-operatively and one year post-operatively using the Oxford Shoulder Score (OSS) and MRI. The cross-sectional area and distribution of the type of muscle fibre were assessed on biopsies, which were taken at surgery and one year post-operatively. Paired samples from eight patients were analysed. There were three men and five women with a mean age of 63 years (50 to 73). RESULTS: All but one patient showed improvement in OSS (p = 0.004). The mean increase in the cross-sectional area of the muscle was 1220 µm2 (-801 to 3712; p = 0.03). There was a reduction of type 2a fibres (p = 0.02). A clear relationship could not be seen between the MRI findings and the histological appearances. CONCLUSION: This is the first study to provide evidence that atrophy of the supraspinatus muscle is reversible. Changes in the types of fibre are discussed. MRI assessment of muscle atrophy may not be fully representative of myofibre atrophy. Cite this article: Bone Joint J 2016;98-B:1389-94.