Lower muscle regenerative potential in full-thickness supraspinatus tears compared to partial-thickness tears

Abstract

Background and purpose Rotator cuff tears are associated with secondary rotator cuff muscle pathology, which is definitive for the prognosis of rotator cuff repair. There is little information regarding the early histological and immunohistochemical nature of these muscle changes in humans. We analyzed muscle biopsies from patients with supraspinatus tendon tears.

Methods Supraspinatus muscle biopsies were obtained from 24 patients undergoing arthroscopic repair of partial- or full-thickness supraspinatus tendon tears. Tissue was formalin-fixed and processed for histology (for assessment of fatty infiltration and other degenerative changes) or immunohistochemistry (to identify satellite cells (CD56+), proliferating cells (Ki67+), and myofibers containing predominantly type 1 or 2 myosin heavy chain (MHC)). Myofiber diameters and the relative content of MHC1 and MHC2 were determined morphometrically.

Results Degenerative changes were present in both patient groups (partial and full-thickness tears). Patients with full-thickness tears had a reduced density of satellite cells, fewer proliferating cells, atrophy of MHC1+ and MHC2+ myofibers, and reduced MHC1 content.

Interpretation Full-thickness tears show significantly reduced muscle proliferative capacity, myofiber atrophy, and loss of MHC1 content compared to partial-thickness supraspinatus tendon tears.

KL, OL and LE designed the clinical study (patient recruitment and biopsy procedure). KL assessed the patients and obtained the biopsy tissue. KL and AS designed and tested the methods, and conducted data collection and statistical analysis. All authors contributed to the writing of the manuscript.

We gratefully acknowledge the excellent technical assistance of Julie Lorette and co-workers at the Center for Translational and Applied Genomics, Vancouver, Canada, and of Ingeborg Løstegaard Goverud at the Department of Pathology, Oslo University Hospital, Norway.

All the authors declare that there are no competing interests. AS received a Michael Smith Scholar award. The study was funded by the Canadian Institutes of Health Research and by Lovisenberg Diaconal Hospital.