Characterizing histological fatty accumulation, muscle atrophy, and fibrosis in relation to re-tear and revision after primary rotator cuff repair: a mean 3-year follow-up study

Background: The failure rate following primary arthroscopic rotator cuff repair (RCR) is high. There is little existing literature reporting on failure rates in the context of the histological degree of fatty accumulation, fibrosis, and atrophy of the rotator cuff (RC) muscles. The objective of this study was to examine the association between histological fatty accumulation, fibrosis, and myofiber size of the RC muscles and re-tear and revision rates in patients who underwent primary arthroscopic RCR at a minimum of 1-year follow-up. Methods: This is a prospective study of patients who underwent primary arthroscopic RCR by a single surgeon at an academic tertiary institution between September 2020 and November 2023. All patients were indicated for RCR with a diagnosis of supraspinatus tear and had no prior RC surgery. Pre-operatively, RC tear size and RC muscle fatty degeneration using the Goutallier classification were graded on magnetic resonance imaging. Supraspinatus muscle biopsies were obtained at the time of surgery. Biopsy specimens were cross-sectioned and stained with LipidTOX and LAMININ to visualize lipid accumulation and quantify myofiber cross-sectional area at a histological level, respectively. FIBRONECTIN staining was performed to quantify histological fibrosis. Medical records were reviewed for RC re-tear, re-operation, or revision surgery. Patients were included if they had a minimum follow-up of at least 1 year, either by phone call or chart review of the latest visit with an orthopedic provider confirming survivorship. Results: A total of 53 patients (53 shoulders) underwent primary arthroscopic RCR and met inclusion criteria. Nineteen tears were partial thickness, and the remaining 34 full-thickness tears were roughly evenly distributed between small, medium, large, and massive sizes. Median Goutallier score was 1. Seven (13%) patients experienced retears confirmed on magnetic resonance imaging. Five patients (9%) had undergone revision (mean time to revision 21.8 months) while 48 patients were revision-free with a minimum follow-up of at least 1 year (mean follow-up 38.8 months). Reasons for revision included RC re-tear in 4 patients and glenohumeral arthritis in 1 patient. Revisions included revision RCR (3) and reverse total shoulder arthroplasty (2). There were no significant differences in demographics, tear size, repair type, Goutallier classification, LipidTOX/region of interest, average myofiber cross-sectional area, and % area FIBRONECTIN between patients with and without re-tear, and with and without revision. Conclusion: Histological fatty accumulation, fibrosis, and myofiber sizes of the RC muscles were not associated with increased re-tear or revision rates following primary arthroscopic RCR at a mean 3-year follow-up.