Primary open anterior shoulder stabilization: a long-term, retrospective cohort study on the impact of subscapularis muscle alterations on recurrence

Background: Post-traumatic anterior shoulder instability patients may present histopathologic lesions within the subscapularis muscle compatible with a scarring process associated with disuse atrophy. We hypothesized that such lesions identified on intraoperative biopsy at the time of primary anterior shoulder stabilization would predict a higher risk of postoperative instability recurrence. Methods: Of 52 eligible patients (52 shoulders) who had undergone subscapularis muscle biopsy during primary anterior open labral repair and capsulorrhaphy, 35 (mean age at surgery, 27.2 years; male sex, 71.4%) were retrospectively evaluated (mean follow-up, 12.9 years; range, 10.9-14.5 years). Primary outcome was shoulder instability recurrence. Secondary outcomes included shoulder range of motion, functional scores, and radiological analysis of glenohumeral joint degenerative changes. Results: Overall five patients (14.3%) presented shoulder instability recurrence. Twelve patients with histopathologic lesions had significantly more instability recurrence than 23 without histopathologic changes (33.3% vs. 4.3%; risk difference, 29% [95% CI 1; 57]; p = 0.038). Patients without histopathologic changes had significantly reduced external rotation with arm at side (ER1; -11.9 degrees; p = 0.001) and with shoulder abducted to 90 (ER2; -14.9 degrees; p = 0.001) on the operated side when compared to the contralateral side. Patients with histopathologic lesions had only ER2 significantly reduced (-8.9 degrees; p = 0.031). There was no substantial difference regarding functional and quantitative radiological scores between both patients' groups. Conclusions: Histopathologic changes within the subscapularis muscle at the time of primary open labral repair and capsulorrhaphy were associated with an increased risk of shoulder instability recurrence. Further investigations are needed to assess the impact of dedicated postoperative rehabilitation programs for patients presenting these lesions. Their recognition on preoperative magnetic resonance imaging should also be investigated; non-anatomical repairs could be an option in these cases.