Evaluation of subscapularis morphology following shoulder instability surgery: a retrospective magnetic resonance imaging-based comparison of open and arthroscopic techniques

Background: Open anterior shoulder stabilization with subscapularis takedown remains an important surgical option in selected cases, including revision surgery, significant capsular laxity, and contact athletes. However, concerns persist regarding potential long-term adverse effects on subscapularis muscle morphology, including atrophy and fatty infiltration, which have contributed to a preference for arthroscopic techniques. Methods: Consecutive patients undergoing open or arthroscopic shoulder stabilization by a single surgeon between 2007 and 2022 were retrospectively reviewed. Patients were included if pre-operative and post-operative MRI scans were available at a minimum of 6 months following surgery. Subscapularis morphology was assessed on T1-weighted parasagittal magnetic resonance image (MRI) using established measurement techniques, including muscle dimensions and cross-sectional area at standardized levels. Fatty infiltration was graded using the Goutallier classification, and muscle atrophy was quantified using the upper-to-total cross-sectional area ratio. Two blinded observers independently reviewed all imaging, and inter-rater reliability was assessed using intraclass correlation coefficients. Results: Eighty-three patients met the inclusion criteria (22 open, 61 arthroscopic). No statistically significant differences were observed in subscapularis muscle dimensions, cross-sectional area, or atrophy indices between pre-operative and post-operative imaging in either group. Goutallier grade remained unchanged in the majority of patients, with minimal progression observed in isolated cases. Inter-rater reliability was good to excellent across all measurements. Conclusion: In this selected cohort with post-operative imaging, no consistent MRI evidence of subscapularis atrophy or fatty infiltration was identified following either open or arthroscopic stabilization. These findings suggest that, when carefully handled and repaired, open subscapularis takedown may not inevitably result in adverse morphologic change.