Association Between Preoperative Rotator Cuff Strength Ratio and Functional Outcomes in Patients with Postoperative Retear After Arthroscopic Rotator Cuff Repair

Background/Objectives: Structural retear after rotator cuff repair does not always correspond to poor clinical outcomes. Functional factors may help explain this discrepancy and may have rehabilitation relevance in patients with postoperative retear. This study aimed to evaluate the association of preoperative external-to-internal rotation strength ratio for postoperative pain and functional outcomes in patients with retear after arthroscopic rotator cuff repair. Methods: This retrospective cohort study included 72 patients who underwent arthroscopic rotator cuff repair at a tertiary referral center between January 2015 and December 2019 and whose magnetic resonance imaging performed 5–6 months after surgery revealed postoperative retear. Patients were classified according to the preoperative external-to-internal rotation strength ratio into a normal group (NG; ratio, 60–80%; n = 34) and an abnormal group (AG; n = 38). Postoperative outcomes were assessed at 1 year and 2 years using functional and pain visual analog scale (FVAS and PVAS), the American Shoulder and Elbow Surgeons (ASES) score, and Constant score. Two-way repeated measures analysis of variance (ANOVA) was used to assess group and time effects and group × time interaction. Results: No significant between-group differences were observed at baseline for PVAS and FVAS scores, ASES score, or Constant score. During follow-up, NG showed significantly lower PVAS values at 1 year (p = 0.007) and 2 years (p = 0.009), significantly higher FVAS scores at 1 year (p = 0.002) and 2 years (p = 0.007), significantly higher Constant scores at 1 year (p = 0.019) and 2 years (p = 0.020), and significantly higher ASES scores at 2 years than the AG (p = 0.041). Repeated-measures ANOVA demonstrated significant time effects for all outcome measures (all p < 0.001) and significant group effects for PVAS (p = 0.007) and FVAS scores (p = 0.002) and ASES (p = 0.016) and Constant scores (p = 0.012). No significant group × time interaction was observed for any outcome measure. Conclusions: A normal preoperative external-to-internal rotation strength ratio was associated with better pain and functional outcomes in patients with structurally confirmed postoperative retear after arthroscopic rotator cuff repair. These findings suggest that preoperative rotator cuff strength balance may provide clinically useful information for postoperative functional stratification.