Preoperative Scaption and External Rotation Strength Deficits Are Predictive of Retear After Rotator Cuff Repair

PURPOSE: To investigate the role of preoperative shoulder muscle strength as a predictive factor of retear after rotator cuff repair. METHODS: This retrospective study reviewed factors related to rotator cuff retears in patients who underwent arthroscopic rotator cuff repair. The patients included in the study were those who underwent surgery for full-thickness rotator cuff tears diagnosed on preoperative magnetic resonance imaging (MRI), or for partial-thickness tears involving more than 80% of the tendon thickness with an anterior-posterior tear diameter of at least 1.5 cm. The study subjects were followed for a minimum of 1 year. All patients underwent preoperative assessments, including the American Shoulder and Elbow Surgeons score and Constant score evaluation. Additionally, the preoperative muscle strength was evaluated using an isometric handheld dynamometer in 6 positions (scaption, elbow flexion, internal rotation, external rotation, belly press, and lift-off). Rotator cuff retears were assessed using MRI postoperatively. The statistical analysis in this study was conducted using univariate analysis to identify candidate predictors of retear. Subsequently, multivariate logistic regression was used to determine independent predictors. A logistic regression analysis using a forward stepwise technique was performed to identify independent predictors of rotator cuff retear while controlling for potential confounders. The significance level was set at P < .05 for all analyses. RESULTS: Data were collected retrospectively from 699 patients who underwent arthroscopic rotator cuff repair between January 2014 and December 2018. All patients included in the study underwent MRI at an average of 5.4 months after rotator cuff repair, and a mean follow-up duration was 32.2 months (range, 12-123 months) for all patients. Among the total patients included in this study, 83 experienced retear, resulting in a retear rate of 11.87%. A higher proportion of patients with intact repairs achieved minimal clinically important difference improvement in American Shoulder and Elbow Surgeons scores compared with those with retears (71.3% vs 55.4%, P = .003); minimal clinically important difference achievement for Constant score did not differ significantly between groups (55.8% vs 44.6%, P = .053). Univariate analyses revealed that age (P = .043), Constant score (P = <.001), elbow flexion strength (P = .049), scaption strength (P = <.001), external rotation (P = <.001), and lift-off (P = .019) were statistically significant. Age, Constant score, and deficits in scaption and external rotation strength were independent predictors of rotator cuff retear. Age (P = .019), Constant scores (P = .006), and preoperative strength deficits in scaption (P = .045) and external rotation strengths (P = <.001) between the injured and uninjured sides. CONCLUSIONS: Age, Constant score, and preoperative differences in scaption and external rotation muscle strength deficits between the injured and uninjured sides are significant predictors of rotator cuff retear after repair surgery. Because MRI is often unavailable, muscle strength measurement offers a practical indirect indicator for retear risk. LEVEL OF EVIDENCE: Level III, retrospective cohort study.