BACKGROUND: Subscapularis management is a critical component to the success of anatomic total shoulder arthroplasty (TSA). Failure to heal the subscapularis can result in pain, weakness, loss of function, and revision. However, not all patients have poor outcomes. The purpose of this study is to compare patients with normal and dysfunctional subscapularis function following TSA in regard to (1) patient-reported outcome measures (PROMs); (2) range of motion (ROM) and strength; (3) achievement of minimal clinically important differences (MCIDs); and (4) specific functional internal rotation tasks.
METHODS: A retrospective review of patients treated with TSA for osteoarthritis with a minimum 2-year follow-up was performed to identify patients with subscapularis dysfunction. Subscapularis dysfunction was diagnosed when any degree of weakness in internal rotation was detected on physical examination (positive belly press sign). These patients were case controlled matched on a 1:3 ratio to patients with normal subscapularis function based on age and sex. PROMs, measured active motion, revision rates, patient satisfaction, and postoperative radiographic findings were compared. Population-specific institutional anchor-based MCID values were used to compare the improvement in PROM.
RESULTS: Of the 668 patients included, 34 patients (5.1%) demonstrated evidence of subscapularis dysfunction. Mean follow-up for the normal subscapularis function cohort was 63.4 ± 29.7 and 58.7 ± 26.8 for the dysfunctional subscapularis cohort. Patients with subscapularis dysfunction demonstrated significantly worse postoperative Simple Shoulder Test, Single Assessment Numerical Evaluation, visual analog scale (VAS) function, VAS pain, and American Shoulder and Elbow Surgeons Standardized Shoulder Assessment Form (ASES) scores with higher rates of unsatisfactory results when compared to patients with normal subscapularis function. Abduction, elevation, internal rotation ROM, along with supraspinatus and external rotation strength were also significantly worse in the dysfunctional group. Similarly, these patients were more likely to have decreased ability to perform functional internal rotation tasks, with only 47% of the patients being able to reach the small of their back compared to 85% with normal subscapularis function. Radiographically, the dysfunctional cohort demonstrated higher rates of anterior subluxation (56% vs. 7%; P < .001) and glenoid loosening (24% vs. 5%; P = .004). Similarly, revision rates were significantly higher for patients with subscapularis dysfunction (8 patients, 23.5%). Nonetheless, the dysfunctional subscapularis cohort demonstrated improvements in VAS pain (4.0 ± 3.7) and ASES (46.4 ± 35.9) scores that exceeded MCID thresholds.
CONCLUSION: Patients who develop subscapularis dysfunction after TSA have significantly worse PROMs, ROM, functional tasks of internal rotation, and radiographic outcomes, as well as increased rates of revision. Although patients show worse outcomes and high revision rates compared with their normal-functioning counterparts, these patients maintained improvement above MCID thresholds for pain and function at a mean 5-year follow-up.