Rotator cuff muscle imbalance associates with shoulder instability direction.

BACKGROUND: Although muscle weakness and/or imbalance of the rotator cuff are thought to contribute to the development of shoulder instability, the association between muscular dysfunction and shoulder instability is not completely understood. The purpose of this study was to evaluate rotator cuff and deltoid muscle cross-sectional areas in different types of shoulder instability (anterior, posterior, and multidirectional instability [MDI]) and to determine the associations between muscular imbalance and shoulder instability direction. METHODS: Preoperative magnetic resonance images of patients with shoulder instability who subsequently underwent arthroscopic glenohumeral labral repair or capsular plication were evaluated. Shoulder instability was classified into 3 categories by direction: (1) anterior, (2) posterior, and (3) MDI. The rotator cuff (supraspinatus, subscapularis, and infraspinatus + teres minor) and deltoid (anterior and posterior portions, and total) muscle areas were measured on T1 sagittal and axial slices, respectively. The ratios of the subscapularis to infraspinatus + teres minor area and the anterior deltoid to posterior deltoid area were calculated to quantify the transverse force couple imbalance. RESULTS: A total of 189 patients were included, where each group consisted of 63 patients. The infraspinatus + teres minor muscle area was smaller than the subscapularis muscle area in the anterior instability group (P = .007). The subscapularis muscle area was smaller than the infraspinatus + teres minor muscle area in the posterior instability and MDI groups (P ≤ .003). The anterior deltoid muscle area was smaller than the posterior deltoid muscle area in all groups (P ≤ .001). The subscapularis-to-infraspinatus + teres minor area ratio in the anterior instability group (1.18 ± 0.40) was higher than that in the posterior instability and MDI groups (0.79 ± 0.31 and 0.93 ± 0.33, respectively; P < .001). There was no difference in the anterior deltoid-to-posterior deltoid area ratio among the 3 groups. CONCLUSION: Patients with anterior instability have smaller muscle area of the posterior rotator cuff as compared with the anterior rotator cuff. In contrast, patients with posterior instability and MDI have smaller muscle area of the anterior rotator cuff as compared with the posterior rotator cuff. Thus, the direction of shoulder instability is associated with rotator cuff muscle area.

COVID-19-related rotator cuff repair delay.

BACKGROUND: Although nonoperative treatment is effective for degenerative rotator cuff tears (RCTs), it remains unclear whether the delay created by a trial of nonoperative treatment negatively influences the outcome of a subsequent surgical repair. In March 2020, the COVID-19 pandemic resulted in an involuntary delay in the surgical treatment of rotator cuff disease, creating a natural experiment. The purpose of this study was to evaluate the outcomes and healing of patients who underwent delayed surgical treatment of chronic degenerative RCTs as compared with the nondelayed surgical treatment of RCTs. METHODS: This was a prospective study of two groups: patients planned to undergo arthroscopic rotator cuff repair between March 16, 2020 and May 1, 2020-the end of the ban on elective surgery-and patients who underwent rotator cuff repair starting six weeks after the ban on elective surgery had been lifted. Preoperatively and at six months postoperatively, we collected the Simple Shoulder Test, the American Shoulder and Elbow Surgeons (ASES) score, and the visual analog scale for pain. We also obtained magnetic resonance imaging (MRI) at six months postoperatively. A power analysis was conducted, and assuming a mean ± standard deviation ASES score of 93.1 ± 13.9 points and a minimum clinically important difference in the ASES score of 27.1 points, 7 patients per group (14 patients in total) would be necessary to have 90% chance of finding a difference. RESULTS: We included 15 patients within each group and obtained 100% follow-up at six months. In the delay group, the mean ± standard deviation delay was 63 ± 24 days. There were no significant preoperative differences between groups in demographics or tear characteristics. Intraoperatively, there were no differences between groups in repair characteristics. Using a repeated-measures analysis of variance, there were significant preoperative vs. postoperative differences in ASES scores (P < .001), visual analog scale scores (P < .001), and Simple Shoulder Test scores (P < .001), but no differences between groups (P = .910, .519, and 0.852, respectively). On MRI, within the delay group, 58% had healed, whereas within the control group, 85% had healed (P = .202). CONCLUSION: COVID-19 caused a two-month delay in the operative treatment of RCTs. This delay did not significantly alter patient-reported outcomes. This delay resulted in a 27% difference in MRI healing rates, which was not statistically significant in this small study. Larger studies should be conducted as our results suggest that a delay in treatment may negatively impact healing rates.