The critical shoulder angle was not associated with risk of retear after arthroscopic rotator cuff repair.
Rotator cuff tears (RCTs) are common among older patients and cause limited range of motion and loss of strength, leading to worse functional activity for patients. Surgical repair is common for these patients, but high failure rates still exist. Anatomical risk factors, including the critical shoulder angle (CSA), have been used in an attempt to predict risk of rotator cuff tears. Some studies suggest that increasing CSA is associated with increasing incidence of RCTs, while others have found no such relationship. More recently, there has been increased interest in assessing the correlation between CSA and retear rate following arthroscopic repair. Some studies suggest higher CSAs correlate with a higher rate of retear, while others have inconclusive results. Given the discrepancies of prior investigations and minimal comparisons to clinical outcomes of patients, the aim of the current study was to determine whether higher CSAs correlated with an increased retear rate and if there are any associations between CSA and patient-reported outcome (PROs). It was hypothesized that there would be no correlation between CSA and retear rate or PROs.
A total of 164 consecutive arthroscopic rotator cuff repair patients were retrospectively reviewed. Patients were split into a retear group, which included 18 patients, and a non-retear group, which included 146 patients. CSA was measured as the angle between the superior and inferior bone margins of the glenoid and the most lateral border of the acromion, as defined by Moor et al. Patient-reported outcomes (PROs), including PROMIS 10 score, American Shoulder and Elbow Surgeons (ASES) score, Brophy score, and visual analog pain scores (VAS) were recorded post-operatively. A minimum of 6-month follow-up was required.
The average CSA was 31.2 ± 4.5° for the retear group and 32.2 ± 4.7° for the non-retear group (p = 0.43). No correlations were found between CSA and PROMIS score (p = 0.32, r = -0.11), ASES score (p = -0.42, r = -0.10), Brophy score (p = -0.42, r = -0.10), or VAS (p = 0.72, r = -0.03). A post-hoc power analysis demonstrated a power of 0.14 and an effect size of 0.22. Over 1,500 patients in would be required to reach a power of 0.8.
The current study found no relationship between CSA and retear rates or PROs, supporting the hypotheses. While the study is underpowered, the number of patients required to be sufficiently power is so large that it is unlikely to be clinically relevant. As such, there is likely no true difference in our dataset. Given continued conflicting evidence, CSA cannot be considered a reliable measure to assess rotator cuff retear risk at this time.
Clinical Significance: Critical shoulder angle had no correlation to retear rate or functional patient-reported outcomes in the current cohort of patients. At this time, CSA should not be considered a reliable measure to assess rotator cuff retear risk after arthroscopic repair given conflicting results from the literature.