Risk factors for atraumatic isolated subscapularis tear: glenoid retroversion.

Background: Subscapularis tendon (SSC) tears have recently become an area of current research focus. However, the risk factors for atraumatic isolated SSC tears, particularly anatomical factors, remain poorly determined. Therefore, the purpose of this study was to identify the associated factors contributing to isolated SSC tears.

Methods: This study involved single shoulders of 605 subjects drawn from a cohort of rural residents. The inclusion criteria required each subject to sign an informed consent document and to have a complete clinical evaluation. The exclusion criteria comprised the absence of a complete magnetic resonance imaging study, current medication use that might have affected serum lipid levels, a history of shoulder trauma or surgery, and the presence of osteoarthritis, calcific tendinitis, frozen shoulder, or superior or posterosuperior rotator cuff tear. Diagnoses of isolated SSC tear were based on magnetic resonance imaging findings. Logistic regression analysis was conducted using demographic, physical, social, anatomical, comorbidities, and serological parameters. Anatomical variables included the supraspinatus fossa glenoid angle on axial (SGAX), a method to measure glenoid version, coracohumeral distance on axial and sagittal plans, and coracoid index. When multicollinearity among studied variables was detected, separate multivariable analyses were performed to address this issue, with each analysis including only one of those multicollinear variables along with the other significant variables obtained from univariate analyses.

Results: Among anatomical variables, coracohumeral distance on axial and sagittal planes, as well as the coracoid index, did not show significant associations. However, SGAX, an index of glenoid version, was found to be significantly associated with atraumatic isolated SSC tears. Greater glenoid retroversion is significantly associated with atraumatic isolated SSC tears, along with age, waist circumference, dominant side involvement, manual labor, diabetes, metabolic syndrome, and biceps tendon injury (P ≤ .013).

Conclusions: The SGAX, serving as an index for glenoid version, is an independently associated factor for atraumatic isolated subscapularis tendon tears, with greater glenoid retroversion being an anatomical risk factor for these tears, along with overuse-related factors such as dominant-side involvement and manual labor, as well as metabolic factors such as obesity, diabetes, metabolic syndrome, and biceps tendon injury.