Understanding the Independent Risk Factors of Anterior Shoulder Dislocation Using MRI

Anterior shoulder dislocation is the most common dislocation in the musculoskeletal system, frequently occurring in traumatic events and athletic activities. Many anatomical features of this joint have been reported to be risk factors for anterior shoulder dislocation with inconsistent findings, in which these features can be detected using magnetic resonance imaging (MRI) as a safe observational tool rather than a diagnostic one. This study aims to determine the independent and most relevant risk factor(s) of anterior shoulder dislocation.

This retrospective case-control study was based on 2 groups (control and dislocated) of 49 MRI series each. These MRI series were selected after reviewing 3950 MRI series from patients who visited the orthopaedic clinic at a university hospital for shoulder issues. The study measured and statistically compared various parameters between the 2 groups, including glenoid version, coracohumeral distance, humeral containing angle, glenoid height, depth and width (diameter), humeral head diameter, glenoid width-to-depth ratio, glenoid height-to-diameter ratio, and humeral diameter-to-glenoid width ratio.

Each group consisted of 49 MRI series from patients aged 17-75 years. The independent parameters associated with anterior shoulder dislocation were the height-to-width ratio and width-to-depth ratio with cut-off points of >1.65 and >13.15, respectively (P < 0.05). Other investigated risk factors were either not associated or were not significant predictors of shoulder dislocation.

This study found that the glenoid width-to-depth ratio and the glenoid height-to-diameter ratio are the most relevant independent risk factors for developing anterior shoulder dislocation. A higher glenoid width-to-depth ratio and a higher glenoid height-to-diameter ratio were both associated with an increased risk of anterior shoulder dislocation compared with lower ratios.