Three-dimensional Capsular Volume Measurements in Multidirectional Shoulder Instability

BACKGROUND: In a previous study undertaken to quantify capsular volume in rotator cuff interval or axillary pouch, significant differences were found between controls and patients with instability. However, the results obtained were derived from two-dimensional cross sectional areas. In our study, we sought correlation between three-dimensional (3D) capsular volumes, as measured by magnetic resonance arthrography (MRA), and multidirectional instability (MDI) of the shoulder. METHODS: The MRAs of 21 patients with MDI of the shoulder and 16 control cases with no instability were retrospectively reviewed. Capsular areas determined by MRA were translated into 3D volumes using 3D software Mimics ver. 16 (Materilise, Leuven, Belgium), and glenoid surface area was measured in axial and coronal MRA views. Then, the ratio between capsular volume and glenoid surface area was calculated, and evaluated with control group. RESULTS: The ratio between 3D capsular volume and glenoid surface area was significantly increased in the MDI group (3.59 ± 0.83 cm(3)/cm(2)) compared to the control group (2.53 ± 0.62 cm(3)/cm(2)) (p<0.01). CONCLUSIONS: From these results, we could support that capsular volume enlargement play an important role in MDI of the shoulder using volume measurement.