Evaluation of Inferior Capsular Laxity in Patients with Atraumatic Multidirectional Shoulder Instability with Magnetic Resonance Arthrography.

OBJECTIVE

To compare inferior capsular redundancy by using magnetic resonance arthrography (MRA) images in patients with multidirectional instability (MDI) of the shoulder and control subjects without instability and thereby develop a screening method to identify the presence of shoulder MDI.

MATERIALS AND METHODS

The MRA images of patients with MDI of the shoulder (n = 65, 57 men, 8 women; mean age, 24.5 years; age range, 18-42 years) treated over an eight-year period were retrospectively reviewed; a control group (n = 65, 57 men, 8 women; mean age, 27.4 years; age range, 18-45 years) without instability was also selected. The inferior capsular redundancy was measured using a new method we named the glenocapsular (GC) ratio method. MRA images of both groups were randomly mixed together, and two orthopedic surgeon reviewers measured the cross-sectional areas (CSAs) and sagittal capsule-head ratios on oblique sagittal images, as well as the axial capsule-head ratios on axial images and GC ratios on oblique coronal images.

RESULTS

The CSAs and GC ratios were significantly higher in patients than in controls (both, < 0.001); however, the sagittal capsule-head ratios and axial capsule-head ratios were not significantly different ( = 0.317, = 0.053, respectively). In addition, GC ratios determined the presence of MDI more sensitively and specifically than did CSAs. A GC ratio of > 1.42 was found to be most suggestive of MDI of the shoulder, owing to its high sensitivity (92.3%) and specificity (89.2%).

CONCLUSION

GC ratio can be easily measured and used to accurately screen for MDI of the shoulder.