Anterior shoulder instability: diagnostic criteria determined from prospective analysis of 121 MR arthrograms.

PURPOSE

To determine magnetic resonance (MR) arthrographic criteria in the diagnosis of anterior glenohumeral instability.

MATERIALS AND METHODS

In 121 patients with diagnoses proved surgically, the labrum, glenohumeral ligaments, and capsular insertion types were assessed prospectively with gadolinium-enhanced MR arthrography. Findings were compared in stable and unstable shoulders.

RESULTS

Operative results showed 59 normal, 57 torn, and five deficient labra. In 37 unstable shoulders, 31 had discrete inferior labral-ligamentous lesions and six had capsular laxity. MR arthrograms showed labral abnormalities with 92% sensitivity, 92% specificity. Inferior labral-ligamentous lesions enabled prediction of anterior instability with 76% sensitivity (capsular laxity was missed in all shoulders), 98% specificity. Inferior labral-ligamentous abnormalities were strongly associated with unstable shoulders (P << .0001), whereas noninferior labral-ligamentous abnormalities were related to stable shoulders (P = .01). Capsular insertion types showed no significant differences between stable and unstable shoulders (P > .8).

CONCLUSION

On MR arthrograms, inferior labral-ligamentous abnormalities were most closely correlated with anterior glenohumeral instability. Capsular insertion sites had no role in the prediction of shoulder instability.