Which labral lesion can be best reduced with external rotation of the shoulder after a first-time traumatic anterior shoulder dislocation?

INTRODUCTION: Immobilization in external rotation after a first-time traumatic anterior shoulder dislocation has been shown to improve the position of the labroligamentous lesion relative to the glenoid rim. The purpose of the present study was to evaluate the effect of the external rotation position of the shoulder on different types of labroligamentous lesions in patients with first-time traumatic anterior shoulder dislocation by using MRI.

PATIENTS AND METHODS: We performed a standardized MRI in internal and external rotation of the shoulder after initial reduction in 34 patients with a first-time traumatic anterior shoulder dislocation. Labroligamentous lesions were classified as Bankart, Perthes, or nonclassifiable. Four distinct grades were used to classify the amount of plastic deformation of the anterior labroligamentous structures. The position of the labrum was defined relative to the tip of the glenoid rim by measuring the dislocation and separation.

RESULTS: In all patients, dislocation and separation of the labrum relative to the rim of the glenoid were significantly improved in shoulders in the external rotation position compared to those in the internal rotation position. We observed 15 Bankart, 15 Perthes, and 4 non-classifiable lesions. No HAGL or GLAD lesions were found. Fourteen patients showed a plastic deformation grade I, 16 showed grade II, 3 showed grade III, and 1 showed grade IV. In regression analysis, the odds ratio was 1.100 for the type of lesion and 1.660 for the grade of plastic deformation. Perthes lesions (with an intact anterior scapular periosteum) and grade I plastic deformations showed the best labral reduction on the external rotation MRI.

CONCLUSION: Placing the shoulder in external rotation after a first-time traumatic shoulder dislocation, significantly improves the position of the labroligamentous lesion on the glenoid rim. Perthes lesions that showed a low grade of plastic deformation displayed better reduction in external rotation and then compared to Bankart or other lesions that showed a high grade of plastic deformation. In conclusion, immobilization of the shoulder after a first-time traumatic shoulder dislocation is most effective in patients with Perthes lesions that show low grade plastic deformation.