Magnetic Resonance Arthrography Findings of the Glenohumeral Joint in the Abduction External Rotation Position in Symptomatic Anterior Instabilities: Comparison Between Overhead Throwing Disorders and Traumatic Shoulder Dislocation.

Background: The utility of indeterminate magnetic resonance (MR) imaging findings in identifying shoulder pathology in overhead throwing athletes is yet to be determined. The assessment of capsular redundancy on MR arthrography, specifically in the abduction external rotation (ABER) position, could help accurately distinguish between throwing disorders involving internal impingement and those involving anterior instability. Purpose: To compare MR arthrography findings in the ABER position between patients with internal impingement with anterior instability and those with traumatic shoulder dislocation. Study Design: Cross-sectional study; Level of evidence, 3. Methods: This study included patients who had subtle glenohumeral instability, as indicated by a positive anterior apprehension test and relocation test results. Those with voluntary and multidirectional instability and with large glenoid bone loss (>25%) were excluded. In total, 95 shoulders (86 male, 9 female; mean age, 23.9 ± 9.4 years) that had undergone arthroscopic procedures were divided into 2 groups: 35 shoulders in the throwing group with internal impingement with anterior instability and 60 in the traumatic dislocation group. We classified the anterior glenohumeral capsular ligaments on MR arthrography in the ABER position into the following 4 types based on a previous report: taut, avulsion, crescent, and fluctuation sign. Compared with arthroscopy, MR arthrography in the side position was evaluated for its accuracy in detecting rotator cuff and labral injuries. Results: MR arthrography in the ABER position revealed that the fluctuation sign in 71% of shoulders in the throwing group was significantly greater than that in 12% of shoulders in the dislocation group (P < .001). MR arthrography revealed that rotator cuff and posterosuperior labral injuries were present in 83% and 71% of shoulders in the throwing group, which was significantly greater than the 20% and 23% of shoulders in the dislocation group (P < .001). Conclusion: The fluctuation sign on MR arthrography in the ABER position could potentially detect characteristic lesions in throwing athletes with internal impingement with anterior instability.