Dynamic Radiologic Evaluation of Horizontal Instability in Acute Acromioclavicular Joint Dislocations

This study from Salzburg, Austria evaluated a novel approach to radiological evaluation of acute acromioclavicular (AC) joint injuries. The authors felt that the traditional Zanca and axillary lateral views failed to adequately characterize horizontal instability in AC joint injuries. To that end, they used supine axillary lateral views with the arm in 90° of abduction and 60° of flexion and developed a gleno-acromio-clavicular angle (GACA) to quantify the anteroposterior translation of the clavicle. Twenty-five patients with first-time acute AC joint injuries were enrolled, and the absolute GACA difference between the neutral and anterior position of the injured arms was compared with the GACA difference in the uninjured arms, which served as controls. Eleven of the 25 subjects showed no evidence of horizontal instability, with the average GACA difference between neutral and anterior positions demonstrating no discrepancy between injured and uninjured shoulders (7.1° ± 4.8° vs. 7.1° ± 5.5°, respectively). Fourteen of the 25 subjects had anteroposterior translation, with a GACA difference of 30.3° ± 14.3° (p<0.001). Twenty-four percent of the entire study population (2 patients with Rockwood type II injuries and 4 patients with type III injuries) had normal axillary views when evaluated by the traditional radiographic method but were found to have anteroposterior instability when the functional axillary views were used. The authors concluded that functional axillary radiographic evaluation is an effective tool at detecting horizontal instability in acute AC joint injuries.