Instability pattern of acromioclavicular joint dislocations type Rockwood III. Relevance of horizontal instability

There is no evidence-based treatment algorithm established for acromioclavicular joint (AC joint) dislocation classified as type Rockwood III injury. Recent meta-analyses revealed no advantage of surgical treatment compared to the non-operative approach. Both surgical and non-surgical approaches have been reported with inconsistent results. Therefore, the hypothesis of the current study was that patients classified as having Rockwood grade III injury may have different degrees of horizontal AC joint instability. A total of 18 consecutive patients who had sustained a dislocation of the AC joint classified as Rockwood III were evaluated radiologically to quantify the horizontal instability of the AC joint. The specific radiological investigation included lateral stress x-rays (Alexander view) und axial stress x-rays with the affected arm in a horizontal adduction position. The dynamic horizontal instability of the AC joint was found to be independent of the vertical dislocation measured in the Rockwood classification. For further treatment studies Rockwood III injuries should be distinguished in patients presenting with or without a substantial horizontal AC joint instability.