The correlation between acromial osteolysis and acromion types in the treatment of acromioclavicular joint dislocation with hook plate

This study aimed to radiologically evaluate the effect of hook plates used in the treatment of acromioclavicular joint (ACJ) dislocations on the development of subacromial osteolysis (SAO) according to acromion types. A total of 43 patients with mean age of 38.5 (19–77) years who were diagnosed with AC dislocation and applied neutral clavicular hook plate between 2013 and 2020 were retrospectively evaluated. Acromion types were determined by measuring acromion slope angle on lateral shoulder radiography and 3-dimensional (D)-CT of the patients. Presence of SAO was classified according to the severity of erosion in the subacromial region (grade I: minimal osteolysis, grade II: subacromial erosion <2 mm, grade III: subacromial erosion >2 mm, grade IV: cut-through of the acromion) on postoperative 3D - CT and correlation with acromion types was analyzed. Incidence of SAO was significantly higher among type 1 acromion compared to type 2 and type 3 acromion (P = .003). While osteolysis was observed in 21 patients, no osteolysis was observed in 22 patients. Osteolysis occurred in all patients with type 1 acromion, 7 patients with type 2 acromion, and 5 patients with type 3 acromion. Since the hook tip in the sagittal plane passes posterior to the center of the acromion and the concavity of the subacromial surface is inadequate in the type 1 acromion, we believe that the increased pressure applied by the hook tip on the subacromial cartilage increases the risk of SAO. We predict that the use of hook plates with an angle of 15-20 degrees, similar to the patient’s AC angle, rather than neutral hook plate, will reduce the risk of osteolysis in patients with type 1 acromion.