Effect of subacromial erosion shape on rotator cuff and clinical outcomes after hook plate fixation in type 5 acromioclavicular joint dislocations: a retrospective cohort study

Background Surgical fixation using hook plates is widely used in the treatment of acromioclavicular (AC) joint dislocations. The purpose of this study was to evaluate the incidence and shape of subacromial erosions after removal of the hook plate in type 5 AC joint dislocations. Further, we evaluated the effect of the shape of the subacromial erosion on the rotator cuff. Methods We retrospectively reviewed 30 patients who underwent hook plate fixation for type 5 AC joint dislocations at our hospital between December 2010 and December 2018. Patients with a follow-up of at least 1 year were included. Clinical outcomes were assessed using the final follow-up Constant-Murley, Korean Shoulder, and visual analog scores. To ensure that the appropriate reduction was well maintained, the coracoclavicular distances of the injured and contralateral sides were evaluated at the last follow-up. Computed tomography was performed to investigate the presence and shape of the subacromial erosion after hook plate removal at 4 months after surgery. Ultrasonography was performed to investigate the presence of rotator cuff lesions at the last follow-up. Clinical and radiological outcomes were compared between groups divided according to the presence and types of subacromial erosions. Results Subacromial erosion was observed in 60% of patients (18/30): 13, 2, and 3 simple groove, cave, and marginal protrusion types, respectively. Four patients showed reduction loss at the final follow-up. There were no significant differences in clinical and radiological outcomes between the groups with and without subacromial erosion. Moreover, there were no significant differences between groups according to the types of subacromial erosion. There were no rotator cuff lesions, such as partial tears, in the injured shoulders. Conclusions Hook plate fixation may induce subacromial erosions. However, the subacromial erosions caused by the hook plate did not affect the clinical outcomes of type 5 AC joint dislocations. Moreover, regardless of its shape, the subacromial erosion did not affect the clinical outcomes nor cause rotator cuff lesions after plate removal.