Predictive value of implant removal time and acromion-hook angle on subacromial osteolysis following hook plate fixation for acromioclavicular dislocation.

Background: Subacromial osteolysis is a typical complication following hook plate fixation for acromioclavicular (AC) dislocation. Many factors can affect the occurrence and progression of subacromial osteolysis (SAO). The objective of this study was to investigate the predictive value of the implant removal time and acromion-hook angle for subacromial osteolysis following hook plate fixation for AC dislocation.

Methods: We conducted a retrospective study of 66 patients who underwent hook plate fixation for AC dislocations. The presence and severity of subacromial osteolysis were assessed at the time of implant removal. Univariate and multivariate logistic regression analyses were conducted to identify the characteristics associated with subacromial osteolysis. Receiver operating characteristic (ROC) analysis was performed to evaluate the predictive performance of the implant removal time and acromion-hook angle.

Results: Of the 66 patients, 48 had subacromial osteolysis. Univariate analysis revealed that the implant removal time and acromion-hook angle were associated with subacromial osteolysis. Multivariate analysis revealed that the acromion-hook angle was the only factor independently associated with subacromial osteolysis. In the ROC analysis, the optimal cut-off values of implant removal time were 5.5 months for predicting the occurrence of osteolysis and 11.9 months for predicting the severity of osteolysis. The acromial-hook angle cut-off values were 10° for predicting the occurrence of osteolysis and 16° for predicting the severity of osteolysis.

Conclusion: The implant removal time and acromion-hook angle were significant risk factors for subacromial osteolysis following hook plate fixation. We recommend removing the implant within 5.5 months to minimize osteolysis risk and no more than 11.9 months to prevent severe osteolysis. Maintaining the acromion-hook angle at 10° or less is advised, whereas an angle of 16° or more may indicate a greater risk of severe osteolysis.