Subacromial Erosion after Hook Plate Fixation in Acute Acromioclavicular Joint Dislocation

Abstract Background: This study was to analyze the clinical results of locking hook plate fixation for acute acromioclavicular joint (ACJ) injury and to find out the incidence of subacromial erosion, carry out quantitative analysis and identify risk factors. Methods: The study was conducted on 35 patients who underwent the locking hook plate fixation for acute ACJ joint injury. The clinical outcomes were evaluated measuring the visual analog scale (VAS) for pain, and the University of California at Los Angeles (UCLA) score. The computed tomography (CT) was conducted to measure the subacromial erosion. The acromioclavicular slope (AC slope) of the unaffected side, the acromion-hook angle (AH angle), the acromioclavicular anteroposterior distance (AC-AP distance), and the preoperative acromioclavicular interval (ACI) of the affected side were analyzed to identify the risk factors of subacromial erosion. Results: The mean preoperative VAS score was 7.6 points, which improved by a significant level of 0.3 at the final follow-up (P <0.001). The UCLA score at the last follow-up was 32.3 points, which was higher than the preoperative average of 15.2 points (P = 0.003). According to the computed tomography (CT) findings, subacromial erosion was found in all cases, and the mean value was 5.0mm, which is 53% of the entire acromion thickness. The AC slope (B=-0.159, P<0.001) and AC-AP distance (B=0.233, P=0.004) were found to have a significant influence on postoperative subacromial erosion. The AC slope showed a negative correlation with the amount of erosion, while the AC-AP distance showed a positive correlation with erosion. onclusion: The study was able to obtain satisfactory clinical and radiological results after locking hook plate fixation for acute ACJ injury. The CT findings revealed that subacromial erosion occurred in all cases, and the mean erosion depth was about 50% of the acromial thickness. If the preoperative AC slope of the unaffected side was more acute and the AC-AP distance was larger, the incidence of subacromial erosion was higher. Level of evidence: Therapeutic Level IV Retrospectively registered study: This study was retrospective in nature, and final approval of informed consent exemption by the institutional review board was obtained (KHUH IRB 2019-04-079)