Morphological Characteristics of Acromion and Acromioclavicular Joint in Patients with Shoulder Impingement Syndrome and Related Recommendations: A Three-Dimensional Analysis Based on Multiplanar Reconstruction of Computed Tomography Scans.

To find out which structure is crucial for the formation of shoulder impingement syndrome with the purpose of directing surgical procedures of subacromial decompression and discussing whether it is necessary to manage acromioclavicular joint during operation and how to do it properly. Methods This was a retrospective study. Clinical data and preoperative computed tomography (CT) images were collected from patients who were diagnosed with rotator cuff tears between January 2017 and August 2019 (sample size: 46) and those who were diagnosed without rotator cuff tears between March 2018 and August 2019 (sample size: 44) in our institution, respectively. Three-dimensional models of shoulders were established by multiplanar reconstruction of CT scans and measurements were performed on these models. The parameters such as the acromial length and width, the axial tilt, and the distance from acromial margin to glenoid plane were measured in an adjusted axial plane, and the critical shoulder angle and the spatial volume under acromioclavicular joint were measured in an adjusted coronal plane. The demographic characteristics, the acromial morphology and the spatial volume under acromioclavicular joint were compared to find significant differences between the two groups. The association between the axial tilt and the distance from acromial margin to glenoid plane was evaluated by an ordinary least squares linear regression. Results The patients with rotator cuff tears consisted of 16 males and 30 females, among which 30 right shoulders and 16 left shoulders were included. The patients without rotator cuff tears consisted of 28 males and 16 females, among which 15 right shoulders and 29 left shoulders were involved. Significant differences between the groups were found in the acromial width (3.332 cm vs 3.111 cm), the axial tilt (33.765° vs 23.829°), the critical shoulder angle (32.630° vs 30.363°), the distance from anterior 3 cm of lateral acromial margin (range, 2.476 cm-3.302 cm vs 1.993 cm-3.089 cm), and anterior 0.9 cm of medial acromial margin (range, 0.967 cm-2.369 cm vs 0.668 cm-1.993 cm) to glenoid plane, and the spatial volume under acromioclavicular joint (1.089 cm vs 1.446 cm) in the two groups. No significant differences were found in the age (60.0 years vs 58.3 years) or the acromial length (4.187 cm vs 4.184 cm). Significant association was revealed by linear regression analysis between the axial tilt and the distance from anterior two-thirds of lateral acromial margin to glenoid plane, and similar association was also found in the anterior half of medial margin. Conclusion Anterior two-thirds of lateral acromial margin, anterior half of medial acromial margin, and inferior aspect of acromioclavicular joint are crucial structures and need to be fully decompressed when treating patients with rotator cuff tears.