Evaluation of three-dimensional in vivo scapular kinematics and scapulohumeral rhythm between shoulders with a clavicle hook plate and contralateral healthy shoulders

Purpose: Acromioclavicular-coracoclavicular ligament injury occurs frequently, and the clavicle hook plate technique is an easy-to-use treatment method. However, complications such as subacromial impingement syndrome, synovitis, erosion, osteolysis, post-operative pain, and post-operative limitations in range of motion have been reported. We aimed to evaluate the use of the clavicle hook plate in the shoulder joints and to compare in vivo three-dimensional (3D) scapular kinematics and scapulohumeral rhythm between the shoulders with a clavicle hook plate and contralateral normal shoulder joints. Methods: Ten male patients (aged 40.5 ± 14.4 years) who underwent clavicle hook plate fixation for an acromioclavicular-coracoclavicular ligament injury were selected. Computed tomography and fluoroscopy were conducted on both the shoulder joints, and 3D models were created. Using a 3D-2D model-image registration technique, we determined the 3D coordinates of the scapula, and we measured the scapular kinematics and scapulohumeral rhythm. Results: The values for upward rotation, posterior tilt, and external rotation in the two groups increased in proportion with humeral elevation, showing significant differences between the two groups (p < 0.05). Overall, the value in the clavicle hook plate group (group H) was smaller than that in the control group (group C) by 23.5% (6.7°) of upward rotation and 64.8% (18.9°) of posterior tilt. However, the external rotation in group H was greater than that in group C by 32.3% (2.3°). In overall value, there was a significant difference not in upward rotation and external rotation, but in posterior tilt. During humeral elevation, the overall changes in scapulohumeral rhythm were 4.65 ± 2.45 in group H and 3.8 ± 0.8 in group C, and statistical differences were not detected between the two groups. Conclusions: Clavicle hook plate fixation changes the scapular kinematics and scapulohumeral rhythm; thus, when clavicle hook plate fixation is complete, the implant should be promptly removed.