Three-dimensional scapular dyskinesis in hook-plated acromioclavicular dislocation including hook motion

Background: The purpose of this study is to analyze the 3-dimensional scapular dyskinesis and the kinematics of a hook plate relative to the acromion after hook-plated acromioclavicular dislocation in vivo. Reported complications of acromioclavicular reduction using a hook plate include subacromial erosion and impingement. However, there are few reports of the 3-dimensional kinematics of the hook and scapula after the aforementioned surgical procedure. Methods: We studied 15 cases of acromioclavicular dislocation treated with a hook plate and 15 contralateral normal shoulders using computed tomography in the neutral and full forward flexion positions. Three-dimensional motion of the scapula relative to the thorax during arm elevation was analyzed using a computer simulation program. We also measured the distance from the tip of the hook plate to the greater tuberosity, as well as the angular motion of the plate tip in the subacromial space. Results: Decreased posterior tilting (22 degrees +/- 10 degrees vs 31 degrees +/- 8 degrees) in the sagittal plane and increased external rotation (19 degrees +/- 9 degrees vs 7 degrees +/- 5 degrees) in the axial plane were evident in the affected shoulders. The mean values of translation of the hook plate and angular motion against the acromion were 4.0 +/- 1.6 mm and 15 degrees +/- 8 degrees, respectively. The minimum value of the distance from the hook plate to the humeral head tuberosity was 6.9 mm during arm elevation. Conclusions: Acromioclavicular reduction using a hook plate may cause scapular dyskinesis. Translational and angular motion of the hook plate against the acromion could lead to subacromial erosion. However, the hook does not seem to impinge directly on the humeral head.(C) 2017 Journal of Shoulder and Elbow Surgery Board of Trustees. All rights reserved.