Purpose: To quantitatively measure the 3-dimensional (3D) glenohumeral translations during dynamic shoulder abduction in the scapular plane, using a biplane fluoroscopy system, in patients with supraspinatus rotator cuff tears.
Methods: A custom biplane fluoroscopy system was used to measure the 3D position and orientation of the scapula and humerus of 14 patients with full-thickness supraspinatus or supraspinatus and infraspinatus rotator cuff tears and 10 controls as they performed shoulder abduction over their full range of motion. The 3D geometries of the scapula and humerus were extracted from a computed tomography scan of each shoulder. For each frame, the 3D bone position and orientation were estimated using a contour-based matching algorithm, and the 3D position of the humeral head center was determined relative to the glenoid. For each subject the superior-inferior and anterior-posterior translation curves were determined from 20° through 150° of arm elevation.
Results: The humeral head in shoulders with rotator cuff tears was positioned significantly inferior compared with controls for higher elevation angles of 80° to 140° (P < .05). For both groups the humeral head translated inferiorly during shoulder abduction from 80° (P = .044; rotator cuff tear v controls: -0.2 ± 1.3 v 1.2 ± 1.4 mm) up to 140° (P = .047; rotator cuff tear v controls: -1.3 ± 2.2 v 0.44 ± 1.4 mm). There was no significant translation in the anterior- posterior direction.
Conclusions: Patients with well-compensated single or 2-tendon rotator cuff tears show no dynamic superior humeral head migration but unexpectedly show an inferior shift during active elevation. It is unclear whether the size of the translational differences found in this study, while statistically significant, are also of clinical significance.
Level of evidence: Level III, comparative study.
Copyright © 2016 Arthroscopy Association of North America. Published by Elsevier Inc. All rights reserved.