Rotator cuff tears are a common cause of shoulder pain, weakness, and decreased range of motion. One of the primary functions of the rotator cuff is stabilization of the shoulder joint by compressing the humeral head into the glenoid cavity and allowing concentric rotation of the joint. This dynamic stabilization relies on balanced muscle force couples around the joint in the transverse and coronal planes. In the transverse plane, this balance is maintained by the subscapularis muscle anteriorly and the infraspinatus and teres minor muscles posteriorly. In the coronal plane, the force couple is the balance among the deltoid muscle, the rotator cuff, and the weight of the arm.
While it is theorized that a tear in the rotator cuff could disrupt the balanced muscle forces, how it alters glenohumeral kinematics remains to be defined. A variety of methods have been used in the literature to statically measure translation of the humeral head relative to the glenoid during shoulder elevation. Previous methods of measuring glenohumeral joint motion with a torn rotator cuff have relied on cadaveric simulations, 2-dimensional (2D) radiographs, and static 3-dimensional (3D) radiographs. It has been reported that proximal migration of the humeral head occurs during elevation, and this has become clinically accepted. However, each of these static measurement techniques is associated with limitations, and the results have not been validated by an in vivo dynamic 3D joint motion study.
This study used a dynamic 3D method of analyzing glenohumeral kinematics following rotator cuff teardbiplane fluoroscopy with computed tomography (CT). Biplane fluoroscopy is a recently emerging, highly accurate way to measure the in vivo 3D kinematics of the bony structures of a joint. It has had some use on the shoulder joint but limited work on the kinematic effects of rotator cuff tears. Bey studied patients postoperatively to determine how well surgical repair of the rotator cuff returned glenohumeral kinematics compared with asymptomatic controls.
The purpose of this study was to quantitatively mea- sure the 3D glenohumeral translations during dynamic shoulder abduction in the scapular plane, using a biplane fluoroscopy system, in patients with supraspinatus rotator cuff tears. It was hypothesized that during shoulder abduction in the scapular plane (scaption), subjects with rotator cuff tears would demonstrate dynamic superior migration of the humeral head relative to subjects with asymptomatic shoulders.