Pathomechanics of Frozen shoulder: A basic research perspective

Abstract

Normal kinematics of glenohumeral joint is dependent on the coordinated function of dynamic and static stabilizers. Among the static stabilizers or a part of the dynamic stabilizer, the glenohumeral capsule would contribute little to the stability of the joint. Nevertheless, the maintenance of the normal glenohumeral relationship still depends on the reinforcement of the capsule by ligaments and the attachment of the muscle tendons of the rotator cuff mechanism. Therefore, the capsular stiffness and resulting premature capsular tightening at early phase of humeral motion can induce the kinematic alteration that occurred at the scapulohumeral and scapulothoracic joint (Rundquist et al., Arch Phys Med Rehabil 84:1473–1479, 2003; Vermeulen et al Ann Rheum Dis 61:115–120, 2002). However, little is known regarding an altering capsular mechanics present in idiopathic frozen shoulder. A recent study using electromagnetic tracking sensors indicated that capsular stiffness caused substantial kinematic deficits during humeral range of motion and alteration of scapulohumeral rhythm (Lin et al., J Orthop Res 24(5):1044–1051, 2006; Rundquist et al. Arch Phys Med Rehabil 84:1473–1479, 2003; Vermeulen et al., Ann Rheum Dis 61:115–120, 2002). Further studies elucidating the pattern of load transmission in pathologic capsule, as well as data on altering scapular and humeral positions during physiologic arm motion are required to more fully characterize the pathomechanics of idiopathic frozen shoulder.