Development of a Method for Analyzing Three-Dimensional Scapula Kinematics

Abstract

Background Scapula mobility complicates upper extremity kinematics assessment. Existing methods are diverse, providing inconsistent results. The current gold standard (bone pins) is prohibitively invasive. The purposes of the current study are to describe a virtual projection alternative to surface markers for video motion capture (VMC) of the scapula and to compare the results of the projection and surface marker methods to the results of similar existing methods. Methods Ten participants were evaluated using VMC. Surface markers were applied to the trunk and arm in accordance with existing guidelines. Three markers were affixed to plastic base on the skin over the acromion process. Other scapular landmarks were digitized in a neutral position. These landmarks' locations were defined in reference to the acromion cluster and used to generate the projection. Humerothoracic, glenohumeral, and scapulothoracic kinematics were evaluated during shoulder abduction, flexion, and scaption. Joint angles produced by the surface markers and the projection were compared by Bonferroni-adjusted t tests. The results were compared to prior findings in the literature. Results The projection resulted in greater scapulothoracic upward rotation, internal rotation, and anterior-posterior tilt and less glenohumeral elevation ( p<.0055) than did surface markers. The virtual scapula produced greater estimates of scapular mobility than did surface markers, corresponding to pre-existing results from similar methodologies. Conclusions The result is a noninvasive measurement tool that produces different and superior results than do scapula surface markers. Measuring scapula kinematics via VMC without bone pins will facilitate future investigations into interactions between upper extremity injury, kinematics, and activity performance.