The measurement of three dimensional scapulohumeral kinematics - a study of reliability

Objective: To validate a system, using electromagnetic movement sensors, for the simultaneous measurement of scapular and humeral positions. Design: The study was designed to analyse the repeatability and to quantify the inherent measurement errors, using two observers to measure the movements of five normal subjects. Background. Following an earlier study of a system to measure three dimensional scapula motion, the method has been developed to incorporate simultaneous measurement of humeral and scapular position using a new design of scapula locator and a two-channel measurement system. Methods: The system was used to measure the scapula movements accompanying abduction of the shoulder. The scapula locator was applied at 10 degrees intervals of abduction. This was measured initially using a fluid filled goniometer, but, in a second part of the study, using an additional motion sensor. Results: In the single channel study, the 95% confidence intervals were less than 4 degrees and 10 mm. When simultaneous measurement of arm position was performed the confidence intervals were little changed. Conclusions: A new system for the measurement of scapulohumeral relationships has been shown to have good inter-and intraobserver reliability. This study opens the way for a full investigation of the scapula motion accompanying three dimensional shoulder motion in both normal subjects and in patients having shoulder pathology.