Validation and repeatability of a shoulder biomechanics data collection methodology and instrumentation.

The purpose of our study was to establish criterion-related validity and repeatability of a shoulder biomechanics testing protocol involving an electromagnetic tracking system (Flock of Birds [FoB]). Eleven subjects completed humeral elevation tasks in the sagittal, scapular, and frontal planes on two occasions. Shoulder kinematics were assessed with a digital inclinometer and the FoB. Intrasession and intersession repeatability for orthopedic angles, and humeral and scapular kinematics ranged from moderate to excellent. Correlation analyses revealed strong relationships between inclinometer and FoB measures of humeral motion, yet considerable mean differences were noted between the measurement devices. Our results validate use of the FoB for measuring humeral kinematics and establish our testing protocol as reliable. We must continue to consider factors that can impact system accuracy and the effects they may have on kinematic descriptions and how data are reported.