Accuracy and reliability of three methods of recording scapular motion using reflective skin markers

The accuracy and reliability of three methods of recording scapular motion using reflective skin markers, such as rAMC method, aAMC method, and the 3AM method was studied. Twelve healthy subjects participated in this study that were of 26.1 years, weight 71.5 kg, and height 1.75m. Ten were right-hand dominant. They were free from any clinical upper limb disorders or pain. Scapular rotations were recorded using an optoelectronic tracking system. Three protocols were used to analyze scapular motion: three markers placed directly on the scapula (called the 3AM method), a rigid, and an anatomical acromion marker cluster. Palpation recordings were carried out independently from the other methods so as not to promote one particular method. Overall, the most accurate method was the aAMC with a mean RMSE of 5.05°. The 3AM method produced a mean RMSE of 5.65° and five rotations out of six were significantly different from those obtained using the palpation approach. This study shows that the 3AM method provides a significant underestimation of the motion of almost all rotations.