Altered Scapular Time Series in Individuals With Subacromial Pain Syndrome.

Altered scapular movement in subacromial pain syndrome has been demonstrated using discrete data reduction approach. However, this approach does not consider the data collinearity and variability, and scapular translations are poorly investigated in symptomatic individuals. The purpose of this study was to investigate the scapular rotation and translation of asymptomatic individuals and those with subacromial pain syndrome during arm motions using principal component analysis. Scapulothoracic kinematics were evaluated in 47 participants with subacromial pain syndrome and 50 asymptomatic individuals. The symptomatic group had increased range of scapular anterior/posterior tilt during arm elevation (P = .01, effect size = .59) and arm lowering (P < .01, effect size = .61), and increased range of scapular forward/backward translation during arm lowering (P < .01, effect size = .60) compared with the asymptomatic group. In addition, the symptomatic group had a reduced difference in anterior tilt angular velocities between the early-arm and mid-arm lowering phases and between the mid- and late-arm lowering phases compared with the asymptomatic group (P = .03, effect size = .44). This study demonstrated that scapular anterior/posterior tilt motion and angular velocity and scapular forward/backward translation of symptomatic individuals were different from asymptomatic individuals when considering the entire arm movement.