Abstract
OBJECTIVE: Rotator cuff tears can influence shoulder kinematics and severely impair function. However, there have been no studies on three-dimensional (3D) shoulder kinematics in massive rotator cuff tear (MRCT) patients. Hypothesizing that MRCT patients could demonstrate significantly changed scapular kinematics during arm elevation in the scapular plane, we compared 3D scapular kinematics in the scapular plane between MRCT patients and healthy elderly subjects. METHODS: We assessed 15 shoulders of 11 MRCT patients and 16 shoulders of 16 healthy subjects. With the subjects seated, we used an electromagnetic tracking system to calculate the upward rotation, posterior tilt, and internal rotation of the scapula at 10° increments from 30° to 120° with respect to the thorax. We performed two-way analysis of covariance with the initial position of the scapular motion as the covariate and performed multiple comparisons using the Bonferroni method. RESULTS: MRCT patients exhibited significantly higher scapular upward rotation than did the healthy subjects (P < 0.05). There were no significant differences between groups with regard to posterior tilt and internal rotation. CONCLUSIONS: This study indicated that when MRCT patients elevated their arms, they exhibited a significantly higher scapular upward rotation at low- to mid-range elevations compared with that of healthy subjects. This difference may have resulted from a compensatory effect in response to the decreased elevation torque caused by the loss of rotator cuff function. These results may assist rehabilitation strategies to improve active arm elevation in MRCT patients.