Changes in shoulder muscle activities and glenohumeral motion after rotator cuff repair: an assessment using ultrasound real-time tissue elastography.

Background: Although rotator cuff repair is performed to restore the function of the rotator cuff muscles and glenohumeral (GH) joint motion, little has been known regarding the recovery process. The purpose of this study was (1) to investigate changes over time in activities of the supraspinatus and deltoid muscles assessed by ultrasound real-time tissue elastography (RTE) after rotator cuff repair and (2) to determine contributions of the activities of these muscles to the GH joint motion.

Methods: Twenty patients after rotator cuff repair and 13 control participants were enrolled in this study. Elasticity of the supraspinatus and middle deltoid muscles were measured at rest and 30° of humerothoracic elevation in the scapular plane (scaption) by using RTE. The elasticity at 30° of scaption was normalized to that at rest in each muscle to quantify their muscle activities. In addition, the supraspinatus-to-middle deltoid (SSP/MD) ratio for the normalized elasticity was calculated. The GH elevation angle was measured with a digital inclinometer, which was calculated by subtracting the scapular upward rotation angle from 30° of scaption. For patients after rotator cuff repair, all measurements were performed at 6 weeks, 8 weeks, 3 months, and 6 months after surgery. Rotator cuff integrity was examined with magnetic resonance imaging at 6 months after surgery.

Results: Fifteen of 20 patients who remained intact at 6 months after surgery completed this study. The supraspinatus activity at 6 weeks was significantly smaller than that at 3 months (P = .006) and 6 months (P = .010). There was no significant difference in the supraspinatus activity between the patients at 3 months and the control participants (P = .586). The middle deltoid activity at 6 weeks was significantly greater than that at 6 months (P = .003). There was positive correlation between GH elevation angle and the activity of the supraspinatus relative to the deltoid at 6 weeks (r = 0.75, P = .001) and 8 weeks (r = 0.53, P = .041).

Conclusion: The supraspinatus activity increased from 6 weeks to 3 months after surgery. The supraspinatus activity at 3 months after surgery was the same level as that in healthy individuals. On the other hand, the deltoid activity decreased from 6 weeks to 6 months after surgery. The increase in activity of the supraspinatus relative to the deltoid was likely to be related to the increase in GH elevation during postoperative at 8 weeks.