Time-course changes in active stiffness of the supraspinatus muscle after arthroscopic rotator cuff repair.

Abstract

This study aimed to investigate the time-course changes in the active stiffness of the supraspinatus muscle after arthroscopic rotator cuff repair. Eight male patients (mean age 61.5 ± 9.4years) who underwent arthroscopic rotator cuff repair for small to medium tears were recruited for this study. Movement tasks included 30° shoulder isometric abduction and maximal voluntary isometric contraction of shoulder abduction in the scapular plane. The stiffness of the supraspinatus (anterior superficial, anterior deep, posterior superficial, and posterior deep regions), upper trapezius, and middle deltoid muscles in bilateral shoulders was recorded using ultrasound shear wave elastography. For each subject, the measurement was performed preoperatively and 3, 6, and 12months postoperatively. The stiffness of the affected anterior superficial region of the supraspinatus muscle 12months postoperatively was significantly higher than that measured preoperatively and 3months postoperatively (p < 0.05); it was significantly higher at 6months postoperatively than at 3months postoperatively (p < 0.05). Further, the maximal voluntary isometric contraction had significantly improved 12months postoperatively compared to that measured preoperatively and 3months postoperatively (p < 0.05). The stiffness of the affected upper trapezius and middle deltoid muscles 12months postoperatively was significantly lower than that preoperatively (p < 0.05). The maximal voluntary isometric contraction 12months postoperatively possibly increased because of improvement in the active stiffness of the anterior superficial region. Active stiffness of the anterior superficial region may improve 6months rather than 3months postoperatively because of the different stages of muscle force, structural repair tendon strength, and remodeling.