Abduction moment arms of rotator cuff tendons and deltoid muscles after acromioplasty and coracoacromial ligament section

Scientifically, it has been questioned if the coracoacromial ligament has a significant role of serving as a pulley for the supraspinatus tendon. The purpose of this study was to examine the changes of abduction moment arms of the rotator cuff and deltoid muscle after anterior acromioplasty. In normal condition and after sectioning of the coracoacromial ligament and acromioplasty, abduction moment arms of four cuff tendons and three portions of the deltoid were obtained with four cadaver shoulders by computing the slope of the tendon excursion versus the glenohumeral abduction angle curve using a magnetic tracking device. In intact joints, the abduction moment arms of the supraspinatus increased from 20 mm to 27 mm with the arm abducted from 0° to 30°, which showed a better condition of the glenohumeral abduction. Then, they decreased to 23 mm with arm in 60° abduction. After sectioning of the coracoacromial ligament and acromioplasty less than 4 mm thick, the abduction moment arms of supraspinatus did not increase. This finding suggested that the coracoacromial ligament and acromion, anatomically, did not serve as pulleys for the supraspinatus tendon. However, the abduction moment arm of the middle deltoid decreased after an acromioplasty.