The static rotator cuff does not affect inferior translation of the humerus at the glenohumeral joint.
BACKGROUND
The static contribution of the rotator cuff to the inferior stability of the shoulder is poorly understood. The purpose of this study was to determine the effect of static rotator cuff muscles on the inferior stability of the glenohumeral joint.


METHODS
The humeral head positions relative to the glenoid were obtained in 12 shoulder specimens under the following conditions: with and without a 1.5-kg load; with the humerus adducted and abducted 90 degrees; and in three stages of dissection: (1) before release of any of the rotator cuff muscles, (2) after release of the supraspinatus or the cuff muscles other than the supraspinatus, and (3) after release of all of the cuff muscles. The order of release was changed in two ways: release of the supraspinatus followed by the release of other muscles in one group, and the opposite order in the other group.


RESULTS
In both adduction and abduction, there were no significant differences in the positions of the humeral head either among the three stages of release or between the two different orders of release.


CONCLUSIONS
The static contribution of the cuff muscles to the inferior stability of the shoulder is insignificant.
Itoi
E
E
Department of Orthopedic Surgery, Akita University School of Medicine, Japan.
Motzkin
N E
NE
Morrey
B F
BF
An
K N
KN
D001696:Biomechanical Phenomena; D006801:Humans; D006811:Humerus / Q000502:physiology; D066298:In Vitro Techniques; D007593:Joint Instability / Q000503:physiopathology; D009068:Movement; D017006:Rotator Cuff / Q000502:physiology*; D012785:Shoulder Joint / Q000502:physiology*