In vitro kinematics of the shoulder following rotator cuff injury.
BACKGROUND
Tears in the rotator cuff may result in altered mechanics of the glenohumeral joint. It is not unusual for some patients with cuff tears to exhibit near normal motion with the injured shoulder, while other patients with the same magnitude of injury are unable to achieve full elevation on the injured side.


METHODS
The effect of simulated tears of the rotator cuff on active glenohumeral joint kinematics was investigated by testing eight cadaveric specimens using an in vitro shoulder simulator. Active abduction of the humerus was produced by applying forces to simulate loading of the supraspinatus, subscapularis, infraspinatus/teres minor, and the anterior, middle, and posterior thirds of the deltoid. Three sequential 1cm lesions were created in the rotator cuff, the first two in the supraspinatus tendon and the third in the subscapularis tendon.


RESULTS
The plane of abduction moved posteriorly and became more abnormal throughout abduction with increased tear size. No difference was observed in the internal/external rotation of the humerus or the position of the humeral head on the glenoid during elevation.


CONCLUSIONS
In order to generate the motions achieved by the intact joint, patients with rotator cuff insufficiency likely employ other muscle groups. Retraining muscle groups surrounding the glenohumeral joint may decrease the need for surgical interventions.
Kedgley
Angela E
AE
Bioengineering Research Laboratory, Hand and Upper Limb Centre, St. Joseph's Health Care London, 268 Grosvenor Street, London Ontario, Canada N6A 4L6.
Mackenzie
Geoffrey A
GA
Ferreira
Louis M
LM
Johnson
James A
JA
Faber
Kenneth J
KJ
D000368:Aged; D001696:Biomechanical Phenomena; D002102:Cadaver; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009038:Motion; D009068:Movement; D016059:Range of Motion, Articular; D000070636:Rotator Cuff Injuries; D012782:Shoulder / Q000033:anatomy & histology / Q000502:physiology*; D013708:Tendon Injuries / Q000473:pathology; D013710:Tendons / Q000473:pathology; D016474:Weight-Bearing