Orthop Res 2002 May;20(3):439-46
The effect of rotator cuff tears on reaction forces at the glenohumeral joint.
Parsons IM, Apreleva M, Fu FH, Woo SL.
of Orthopaedic Surgery, Musculoskeletal Research Center, University of
Pittsburgh, PA 15213, USA.
The rotator cuff muscles maintain
glenohumeral stability by compressing the humeral head into the glenoid.
Disruption of the rotator cuff compromises concavity compression and can
directly affect the loads on the glenohumeral joint. The purpose of this study
was to quantify the effect of rotator cuff tears on the magnitude and
direction of glenohumeral joint reaction forces during active shoulder
abduction in the scapular plane using nine cadaveric upper extremities. Motion
of the full upper extremity was simulated using a dynamic shoulder testing
apparatus. Glenohumeral joint reaction forces were measured by a universal
force-moment sensor. Five conditions of rotator cuff tears were tested:
Intact, Incomplete Supraspinatus Tear, Complete Supraspinatus Tear,
Supraspinatus/Infraspinatus Tear, and Global Tear. Reaction forces at the
glenohumeral joint were found to steadily increase throughout abduction and
peaked at maximum abduction for all conditions tested. There were no
significant differences in reaction force magnitude for the intact condition
(337 +/- 88 N) or those involving an isolated incomplete tear (296 +/- 83 N)
or complete tear (300 +/- 85 N) of the supraspinatus tendon. Extension of
tears beyond the supraspinatus tendon into the anterior and posterior aspect
of the rotator cuff led to a significant decrease in the magnitude of joint
reaction force (126 +/- 31 N). Similarly, such tears resulted in a significant
change in the direction of the reaction force at the glenohumeral joint. These
results suggest that joint reaction forces are significantly affected by the
integrity of the rotator cuff, specifically, by the transverse force couple
formed by the anterior and posterior aspects of the cuff. The quantitative
data obtained in this study on the effect of rotator cuff tears on magnitude
and direction of the reaction force at the glenohumeral joint helps clarify
the relationship between joint motion, joint compression and stability.