Kevin McQuade, PT, MPH, PhD
Department of Rehabilitation Medicine
"Clinical Quantification of Shoulder Joint Laxity: The Influence
of Active Muscle Contraction"
ABSTRACT
Objective: Measure stiffness of the glenohumeral joint during clinical
laxity testing with and without muscular contraction of the Internal rotators.
Design: Cross-sectional study of normal shoulders.
Background: Clinical examination for shoulder instability is based
on subjective impression, and is only performed passively. Our study presents
a method for quantitative clinical examination of the shoulder under both
passive and active muscle contraction conditions. We hypothesized that in
a normal shoulder, contraction of the internal rotators will increase the
stiffness of the glenohumeral joint, effectively constraining the head of
the humerus against anterior directed forces.
Methods: 10 subjects were instrumented with electromagnetic sensors
to record glenohumeral linear displacements. A mini-force transducer recorded
forces applied to subjects during anterior drawer testing (forced anterior
glenohumeral displacement), which was performed passively, and during isometric
contraction of internal rotators.
Results: Only mild contraction of the internal rotators is needed
to significantly increase the stiffness to anterior directed forces. Greater
muscular activation does not result in further increased stiffness.
Conclusion: Objective measurement of glenohumeral stiffness during
passive and active muscular contraction may be useful for evaluating the
capacity of rotator cuff muscles to stabilize the shoulder. The concept of
more strength is better, for rotator cuff strengthen programs is questioned.
Relevance: The method presented in this study may have useful applications
as a diagnostic tool for discriminating dysfunctional rotator cuff activation,
as an outcome measure for surgery and rehabilitation, and as a didactic
tool for teaching shoulder examination by providing immediate objective
feedback to the examiner.