Anterior glenohumeral force/translation behavior with and without rotator cuff contraction during clinical stability testing

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. Ten 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.