Patterns of stiffness during clinical examination of the glenohumeral joint

Objective. The purpose of our study was to develop a quantitative technique for performing clinical laxity tests, and to characterize the force-displacement response patterns in normal shoulders during two commonly applied clinical tests in different arm positions. Design. The study was an in vivo clinical experiment, Background. We developed a method to objectively quantify the effects of clinical laxity testing at the shoulder. No previous studies have measured the applied force during clinical testing along with the displacement so that glenohumeral joint stiffness could be determined in vivo. Methods. Manually applied forces were measured and shoulder displacement was recorded using electromagnetic tracking sensors during clinical stability testing in 21 subjects with normal shoulders. End-range stiffness was calculated and compared across all test conditions using repeated measures analysis of variance. Results. The maximum force applied by the examiner to reach clinical end-point across all tests ranged from 101-113 N The stiffest position for posterior drawer test was at 180 degrees C of abduction with the arm in internal rotation. This position was the most compliant position for the anterior drawer test. Only by internally rotating the arm did the force-dislpacement pattern change significantly (P< 0.05). For anterior drawer tests, the patterns changed significantly (P < 0.05) only when the arm was in external rotation. Conclusions. Results showed that end-range stiffness was predominantly dependent on humeral rotation angle and not effected by arm abduction angle for the three angles studied. Stiffness from anterior drawer tests was highest with the arm in external rotation, and stiffness from posterior drawer tests was highest with the arm in internal rotation.