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-displa cement response patterns in normal shoulders during two commonly applied cl inical 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 cl inical laxity testing at the shoulder. No previous studies have measured th e 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 wa s recorded using electromagnetic tracking sensors during clinical stability testing in 21 subjects with normal shoulders. End-range stiffness was calc ulated and compared across all test conditions using repeated measures anal ysis of variance. Results. The maximum force applied by the examiner to reach clinical end-po int across all tests ranged from 101-113 N The stiffest position for poster ior 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 dr awer test. Only by internally rotating the arm did the force-dislpacement p attern change significantly (P< 0.05). For anterior drawer tests, the patte rns changed significantly (P < 0.05) only when the arm was in external rota tion. Conclusions. Results showed that end-range stiffness was predominantly depe ndent 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 tes ts was highest with the arm in internal rotation.