The development of an in vitro glenohumeral testing rig

Until recently the accurate measurement of contact loads acting in the glenohumeral joint have been difficult to calculate and define. Now, contact forces and moments are measured in vivo using telemeterised shoulder implants. This method limits testing opportunities so a dynamic shoulder testing apparatus has been developed to examine glenohumeral joint motion and forces. This in vitro study evaluated the accuracy of forces generated in the glenohumeral joint using an instrumented prosthetic implant. Forces were applied to cables to simulate loading of the supraspinatus, subscapularis, infraspinatus/teres minor, long head biceps and anterior, middle, and posterior deltoid muscles. The test rig reproduces the 6DoF of the glenohumeral joint and accurately recreates the contact forces measured in vivo. This test rig will allow many more tests to be simulated including comparison of fixation methods and high impact injuries.