Total shoulder arthroplasty is an effective treatment for glenohumeral osteoarthritis. However, it still suffers from a substantial rate of mechanical failure, which may be related to cyclic off-center loading of the humeral head on the glenoid. In this work, we present the design and evaluation of a glenohumeral joint robotic simulator developed to study glenohumeral translations. This five-degree-of-freedom robot was designed to replicate the rotations (±40deg, accuracy 0.5deg) and 3D forces (up to 2kN, with a 1% error settling time of 0.6sec) that the humeral implant exerts on the glenoid implant. We tested the performances of the simulator using force patterns measured in real patients. Moreover, we evaluated the effect of different orientations of the glenoid implant on joint stability. When simulating realistic dynamic forces and implant orientations, the simulator was able to reproduce stable behavior by measuring the translations less than 24 mm of the humeral head with respect to the glenoid implant. Simulation with quasi-static forces showed dislocation in extreme ranges of implant orientation. The robotic glenohumeral simulator presented here was able to reproduce physiological glenohumeral forces, and may therefore be used to further evaluate the effects of glenoid implant design and orientation on joint stability.

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