Kinematics, kinetics, and finite element analysis of commonplace maneuvers at risk for total hip dislocation.

Dislocation remains a disturbingly frequent complication of total hip arthroplasty (THA). Over the past several years, increasingly rigorous biomechanical approaches have been developed for studying dislocation, both experimentally and computationally. Realism of the input motion challenge data has lagged behind most other aspects of this body of work, and anterior dislocation maneuvers remain unstudied. To enhance realism of biomechanical studies of dislocation, motion data are here reported for ten THA-aged subjects, each repeatedly performing seven maneuvers known to be dislocation-prone. An optoelectronic motion tracking system and a recessed force plate captured the kinematics and ground reaction forces of these maneuvers. Using an established inverse dynamics model to estimate hip joint loading, 354 motion trials were evaluated using an existing finite element model of THA dislocation. Worst-case-scenario THA constructs were simulated (22 mm femoral head, acetabular cup orientations at the limit of the accepted safe zone), in order to deliberately induce impingement and dislocation. The results showed a high incidence of computationally predicted dislocation for all movements studied, but also that risk was very maneuver-dependent, with patients being six times more likely to dislocate from a low-sit-to-stand maneuver than from stooping. These new motion data hopefully will help facilitate systematic efforts to reduce the incidence of dislocation.