Development of a motion-controlled in vitro elbow testing system.

Joint simulators can be used to study motion pathways of a human joint, to investigate changes in joint stability following injury, and to formulate improved reconstructive and rehabilitative procedures. Our objectives were: to develop a laboratory-based, motion-controlled elbow testing apparatus capable of simulating tendon (muscle) loading and displacement in a cadaveric specimen; to describe its performance while testing stable and unstable elbows; and to compare its operation to that of a previously designed load-controlled device. Velocity control of a pneumatic actuator was achieved using a custom-written, closed-loop feedback controller. This actuator was incorporated into an elbow testing system that used additional pneumatic actuators and a combination of motion- and load-control to achieve desired motions. Simulations achieved with this apparatus demonstrated small magnitudes of error in actuator position and highly repeatable flexion pathways with the specimens positioned in vertical, varus, and valgus orientations. The repeatability in motion pathways generated in both a stable and unstable elbow model was equivalent to or better than for similar tests performed using the load-controlled system, and the velocity of the resulting elbow motion was more reproducible.