Joint simulators can be used to study motion pathways of the human joint, to investigate changes in joint stability following injury, and to formulate improved reconstructive and rehabilitative procedures. The objectives of this work were to develop a laboratory-based elbow testing apparatus capable of simulating tendon (muscle) loading and displacement in a cadaveric specimen, and to quantify the resulting kinematics. Investigations of posterolateral rotatory instability (PLRI) of the elbow were conducted.

In order to describe the kinematics in clinically-relevant terms, an elbow coordinate system (ECS), which employed a Floating Axis analysis, was developed. Motion was quantified using an electromagnetic tracking system, whose (translational) accuracy was determined to be 0.1 ± 0.1 mm in tests performed using a custom-made articulator.

Using joint kinematics as an outcome measure, it was shown in a passive testing model that both the radial and lateral ulnar collateral ligaments were important stabilizers against PLRI of the elbow. In the same model, variations in coordinate system location and orientation were shown to affect the absolute magnitude of the motions measured, but not the relative changes in motion pathways that occur as a result of experimental to intervention.

To examine the effects of muscle loading on elbow motion pathways in both the stable and unstable elbow, simulated motion of the elbow and forearm was conducted using a load-controlled testing system. Loads were applied to relevant arm tendons using pneumatic actuators. It was determined that regardless of the tendon loading ratios employed, the elbow motion pathways were repeatable provided that the motion was generated solely by the tendon loads.

A motion-controlled elbow testing apparatus, capable of higher precision with regard to motion control, was subsequently developed. Velocity control of a pneumatic actuator was achieved using a custom-written PID controller. Bench-top testing indicated this system could achieve targeted motions with an RMS error of 0.43 mm. This actuator was incorporated into an elbow testing system that used a combination of motion and load control to achieve desired motions. A series of experiments demonstrated small magnitudes of error in actuator position, and highly repeatable flexion simulations 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 better than for similar tests performed using the load-controlled system, and the rate of elbow motion achieved was slower and more controlled.

This approach will allow numerous disorders of the upper limb to be more fully investigated in the laboratory prior to their clinical application.