Simulation of Elbow and Forearm Motion In Vitro Using an Active Controlled Testing System

The purpose of this study was to compare variable ratios to constant ratios testing on the kinematics of the elbow and forearm using a load-controlled testing apparatus that simulates active muscle loading. Two fresh-frozen upper extremities were tested which were two sides of one donator. Four muscle loading ratios were achieved by employing pulley-weight system attached to the tendons of the brachialis, biceps, triceps and brachioradialis. Three of those were constant ratio loadings based on different combinations of the EMG data and the muscle pCSA, and the fourth was a variable ratio loading calculated using EMG assisted dynamic simulating analysis. Motion of the radius and ulna relative to the humerus was measured with an electromagnetic tracking system. Comparing with the three constant-EMG loadings, the internal-external motions (of the forearm relative to the humerus) of the variable ratio loading increased slowly after 75°of flexion in both sides. And the varus-valgus angulation was bigger different for the third constant-EMG ratio loading testing to the other three loadings. Therefore, elbow kinematics of the two sides were similar, but the four sets of loadings can not produce similar kinematics output.