Three-dimensional rotation of the elbow

With the present emphasis on prosthetic joint replacement in orthopedic surgery, the need for basic biomechanical information for different body joints is in great demand. The lack of such information for the elbow has motivated the present study. An attempt is therefore made to measure the rotatory component of cadaver elbows under passive motion. The results obtained will be used to justify certain noninvasive means to measure three-dimensional angular motion for living subjects. Using biplanar radiographs, cadaver forearms were studied under the passive motions of flexion-extension and supination-pronation. The coordinate axes for the forearm, radius and ulna were defined based on imbedded Kirschner wires. The three-dimensional rotation of the forearm with respect to the humerus, as well as the relative motion among the radius, ulna and humerus, were analyzed based on Eulerian angles. The relationship between the primary modes of motion and the inherent secondary motion was defined and analyzed. No translational motion within the joint was considered because of the tight constraint of the ligamentous structure. However, this hypothesis was examined by monitoring the variation of the displacement of the moving coordinate center. The implications of these findings to the surgical treatment of elbow problems were speculated on.