Orientation of axes in the elbow and forearm for biomechanical modeling

To extend an already existing three-dimensional (3-D) model of the shoulder (Van der Helm, 1994) a cadaver study was performed in which quantitative information on the 3-D orientations of rotation axes in the upper extremity was collected. To calculate axes, we measured the glenohumeral, humeroulnar and ulnoradial movements on five human cadaver arms (four right arms, one left). Movement was measured with an electromagnetic tracking system which sensors were directly attached to scapula, humerus, ulna and radius. In addition, a series of anatomical landmarks was measured. From the tracking data, the Instantaneous Helical Axes (IHA) were calculated, as well as the resulting optimal mean Gleno-Humeral (GH) center of rotation, Flexion-Extension (FE) axis and Pronation-Supination (PS) axis. To allow for the construction of a musculoskeletal model, anatomical landmarks, were transformed from the global measurement co-ordinate system to separate local co-ordinate systems, related to the rotation center and axes of rotation. The FE- and PS-axis could be determined accurately and were found to be almost perpendicular (88.9 ± 5.1°) and crossed at 3.3 ± 0.8 mm. It is suggested that forearm movements can be modelled with a two Degree-of-Freedom model.