In-vivo kinematic analysis of forearm rotation using helical axis analysis

Background: Controversy still exists regarding the location and nature (static or dynamic) of the forearm joint axis. This might be due to inconsistent results from in-vitro data and less precise methods of analysis. We present the first in-vivo kinematic analysis of normal forearm joint rotation described by helical axis analysis. Methods: Data obtained from computed tomography images of both forearms of five healthy volunteers was used to calculate finite helical axis parameters from transformation matrices. Four positions were analyzed: maximum pronation, maximum supination, 60° pronation, and 60° supination. Kinematic analysis focused on the motion of the radius around the ulna. Findings: The forearm axis as defined by finite helical axis extended from the radial head between its kinematic center and the proximal radioulnar joint, to the dorsal region of the ulnar head at the distal radioulnar joint. The axis was found to be variable. Interpretations: Helical axis analysis has precisely defined the nature and location of the forearm axis. This new information of forearm kinematics defined by finite helical analysis, may be useful in implant design, and in guiding surgeons in their reconstruction of instabilities of the distal and proximal radioulnar joint.