NORMAL KINEMATICS OF THE INTEROSSEOUS MEMBRANE DURING FOREARM PRONATION-SUPINATION — A THREE-DIMENSIONAL MRI STUDY

Abstract

We studied in vivo dynamic shape changes of the interasseous membrane (IOM) during forearm rotation using three-dimensional magnetic resonance imaging (3D-MRI), and simultaneously analysed 3D-motion of the forearm rotation. Wavy deformities were seen in the IOM in the pronated position, and similar small changes were also seen at maximum supination (average 82°) and in the neutral position. These dynamic changes mainly occurred in the membranous part of the IOM, whereas the tendinous part demonstrated minimal dynamic changes during rotation in all subjects. On the dorsal aspect, deformity around the dorsal oblique cord was seen at maximum pronation. From this 3D-MRI observation, the tendinous part is considered to be taut during rotation to provide stability between the radius and ulna, because of its straightness and less dynamic changes. The more deformable membranous part is important to allow for smooth rotation, since it lies at a distance from the rotation axis. Inelasticity developing in the membranous part from trauma may pre-dispose to pronation-supination contracture. The radius rotated around the ulna from maximum supination to 45° pronation. At maximum pronation (average 75°), the radius translated average 1.8 mm palmarly and rotated average 4.0° ulnarward on the ulna. Incongruity of the distal radioulnar joint, contraction of the pronator quadratus and torsion between the radius and ulna at maximum pronation may produce this irregular motion of the radius and cause the dynamic changes of the IOM.