Bilateral symmetry assessment of healthy forearm kinematics using 4D-CT

Advanced stage distal radio-ulnar joint (DRUJ) injury may warrant radius corrective osteotomy or arthroplasty. These procedures aim to restore geometry, function and kinematics and could benefit from preoperative planning where the contralateral forearm is typically used as reference. Natural variations regarding geometry and function between forearms are known but kinematic differences are not. This work aimed to quantify bilateral differences in forearm kinematics. Consequently, 4D-CT data of ten healthy volunteers was acquired, imaging motion of both forearm joints. Segmentation and registration of the radius and ulna bones resulted in a 3D representation of forearm rotation. Subsequently, the forearm rotation axis, radius translation along the ulna and radius rotation around its own inertial axis were calculated. The rotation axis of the right arm was mirrored to set up a comparison with the left arm. All other differences were calculated directly. The mean angle and distance between forearm rotation axes were 0.6° and 0.8 mm. The mean difference in radius translation along the ulna was 0.9 mm. On average, radius rotation around the radius' inertial axis differed 2.6°, between forearms. This study's findings can benefit DRUJ surgery preoperative planning and postoperative kinematic evaluation. Level of evidence: IV.