In Vivo The Biomechanics Changes In Malunited Distal Radius Fractures

Background: Patients with a malunited distal radius often have painful and limitedulnar deviation and flexion and extension. The purpose of this study was to determine ifthe kinematics of carpal bones, radiocarpal contact areas, and the length of carpalligaments were altered in patients with malunited distal radius fractures.Methods: We obtained computed tomography scans of the wrists of8volunteers withone side malunited distal radius fractures at5positions for both wrists: the neutral positionof the carpus;20°of ulnar deviation;20°of flexion;20°of extension; and40°of extension.The malunited distal radius fractures have dorsal angulation between10°and20°(average14.9±4.1°) and the ulnar variation≤3mm. The3-dimensional carpal and distal radioulnarjoint structures were acquired with customized software. We analyzed changes in thekinematics of scaphoid, lunate, triquetrum, and capitate, the center of contact areas of theradiocarpal joints, and the lengths of8palmar and dorsal wrist ligaments for both thenormal and dieased wrists.Results: The results contained3parts: First, the kinematics of the carpal bones. In ourstudy, the capitate, scaphoid, lunate, and triquetrum were significantly more flexed in thewrist with malunited distal radius (p<0.05or p<0.01) compared with the contralateraluninjured side, but we found no significant changes in pronation or supination at all of the5positions. Scaphoid was significantly more radial deviated when the wrist was placed atulnar deviation20°or at extension20°; Triquetrum was significantly more ulnarly deviatedat neutral,20°of flexion, and20°of extension of the wrist. Second, at the neutral position,the center of the radioscaphoid articular contact site was significantly translated to thedorsal of the scaphoid fossa compared with the uninjured wrist. When the wrist flexed20°,the center of the radioscaphoid articular contact site was significantly shifted to the dorsaland ulnar of scaphoid fossa; The center of the radiolunate articular contact map wassignificantly shifted to the ulnar of lunate fossa; Third, the dorsal radiocarpal (DRC)ligament was significantly lengthened at neutral,20°of ulnar deviation, and20°of flexion.The long radiolunate ligament (LRL) was significantly shortened at neutral position. The UT ligment was significantly lengthened at20°of ulnar deviation, and20°of extension.Conclusions: With mild degree of dorsal angulated malunion of the distal radiusfracture (average dorsal tilt:14.9°±4.1°), significant and drastic changes in radioscaphoidand radiolunate contact characteristics,3-D positions of carpal bones, and in vivo length ofprincipal wrist ligaments occur. The changes are seen at multiple wrist positions, especiallyat neutral, ulnar deviation, and extension.