title: In vivo changes in contact regions of the radiocarpal joint during wrist hyperextension.
abstract: OBJECTIVE
  Distal radius and scaphoid fractures commonly occur after a fall with the hand outstretched and wrist hyperextended. We investigated contact characteristics of the radiocarpal joint in neutral position, hyperextension, and hyperextension combined with radial deviation in vivo.
  
  
  METHODS
  Eight volunteers without a known history of wrist injury were enrolled. We obtained computed tomography scans with 3-dimensional reconstructions of the subjects' right wrists in neutral, hyperextension, and hyperextension with 10° of radial deviation. The contact regions of the radiocarpal joint were mapped. The direction and distance of changes in the contact region centers were recorded and analyzed.
  
  
  RESULTS
  From neutral position to hyperextension, the contact of the scaphoid substantially shifted from the middle to the dorsal part of the articular surface of the radius in 5 of the 8 wrists. With these wrists further deviated radially, the contact shifted to the surface over the radial styloid. In the other wrists, the contact of the scaphoid remained in the center of the radial articular surface. In all wrists, the contact of the radius on the scaphoid shifted from the proximal lateral surface of the scaphoid to the proximal dorsal surface of the scaphoid, and the contact of the radius on the lunate shifted dorsally.
  
  
  CONCLUSIONS
  During wrist hyperextension, the contact of the scaphoid on the distal radius exhibited 2 possible types of changes: either shifting from the mid-portion to the dorsal ridge of the articular surface of the radius or remaining at the center of the articular surface. Combined wrist hyperextension with radial deviation caused the scaphoid to contact the radius over the radial styloid. The contact of the radius on the scaphoid shifted from proximal lateral to proximal dorsal scaphoid, and that on the lunate shifted dorsally.
  
  
  CONCLUSIONS
  This study provided in vivo mechanical findings to improve our understanding of the mechanism of hyperextension injuries of carpus.
authors.affiliation: Department of Hand Surgery, Hand Surgery Research Center, Affiliated Hospital of Nantong Univeristy, Nantong, Jiangsu, China. jinbotang@yahoo.com
authors.forename: Jin Bo
authors.initials: JB
authors.lastname: Tang
authors.forename: Yan Rong
authors.initials: YR
authors.lastname: Chen
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena; D002348:Carpal Bones / Q000000981:diagnostic imaging / Q000503:physiopathology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D016059:Range of Motion, Articular; D014057:Tomography, X-Ray Computed; D014954:Wrist Injuries / Q000000981:diagnostic imaging / Q000503:physiopathology*; D014955:Wrist Joint / Q000503:physiopathology*; D055815:Young Adult