Severity of scapholunate instability is related to joint anatomy and congruency.
OBJECTIVE
To determine whether the bony architecture of the distal radius and proximal scaphoid have a role in stabilizing the scaphoid, and to determine whether a relationship between the bony geometry measurements and the amount of wrist constraint could be determined.


METHODS
Eight cadaver wrists were tested in a wrist joint motion simulator. The level of scapholunate instability after sectioning the scapholunate interosseous, radioscaphocapitate, and the scaphotrapezium ligaments was determined and related to radiographic measurements of volar tilt, lateral tilt (ulnar tilt of the radioscaphoid fossa), the depth of the radioscaphoid fossa, and 6 radii of curvature measurements of the proximal scaphoid and distal radius. The force to dorsally dislocate the scaphoid out of the radioscaphoid fossa was computed.


RESULTS
The radioscaphoid fossa and scaphoid curvatures were larger in those wrists that did not show gross instability after ligamentous sectioning in the wrist simulator. Similarly, those wrists with a deeper radioscaphoid fossa and greater volar tilt were also more stable. The force required to dislocate these wrists was greater than in those wrists that showed gross carpal instability.


CONCLUSIONS
This study suggests that the bony anatomy of the radius and scaphoid have a role in stabilizing the carpus after ligament injury. The effect of ligament sectioning on producing carpal instability may be moderated by the bone geometry of the radiocarpal joint. This may explain why some people may have a tear of the scapholunate interosseous ligament but not present with clinical symptoms.
Werner
Frederick W
FW
Department of Orthopedic Surgery, SUNY Upstate Medical University, Syracuse, NY 13210, USA. wernerf@upstate.edu
Short
Walter H
WH
Green
Jason K
JK
Evans
Peter J
PJ
Walker
Jacquelyn A
JA
D001696:Biomechanical Phenomena; D002102:Cadaver; D006801:Humans; D007593:Joint Instability / Q000503:physiopathology*; D008023:Ligaments, Articular / Q000293:injuries / Q000503:physiopathology; D012667:Lunate Bone / Q000033:anatomy & histology / Q000503:physiopathology*; D016059:Range of Motion, Articular / Q000502:physiology; D021361:Scaphoid Bone / Q000033:anatomy & histology / Q000503:physiopathology*; D014955:Wrist Joint / Q000033:anatomy & histology / Q000503:physiopathology*