Pathomechanisms of ulnar ligament lesions of the wrist in a cadaveric distal radius fracture model

BACKGROUND AND PURPOSE Mechanisms of injury to ulnar-sided ligaments (stabilizing the distal radioulnar joint and the ulna to the carpus) associated with dorsally displaced distal radius fractures are poorly described. We investigated the injury patterns in a human cadaver fracture model. METHODS Fresh frozen human cadaver arms were used. A dorsal open-wedge osteotomy was performed in the distal radius. In 8 specimens, pressure was applied to the palm with the wrist in dorsiflexion and ulnar-sided stabilizing structures subsequently severed. Dorsal angulation was measured on digitized radiographs. In 8 other specimens, the triangular fibrocartilage complex (TFCC) was forced into rupture by axially loading the forearm with the wrist in dorsiflexion. The ulnar side was dissected and injuries were recorded. RESULTS Intact ulnar soft tissues limited the dorsal angulation of the distal radius fragment to a median of 32(o) (16-34). A combination of bending and shearing of the distal radius fragment was needed to create TFCC injuries. Both palmar and dorsal injuries were observed simultaneously in 6 of 8 specimens. INTERPRETATION A TFCC injury can be expected when dorsal angulation of a distal radius fracture exceeds 32(o). The extensor carpi ulnaris subsheath may be a functionally integral part of the TFCC. Both dorsal and palmar structures can tear simultaneously. These findings may have implications for reconstruction of ulnar sided soft tissue injuries.