Biomechanical Stability of Volar Plate Only Versus Addition of Dorsal Ulnar Pin Plate: A Dorsal Ulnar Fragment, C-3-Type, Distal Radius, Cadaver Fracture Model

Objective: To determine if the addition of a dorsal ulnar pin plate provides improved stability characteristics in the management of intra-articular distal radius fractures with an associated dorsal ulnar fragment. Methods: OTA/AO type C3 fractures, with a dorsal ulnar fragment of one-third or one-half the width of the distal radius, were simulated in 9 matched pairs of fresh-frozen cadaveric arms randomized between fixed-angle volar plate only versus volar plate with addition of a dorsal ulnar pin plate. Prepared specimens were mounted in a custom load frame and loaded in extension with stepwise cyclic load increase. Dorsal plane interfragmentary displacements were compared between the 2 fixation constructs at 50-N and 100-N cyclic load. Results: The addition of the dorsal ulnar pin plate significantly reduced interfragmentary displacements for the dorsal ulnar fragment at the 50 N load application, resulting in mean interfragmentary displacements of -0.1 +/- 0.2 mm in comparison to -0.3 +/- 0.2 mm with the volar plate-only construct. No other interfragmentary displacement comparisons were significant. No differences were found comparing the one-third and one-half size fragments. Conclusions: The addition of a dorsal ulnar pin plate improved stability characteristics with respect to the dorsal ulnar fragment.