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Biomechanical Assessment of the Dorsal Spanning Bridge Plate in Distal Radius Fracture Fixation: Implications for Immediate Weight-Bearing
Jerry I Huang, MD1; Bret Peterson, MD1; Kate D Bellevue, MD1; Nicolas Lee, MD2; Sean Smith, MSc2; Safa Herfat, PhD2
1University of Washington Medical Center, Seattle, WA; 2University of California San Francisco Medical Center, San Francisco, CA

Treatment of high-energy comminuted distal radius fractures remains a difficult challenge, especially in the setting of polytrauma patients with multiple injuries who require use of the upper extremity for mobilization. We sought to compare the biomechanical stability of the 2.4 mm spanning dorsal bridge plate to a standard volar distal radius locking plate in a distal radius fracture model, during simulated crutch weight-bearing.

Five paired cadaveric specimens were each mounted to a crutch handle for the hand and potted proximally in the forearm (Fig. 1). A standard 1 cm dorsal wedge osteotomy was created in the metaphysis to simulate an unstable distal radius fracture with dorsal comminution. The fracture was fixated with either a volar distal radius locking plate (VLP) or a dorsal spanning bridge plate (DBP) with fixation in the index metacarpal distally and the radius proximally. Optical motion tracking sensors were attached to the proximal and distal segments. All specimens were mounted to a servohydraulic test frame and loaded in compression at 1 mm/s until failure. Failure was defined as 2 mm of gap site displacement.

The volar locking plate construct was significantly more stable to axial load in a crutch weight-bearing model than a 2.4 mm dorsal spanning bridge plate. The failure load to displace the fracture by 2 mm was 493 123 N for the VLP constructs compared to 332 138 N for the DBP constructs (p < 0.01). Stiffness did not significantly differ (p=0.07) between the constructs (DBP: 32.4 17.2 N/mm vs. VLP: 51.4 26.0 N/mm). Consistent failure mechanisms were observed in the two groups. In the dorsal bridge plates, the wrist flexed with progressive axial loading, causing the plate to bend (Figure 2). For the volar plate specimens, failure occurred with axial compression of the fracture site and dorsal collapse.

Conclusion and Discussion
The dorsal spanning bridge plate was less stable to axial load than standard volar distal radius locking plates in our crutch weight-bearing model for distal radius fractures. Based on our results, the 2.4 mm dorsal bridge plate remains a good option for highly comminuted intra-articular distal radius fractures but may not offer advantages in early weight-bearing or transfer in polytrauma patients. A stiffer, thicker 3.5 mm dorsal spanning plate may be considered if the goal is early crutch weight-bearing through the injured extremity.

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