Evaluation of a novel, nonspanning external fixator for treatment of unstable extra-articular fractures of the distal radius: Biomechanical comparison with a volar locking plate

Purpose: To compare the stability of a novel, nonspanning external fixator with a standard volar locked plate for treatment of unstable distal radius fractures. Methods: A simulated, unstable, extra-articular distal radius fracture was created in six matched pairs of fresh frozen human distal radii. One of each pair was treated with a nonspanning external fixator (Mirza Cross Pin Fixator (CPX), A.M. Surgical Inc. Smithtown, NY] and the other was treated with a volar locked plate [Distal Volar Radial Plate (DVR), Hand Innovations, Miami, FL]. Each specimen was axially loaded in central, dorsal, and volar locations, loaded in cantilever bending in volar to dorsal, dorsal to volar, and radial to ulnar directions and loaded in torsion. Load-displacement curves were generated to determine the construct stiffness for each loading schema, with comparisons made between the two treatment groups. Specimens were then cyclically loaded with 50 N axial loads applied for 1,000 and 10,000 cycles. Measurement of construct stiffness was repeated and comparisons made both between the two treatments and within treatments to their precycling stiffness. Results: There was no significant difference in the mechanical stiffness of the nonspanning external fixator and the volar locking plate after axial loading in any of the loading modalities. Cyclic loads of 1,000 and 10,000 cycles resulted in no significant difference in construct stiffness between the nonspanning external fixator and volar locked plate. However, the nonspanning external fixator demonstrated decreasing stiffness after cyclic loading with 10,000 cycles (p < 0.02). Conclusion: This study demonstrated no significant difference in the mechanical stiffness of the CPX nonspanning external fixator and volar locked plate in a cadaveric fracture model. Both constructs appear to be biomechanically equivalent in this experimental model; however, this is only one factor in the choice of fixation device for the management of unstable distal radius fractures.