A Biomechanical Analysis of Fixation of Intra-Articular Distal Radial Fractures with Calcium-Phosphate Bone Cement

Abstract

Background: Calcium phosphate cement has been used to treat unstable fractures of the distal end of the radius with the intent of avoiding the stiffness and morbidity associated with prolonged immobilization in a cast or external fixation. The purpose of this study was to compare the stability of the fracture fragments after fixation with augmented calcium phosphate cement with that after alternative methods of percutaneous fracture treatment.Methods: Both an osteotomy and osteoclasis were used to create a model of an intra-articular fracture of the distal part of the radius (AO type C2) with dorsal bone loss in seven pairs of fresh-frozen upper extremities. One wrist from each pair was fixed with an external fixator and three Kirschner wires, and the contralateral wrist was fixed with calcium phosphate cement (Norian SRS) and three Kirschner wires (augmented calcium phosphate cement). Sequentially increasing loads, up to a total of 100 N, were then applied to the major flexors and extensors of the wrist. Fracture fragment motion was measured by the Optotrak three-dimensional system.Results: Fixation with cement alone failed at the bone-cement interface at <80 N in all specimens. With use of an analysis of variance, augmented external fixation was found to provide significantly increased stability to the radial fragment compared with that provided by augmented calcium phosphate cement in four of the six axes tested (e.g., mean motion [and standard deviation] in flexion-extension was 3.0° ± 2.93° versus 11.1° ± 13.08°, respectively; p = 0.001). Augmented calcium phosphate cement was found to provide greater stability for the radial fragment than were Kirschner wires alone in three axes (e.g., mean motion in flexion-extension was 11.1° ± 13.08° versus 36.5° ± 13.03°, respectively; p = 0.001).Conclusions: Calcium phosphate cement alone is insufficient to withstand physiologic flexion-extension motion of the wrist without supplemental wire fixation. When supplemented with Kirschner wires, fixation with bone cement is more stable than are Kirschner wires alone, but it is significantly less stable than augmented external fixation.Clinical Relevance: When performing studies of fracture fixation strengths, it is essential to simulate the shear and rotational forces encountered during normal wrist motion. On the basis of the physiologic biomechanical testing in this study, we recommend supplemental fixation if calcium phosphate cement is chosen for fixation of unstable distal radial fractures.