Session IX - Upper Extremity

*A Biomechanical Analysis of Norian Calcium-Phosphate Bone Cement in an Intraarticular Distal Radius Fracture Model

Thomas F. Higgins, MD; Seth D. Dodds, MD; Scott W. Wolfe, MD; Yale University, New Haven, CT; University of Utah, Salt Lake City, UT (all authors ­ a-Unrestricted Research Grant Norian Corporation)

Purpose: Resorbable calcium-phosphate bone cement (CPBC) has recently been approved for the fixation of a distal radius fracture (DRF) with dorsal metaphyseal comminution and bone loss. Cadaveric wrist fractures fixed with cement have demonstrated excellent mechanical strength in compression, but the rotational and torsional forces encountered by the distal radius have not been examined. It has been reported that CPBC may be used to stabilize an unstable DRF and to avoid the stiffness and morbidity encountered with use of a cast or external fixation. We compared the stability of intraarticular fracture fragments with augmented CPBC fixation, with augmented external fixation, and with K-wire fixation alone, when exposed to physiologic loads and range of motion. We hypothesized that CPBC would provide comparable stability to augmented external fixation, yet allow full motion of the wrist under physiologic loading conditions.

Methods: A three-part, intra-articular DRF (OTA type C2) with dorsal bone loss was created in seven pairs of fresh-frozen upper extremities. One wrist from each pair was fixed with a standard external fixator and three interfragmentary K-wires. The contralateral wrist of the pair was fixed with CPBC (Norian SRS) and K-wires in the same positions. Sequentially increasing loads were then applied to the major wrist flexor and extensor tendons, up to a total of 100 N, to simulate physiologic loads and loading patterns. Movement of the radial and ulnar fracture fragments was measured.

Results: Fixation with CPBC alone failed at the bone-cement interface at 80 N in all specimens. Statistical analysis revealed differences among the three fixation techniques (external fixation, CPBC, and K-wires alone). In the planned comparisons, external fixation was found to provide significantly increased stability to the radial fragment when compared with CPBC in four of the six rotations tested (flexion/extension 2.97 _ 2.93_ vs. 11.07 _ 13.08_, P = 0.008) and for the ulnar fragment in all six rotations. CPBC was found to provide greater stability than K-wires alone for the radial fragment in three rotations (flexion/extension 11.07 _ 13.08_ vs. 36.49 _ 13.03_, P < 0.001) and for the ulnar fragment in five of six rotations.

Discussion: On the basis of our data, it is evident that CPBC alone is insufficient to withstand wrist flexion-extension motion without supplemental wire fixation. When supplemented with three K-wires, the bone cement is more stable than K-wires alone, but it is still significantly less stable than when fully augmented by the currently used pattern of external fixation augmented with K-wires.

Conclusion: Our biomechanical study of CPBC for treatment of intraarticular DRF showed that, under physiologic loads in vitro, cement must be supplemented with K-wires. We found that this fixation was not as stable as the standard external fixation with K-wires commonly used today.