A Biomechanical Cadaveric Comparison of Three Fixation Methods for Bennett Fractures

Bennett fractures are inherently unstable intra-articular fractures of the first metacarpal base and are subject to multiple deforming forces. Suboptimal treatment can lead to fracture displacement, malunion, and post-traumatic arthritis of the carpometacarpal joint. The purpose of this study was to evaluate three fixation techniques for the stabilization of Bennett fractures. Our hypothesis was that screw fixation would be stiffer than the other methods.

Thirty fresh frozen cadaver hands were obtained. Bennett fractures were created by a fellowship-trained hand surgeon. Specimens were then randomized to fixation with one of three techniques: two 1.2 mm (0.047 in) Kirschner wires (K-wires), two 1.2 mm cortical lag screws, or a single 1.7 mm (0.067 in) headless compression screw with a minisuspensory cortical button construct (suture-button/screw). The specimens were loaded in displacement-controlled axial compression until failure. Radiographs were taken before and after testing to compare the final displacement and method of failure. Interfragmentary motion and applied load were recorded. The maximum force and relative motions of the first metacarpal and Bennett fragment were filtered and calculated.

The median force to failure for screw, K-wire, and suture-button/screw were 166.6 N (38.9-590.3), 98.4 N (41.9-444.0), and 97.5 N (24.5-242.6), respectively, with no significant differences between constructs. Similarly, there were no significant differences in median displacement measured in three-dimensional space (5.7 mm (1.6-8.4), 5.7 mm (1.9-11.5), and 6.1 mm (3.9-17.9), respectively, or stiffness (37.2 N/mm (5.6-345.0), 22.8 N/mm (2.0-113.8), and 14.3 N/mm (5.5-285.9), respectively, between the groups.

All three methods of Bennett fracture fixation performed similarly at time zero in this in vitro biomechanical study.

The results of the present study may be taken into consideration along with patient factors and fracture characteristics when treating Bennett fractures.