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Metacarpal Neck Fracture Fixation: a Biomechanical Comparison of Three Techniques
Eric M Padegimas, MD1; Nicole Weikert, BS2; Samuel Greulich, BS2; Sorin Siegler, PhD2; Asif Ilyas, MD1; Christopher Jones, MD1
1Thomas Jefferson University Hospital, Philadelphia, PA, 2Drexel University, Philadelphia, PA
Introduction: Metacarpal fractures represent approximately 40% of all hand fractures with an incidence of 1.5 million injuries annually. Surgical options, when indicated, include fixation with K-wires, screws, plates, external fixators, and intramedullary nails. While usually successful, surgery can yield a complication rate of up to 36%. In response to this, intramedullary headless compression screw (HCS) fixation has been suggested, with promising initial clinical reports. The purpose of this study is to evaluate the mechanical properties of HCS fixation of a metacarpal neck fracture compared to more established techniques of K-wire cross-pinning and locking plate fixation.
Methods: A metacarpal neck fracture model was created in 36 fourth generation composite Sawbones by removing a volar-based bone wedge using a custom cutting jig to simulate a typical apex dorsal fracture, unstable in flexion. Twelve bones each were then fixed by one of three methods: retrograde cross-pinning with two 1.2 mmK-wires (KW), 2.0 mm dorsally placed T-plate with six 2.0 mm locking screws (LP), or 3.0 mm retrograde HCS fixation. A 3-D printed fixation jig was used to assure all hardware was identically placed. Models were potted at the base and mounted vertically in a materials testing machine, employing a cable tensioned over the metacarpal head to simulate forceful grip loading. (Figure 1). Cyclic loading to 40N (simulating finger active range of motion exercises) and failure testing was performed. Load, displacement, and failure mode were recorded. Failed bone models are shown in Figure 2.
Results: Average final stiffness of the HCS construct (7.3±0.7N/m) was significantly greater than the KW model (5.8±0.5N/m; p<0.001) and significantly less than the intact bone (9.6±0.8N/m; p=0.02) and LP (9.5±1.9N/m; p=0.006) models. With cyclic loading to 40N, the LP exhibited significantly less displacement (0.2±1.3mm) compared to the HCS (2.5±2.3mm; p=0.01) and KW (2.8±1.0mm; p<0.001) while the KW and HCS models exhibited similar displacement with cyclic loading (p=0.73) (Figure 3). Load to failure for the HCS model (215.5±39.0N) was nonsignificantly lower than the KW model (279.7±100.3N; p=0.68) and significantly lower than the LP model (267.9±44.1N; p=0.007) (Figure 4).
Conclusion: The HCS provided comparable mechanical properties to K-wire cross-pinning against a physiologic cyclic loading simulating an early active range of motion protocol. The DP construct allowed significantly less displacement and had the highest strength. Though this benefit should be weighed against the more extensive surgical dissection required.
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