Biomechanical Comparison of Two Plantar Lapidus Plating Systems.

Background: Hallux valgus (HV) is a common forefoot deformity that often leads to foot pain and functional limitations, requiring surgical intervention when conservative treatments fail. Tarsometatarsal arthrodesis is a widely used procedure for severe HV deformities, with plantar plate fixation demonstrating superior biomechanical outcomes. However, the biomechanical equivalence of different plantar plate designs remains unclear. Specifically, there is a lack of biomechanical studies comparing how design variations affect load distribution, durability, and the risk of material failure postoperatively. This study aims to address this gap by evaluating the biomechanical performance of 2 commonly used plantar plate designs.

Methods: This study involved a biomechanical analysis of 2 widely used plantar Lapidus plating designs: U-shaped plates and straight-shaped plates. A total of 20 fresh frozen cadaveric feet from 10 donors were included. The plates were assigned randomly to each specimen, and tarsometatarsal arthrodesis was performed according to the manufacturers' guidelines. Mechanical testing was conducted using a universal testing machine, focusing on cyclic loading and maximum load capacity to assess the mechanical stability of each system. Cyclic loads were systematically applied in 4 increments, culminating in a ramp test to ascertain the maximum load to material failure.

Results: Both the U-shaped and the straight-shaped plantar Lapidus plates demonstrated commendable mechanical stability under cyclic loading, with nearly no significant differences in stiffness across the 4 cyclic loading force cycles. In the maximum load capacity test, the straight-shaped plate showed a higher mean load capacity (540.6 N, SD = 36.09) compared with the U-shaped plate (446.6 N, SD = 91.32), with a statistically significant difference (P = .03) and a large effect size (Cohen d = 1.56).

Conclusion: This biomechanical study demonstrated that both U-shaped and straight-shaped plantar Lapidus plating systems provided comparable mechanical performance under stepwise cyclic loading conditions. The straight-shaped plates showed a higher failure rate during cyclic loading but achieved a significantly greater maximum load capacity in the final load-to-failure test. In contrast, the U-shaped plates were more consistent under repeated loading, suggesting potential advantages in fatigue resistance. These findings may reflect a trade-off between repetitive load endurance and maximum load-bearing capacity. Although these results offer biomechanical insight into the design-specific behavior of 2 commonly used plantar plating systems, their clinical relevance should be interpreted with caution, given the limitations of cadaveric testing, the absence of biological bone healing, and small sample sizes. Further clinical and long-term outcome studies are needed to confirm whether the observed mechanical differences translate into meaningful differences in patient function or fusion success.

Level of evidence: Level V, preclinical biomechinal study.