Screw Fixation Compared to H-Locking Plate Fixation for First Metatarsocuneiform Arthrodesis: A Biomechanical Study

Abstract

Background: Several different techniques have been used for fixation of first metatarsocuneiform (MTC) joint arthrodesis, a standard treatment for arthritis, instability, and deformity of the MTC joint. Improved plating systems using locking designs are now available, but no studies have yet compared this construct with other methods. We compared load to failure with a locking plate design versus standard crossed-screw fixation. Methods: Ten matched pairs of fresh frozen cadaver feet were used. The bone density of each pair was measured with DEXA scanning. One foot of each pair was randomly assigned to have a dorsomedial Normed H titanium locking plate (Normed Medizin-Technik Vertriebs-GmbH, D-78501 Tuttlingen, Germany) applied to the first MTC joint. On the other foot of the pair, fixation of the first MTC joint was done with crossed ACE DePuy 4.0 (DePuy/Ace, Warsaw, IN) titanium cannulated screws. The first metatarsal and first cuneiform were then isolated and planted in an epoxy resin. The specimens were loaded to failure in a four-point bending configuration using a MTS Mini Bionix test frame (MTS Systems Corp., Eden Prairie, MN). Failure was defined as displacement of more than 3 mm at the arthrodesis site. The Student t-test was used to determine any observed differences, with significance set at p ≤ 0.05. Results: The mean maximal load to failure was 140.08 N (SD ± 77.1) for screw fixation alone and 58.09 N (SD ± 11.86) for the H-locking plate. This difference was statistically significant ( p = 0.008). The mean stiffness of the construct for screw fixation alone was 83.10 N/mm (SD ± 49.8) and 19.96 N/mm for the H-locking plate. This difference also was statistically significant ( p = 0. 004). Conclusion: Screw fixation for first MTC arthrodesis created a stronger and stiffer construct than did the H-locking plate. This was likely due to the mechanical design of the implants. Compression across the MTC joint could be applied with the screws, but the plate relied on a fixed angle design with no compression.