Biomechanical Comparison of the Influences of Two Proximal Metatarsal Osteotomies on First Ray Articular Contact Characteristics

Abstract

Category: Bunion Introduction/Purpose: Proximal metatarsal osteotomies are commonly employed to treat moderate to severe hallux valgus deformities. An understudied area with respect to these procedures is the effect on articular contact properties following the surgeries. Potential long-term risks include altered joint mechanics and possible arthritic progression. A biomechanical comparison of articular characteristics of the proximal opening wedge and Ludloff osteotomies was performed in this study. It is hypothesized that the proximal opening wedge osteotomy (POWO) would lead to greater alterations in articular contact properties along the first ray. Methods: Seven paired fresh-frozen below-knee cadaveric limbs with hallux valgus deformity were selected. The first ray inclusive of the navicular-medial cuneiform articulation was dissected and potted in resin. Specimens in each pair were tested in the intact state and then randomized to receive either a Ludloff or POWO. A 4 mm opening wedge osteotomy was used in all cases. The FHL was dissected and isolated. Testing was conducted in a customized apparatus with the cuneiform pinned to the apparatus and positioned at 10 degrees of declination. Loading of the FHL was conducted to 100 N utilizing an instrumented tensioner. A 28 N load was added at the distal phalanx to simulate the ground reaction force(Fig.1). First MTP and TMT articular properties were recorded simultaneously using two pressure sensors. For each state, a pressure map was generated and contact area, peak pressure and center of pressure were calculated. Results: Average peak pressure was noted to be elevated at the MTP (4.6 mPa vs 6.9 mPa, P = 0.08) and TMT (3.3 mPa vs 5.1 mPa, P = 0.16) joints when comparing the Ludloff and the POWO respectively, but was not significant. Contact area was also noted to be lower in the POWO vs Ludloff states for the MTP (86. 6mm2 vs 69.1mm2, P = 0.15) but not the TMT joints (89.1 mm2 vs 88.5mm2, P = 0.96). A trend towards decreased contact force within the TMT joint was noted following opening wedge osteotomy relative to the intact state (103.8 N vs 113.9 N, P = 0.31), while forces were elevated at the MTP joint (104.3 N vs. 96.0 N, P = 0.63), although not statistically significant. Conclusion: POWO can potentially change articular contact characteristics along the TMT and MTP articulations of the first ray. This could possibly lead to altered loading patterns and possible long-term arthritic progression versus other osteotomies. However, it is unlikely that the changes observed with the sizes of the osteotomy commonly used would lead to long term significant consequences.