Biomechanical comparison of mini-plate and screw fixation in minimally invasive distal metatarsal osteotomy for hallux valgus

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Aims: To biomechanically compare the stability of mini-plate and dual-screw fixation following minimally invasive distal metatarsal osteotomy for hallux valgus, with an emphasis on early-stage stability under clinically relevant loading conditions. Methods: Three fixation configurations were evaluated: mini-plate fixation with two (PS2) or three (PS3) locking screws and dual-screw fixation (DS). Finite element analysis (FEA) was performed to quantify displacement and stress distribution under controlled bending and torsional loading, providing insight into internal load transfer mechanisms not accessible experimentally. Fresh-frozen human cadaveric specimens then underwent distal chevron metatarsal osteotomy and fixation according to each configuration (n = 3 per group). Cyclic and static bending tests were performed to simulate early postoperative weightbearing, and displacement responses were recorded. FE predictions were compared with experimental displacement trends. Results: Under bending loads, both FEA and cadaveric testing consistently demonstrated that PS3 exhibited the smallest displacement, followed by PS2, with DS showing the greatest instability. FE analysis further revealed that mini-plate fixation reduced bone stress at the osteotomy site but increased implant stress, whereas DS showed higher bone stress concentration. Under torsional loading, FE results indicated lower displacement but higher bone stress in DS. Cadaveric cyclic tests confirmed the superior stability of PS3, showing the least displacement accumulation over 1,000 cycles (p < 0.05). In static testing, PS3 achieved the highest failure load (~423 N), followed by PS2 (~248 N), while DS showed the lowest (~205 N). Conclusion: Mini-plate fixation, particularly PS3, provides superior resistance to bending-induced micromotion compared with DS, with consistent agreement between FE predictions and experimental findings. FEA further elucidated internal stress distribution, highlighting increased bone stress concentrations in DS. Overall, mini-plate fixation offers a more stable and clinically reliable construct for maintaining correction during early postoperative weightbearing.

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