Impact of First Metatarsal Shortening on Forefoot Loading Pattern: A Finite Element Model Study

Abstract Backgrounds Shortening of the first metatarsal is common following hallux valgus correction procedure. However, it remains controversial whether post-operative complications such as transfer metatarsalgia can be simply attributed to excessive shortening of first metatarsal. This study investigated the relationship between first metatarsal shortening and forefoot loading pattern: The goal was to determine whether and to what extent the first metatarsal might be shortened effectively reducing the risks of complications.Methods A finite element model of the human foot simulating the push-off phase of the gait was established and validated by subject-specific plantar pressure data. Various levels of first metatarsal osteotomy were sequentially applied to the model, and model predictions in terms of pressure and force distributions under each foot rays are obtained.Results Results show that the plantar pressure of the first ray decreased with increasing shortening level; the pressure of the lateral rays continued to rise. However, when the shortening reaches 6 mm, the load ratio of the middle rays exceeds a critical threshold of 55%—this was considered risky. Under such circumstances, the loading ratio at the central rays could still be manipulated to normal if the distal end of the first metatarsal could be displaced in the dorsal-to-plantar direction by 3 mm.Conclusions During the first metatarsal osteotomy, a maximum of 6 mm of shortening length is considered to be within the safe range. Whenever a higher level of shortening is necessary, pushing down the distal metatarsal segment could be a compensatory procedure to maintain normal plantar force distributions.