Functional restoration and risk of non-union of the first metatarsocuneiform arthrodesis for hallux valgus: A finite element approach.

First metatarsocuneiform arthrodesis is one of the surgical interventions to correct hallux valgus, especially those with hypermobile first ray. There is lacking of biomechanical investigations to assess this operation. The objective of this study was to explore the functional restoration and the risk of non-union after the surgery via finite element analysis. A three-dimensional foot model was constructed from a female aged 28 via magnetic resonance imaging. Thirty bones and encapsulated bulk tissue were modeled. Walking stance was simulated by the gait analysis data of the same participant. Parts of the first metatarsal and cuneiform were resected and the bone graft was assigned with the same stiffness as adjacent bones to resemble the surgery of first metatarsocuneiform arthrodesis. The third principal stress of the first metatarsal at midstance (25% stance) and push off (60% stance) was increased by 76% and 139% respectively after the operation, while that of the second metatarsal was decreased by 14% and 66%. The operation reduced the medial deviation of the first metatarsal head by about 3.5mm during initial push off (60% stance). Besides, the bone graft could experience tensile stress inferiorly (26.51MPa). In conclusion, the increase of stress on the first metatarsal and the reduced medial excursion of the first metatarsal head after the simulated operation reflected that metatarsocuneiform arthrodesis could restore the load-bearing function of the first ray. However, inter-fragmentary compression could not be guaranteed. The appropriate course of hardware and non-weight-bearing protocol should be noted and further investigated.