Development of an extraosseous nitinol implant for the hallux valgus treatment: Preliminary mechanical investigations, design and numerical simulation

Abstract

The hallux valgus is a complex malposition of the first ray which occurs in 2-4% of the population. The deformity causes problems and pain during walking due to the defected functionality of the joint. Standard implants used for mild and moderate corrective surgery of the big toe - the Scarf osteotomy - are titanium bone screws and plates and do require well-experienced surgeons. The developed implant, an extraosseous clip, allows the surgeon a controlled and reproducible correction with a reduced number of surgical steps. The clip is made of Nitinol, a shape memory alloy. Due to the superelastic characteristics of Nitinol the clip gets a spring-like effect acting as a clamping force on the reconstructed bone fragments. The final design was created by anatomical tests, mechanical calculations and a finite element analysis. The minimum clamping force per clip is 43 N, offering a threefold mechanical safety compared to the acting forces in the post-operative shoe (OrthoWedge, co. Darco) calculated by biomechanical assumptions. As a next step the calculated figures need to be validated by mechanical testing. © 2012 by Walter de Gruyter. Berlin. Boston.