[Lesser Metatarsals Load after Minimally-Invasive Surgery for Hallux Valgus Correction: A Finite Element Model]

To analyze the biomechanical consequences on the lesser metatarsals using different screw configurations for fixation of the minimally-invasive Chevron-Akin (MICA) osteotomy, through the finite element method (FEM).

A FEM model was developed from a computed tomography scan of a moderate HV deformity. Five different screw configurations were tested. We measured the maximal tension in the lesser metatarsals for each screw configurations, in physiological and supraphysiological loads.

The lesser metatarsals received the lowest loads when the first metatarsal osteotomy was fixed with one intramedullary and one bicortical screw, with tensile load values varying between 30 and 70 MPa in physiological loads, and 50 to 350 MPa in supraphysiological loads. In all fixing techniques, the 2nd and 4th metatarsals received the highest loads, especially in groups 3 (2 bicortical screws) and 5 (only 1 bicortical screw), with values reaching up to 230 and 600 MPa in physiological and supraphysiological loads, respectively. Regardless of the fixation technique, the region of the lesser metatarsals that received the most load was the diaphysis.

After MICA surgery to correct HV, there is an increase in tension forces on the lesser metatarsals, especially the second and fourth. The technique of fixing the first metatarsal with one bicortical and one intramedullary screw showed the lowest values on the lesser metatarsals load. Furthermore, for physiological and supraphysiological loads, independently of the technique, the forces were concentrated mainly on the metatarsal shaft.