Biomechanics Aspects for Silastic Implant Arthroplasty Simulation of the First Metatarsophalangeal Joint

Abstract

This work focuses on the biomechanical simulation of surgery for total replacement of the first metatarsophalangeal joint (MTPJ) allowed us to identify and analyze several key aspects for finite element simulation of hallux rigidus pathology. Predicting the optimal response of a finite element model (FEM) depends on proper characterization. At this part of the work, those conditions that have a direct or indirect influence on the model that can change its behavior should be considered. For this purpose, we presented in this work a finite element model which include 26 bones: 14 phalanges, 5 metatarsals, 3 cuneiform bones, 1 cuboid, 1 navicular, 1 talus and 1 calcaneus, all of them include articular cartilage. In addition, the model also considers: thin ligaments, long ligaments, muscles and a joint implant. Loads and boundary conditions included: a pretension in the flexor caused by position analysis, a distributed load in the talus in its normal and tangential component, a restriction of movement of some points in the phalanges and calcaneus and the contact conditions between flexor and extensor created from surfaces in the bone volumes. Moreover, the selection of support and constrains regions in the phalanges and calcaneus area must be carefully selected to reproduce the conditions of real support and interaction with adjacent tissues not simulated. These conditions have influence in the structural biomechanical response of each tissue and in contact regions, leading to unexpected behavior if they are wrong selected. In addition, results showed that care must be taken in the mechanical characterization of each tissue, selecting the mechanical properties, pretension, geometry and critical position according to in vitro results or MRIs. Biomechanical aspects reported in this work allow to take into account fundamental details to improve future simulations of this pathology as well as to improve the correlation with experimental results. These biomechanical aspects provide knowledge for finite element simulation of the arthroplasty for the first metatarsophalangeal joint, this allow us to generate a virtual model for arthroplasty of the hallux rigidus to predict, prevent and improve surgical techniques for implantation of prostheses in the first metatarsophalangeal joint.

Structural assessment of pre-flexion in silicone implants for arthroplasty of the first metatarsophalangeal joint

“…Swanson implants are one of most silicone implants frequently used for joint reconstruction; specifically, for the metacarpophalangeal and metatarsophalangeal joints. 1,6,7,12–19 Some other implants as Tornier have been created with an axial offset hinge design, which reduces stress on the prosthesis and improves biomechanical function, a characteristic that is not considered in Swanson implants. Moreover, joint flexion for Swanson implant has been measured after implantation finding a mean active and passive arc of motions of 36.80° (SD 19.13) and 46.82° (SD 17.19), respectively.…”