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

The development of numerical models to analyze pathologies and implants related to the first metatarsophalangeal joint of the foot remains an issue for attention. The structural effects of implants pre-flexion have been discarded in several finite elements analyses due to complexities to achieve these positions. This work aims to evaluate if the pre-flexion stress state should be included or could be discarded when only flexion is applied in two different silicone commercial implants, Swanson and Tornier, during a gait cycle. Finite element models were created for silicone implants. Both models were discretized using high-order finite elements. The hyperelasticity constitutive material model of Arruda-Boyce was used, based on experimental data; its behavior was compared with linear elastic models reported and used frequently assuming small and large deformations and applying to the Swanson and Tornier implants a flexion angle of 64°, which corresponds to in vivo measurements reported after implantation. Comparison between models, regarding hyperelastic model, showed mean variations of up to 32.5% for stresses and 14.01% for bending moment in Swanson implant, while for Tornier implant mean variations of 29.73% and 632.55% was obtained for stress and bending moment respectively. The maximum stress value obtained for the hyperelastic model in the Swanson implant reached a value of 22.82% of the tensile strength of the implant material while in the Tornier implant reached a value of 25.92%, the above values were evaluated at a flexion angle of 64°. The results suggest considering in finite element analyses not only the stress state generated to achieve critical flexion position in pleflexed implants models but also the hyperelastic material behavior of silicone for implants to avoid dismissing the non-linear structural behavior of hyperelastic materials.

Effectiveness of calcaneal osteotomy in surgical treatment of foot conditions: A Prisma statement guidelines compliant systematic review.

Calcaneal osteotomy is a commonly established method used to correct various foot malalignment surgery problems that produce varus and valgus hindfoot abnormality as well as Haglund's deformity, cavovarus foot reconstruction, flatfoot deformity, plantar fasciitis, posterior tibial tendon insufficiency and planovalgus foot. After decades, several procedures in orthopaedic foot surgery have been suggested for reducing the risk of wound and neurovascular complications. The goal of this Prisma statement guidelines compliant systematic review was to establish the effectiveness and safety of calcaneal osteotomy in foot surgery. We have performed a novel systematic review of the current published literature in order to evaluate the scientific evidence now available on this association, assigning predefined exclusion and inclusion criteria. Eight investigations were selected which had 191 cases. The adult flatfoot, tibialis posterior reconstruction and cavovarus foot deformity were treated with different procedures of calcaneal osteotomy techniques. The adequate level of effectiveness of calcaneal osteotomy is associated with the kind and location of the incision, with or without screw application, in each specific foot condition. There is a limited number of scientific investigations of the effectiveness and safety of the different kinds of calcaneal osteotomy in foot surgery, and there is the need to enhance outcome knowledge on this foot surgery technique.

Effectiveness of the Lapidus plate system in foot surgery: A PRISMA compliant systematic review.

Lapidus arthrodesis is an established standard procedure to correct various foot surgery problems and hallux limitus, hypermobility of the first ray, hallux abductus valgus, and symptomatic lesser metatarsal. After decades, many fixation methods in the orthopaedic surgery industry have been developed for decreasing complications and improving this technique. The aim of this PRISMA compliant systematic review is to analyse the effectiveness of several lapidus plate systems in foot surgery. We have carried out the first systematic review of the relevant published literature so as to systematically evaluate the scientific knowledge available now on this association, assigning predefined eligibility criteria. Fourteen studies were selected which had an overall of 738 cases. The first tarsal metatarsal joint and hallux valgus were treated by the application of different types of Lapidus plate system. The optimal level of the fixation in these procedures is related with the type and system insertion place of the plate with or without screw in each specific foot disease. There is an insufficient number of studies about the effectiveness of the different types of Lapidus plate system in foot surgery, and there is a need to increase outcomes knowledge on the level of the fixation, sort of the system, and insert place in foot surgery.

Structural interaction between bone and implants due to arthroplasty of the first metatarsophalangeal joint.

BACKGROUND: Currently, the metatarsophalangeal joint replacement through a restorative arthroplasty, where implants are used, is a viable invasive surgical medical procedure in the treatment of severe cases of osteoarthritis in this joint, better known as hallux rigidus. However, few things are known about the postoperative complications that implants can cause on the joint, like Swanson and Tornier implants.Research in this field can provide a valuable information that would help the specialist surgeon in the decision-making during the selection of the more suitable joint implant in each patient, as well as the redesign of the devices, to make them more efficient, durable and biocompatible with the human body. METHODS: The aim of this work is to perform a structural biomechanical analysis of a restorative arthroplasty of the first metatarsophalangeal joint, and to analyze the interaction between bone and medical grade silicone implants. For that, a simulation of a foot with Swanson and Tornier joint implants were performed to evaluate the stress/strain distribution during a critical stage (toe-off). RESULTS AND CONCLUSIONS: Principal stresses obtained for the first metatarsal with both implants suggest that failure is induced in this bone because, values exceed (up to 136.84% for Swanson model) the tensile strength reported for phalange trabecular bone, which may be related to osteolysis. Stress and strain values obtained in this work suggest that arthroplasty surgery with Swanson implant is more likely to cause postoperative complications versus Tornier implant.

Mechanical Stress Redistribution in the First Metatarsal Bone After Autologous Bone Harvesting.

BACKGROUND: The first metatarsal bone is a viable source for autologous bone grafting in foot and ankle surgery and may serve as another convenient graft site to correct a flail toe deformity. We aimed to determine how progressive bone removal from the first metatarsal affects the mechanical redistribution of the foot and whether this bone removal increases the risk of fracture. METHODS: A three-dimensional finite element model developed from computed tomographic images obtained from a healthy man were used to evaluate traction stresses on the first metatarsal bone as a function of applied loads on the talus and Achilles tendon at two phases of the gait cycle (and according to the depth of bone removal). RESULTS: Simulations indicated that when maximum load was applied to the Achilles tendon, tensile stress increased from 2.049 MPa in the intact foot to 5.941 MPa in the area of maximum bone harvest during the stance phase. Furthermore, as the volume of bone extracted from the first metatarsal increased, there was a redistribution of stress that differed significantly from that of the intact foot. CONCLUSIONS: Although the maximum stress on the first metatarsal was not significantly affected by increasing the volume of bone harvested, the ankle should be splinted in plantarflexion during the postoperative period to eliminate the stance phase of gait and reduce the risk of metatarsal fracture.