Modeling of Osteotomies of the First Metatarsal Bone on a Complete Foot Model in Normal and Osteoporotic Conditions

Hallux valgus deformity of the first toe (HV) is a widespread orthopedic pathology. The prevalence of HV varies from 23 to 46% among the adult population. With severe deformity, surgical intervention in the form of osteotomy of the first metatarsal (M1) remains the gold standard for the treatment of HV. The most common M1 osteotomies are scarf and chevron. Previously, the strength characteristics of these and other osteotomies were studied on isolated bone models and complete foot models. However, in conditions of osteoporosis and considering the action of the main muscles of the foot, this was not done. The biomechanical significance of osteoporosis is due to its negative effect on the strength properties of bone tissue. In patients of the older age group, a simultaneous increase in the frequency and severity of HV and osteoporosis is natural. This paper presents a new, experimentally validated, improved biomechanical model of the foot. The model includes realistic geometry, bone, as well as soft tissues, and ligamentous apparatus. The modeling considered the influence of the patient’s body weight, Achilles tendon tension and the forces of the main five muscles of the foot. The developed model was used for a comparative analysis of the stress-strain state of scarf and chevron osteotomies M1 in normal condition and in osteoporosis of bone tissue. The stresses in the fragments of the scarf osteotomy were higher than the stresses in the fragments of the chevron osteotomy by 15–21% (on average by 18%). The stresses in the screws of the scarf osteotomy turned out to be higher than the stresses in the screw of the chevron osteotomy by 21–33% (on average by 28%). With a decrease in the quality of cortical bone tissue, equivalent stresses in both screws and fragments of M1 osteotomies increase significantly (by 50–100%). The relative displacements of bone fragments also increase by 33–50%. It has been shown that both types of osteotomies provide sufficient stability and strength under the studied loads, simulating the vertical position of the human body.