Biomechanical Modeling of Osteotomies of the First Metatarsal Bone in Normal and Osteoporotic Conditions

Hallux valgus is a widespread pathology. Osteotomy of the first metatarsal bone is the gold standard for its treatment. The success of this surgical intervention depends, among other factors, on the stability of the “bone-fixation” system. Previous studies assessing the biomechanical properties of various first metatarsal osteotomies have examined the influence of osteotomy type, degree of fragment displacement, as well as the number and positioning of screws. In these studies, the biomechanical properties of bone tissue corresponded to normal values of conventionally healthy patients. Older patients are characterized by a high prevalence of osteoporosis. This disease manifests in reduced mineral density and mechanical properties of bone. The effect of osteoporosis on the biomechanical parameters of first metatarsal osteotomy models has not been previously studied. The aim of this work was to evaluate the stability of first metatarsal osteotomies under normal bone density and osteoporotic conditions, as well as to assess the robustness of biomechanical models of the most common osteotomy types to minor variations in screw positioning and bone-cutting plane geometry. For this purpose, 36 biomechanical models of scarf and chevron osteotomies were created, varying screw placement, bone-cutting plane geometry, cortical thickness, and elastic modulus. Finite element analysis was used to assess the stress-strain state of the osteotomy models. Model validation was performed based on natural cantilever bending tests of first metatarsal osteotomies in universal testing machine. The study demonstrated the robustness of scarf and chevron osteotomy models to minor changes in geometric parameters. Chevron osteotomy proved more stable than scarf. Additionally, scarf osteotomy generated significantly higher bone stresses compared to chevron. It was found that even under osteoporotic conditions, both osteotomy types can provide sufficient stability and strength in terms of screw breakage and bone tissue damage.