Biomechanics of foot and ankle

The human foot-and-ankle is a highly developed, biomechanically complex structure which sustains the weight of the body and facilitates forces transmission during propulsion. Apart from 28 bones, the foot is composed of more than 30 joints surrounded by more than a hundred of muscles, tendons, and ligaments. The geometry of the foot and the balance-controlling mechanism of the body enabled us on a variety of motions, including walking, running, and jumping. However, the high and complicated load on the foot impose risk of the foot injury, trauma, and other problems. Common foot disorders include hallux valgus, bunion, flatfoot, plantar fasciitis, heel pain, and Achilles tendonitis. Ankle fracture in elderly people is a major burden in developed countries with an aging population. There was a threefold increase in the incidence of ankle fractures in elderly people in the last century. Aging and overweight also contribute to the chance of foot problems. Besides, calcaneal fracture is common for young and physically active population and may turn into degenerative or traumatic arthritis after serious injuries. Both surgical and conservative methods have been adopted to treat foot problems and diseases. Most of the interventions targeted the treatment on the problem site but the effect of the foot problems could extend beyond the site to adjacent regions or the entire foot. Assessment and evaluation of the biomechanical environment and the variations before and after the intervention could help intervention design, planning and thus minimizes complications. Experimental methodologies, such as motion capture analysis, pedobarography, and cadaveric experiments have been developed to quantify foot biomechanics. However, the internal biomechanics of the foot, such as the stress distributions within bones and soft tissues is not easy to measure by experiments. Computational methods or platforms such as the finite element (FE) analysis are useful tools to investigate biomechanics of the musculoskeletal structures. This evaluation method has been used to study injury mechanism, improve prosthetic and orthotic designs, and predict surgery outcome, in addition to promoting fundamental understanding of foot biomechanics. In this chapter, four common foot problems and interventions of the foot and ankle were analyzed by FE models including hallux valgus, ankle arthroplasty, tarsometatarsal joint fusion, and calcaneal fractures.