Study on metatarsal stress and correction methods at three different foot varus angles

This research introduces a biomechanical correction technique that applies two-plane and three-point force to mitigate metatarsal fractures caused by excessive stress resulting from progressive hindfoot varus deformity following stroke. The aim is to optimize the distribution of stress across the metatarsals, thereby reducing the incidence of stress-induced injuries. A modified constitutive equation, accounting for the mechanical behavior of soft tissues, is used to compute stress in each metatarsal under static standing conditions at varus angles of 0°, 10°, 15°, and 20°. To assess the method’s effectiveness, peak stress values of the metatarsals are compared before and after correction. The analysis reveals that increasing varus angles lead to a progressive escalation in peak stress at the fifth metatarsal. At a varus angle of 20°, stress increases by 30.11% relative to a normal foot, with the highest concentration observed at the base of the fifth metatarsal. Under correctional force conditions involving three-point loading in both the coronal (20 N, 10 N, 25 N) and horizontal (10 N, 20 N, 25 N) planes, no medial displacement or adduction of the forefoot phalanges is detected. Additionally, the calcaneal angle is reduced from 10° to 7.25°, accompanied by a 15.28% reduction in peak fifth metatarsal stress. These findings suggest that the worsening of hindfoot varus deformity causes a nonlinear increase in fifth metatarsal stress, which significantly elevates the risk of stress fracture. The proposed corrective approach effectively alleviates this stress and addresses the deformity, thereby enhancing medial load distribution. This methodology provides a scientifically validated framework for biomechanical correction and rehabilitation of individuals with hindfoot varus deformity following stroke.