Finite Element Modelling of Foot Bones In A Patient With Chronic Osteomyelitis

Abstract

Spina bifida is one of the rare neural tube defect with an incidence of 0.1-1% worldwide[1]. Combordities that arise secondary to Spina bifida include musculoskeletal, urologic and orthopedic abnormalities. Chronic osteomyelitis secondary to Spina Bifida is a very debilitating condition. Besides pain, long disease course and inconvenience of repeated infections, chronic osteomyelitis can play an integral role in causal pathways leading to minor and major lower extremity amputation. Charcot neuroarthropathy is a complication which can arise in foot with chronic osteomyelitis. Equinovarus talipses is a deformity that occurs due to destroyed and osteolytic bones occurring because of this chronic disease as this can lead to altered biomechanics of lower extremity. Anatomy, etiology and pathophysiology of chronic osteomyelitis are well documented. But mechanical effects of this condition on foot bones are still questionable. This chronic disease’s repeated infections can lead to severe consequences like cellulitis, altered biomechanics and ultimately amputation. Hence, the social and economic burden of this disease remains very high. It is important to understand the biomechanics of lower extremity affected from chronic osteomyelitis to determine the design of customized orthoses and implantable prostheses for the patient’s rehabilitation. This project is an integrated approach involving patient-specific finite element modelling to investigate the von Mises Stress distribution of healthy and chronic osteomyelitis affected foot bones of same patient in standing position. The geometrical complexity and mechanical behaviour of foot bones implies the use of reverse engineering tools for accurately simulating the biomechanical properties and for material constitutive modelling. The developed models successfully determined the biomechanics of diseased foot and its comparative study with normal foot’s stress distribution. The models are validated with comparison of von Mises Stresses in developed model of normal foot bones with established literature data. After the stress distribution analysis of osteomyelitis affected foot bones, it is concluded that abnormal biomechanics of osteomyelitis affected foot can cause ulcers and futher derangement of pedal architecture due to increased pressured on ankle bones like Talus, Navicular and Tibia. Moreover, stresses on Metatarsals and Phalanges are much lower than normal ranges making these bones osteolytic and can become a cause for stress shielding effect. The 3-d bio-printable bones as replacement of destroyed foot bones is the newly emerged application of additive manufacturing in biomedical field. The key focus in this research is to improve the abnormal biomechanics of osteomyelitis affected foot bones of patient considered in this study. Hence to achieve this objective, the destroyed foot bones can be resected and replaced by implantable prostheses which can be fitted in the voids created after removal of deformed bones. So in compliance with the existing literature, 3 designs of prostheses based on bio-printable bones are modelled for the particular anatomy of diseased foot considered in this viii study. The 3-D bio-printable prostheses are tied with the osteomyelitis affected foot bones to mimic the geometry of normal foot. The results indicated that the stress distribution in osteomyelitis affected foot becomes in agreement with that of normal foot with Talo-Calcaneal and Talus-Navicular-Calcaneal prostheses developed in this research more accurately than implantable Calcaneal prosthesis. Briefly, the results obtained from this study are quite promising and poses new avenues as a tool for better understanding the biomechanics of osteomyelitis of lower extremity. Moreover, the study provides niche to improve the biomechanics of osteomyelitis affected foot with the aid of prosthetic replacements.