Biocomputational comparative study of Rheumatoid Arthritis of the wrist joint before and after arthroplasty; carpal stability analysis

Instability is one of the symptoms associated with Rheumatoid Arthritis of the wrist joint. The instability which is caused by weakened ligaments as well as worn cartilages makes the carpal bones to move freely, causing a painful condition. Wrist arthroplasty is one of the treatments for severe cases of Rheumatoid Arthritis of the wrist joint. This project involved biomechanical analysis of wrist arthroplasty in terms of its ability to provide carpal stability for replacement of the joint severely affected wrist with Rheumatoid Arthritis. The clinical symptoms of the skeletal disease such as the pathological changes of the bone, cartilage, ligaments, tendon as well as the load transfer were used to accurately simulate the wrist joint affected with Rheumatoid Arthritis. To do so, three dimensional models of these two wrist models were developed from computed tomography images which consist of 8 carpal bones, 5 metacarpal bones, the distal radius and ulna. The cartilages were developed based on the shape of the articulation and ligaments were simulated via springs. Hand grip action was simulated as the boundary conditions in which the compressive contact pressure were applied on the model with resultant force of 15.92N in magnitude, distributed over the 5 digits, applied on the metacarpals. Normal, healthy wrist joint was also modelled and functions as the control. Results showed that the stability and load transfer of the wrist after arthroplasty were successfully restored similar to the behaviour of the normal wrist joint. The carpal bones at the model of Rheumatoid Arthritis displaced higher compared to the wrist after treatment, due to the laxity of the ligaments. This high displacement hence leads to the instability of the wrist joint as well as the abnormalities of the load transfer whereby lower load transfer generated at the Rheumatoid Arthritis model. Meanwhile, the model after arthroplasty depicted good stability as well as well load transfer at the forearm in comparison with the normal healthy wrist. These indicate the reliability of the finite element analyses to the clinical findings. These simulations managed to provide the most accurate representations of hand grip action for the pathological wrist as well as the one simulating the treated wrist through arthroplasty. The models developed in this study can be used as a benchmark for simulating other complex human joints as well as simulating their pathological condition and a suitable surgical treatment. Through biomechanical simulation, this project has helped in the understanding of the wrist joint, the pathomechanics of Rheumatoid Arthritis associated with the joint and the development of implants for wrist arthroplasty.