Computational Biomechanics of the Wrist Joint

In this chapter, information on the wrist anatomy, kinematics and its mechanical behaviours is presented. It commences with a brief explanation on the complexity of the joint, which covers the structure of its hard and soft tissues. All the eight bones constructing the joint were categorized into several groups according to their respective positions. The associated tendons together with five main muscles were well identified in the literature, and thus sufficiently presented in this chapter. This complex joint with numerous articulations appears with many articular cartilages, thus the function are thoroughly explained in this chapter. Further details are presented in the following subsections, which cover description on the structure of each bone, the elements constructing the articular cartilage together with the associated pathology condition and the ligamentous structure. All of these components are essential to bring functions to the joint, allowing its mobility and sustainability. Information on the kinematics of the joint is presented in the last sub-section. This chapter provides sufficient information to assist understanding for the subsequent chapters.

Previous experimental and computational studies have outlined several properties and behaviours of the wrist joint. This chapter compiled relevance inputs associated with the biomechanical considerations of the joint, consisting of contact analyses at the articulations and load transmission throughout the joint. The succeeding sections present information on the biomechanical properties of the cartilages and ligamentous structure. It was addressed that due to difficulties in accessing the articulations in the wrist joint, investigations on the articular cartilages were mainly done through computer simulations. For the ligaments, a typical stress strain curve was used to mimic its mechanical behaviour. The principal load behaviour of ligaments with respect to their elongation during constant elongation-rate has evident the existence of the toe-regions, thus addressing its viscoelastic behaviour. Information on current methods in biomechanical modelling—rigid body spring and finite element—is also presented. Greater emphasize was given to the finite element method due to its appropriateness in performing contact analysis in the wrist joint. Facts and findings from previous finite element studies were included to support future understanding.

This chapter begins with information on the pathological conditions associated with the wrist joint. The following section discussed in detail on the rheumatoid arthritis, as it is the most critical disease affecting the joint. Generally, there are three main symptoms: synovial proliferation, cartilage destruction and ligaments laxity. The disease progresses with several cascade events known as pathophysiology. Scapholunate advanced collapse (SLAC) and the destruction of the capitolunate articulation were among of them. The severity of the disease differs according to several categories or classifications established by previous researcher—Larsen-Daale-Eek, Wrightington, Simmen and Hubber. As far as the treatment was concerned, the most problematic option is the wrist arthroplasty attributed to the loosening of the implant and metacarpal perforation, despite of its advantage in preserving joint motion. This option, thus less preferred by medical practitioners as compared to the arthrodesis or bone fusion. However, as the technology progresses, the designs of the implants for arthroplasty were found to be better and better, promising a more reliable treatment for the rheumatic wrist.

The finite element method was used to perform contact analysis in the wrist joint, thus requires its model construction preceding any analyses. The steps and procedures are as explained in this chapter. The three-dimensional model of the healthy wrist was constructed from the CT images of a healthy volunteer. Segmentations were performed on CT images selecting the regions of the cortical and the cancellous bone. The completed three-dimensional model was then constructed consisting of solid linear first order tetrahedral elements. As no soft tissues appeared in CT images, manual constructions of it were performed. The articular cartilages were modelled by extruding the articulating surfaces with a thickness size half of the minimum distance between the two bones. Set of links were used to simulate the ligamentous structure. The model was then compared with anatomical software for precision, assuring its reliability for future consumption.

This chapter presents the information on the biomechanical analysis of the rheumatic wrist using the finite element method. This study was designed to better understand the biomechanical behaviour of the diseased wrist, thus assuring better future treatments. The three-dimensional model of the wrist affected by rheumatoid arthritis was constructed from CT images of the healthy volunteer, by considering ten characteristics involving three main symptoms and seven pathophysiology criteria of the disease. Comparison was made between the simulated healthy wrist which functions as control and the rheumatic wrist model. Both models were assigned with the same loading simulating static hand grip action. It was revealed from the finite element analyses that the RA model produced ten times higher contact pressure at the articulations in comparison with the healthy model. Additionally, normal physiological load transfer changed from primarily through the radial side to an increased load transfer of 5 % towards the ulnar. These significant findings recommend that future treatments should be able to avoid any unphysiological impacts as addressed in this study.

This chapter presents information on finite element analyses (FEA) of stress distribution and contact pressure with the carpal articulation following total wrist arthroplasty (TWA) for rheumatoid arthritis (RA) of the wrist. Results from the previous analyses on the healthy and rheumatic wrist were used for comparison. A TWA model was developed based on parameters of a wrist implant named ReMotion™ total wrist system, and was then applied with the same boundary condition (static hand grip action) as the other two models. FEA has revealed that the contact pressure for the TWA model was five times lower than the RA model. Despite this encouraging finding, small variations in the amount of stress distribution were still present when compared to the healthy model. This comes to a conclusion that the used of TWA could reduces the high contact pressure induced in the RA model thus improving the diseased condition, however, there are rooms for improvement for TWA procedure to restore the biomechanical behaviour of the healthy wrist joint.