The effect of trapeziometacarpal joint passive stiffness on mechanical loadings of cartilages.

Hypermobility of the trapeziometacarpal joint is commonly considered to be a potential risk factor for osteoarthritis. Nevertheless, the results remain controversial due to a lack of quantitative validation. The objective of this study was to evaluate the effect of joint laxity on the mechanical loadings of cartilage. A patient-specific finite element model of trapeziometacarpal joint passive stiffness was developed. The joint passive stiffness was modeled by creating linear springs all around the joint. The linear spring stiffness was determined by using an optimization process to fit force-displacement data measured during laxity tests performed on eight healthy volunteers. The estimated passive stiffness parameters were then included in a full thumb finite element simulation of a pinch grip task driven by muscle forces to evaluate the effect on trapeziometacarpal loading. The correlation between stiffness and the loading of cartilage in terms of joint contact pressure and maximum shear strain was analyzed. A significant negative correlation was found between the trapeziometacarpal joint passive stiffness and the contact pressure on trapezium cartilage during the simulated pinch grip task. These results therefore suggest that the hypermobility of the trapeziometacarpal joint could affect the contact pressure on trapezium cartilage and support the existence of an increased risk associated with hypermobility.

Relationship between trapeziometacarpal joint morphological parameters and joint contact pressure: a possible factor of osteoarthritis development.

The trapeziometacarpal (TMC) joint is the one of the hand joints that is most affected by osteoarthritis (OA). The objective of this study was to determine if specific morphological parameters could be related to the amount of pressure endured by the joint which is one of the factors contributing to the development of this pathology. We developed 15 individualized 3D computer aided design (CAD) models of the TMC joint, each generated from the CT scan of a different participant. For each participant, we measured several crucial morphological parameters: the width and length of the trapezium bone and dorso-volar and ulno-radial curvature, of the trapezium and the metacarpal bone. Each CAD model was converted into a finite element model, of both bones and the cartilage located in between. The joint forces applied during pinch grip and power grip tasks were then applied in order to estimate the contact pressures on joint cartilage for each model. Correlations between joint contact pressures and morphology of the trapezium and the metacarpal bone were then analysed. Important variations of TMC joint pressures were observed. For both pinch and power grip tasks, the strongest correlation with joint contact pressure was with the dorso-volar curvature of the trapezium bone. Our findings indicate that dorso-volar curvature of the trapezium bone has a significant impact on mechanical loadings on the TMC joint. This contributes to understanding the prevalence of OA in certain patients.

The effect of index finger distal interphalangeal joint arthrodesis on muscle forces and adjacent joint contact pressures.

Distal interphalangeal joint arthrodesis is a frequent surgical operation performed to treat severe arthritis. Nevertheless, the angle selected when fusing the joint is arbitrarily chosen without any quantified data concerning its mechanical effects, thus preventing the optimal choice for the patient. In the current study, we realized an experiment and developed a numerical model to investigate the effect of fusion angle on the biomechanics of adjacent non-operated joints. Six participants performed a pinch grip task while arthrodesis was simulated with a metal splint. Kinematic and force data were recorded during this task and used in a biomechanical model to estimate contact pressures in adjacent joints. The biomechanical model involved combining a multibody system and a finite element method. Results showed that the angle of any distal interphalangeal joint arthrodesis influences index finger kinematics and maximal grip force in several participants. For one participant, in the arthrodesis simulation, we observed an increase of 1.9 MPa in the proximal interphalangeal joint contact pressure. Our results provide quantified information about the biomechanical consequences of this surgical operation and its potential long-term effects.