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.

Mechanical performance comparison of two surgical constructs for wrist four-corner arthrodesis via dorsal and radial approaches.

BACKGROUND: Four-corner arthrodesis, which involves fusing four carpal bones while removing the scaphoid bone, is a standard surgery for the treatment of advanced stages of wrist arthritis. Nowadays, it can be performed using a dorsal approach by fixing a plate to the bones and a new radial approach is in development. To date, there is no consensus on the biomechanically optimal and most reliable surgical construct for four-corner arthrodesis. METHODS: To evaluate them biomechanically and thus assist the surgeon in choosing the best implant orientation, radial or dorsal, the two different four-corner arthrodesis surgical constructs were virtually simulated on a 3D finite element model representing all major structures of the wrist. Two different realistic load sets were applied to the model, representing common tasks for the elderly. FINDINGS: Results consistency was assessed by comparing with the literature the force magnitude computed on the carpal bones. The Von Mises stress distribution in the radial and dorsal plates were calculated. Stress concentration was located at the plate-screw interface for both surgical constructs, with a maximum stress value of 413 MPa for the dorsal plate compared to 326 MPa for the radial plate, meaning that the stress levels are more unfavourable in the dorsal approach. INTERPRETATION: Although some bending stress was found in one load case, the radial plate was mechanically more robust in the other load case. Despite some limitations, this study provides, for the first time, quantified evidence that the newly developed radial surgical construct is mechanically as efficient as the dorsal surgical construct.

Estimation of joint contact pressure in the index finger using a hybrid finite element musculoskeletal approach.

The knowledge of local stress distribution in hand joints is crucial to understand injuries and osteoarthritis occurrence. However, determining cartilage contact stresses remains a challenge, requiring numerical models including both accurate anatomical components and realistic tendon force actuation. Contact forces in finger joints have frequently been calculated but little data is available on joint contact pressures. This study aimed to develop and assess a hybrid biomechanical model of the index finger to estimate in-vivo joint contact pressure during a static maximal strength pinch grip task. A finite element model including bones, cartilage, tendons, and ligaments was developed, with tendon force transmission based on a tendon-pulley system. This model was driven by realistic tendon forces estimated from a musculoskeletal model and motion capture data for six subjects. The hybrid model outputs agreed well with the experimental measurement of fingertip forces and literature data on the physiological distribution of tendon forces through the index finger. Mean contact pressures were 6.9 ± 2.7 MPa, 6.2 ± 1.0 MPa and 7.2 ± 1.3 MPa for distal, proximal interphalangeal and metacarpophalangeal joints, respectively. Two subjects had higher mean contact pressure in the distal joint than in the other two joints, suggesting a mechanical cause for the prevalence of osteoarthritis in the index distal joint. The inter-subject variability in joint contact pressure could be explained by different neuromuscular strategies employed for the task. This first application of an effective hybrid model to the index finger is promising for estimating hand joint stresses under daily grip tasks and simulating surgical procedures.