Relation between First Metacarpal Head Morphology and First Metacarpophalangeal Joint Degenerative Joint Disease: A Computer Model.

Abstract

Background: Degenerative Joint Disease (DJD) of the first Metacarpophalangeal (MCP) joint, can severely impair hand function due to pain, stiffness, and reduced range of motion. Anatomical variations in metacarpal head morphology may play a critical role in altering joint biomechanics and stress distribution, potentially accelerating cartilage wear and osteoarthritis progression.

Objective: This study aimed to evaluate the biomechanical impact of different first metacarpal head morphologies on stress distribution within the MCP joint under various positions using computer simulation.

Material and methods: In this computer simulation study, three-dimensional models of the thumb MCP joint were reconstructed from Computed Tomography (CT) scans of healthy subjects. The models were adjusted to represent flat, biplanar, and convex metacarpal head morphologies and were simulated in three positions: neutral, 20° flexion, and 20° extension. Computer simulation was performed using Analysis System (ANSYS) to calculate von Mises stress distributions. Descriptive statistics and one-way Analysis of Variance (ANOVA) were applied to compare stress values between groups.

Results: The flat metacarpal head exhibited the highest stress concentrations, peaking at 138 MPa in 20° extension. Biplanar morphology showed moderate stresses, while the convex shape demonstrated the lowest stress, with a maximum of 58 MPa. The analysis confirmed significant differences between groups (P-value=0.039). Stress increased notably in flexion and extension positions compared to neutral across all morphologies.

Conclusion: Metacarpal head morphology and joint positioning significantly influence MCP joint biomechanics. Flat and biplanar shapes increase stress concentration, potentially elevating DJD risk. Convex morphology offers better stress dispersion, indicating a biomechanical advantage.