Effects of Different Tightrope Angles on Thumb Metacarpal Subsidence

Overview

Thumb basal joint arthritis, also known as carpometacarpal (CMC) joint arthritis, is a common condition that occurs in the hand. A trapeziectomy (removal of the trapezium bone) followed by a suture button suspensionplasty can be used to treat thumb basal joint arthritis. A suture button suspensionplasty involves inserting a tightrope from the thumb metacarpal to the index metacarpal; this prevents it from subsiding towards the wrist due to a lack of support from below, after the removal of the trapezium. OBJECTIVE: In this study, we sought to determine the optimal trajectory for the tightrope in order to prevent subsidence of the thumb metacarpal. METHODS: The software OpenSim was used to model different positions for the tightrope and to see how much the thumb metacarpal would subside with respect to each configuration during simulated thumb pinch. Each simulation was able to calculate the distance the thumb metacarpal subsided during pinch for 0.16 seconds. RESULTS: The results showed that when the tightrope is placed at a higher angle, specifically the T0-I5 position (thumb-0 index-5), the thumb metacarpal will subside the least, subsiding approximately 0.50cm. CONCLUSION: While a higher angled tightrope trends to a smaller amount of thumb metacarpal subsidence, it only subsided 0.05cm less than the worst performing tightrope position, specifically the T5-I5 position. This slightly decreased subsidence may not have a significant effect, clinically. Future studies may include modelling other tightrope trajectories, measuring more thumb motions/activities, and measuring subsidence with repetitive loading to predict long-term thumb metacarpal subsidence.

Competition history

• AJAS 2026 Category not listed

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