Reverse engineering finger extensor apparatus morphology from measured coupled interphalangeal joint angle...

Area of Science:

• Biomechanics
• Human Anatomy
• Kinesiology

Background:

• The extensor apparatus (EA) is crucial for interphalangeal (IP) joint coordination during finger flexion.
• The precise relationship between EA morphology and IP joint coupling is not well understood due to dissection limitations.
• Existing methods struggle to capture the dynamic fiber behavior within the EA during joint motion.

Purpose of the Study:

• To develop a kinematic model of the finger extensor apparatus (EA) that incorporates fiber slackness and tautness.
• To investigate the functional relationship between EA morphology and interphalangeal (IP) joint coupling.
• To validate the model's accuracy against experimental IP joint motion data.

Main Methods:

• A two-dimensional kinematic multi-tendon-string model of the EA was created, including retinacular ligaments.
• Model parameters (string lengths, attachment points) were interactively fitted to previously measured IP joint trajectories from 68 fingers.
• The model's ability to replicate proximal interphalangeal (PIP) and distal interphalangeal (DIP) joint motion was assessed.

Main Results:

• The model accurately reproduced target IP trajectories for PIP joint ranges up to 25°-45°.
• Approximately 50% of models achieved high accuracy across the entire IP joint range, with errors below 12°.
• All models successfully converged to target trajectories during full IP flexion.

Conclusions:

• The developed kinematic model effectively represents functional EA principles and IP joint coupling.
• The model's accuracy suggests its potential utility in biomechanical analysis and clinical applications.
• Potential applications include surgical reconstruction, rehabilitation strategies, and the development of prosthetic replacements for the EA.