Comprehending Optimality of Finger Flexor Tendon Pulley System Using Computational Analysis

Area of Science:

• Biomechanics
• Biomedical Engineering
• Robotics

Background:

• Existing prosthetic and orthotic designs seldom incorporate the kinetostatics of biological finger tendon-pulley systems (TPS).
• The optimality of biological TPS as a design reference remains largely unexplored.

Purpose of the Study:

• To investigate optimal tendon-pulley system (TPS) configurations for finger flexor mechanisms.
• To determine if biological TPS designs are optimal and in what sense, guiding prosthetic and orthotic development.

Main Methods:

• A parametric study was conducted using a computational model of a compliant, flexure-based finger.
• The pseudo-rigid body method simulated various pulley/tendon attachment points, heights, and widths.
• Analysis focused on achieving high flexion range with low tendon tension, bowstringing, and pulley stresses.

Main Results:

• Three optimal TPS configurations were identified: single stiff pulley, two stiff pulleys, or one stiff and one flexible-inextensible pulley per phalange.
• Biological-like TPS configurations require flexible-inextensible distal pulleys on proximal and intermediate phalanges, mimicking joint and cruciate pulleys.
• Optimal designs balance flexion range with minimized actuation tension, bowstringing, and pulley stress.

Conclusions:

• Biological flexor TPS may have evolved for maximal flexion with minimal tension and stress.
• Findings offer valuable insights for designing efficient hand prosthetics and improving TPS reconstruction surgery.