Peripheral median nerve block impairs precision pinch movement.

Area of Science:

• Neuroscience
• Biomechanics
• Hand Surgery

Background:

• The median nerve is crucial for fine motor control of the thumb and index finger.
• Median neuropathies, such as carpal tunnel syndrome, often lead to hand clumsiness.
• Accurate pulp-to-pulp thumb-index finger positioning is vital for many manual tasks.

Purpose of the Study:

• To investigate the impact of a simulated peripheral median nerve lesion on precision pinch movements.
• To quantify changes in thumb and index finger joint motion during precision pinch after median nerve block.

Main Methods:

• A simulated median neuropathy was induced by blocking the median nerve at the wrist with an anesthetic.
• Five subjects performed pulp-to-pulp precision pinch movements before and after the nerve block.
• A marker-based motion analysis system captured digit motion data.

Main Results:

• Simulated median nerve lesion increased radial offset of the thumb tip by 11.2mm.
• Thumb metacarpophalangeal (MCP) range of motion decreased, with compensatory increases at the interphalangeal (IP) joint (MCP:IP ratio changed from 1:4.8 to 1:1.0).
• Index finger MCP range of motion decreased, with compensatory increases at the proximal and distal interphalangeal (PIP and DIP) joints (MCP:PIP:DIP ratio changed from 1:1.1:0.7 to 1:2.4:1.8).

Conclusions:

• Median nerve block significantly degraded precision pinch performance, leading to inaccurate pulp-to-pulp contact.
• Joint motion patterns of the thumb and index finger were altered following the median nerve block.
• This methodology can quantify hand clumsiness in patients with peripheral neuropathies.