Peripheral median nerve block impairs precision pinch movement

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Clin Neurophysiol. 2006 Jul 31

Peripheral median nerve block impairs precision pinch movement.

Li ZM, Nimbarte AD.

Hand Research Laboratory, Departments of Orthopaedic Surgery and

Bioengineering, University of Pittsburgh, Pittsburgh, PA 15213, USA.

OBJECTIVE: The objective of this study was to investigate the effects

of a simulated peripheral median nerve lesion on precision pinch

movement by the thumb and index finger.

METHODS: A median neuropathy was created by blocking the median nerve

at the wrist using an anesthetic. The subjects (n=5) were asked to

perform pulp-to-pulp precision pinch movements before and after the

nerve block. Digit motion data was obtained with a marker-based

motion analysis system.

RESULTS: The radial offset of the thumb tip, as defined by the

minimum distance of the thumb tip to the flexion-extension plane of

the index finger, showed an increase of 11.2mm after the nerve block.

For the thumb, the nerve block caused a decrease in the range of

motion at the metacarpophalangeal (MCP) joint, and a compensatory

increase in the range of motion at the interphalangeal (IP) joint.

The range of motion ratio (MCP:IP) changed from 1:4.8 (pre-block) to

1:1.0 (post-block). The maximum flexion angle at the MCP joint

increased from 18.8 degrees (pre-block) to 33.7 degrees (post-block),

and maximum flexion angle at the IP joint decreased from 42.6 degrees

(pre-block) to 18.8 degrees (post-block). For the index finger, the

nerve block caused a decrease in the range of motion at the MCP

joint, and compensatory increases in the ranges of motion at the

proximal and distal interphalangeal (PIP and DIP) joints. The range

of motion ratio (MCP:PIP:DIP) changed from 1:1.1:0.7 (pre-block) to

1:2.4:1.8 (post-block). The maximum flexion angle at the MCP joint

decreased from 56.8 degrees (pre-block) to 34.6 degrees (post-block),

and the maximum flexion angle at the PIP joint increased from 51.2

degrees (pre-block) to 76.0 degrees (post-block), but the change at

the DIP joint was insignificant.

CONCLUSIONS: The median nerve block caused remarkable degradation of

the pinch performance as quantified by an inaccurate pulp-to-pulp

contact of the thumb to the index finger and an alteration of joint

motion of the digits. SIGNIFICANCE: Many fine manual tasks require

accurate pulp-to-pulp positioning of the thumb to the index finger.

Within the hand, the median nerve is critical to the fine

sensorimotor function due to the motor supply and the sensory endings

to the thumb and index finger. People with median neuropathies (for

example, carpal tunnel syndrome) experience clumsiness while

performing simple manual tasks. The current approach to the

examination of precision pinch movement may be utilized to quantify

the apparent hand clumsiness observed in individuals with peripheral

neuropathy such as carpal tunnel syndrome.