Lower median nerve block impairs precision grip

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J Electromyogr Kinesiol. 2006 Apr 6

Lower median nerve block impairs precision grip.

Dun S, Kaufmann RA, Li ZM.

Hand Research Laboratory, Department of Orthopaedic Surgery,

University of Pittsburgh, E1641 Biomedical Science Tower, 210 Lothrop

Street, Pittsburgh, PA 15213, USA.

The purpose of this study was to investigate precision grip

impairment caused by a lower median nerve block at the wrist. The

median nerve block was achieved by injecting bupivacaine

hydrochloride into the carpal tunnel, which acutely simulated a

median neuropathy. Seven healthy male subjects were instructed to

grip, lift, and hold an instrumented handle within 60s using

precision grip. The same tasks were performed before and after the

nerve block. Force and torque data were recorded using two miniature

6-component force/torque transducers. The precision grip was

quantified by the safety margin (i.e. the difference between the

actual grip force and the minimal grip force to keep the object from

dropping), the variation of grip force, and the migration area of

center of pressure (i.e. the area defined by the center of pressure

at a digit-transducer surface while holding the handle). Two subjects

were unable to complete the precision grip tasks after the nerve

block, and their data were excluded from the analyses. The median

nerve block caused significant increases (P<0.05) in the safety

margin of the grip force (>50%), the grip force variation (>80%), and

the area of center of pressure migration (>250%). Median nerve block

at the wrist impairs the fine motor control during precision grip.

Our results corroborate the important role played by sensory function

in hand fine motor control. Clinically, the measures related to

precision grip have the potential to quantify impairment of hand

function caused by neuromuscular disorders, to monitor the progress

of a hand disorder, and to evaluate the efficacy of a treatment or

rehabilitation procedure.