Quantification of weakness caused by distal median nerve lesion by dynamometry.

INTRODUCTION: In the assessment of hand and upper limb function, grip strength is of major importance. Use of the JAMAR dynamometer has been an accepted test of grip strength and routinely part of the physical examination.

PURPOSE OF THE STUDY: The aim of this study was to determine by means of a median nerve block simulating a patient group if the measurement of different types of grip force can improve the quantification of impairment of the hand beyond the sole power grip measurements.

METHODS: In 29 healthy volunteers, grip force measurement was done by the JAMAR dynamometer for power grip and by a pinch grip dynamometer for pincer grip, precision grip, pinch grip, and palmar abduction. At the power grip, the force of digit 2-5 was measured separately by a sensor glove. For each measurement, 3 trials were recorded subsequently.

STUDY DESIGN: A within-subject research design was used in this prospective study. Each subject served as the control by preinjection measurements of grip and pinch strength. Subsequent measurements after median nerve block were used to examine within-subject change.

RESULTS: In power grip, there was no significant reduction of maximum grip force with median nerve block compared with grip force without block. By measuring the finger forces by a sensor glove, a reduction of force at the individual fingers was found compared with the setting with no block, although significant only at the middle finger (P < .017). With median nerve block, average grip force decreased significantly 20% in pincer grip (P < .021), 29.5% in pinch grip (P < .002), 39.5% in precision grip (P < .001), and 70.7% in palmar abduction (P < .013).

CONCLUSIONS: These experiments suggest a minor role of the measurement of the power grip force in the diagnostics of distal median nerve block with the dynamometer, which could not be substantially improved by the digit forces and the force distribution of the individual fingers. The assessment of other grip forms, such as pincer grasp, precision grip, pinch grip, and especially palmar abduction, leads to a relevant improvement in the diagnostics of distal median nerve lesion.

LEVEL OF EVIDENCE: II.