Monofilaments

Extract

Semmes–Weinstein monofilaments are a semi-quantitative test of sensory loss. The idea, developed by Josephine Semmes and Sidney Weinstein, was to measure touch-pressure in a standardized way by controlling the force of an applied stimulus to the skin [1]. For this they replaced the ‘hairs’ previously used by Von Frey with more durable plastic filaments of variable diameters. Applied to the skin until they bend the monofilaments deliver the same force irrespective of any difference in observer or their degree of unsteadiness. They have been mostly used by orthopaedic surgeons as a tool for sensibility testing in hand surgery rehabilitation. They most likely test the skin receptor known as the Merkel disc which responds to constant touch-pressure. The original ‘long’ test kit of 20 monofilaments was grouped by five descriptive terms which were delineated by comparing with other tests of sensibility in 200 patients with peripheral nerve problems [2]:

Each monofilament is designated by a number which represents a given force and then grouped into colour-coded ranges. Weinstein developed an enhanced version with a textured rounded tip to create a more consistent area of skin surface contact with less likelihood of slippage (Weinstein Enhanced Sensory Test [WEST]) [1]. This is available as a set of five colour-coded monofilaments, attached to a handle, representing the five levels of sensory thresholds described above. This version is the most appropriate for an occupational health practice (Table 1). There is published age- and sex-matched normative data for WEST monofilaments (men and women age <55 years, 0.035 g-f; age >55 years, women 0.15 g-f, men 0.385 g-f) [3].