Semmes-weinstein monofilaments: influence of temperature, humidity, and age

To determine whether the buckling force of Semmes-Weinstein monofilaments is influenced by changes in temperature, humidity, and aging.

We tested 16 Semmes-Weinstein monofilaments from North Coast Medical, varying in age from new to 12 years old. From each kit, we used the 2.83/0.07 g, 3.61/0.4 g, 4.31/2g, and 4.56/4 g filaments. Four observers tested the filaments under temperature/humidity conditions of 26°C/33%, 26°C/80%, 37°C/33%, and 37°C/80%.

Air temperature and humidity both significantly influence buckling force. At 26°C/33% the buckling force varies by an average of 2% from the standard data supplied by the manufacturer, whereas in the other 3 conditions (26°C/80%, 37°C/33%, and 37°C/80%), the buckling force can decrease by as much as 39%. Effect of age was small and not clinically relevant.

The significant changes in buckling force of the Semmes-Weinstein monofilaments in different temperature and humidity conditions might lead to a potential misinterpretation by the examiner regarding the level of peripheral nerve function loss. This could lead to incorrect diagnosis and treatment.

Examiners should be aware when using Semmes-Weinstein monofilaments that the environmental effects of temperature and humidity can affect the accuracy of measurement.