Due to the potential wide variations in monofilament manufacture, all studies using the monofilaments need to report their source of monofilaments, specific calibration, diameter size of monofilament used, and length.

 

In order to compare results from testing with normative studies, the monofilament length should be identical to the 38 mm length of the filament used in the studies. Currently some manufacturers are producing monofilaments at different lengths, and these cannot be compared to normative studies even if the manufacturer used standard lengths in previous normative studies but now at different lengths unless additional comparison studies are done.  Bell-Krotoski JA, Fess EE, Hiltz D, Figarola J: "Threshold Detection and Semmes Weinstein Monofilaments: A Comparative Study", J Hand Ther, 8:155-162, 1995.

 

Measurement of force of application (with a given size monofilament of a specific diameter) is the same as measurement of pressure on application - there is no change in the magnitude of strength, only the way it is calculated; pressure is force/unit area.  The stimulus can be reported in either calculation as desired using a table of the diameters.  But, since the area of a given monofilament is always constant, it is easier for clinicians to understand the units of force rather than pressure.  Reporting force (with constant area) is considered more accurate for the monofilaments, because the monofilaments bend, making the entire area their tip potentially not in full contact with the skin when applied, but rather a crescent shaped edge.

 

Currently our instrument measurement system is being redesigned. When up and running, our monofilaments  are calibrated on tiny strain gauge load cells to assure they fall within specifications for respective monofilament size.

 

Certification of force of application will be available on request for research projects where exacting force of application should be reported in studies. Our plan is to offer certification of force of application i.e. certification of calibration for testing sets professionals use in research studies.  Through the use of instrument measurement equipment designed to sensitively and accurately measure the dynamic force of application of the nylon monofilaments, we will offer the most advanced calibration possible. Check back for further details when available.

Measurement of Diameter: A micrometer is used to measure the diameter of the monofilament (available at Sears or through scientific catalogues).*

Measurement of Stimulus Force of Application: Measurement of the monofilament dynamic force of application requires sophisticated instrumentation that can accurately show and measure its dynamic force and vibration.  Top loading weight and balance scales typically used in laboratories have been found not sufficiently accurate, and measurement required the design of a specific dedicated measurement system.**

*, ** Bell JA, Buford WL: "The Force Time Relationship of Clinically Used Sensory Testing Instruments", Presented at the 37^th Annual Meeting of the American Society for Surgery of the Hand, Aurora, Colorado, 1982.