The Semmes-Weinstein monofilament is a tool used to assess touch sensitivity. It consists of a single, calibrated nylon fiber attached to a handle. These filaments are produced in various thicknesses, each designed to buckle and exert a specific, repeatable amount of force when pressed against the skin. This allows a healthcare provider to measure sensation in a standardized way.
This non-invasive instrument evaluates a symptom, not a condition, and is performed without causing pain. Its design allows for a precise application of pressure, making it a reliable method for tracking changes in sensory perception over time.
Purpose of the Monofilament Test
The primary function of the monofilament test is to screen for peripheral neuropathy, a condition characterized by a loss of sensation, particularly in the extremities. It is frequently used for individuals with diabetes, who are at a heightened risk for this nerve damage. The test is a method for detecting Loss of Protective Sensation (LOPS), the inability to feel stimuli that could cause harm.
Identifying LOPS is important for preventing serious foot-related complications. When a person cannot feel minor injuries like cuts, blisters, or pressure from ill-fitting shoes, these problems can go unnoticed. Without proper care, these wounds can develop into ulcers, become infected, and in severe cases, may necessitate amputation. Early detection of sensory loss allows for preventative measures.
This screening is a component of diabetic foot care that helps stratify a patient’s risk for developing foot ulcers. Based on the findings, a clinician can provide education and resources to mitigate potential injuries.
The Testing Procedure
A healthcare provider will begin by explaining the test and touching the filament to a sensitive area, such as the patient’s hand or arm, so they know what to expect. The patient is then asked to close their eyes or look away to ensure their responses are based on touch and not sight.
The provider will press the monofilament against specific sites on the foot. The filament is applied perpendicular to the skin’s surface with enough force to make it bend into a C-shape for about 1.5 seconds. The patient is instructed to say “yes” each time they feel the sensation. Common testing locations include the bottom of the big toe, the ball of the foot, and the heel.
To ensure accuracy, the provider may perform a “sham” application where the filament does not touch the skin. This helps to verify that the patient is responding accurately. The process is painless and takes only a few minutes to complete for both feet.
Understanding the Results
The standard monofilament used for screening for LOPS is the 5.07, which delivers 10 grams of force when it bends. The inability to detect this filament at one or more standardized sites on the plantar surface of the foot is considered a positive finding for LOPS.
A result indicating LOPS means the patient has a higher risk of developing foot ulcers. Because they cannot reliably feel minor trauma, they are less likely to notice small wounds before they become serious. This lack of sensory feedback can lead to repeated, unnoticed pressure on certain areas of the foot, causing tissue breakdown.
When a patient is found to have LOPS, their healthcare provider will recommend specific preventative strategies. These include daily self-inspections of the feet, guidance on selecting appropriate footwear, and counseling on proper foot hygiene. More frequent clinical foot examinations are also advised to monitor for any changes.