The monofilament test is a quick, non-invasive screening tool used to assess a patient’s protective sensation, particularly in the feet. This examination identifies peripheral neuropathy, a type of nerve damage common in individuals with conditions such as diabetes. Loss of protective sensation means a person may not feel minor cuts, blisters, or pressure sores, which can lead to severe infections and foot ulcers. By detecting this loss early, the test helps healthcare providers identify patients who are at increased risk for serious foot complications and potential amputation.
Essential Equipment and Setup
The examination requires a 10-gram Semmes-Weinstein monofilament, which is a thin nylon thread mounted on a plastic base. This specific monofilament, often labeled as 5.07, is calibrated to exert 10 grams of force when applied to the skin. Before starting, the monofilament should be buckled a few times to remove residual stiffness from storage. The testing environment should be quiet and comfortable to minimize patient distraction and promote an accurate response.
The patient should be positioned either seated or lying down, with their shoes and socks removed. To establish a baseline and familiarize the patient with the sensation, the monofilament should be demonstrated on a non-foot area, such as the hand or forearm. The patient must be instructed to close their eyes during the actual testing and say “yes” whenever they feel the light touch.
Detailed Application Procedure
The monofilament is applied perpendicular to the skin’s surface at specific sites on the foot. The standard protocol typically tests 10 locations, including the tips of the first and third toes, and the areas beneath the first, third, and fifth metatarsal heads on the sole of each foot. The tester should apply the monofilament with a smooth, steady motion, increasing pressure only until the filament bends or buckles into a gentle C-shape.
This buckling confirms that 10 grams of force is delivered to the skin. The contact duration should be approximately one to two seconds before the monofilament is lifted away. The order of application must be randomized so the patient cannot anticipate the next touch point. Avoid applying the filament directly on calloused skin, scars, ulcers, or areas of skin breakdown, as these can provide inaccurate results.
The patient must keep their eyes closed throughout the application procedure to focus only on the sensation. If the patient does not respond at a specific site, the tester may re-apply the monofilament up to two more times to confirm the absence of sensation. Ensure the monofilament does not slide across the skin or make repetitive contact at the same spot.
Interpreting and Clinical Significance of Results
The monofilament test is considered abnormal, or failed, if the patient is unable to perceive the 10-gram force at one or more designated testing sites. An inability to feel the monofilament indicates a loss of protective sensation (LOPS), which is a clear sign of peripheral neuropathy. This means the patient has lost the ability to detect minor trauma.
The loss of this protective mechanism increases the risk of foot ulceration. Patients who fail the test are recognized as being at high risk for these complications, and their results should be documented to track the progression of the neuropathy. An abnormal result often triggers a referral to a specialist, such as a podiatrist, and the implementation of enhanced foot care education and protective footwear recommendations.