The monofilament is a simple and effective screening tool, which makes it possible to detect the loss of protective sensitivity linked to sensory neuropathy, a major risk factor for ulcerative lesions of the foot in diabetics. It makes it possible to identify diabetic patients at risk of ulcerated lesions of the foot with a high sensitivity, ranging from 66 to 91%.

Composition and structure

The monofilament is in the form of a stylet consisting of a plastic support to which is attached a calibrated nylon filament. The gauge used for screening for the risk of ulcerative lesions is gauge 5,07. Placed perpendicular to the patient’s skin, it bends when a force of 10 grams is applied. Perception of 5,07 monofilament is considered the “protective” plantar sensitivity level, that is, the level of plantar sensitivity for which the patient is not exposed to the risk of ulcerative injury.

Sensory neuropathy is a key marker of the risk of foot ulceration in diabetic patients. His diagnosis is essential. This is because diabetic neuropathy is a disorder of the nervous system that occurs as a result of worsening diabetes. It occurs when the blood sugar level is too high for too long, causing damage to the nerves.

This is why it is recommended that diabetic patients have the sensitivity and condition of their feet checked every year to detect any lesions or wounds (diabetic neuropathy, arteritis, etc.). Depending on the risk of lesions, appropriate preventive and / or curative follow-up is then prescribed by the doctor.

The monofilament can detect diabetic neuropathy by assessing the patient’s sensitivity levels:

• the test is negative if the sensitivity to the monofilament is sufficient, that is to say when the patient has performed at least 2 correct answers out of 3 for each of the 3 application sites;
• the test is positive if the sensitivity is insufficient, that is to say when 2 of the 3 answers are false on at least 1 site. The patient is then considered to be at risk of ulceration because the protection of his foot is no longer ensured.

The review is recommended on an annual basis. It must be carried out in a calm manner as follows:

• first apply the monofilament to the patient’s hands and exert pressure so that he knows how to feel;
• the patient should not see whether or not the examiner is applying the filament or where he is applying it;
• the three sites to be tested on each foot are: the plantar surface of the head of the first metatarsal, the head of the fifth metatarsal and the pulp of the hallux;
• apply the filament perpendicular to the surface of the skin with sufficient force to bulge it, for about 2 seconds;
• do not test on a callus, scar or necrotic tissue;
• do not slide the filament over the skin or make repeated contacts in the area being explored;
• do not make rapid movements. Approach, skin contact, and filament removal should last approximately 1,5 to 2 seconds;
• ask the patient if he feels the applied pressure and if it is located on the left or on the right;
• repeat the application twice at the same site, inserting a “dummy test” during which the filament is not applied (in total: 3 questions per site).

The force, with which the monofilament bends, tends to decrease with the number of uses. In practice, it is therefore recommended not to use it for more than 10 patients in the same day. Beyond 10 uses in the same day, a period of 24 hours without use is necessary.

For disinfection, the monofilament can be immersed in a dilute bleach solution (0,1% sodium hypochlorite solution).

The different models

It was in 1960 that Josephine Semmes and Sidney Weinstein developed the monofilament, to study tactile sensitivity. Its first applications concerned nerve compression syndromes and damage to peripheral nerves of traumatic origin.

Today, the Semmes monofilament—Weinstein 5,07 (10 g) has become the recommended diabetic neuropathy screening tool in primary care in France. Chosen and validated by the International Working Group on the Diabetic Foot to define the presence of a risk of chronic ulceration, it has the advantage of being inexpensive, easy to use and reliable.