What are the specific locations on the foot to check for sensation in a diabetic patient using a monofilament test?

Monofilament Testing Sites for Diabetic Foot Examination

The three specific sites that should be tested on each foot during a diabetic monofilament test are the plantar surface of the great toe (hallux), the third metatarsal head, and the fifth metatarsal head. 1

Proper Monofilament Testing Technique

When performing the monofilament test on diabetic patients, follow this structured approach:

1. Testing Environment:

   • Conduct the examination in a quiet, relaxed setting
   • First demonstrate the sensation on the patient's hands or forehead so they know what to expect

2. Patient Positioning:

   • Ensure the patient cannot see where you are applying the filament
   • Position the patient comfortably with foot exposed

3. Application Technique:

   • Use a 10g (5.07 Semmes-Weinstein) monofilament
   • Apply the monofilament perpendicular to the skin surface
   • Use sufficient force to cause the filament to bend or buckle
   • Hold contact for approximately 2 seconds total (approach, contact, removal)
   • Avoid sliding the filament across skin or making repetitive contact at the same site
   • Avoid calluses, ulcers, scars, or necrotic tissue

4. Testing Protocol:

   • Test each of the three sites on both feet
   • Apply the monofilament twice at each site
   • Include at least one "mock" application where no filament is applied
   • Ask the patient whether they feel pressure and where they feel it
   • Protective sensation is present if the patient correctly answers two out of three applications

Clinical Significance

Proper monofilament testing is crucial for early detection of diabetic peripheral neuropathy, which significantly increases the risk of foot ulceration and subsequent amputation. The monofilament examination has been shown to have better reproducibility compared to other neurological examination techniques 2.

Research indicates that the monofilament test focusing on these three specific sites (great toe, third metatarsal, and fifth metatarsal) can detect 90% of patients with peripheral neuropathy 3. This simplified approach makes the test more practical in clinical settings while maintaining excellent sensitivity.

Common Pitfalls to Avoid

• Monofilament degradation: Be aware that monofilaments lose buckling force with repeated use. Consider replacing after 10 patients or 100 compressions 1
• Inadequate pressure: Failing to apply enough force to cause the filament to buckle
• Testing over calluses: This can give false negative results as thickened skin reduces sensitivity
• Skipping mock applications: These are essential to detect patients who may be guessing
• Inconsistent technique: Varying the duration or pressure of application between sites

By following this standardized approach to monofilament testing, clinicians can effectively screen for loss of protective sensation in diabetic patients, allowing for earlier intervention and potentially preventing devastating complications like foot ulceration and amputation.