How to Perform a Sensory Examination of the Leg
A sensory examination of the leg should be performed using a 10-g Semmes-Weinstein monofilament for pressure sensation and a 128-Hz tuning fork for vibration testing, conducted in a quiet setting with the patient unable to see where testing occurs. 1
Preparation and Setting
- Conduct the examination in a quiet and relaxed environment to minimize distractions and ensure accurate patient responses 1
- First demonstrate the sensation on the patient's hands, wrists, elbows, or forehead so they understand what to expect before testing the legs 1
- The patient must not be able to see where or whether you are applying the testing instrument during the actual examination 1
Monofilament Testing (Pressure Sensation)
Testing Technique
- Use a 10-g (5.07 Semmes-Weinstein) monofilament for assessing protective sensation 1
- Apply the monofilament perpendicular to the skin surface 1
- Apply sufficient force to cause the filament to bend or buckle 1
- The total duration of approach, skin contact, and removal should be approximately 2 seconds 1
- Do not allow the filament to slide across the skin or make repetitive contact at the test site 1
Testing Sites on the Foot
- Test three sites on both feet: typically the plantar surface of the first toe, third metatarsal head, and fifth metatarsal head 1
- Apply the filament along the perimeter of, not on, any ulcer site, callus, scar, or necrotic tissue 1
Scoring Method
- At each site, ask the patient two questions: (1) whether they feel the pressure applied ('yes'/'no'), and (2) where they feel the pressure ('left foot'/'right foot') 1
- Repeat the application twice at the same site, but alternate with at least one 'mock' application where no filament is applied (total of three questions per site) 1
- Protective sensation is present if the patient correctly answers 2 out of 3 applications at each site 1
- Protective sensation is absent with 2 out of 3 incorrect answers, indicating the patient is at risk for ulceration 1
Important Caveats
- Be aware that monofilaments lose their buckling force with extended use, which can affect test reliability 1
- Provide positive feedback and encouragement to the patient during testing 1
Tuning Fork Testing (Vibration Sensation)
Testing Technique
- Use a 128-Hz tuning fork for vibration testing 1
- First demonstrate on the patient's wrists, elbows, or clavicle so they know what to expect 1
- Apply the tuning fork on a bony part on the dorsal side of the distal phalanx of the first toe 1
- The tuning fork should be applied perpendicularly with constant pressure 1
Scoring Method
- Repeat the application twice, but alternate with at least one 'mock' application where the tuning fork is not vibrating 1
- The test is positive (normal) if the patient correctly answers at least 2 out of 3 applications 1
- The test is negative (abnormal) with 2 out of 3 incorrect answers, indicating the patient is at risk for ulceration 1
Proximal Testing if Needed
- If the patient cannot sense vibrations on the big toe, repeat the test more proximally at the malleolus and tibial tuberosity 1
Additional Sensory Modalities
- Cotton wisp testing can also be used to assess light touch sensation 1
- For comprehensive evaluation in research settings, pinprick testing for pain sensation and temperature testing may be included 2, 3
- The combination of pinprick and light touch is adequate for diagnostic purposes in patients with radicular pain 3
Clinical Interpretation
- The monofilament test specifically assesses large fiber function and protective sensation; it does not evaluate small fiber neuropathy (pain, temperature) which may be present even with normal monofilament testing 4
- Abnormal findings indicate loss of protective sensation (LOPS), the primary risk factor for diabetic foot ulceration 4
- Patients with intact sensation across all tested sites do not have clinically significant distal sensorimotor polyneuropathy affecting protective sensation at the time of testing 4