How to Check for Foot Drop
To assess for foot drop, observe the patient walking and perform a focused neurological examination that includes testing ankle dorsiflexion strength (asking the patient to pull their foot upward against resistance), observing for steppage gait, and conducting a 10-g monofilament test with at least one additional sensory assessment (pinprick, vibration with 128-Hz tuning fork, or ankle reflexes) to identify loss of protective sensation.
Clinical Observation
Begin by watching the patient walk:
- Look for steppage gait: The patient lifts their knee higher than normal to clear the dropped foot
- Observe foot slap: The foot may slap down when making contact with the ground
- Check for toe dragging: The toes may scrape the floor during the swing phase
Motor Examination
Test ankle dorsiflexion strength 1:
- Ask the patient to pull their foot upward (dorsiflex) against your resistance
- Grade strength using the Medical Research Council (MRC) scale:
- Grade 0: No contraction
- Grade 1: Flicker of contraction
- Grade 2: Movement with gravity eliminated
- Grade 3: Movement against gravity but not resistance
- Grade 4: Movement against some resistance
- Grade 5: Normal strength
Test ankle eversion:
- Have the patient turn the sole of their foot outward against resistance
- Weakness suggests peroneal nerve involvement
Sensory Examination
The neurological exam should identify loss of protective sensation (LOPS) 2, 3:
10-g monofilament test (primary test) 4, 2:
- Test three sites on each foot (typically plantar surface of first toe, third metatarsal head, and fifth metatarsal head)
- Apply perpendicular to skin until filament bends
- Hold for ~2 seconds
- Ask patient "yes/no" if they feel pressure and which foot
- Test each site twice with one mock application
- Protective sensation is present if patient correctly answers 2 out of 3 applications
Add at least ONE additional test 2, 3:
Vibration (128-Hz tuning fork) 4:
- Apply to bony prominence on dorsal distal phalanx of first toe
- Apply perpendicularly with constant pressure
- Ask when vibration stops
Pinprick: Test sensation in affected dermatomes
Temperature: Use warm/cold objects to test discrimination
Ankle reflexes: Tap Achilles tendon
Interpretation: Absent monofilament sensation suggests LOPS; at least two normal tests (with no abnormal test) rules out LOPS 2, 3.
Additional Assessments
Inspect the foot and lower extremity 5:
- Check for muscle atrophy in anterior compartment
- Look for foot deformities (hammertoes, prominent metatarsal heads)
- Assess skin integrity
- Examine for signs of trauma or compression at fibular head
Palpate pulses 6:
- Dorsalis pedis
- Posterior tibial
- Popliteal
- Femoral
Test proprioception:
- Move the great toe up or down while patient's eyes are closed
- Ask patient to identify direction of movement
Localization Strategy
The examination helps localize the lesion 1, 7, 8:
- L5 radiculopathy: Weakness of dorsiflexion AND inversion, sensory loss in L5 distribution, possible back pain
- Peroneal nerve at fibular head (most common): Weakness of dorsiflexion and eversion, sensory loss over dorsum of foot, sparing of inversion
- Sciatic nerve: Additional weakness of ankle plantarflexion and knee flexion
- Anterior horn cell disease: Fasciculations, no sensory loss
Common Pitfalls
- Don't rely solely on pulse examination: Absence of dorsalis pedis pulse can occur in healthy patients; posterior tibial pulse absence is more specific 6
- Don't miss bilateral involvement: Test both feet even if complaint is unilateral
- Don't forget to ask about leg crossing: Habitual leg crossing is a frequent reversible cause of peroneal neuropathy 1
- Don't overlook multiple pathologies: 18% of patients have more than one condition contributing to foot drop 9