Foot Drop – Is It Always a Lumbar Disc?

Foot Drop – Is It Always a Lumbar Disc?

It could also be peroneal nerve entrapment. A drooping foot that you cannot lift upward (foot drop) is a classic sign of an L5 lumbar disc, but the exact same symptom appears when the peroneal nerve on the outer side of the knee is compressed. A tibialis posterior strength test can tell the two apart precisely.

What Is Foot Drop?

The Inability to Lift the Ankle and Toes

The foot drags on the ground when you walk, and the toes catch on the steps when you climb stairs. The hallmark is losing the power to lift the ankle upward (dorsiflexion) or to straighten the toes.

→ There are two main causes: L5 nerve root compression in the lower back, or peroneal nerve entrapment at the knee.

L5 Disc vs Peroneal Nerve Entrapment

Muscle/Function L5 Disc Peroneal Nerve Entrapment
Lifting the Ankle (Dorsiflexion) Weak ✗ Weak ✗
Straightening the Toes Weak ✗ Weak ✗
Turning the Ankle Inward (Inversion)
→ Tibialis Posterior		 Weak ✗ (L5 nerve root innervation) Normal ✓ (via the tibial nerve)
Spreading the Leg Sideways
→ Gluteus Medius		 Weak ✗ (L5 nerve root innervation) Normal ✓
Sensory Changes Lateral lower leg, top of the foot, big toe Lateral lower leg, top of the foot

Tibialis Posterior Strength Test: The Decisive Differentiator

1

Turn the Ankle Inward

Ask the patient to turn the ankle firmly inward (inversion).

2

Examiner’s Resistance

The examiner pushes against the outer side of the foot to apply resistance and grades the strength.

3

Interpreting the Result

Strength normal: Peroneal nerve entrapment (the tibialis posterior runs via the tibial nerve)

Strength weak: L5 disc (compression of the entire nerve root)

Fibular Head Tenderness Test

Checking the Bony Area on the Outer Knee

The peroneal nerve passes around the fibular head (the small round bone on the outer side of the knee). When you press on this area:

  • There is severe tenderness
  • An electric, tingling sensation (Tinel’s sign)
  • The usual leg numbness is reproduced

→ Confirms peroneal nerve entrapment

Why the Peroneal Nerve Gets Compressed

  • Sitting with legs crossed
  • Squatting postures
  • Knee braces or casts
  • Rapid weight loss
  • Prolonged bed rest

Important

If you have been advised to have back surgery for foot drop, be sure to have a fibular head tenderness test and a tibialis posterior strength test before the operation. If it is peroneal nerve entrapment, it can be treated with a simple nerve release or lifestyle correction.

Treatment for Peroneal Nerve Entrapment

We directly relieve the compression around the fibular head.

  • Circulation HD:
    • Releases adhesions around the fibular head
    • Improves circulation around the nerve
    • Reduces nerve sensitivity
  • Lifestyle Correction:
    • No crossing the legs
    • Avoid squatting
    • Use a knee pad
  • Circulation PT:
    • Nerve gliding
    • Ankle strengthening exercises
    • Gait pattern retraining

Frequently Asked Together

Want to Find the Exact Cause of Your Foot Drop?

We evaluate both the lower back and the peripheral nerves to make an accurate diagnosis.

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References

  • Baima J, Krivickas L. Evaluation and treatment of peroneal neuropathy. Curr Rev Musculoskelet Med. 2008;1(2):147-153. PMC2682406
  • Brinjikji W et al. Systematic literature review of imaging features of spinal degeneration in asymptomatic populations. AJNR Am J Neuroradiol. 2015;36(4):811-816. PMID 25430861
  • Koes BW et al. Diagnosis and treatment of sciatica. BMJ. 2007;334(7607):1313-1317. PMID 17585160
  • Erickson M et al. Cervical radiculopathy: a review. Am Fam Physician. 2020;102(11):643-649.