Foot drop is a presentation, not a diagnosis. Localization drives everything that follows — therapy planning, imaging decisions, referral timing, and prognosis.
The two most common culprits are common fibular (peroneal) neuropathy at the fibular head and L5 radiculopathy. At first glance, they can look identical. They are not the same problem, and treating one as the other costs time.
This guide covers the history and exam findings that point one way or the other, the electrodiagnostic patterns that separate them definitively, and a practical sequence for getting to an answer.
At the bedside: what differs
History often points to the site. Ask about onset, positions, external compression, and back symptoms.
Common fibular neuropathy is frequently compressive at the fibular head. Leg crossing, prolonged squatting, significant weight loss, casts or braces, bedrest, and surgical positioning are all common antecedents. Lateral knee pain or paresthesia may be present. Symptoms are typically distal to the knee, and back pain is not part of the picture.
L5 radiculopathy more often comes with low back pain, sometimes with buttock or lateral thigh radiation. Symptoms may vary with lumbar position, coughing, or Valsalva. A history of disc disease or stenosis is common, and sitting, bending, or lifting may aggravate.
The exam finding that does the most work
Inversion.
Tibialis posterior is innervated by the tibial nerve but is L5-predominant. That single fact separates the two conditions more reliably than anything else at the bedside.
- Preserved inversion with weak dorsiflexion and eversion points toward fibular neuropathy. The lesion is distal to the L5 root, so an L5 muscle outside the fibular distribution is spared.
- Weak inversion alongside weak dorsiflexion suggests L5 radiculopathy, because the involvement follows the myotome rather than a single peripheral nerve.
Hip abduction weakness, when present, further favors a root-level process. Plantarflexion is generally preserved in both.
Sensory distribution. Fibular neuropathy typically affects the dorsum of the foot and lateral leg, sparing the plantar surface and anything above the knee. L5 radiculopathy follows a dermatomal pattern that may extend proximally into the thigh or buttock.
Reflexes. Usually unhelpful here. Reflexes are typically normal in fibular neuropathy, and there is no pathognomonic L5 reflex. An attenuated Achilles reflex suggests S1 involvement rather than isolated L5.
Provocative maneuvers. A Tinel sign at the fibular head may reproduce paresthesia in fibular neuropathy. Lumbar extension-rotation or root tension testing may aggravate L5 symptoms.
The electrodiagnostic patterns
This is where the distinction becomes objective. NCS and needle EMG together confirm localization and characterize the injury as axonal, demyelinating, or mixed.
Sensory nerve action potentials
L5 radiculopathy: SNAPs are typically normal. The dorsal root ganglion sits proximal to the compression, so peripheral sensory axons remain intact. Expect normal superficial fibular and sural responses.
Fibular neuropathy: The superficial fibular SNAP is often reduced or absent distal to the lesion.
Timing caveat: in acute presentations, SNAP abnormalities may lag 10 to 14 days behind onset because of Wallerian degeneration. A study performed too early can mislead.
Motor nerve conduction
Fibular neuropathy at the fibular head: The peroneal motor response shows conduction block or focal slowing across the fibular head, with reduced amplitude where axonal loss has occurred. Tibial motor studies are normal.
L5 radiculopathy: Motor conductions are usually normal, since the lesion sits proximal to the segments being studied.
Needle EMG
L5 radiculopathy: Denervation appears in L5-innervated muscles across multiple peripheral nerve distributions — tibialis anterior, extensor hallucis longus, tibialis posterior, peroneals, and frequently gluteus medius. Paraspinal denervation supports a root-level process.
Fibular neuropathy: Denervation is confined to fibular-innervated muscles distal to the fibular head. Tibialis posterior is normal. Paraspinals are normal.
The critical caveat: a normal EMG does not exclude radiculopathy, particularly early in the course or in non-axonal cases. Electrodiagnostic findings are always interpreted alongside the clinical picture.
A practical sequence
1. Screen for red flags and establish the timeline. Acute foot drop with severe back pain, trauma, or a progressive deficit warrants expedited imaging and specialty input rather than a routine workup.
2. Map the weakness precisely. Test dorsiflexion, extensor hallucis longus, eversion, inversion, hip abduction, and plantarflexion. Inversion is the discriminator.
3. Define the sensory boundary. Distal-only involvement of the dorsum and lateral leg favors fibular neuropathy. Dermatomal spread with proximal radiation favors L5.
4. Palpate and provoke. Tinel at the fibular head. Assess for external compression sources. Test lumbar maneuvers for symptom reproduction.
5. Order targeted electrodiagnostics. Request superficial fibular and sural SNAPs, motor conduction across the fibular head, and needle EMG that specifically includes tibialis posterior and paraspinals. Those two muscles are what separate a peripheral neuropathy from root-level disease, and studies that omit them frequently cannot answer the question you asked.
6. Pair with imaging where indicated. Lumbar MRI when radiculopathy is suspected or a deficit is progressing. Imaging of the fibular head region when a mass, ganglion, or scarring is a consideration.
7. Act on the localization. With the site, mechanism, severity, and chronicity documented, treatment sequencing becomes a clinical decision you can make with confidence rather than an inference.
What the report should tell you
A useful electrodiagnostic report answers the questions you asked, in terms you can act on:
- Localization. Peripheral nerve, root level, plexus, or generalized
- Mechanism. Axonal, demyelinating, or mixed
- Severity. Graded, not just present or absent
- Chronicity. Acute, chronic, or evidence of reinnervation
- Clinical correlation, stated plainly
Severity and reinnervation patterns are what inform prognosis and follow-up intervals. A report that says only “abnormal study” has not done its job.
Working with EMG Solutions
We are an electrodiagnostic testing company. All of our providers are physical therapists board certified in clinical electrophysiology through the American Board of Physical Therapy Specialties, and we have performed over 70,000 cases.
Same-day reports. Testing and reporting happen the same day the study is performed. We can often accommodate a same-day referral or a STAT read.
On-site at your practice. We contract with hospitals and clinics to provide EMG/NCS in house. We bring the equipment, electrodes, and needles; you provide a treatment room and table. Your clinic bills and collects, and we invoice monthly. We are already credentialed with nearly all major payors in the Southeast, so adding the service is generally a matter of adding a location. Details are on our partners page.
Or refer to us. We also see patients at our clinic locations in Athens and Huntsville, Alabama.
Coverage. Our providers hold licensure and specialized certification in Alabama, Georgia, and Florida, and we perform on-site services throughout Alabama, Florida, Georgia, Kentucky, North Carolina, Tennessee, and Texas.
Referral guidance. In general, patients with numbness, tingling, radiating pain, or weakness lasting 21 days or longer are appropriate for referral. A full list of indications is on our partners page. Note that payers require NCS and EMG be performed together and on the same day.
Physicians at Hughston Clinic have referred to EMG Solutions since 2003, and frequently ask our specialists to compare or repeat studies performed elsewhere.
Meet our providers, see our FAQ, or contact us at info@emgsolutions.com or 334-318-9023.
In summary
Preserved inversion with a sensory boundary below the knee points toward common fibular neuropathy. Inversion or hip abduction weakness with dermatomal radiation points toward L5 radiculopathy.
NCS and needle EMG settle it — SNAP preservation in root-level disease, focal conduction block or slowing across the fibular head in neuropathy, and a denervation pattern that either respects a single peripheral nerve or follows the myotome.
When you need that answer quickly, we can usually have it to you the same day.
