Root Origin
- Spinal nerve roots: L4, L5, S1 (via the common peroneal nerve, from the sciatic nerve)
- Plexus: Sacral plexus (through the sciatic nerve → common peroneal nerve)
- Type: Mixed (motor and sensory)
Course
- Division from common peroneal. The deep peroneal nerve branches from the common peroneal nerve as it wraps around the fibular neck, within or just deep to the peroneus longus muscle.
- Anterior compartment entry. The nerve pierces the anterior intermuscular septum and the extensor digitorum longus to enter the anterior compartment of the leg. It is now accompanied by the anterior tibial artery — these two structures travel together for the remainder of the course.
- Anterior leg. The nerve descends the anterior leg on the interosseous membrane, between the tibialis anterior (medially) and the extensor digitorum longus (laterally). It supplies all muscles in the anterior compartment along this course.
- Anterior ankle. The nerve crosses the ankle joint anterior to the tibia, passing deep to the extensor retinaculum (the superior and inferior extensor retinacula). It lies between the extensor hallucis longus tendon (medially) and the extensor digitorum longus tendon (laterally) — the "anterior tarsal tunnel." This is the primary entrapment site.
- Dorsal foot. After passing under the extensor retinaculum, the nerve divides into a lateral motor branch (to the extensor digitorum brevis) and a medial sensory branch (to the first web space).
Motor Distribution
| Muscle | Action | Notes |
|---|---|---|
| anatomy/muscles/tibialis-anterior | Dorsiflexion, inversion | The primary dorsiflexor — loss produces foot drop. L4 myotome. |
| anatomy/muscles/extensor-hallucis-longus | Great toe extension, assists dorsiflexion | L5 myotome test — the most sensitive muscle for detecting L5 weakness |
| anatomy/muscles/extensor-digitorum-longus | Extends toes 2-5, assists dorsiflexion | Anterior compartment |
| anatomy/muscles/peroneus-tertius | Dorsiflexion, eversion | Not present in all individuals |
| anatomy/muscles/extensor-digitorum-brevis | Extends toes 2-4 | The only intrinsic muscle on the dorsum of the foot; innervated by the lateral terminal branch after the ankle |
Sensory Distribution
- First web space. The terminal medial sensory branch supplies only the small patch of skin between the great toe and the second toe on the dorsal foot. This is the smallest sensory territory of any major lower extremity nerve.
- Clinical significance: Testing first web space sensation is the specific sensory test for the deep peroneal nerve. Numbness confined to this tiny area with dorsiflexion weakness localizes to the deep peroneal nerve. If numbness extends across the entire dorsal foot, the lesion is at the common peroneal level (involving the superficial peroneal branch as well).
Entrapment Sites
1. Anterior Tarsal Tunnel
- Location: At the anterior ankle, where the nerve passes deep to the inferior extensor retinaculum
- Structure: Compression from tight shoes (lace pressure directly over the dorsal foot), ski boots, or osteophytes from ankle joint osteoarthritis. Edema from ankle sprains can also reduce the space.
- Condition: Anterior tarsal tunnel syndrome
- Presentation: Numbness or burning in the first web space. Weakness of extensor digitorum brevis (subtle — difficult to detect clinically). Dorsiflexion strength is preserved because the anterior leg muscles are innervated well above the ankle. Pain and numbness worsen with tight shoe lacing or prolonged plantar flexion (which stretches the nerve over the ankle).
- MT relevance: Anterior tarsal tunnel syndrome is often caused by external compression — tight shoes, boot lacing, or edema. Loosening footwear and reducing ankle swelling resolve many cases. When working the anterior ankle (post-sprain treatment, ankle mobilization), be aware of the nerve's superficial position beneath the extensor retinaculum.
2. Anterior Compartment (Compartment Syndrome)
- Location: Within the anterior compartment of the leg
- Structure: The anterior compartment is the most common site for acute and chronic exertional compartment syndrome. The rigid fascial boundaries do not expand when compartment pressure rises, compressing the nerve and artery.
- Presentation: Acute compartment syndrome: severe anterior leg pain disproportionate to the injury, pain with passive toe/ankle flexion, tense compartment on palpation, numbness in the first web space, and later loss of dorsiflexion. This is a surgical emergency. Chronic exertional compartment syndrome: anterior leg pain during running that resolves completely with rest, tightness over the anterior compartment, and sometimes transient first web space numbness during exercise.
- MT relevance: Acute compartment syndrome is a surgical emergency — the 6 Ps (pain, pressure, pulselessness, pallor, paresthesia, paralysis) demand immediate referral. Do NOT massage a suspected compartment syndrome — this delays surgical decompression. Chronic exertional compartment syndrome in runners does not respond to massage of the anterior compartment; fasciotomy may be required.
Clinical Tests
| Test | Procedure | Positive Finding | What It Tells You |
|---|---|---|---|
| Resisted ankle dorsiflexion | Patient dorsiflexes the ankle against resistance. | Weakness compared to the opposite side. | Tibialis anterior function — deep peroneal nerve or L4 myotome. The functional test for foot drop. |
| Resisted great toe extension | Patient extends the great toe against resistance. | Weakness. | EHL function — the most sensitive L5 myotome test. Weakness here may precede detectable ankle dorsiflexion weakness. |
| First web space sensation | Light touch in the first web space (between great toe and second toe, dorsal surface). | Decreased or absent sensation in only this small area. | Deep peroneal nerve sensory territory. If only the first web space is numb (not the rest of the dorsal foot), the lesion is deep peroneal, not common peroneal. |
| Anterior compartment palpation | Palpate the anterior compartment for tension, tenderness, and fullness. Compare sides. | Tense, painful compartment with first web space numbness. | Possible compartment syndrome — particularly if symptoms arise during or immediately after exercise. |
Clinical Notes
- First web space numbness is your deep peroneal localizer. The deep peroneal nerve's sensory territory is so small that it serves as a precise localizing test. Numbness in ONLY the first web space with intact dorsal foot sensation elsewhere means the deep peroneal nerve is affected and the superficial peroneal nerve is spared — the lesion is below the common peroneal division point.
- Tight laces cause anterior tarsal tunnel syndrome. Ski boots, ice skates, and tightly laced running shoes compress the deep peroneal nerve against the tarsal bones. Athletes who report dorsal foot numbness that develops during activity and resolves after removing footwear almost certainly have lace compression. The solution is footwear modification — skip the lace eyelet over the dorsum of the foot or use different lacing patterns.
- Compartment syndrome awareness. The anterior compartment is the most common site for exertional compartment syndrome in runners. The MT should know the warning signs: exercise-dependent anterior leg pain that resolves completely with rest, tense anterior compartment during symptoms, and first web space numbness. Do not attempt to treat acute compartment syndrome with massage — this is a fasciotomy indication.
- EHL is the most sensitive L5 myotome test. Before gross ankle dorsiflexion weakness is detectable, the extensor hallucis longus may already be weak. Testing great toe extension against resistance is more sensitive than testing ankle dorsiflexion for early L5 compromise.
Related Nerves
- anatomy/nerves/superficial-peroneal-nerve — The other terminal branch of the common peroneal nerve. Deep peroneal takes the anterior compartment (dorsiflexors); superficial peroneal takes the lateral compartment (evertors). Their sensory territories divide the dorsal foot — deep peroneal gets only the first web space, superficial peroneal gets the rest.
- anatomy/nerves/common-peroneal-nerve — Parent trunk. A common peroneal lesion at the fibular head affects BOTH deep and superficial branches — producing dorsiflexion weakness, eversion weakness, AND broad dorsal foot numbness.
- anatomy/nerves/tibial-nerve — Supplies the opposite side of the leg and foot (posterior/plantar). Together, the deep peroneal and tibial nerves control ankle dorsiflexion-plantar flexion balance.
Key Takeaways
- Supplies all anterior compartment muscles (dorsiflexors) with sensory territory limited to the first web space — this tiny area is the precise localizer for deep peroneal nerve involvement.
- Anterior tarsal tunnel syndrome from tight footwear (ski boots, laces) is the most common entrapment — footwear modification is the primary treatment.
- Acute anterior compartment syndrome compresses this nerve — a surgical emergency. Do not massage a suspected compartment syndrome.
- EHL (great toe extension) is the most sensitive L5 myotome test — test it when suspecting early L5 or deep peroneal compromise.