Tibialis anterior !

The tibialis anterior is the muscle along the front of the shin; it lifts the foot, and its weakness causes foot drop.

Official name: Tibialis anterior muscle

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What it is

The muscle along the front of the shin.

What it does

Lifts the foot when walking.

Key facts

Origin: Lateral tibial condyle and upper half of lateral tibial shaft; interosseous membrane
Insertion: Medial and plantar surfaces of medial cuneiform; base of first metatarsal
Action: Dorsiflexes ankle; inverts foot
Nerve: Deep fibular nerve (L4–L5)
Blood supply: Anterior tibial artery

Relations

Course: Its tendon forms in the lower third of the leg, passes under the superior and inferior extensor retinacula in its own synovial sheath and crosses the front of the ankle to the medial side of the midfoot
Medial: The subcutaneous medial surface of the tibia (the shin)
Lateral: Extensor digitorum longus above and extensor hallucis longus below
Deep: Lateral surface of the tibia and the interosseous membrane; the anterior tibial vessels and deep fibular nerve lie on the membrane in the angle between it and its lateral neighbours
Superficial: The thick, unyielding deep fascia of the leg and the skin

How to find it

With the foot lifted and turned in, the tendon stands out as the largest cord in front of the ankle, just in front of the medial malleolus. The belly is felt just lateral to the sharp anterior border of the tibia.

Examination

Heel walk: inability to keep the forefoot off the ground indicates dorsiflexor weakness (deep or common fibular nerve, L4–L5 roots)
Resisted dorsiflexion and inversion: weakness with a normal tendon outline suggests a nerve or root cause; loss of the tendon outline in front of the ankle suggests a rupture

On imaging

Ultrasound shows its tendon as the largest in front of the ankle. A rupture, usually in older people near the insertion, shows a gap and a retracted stump that may be felt as a lump above the ankle; MRI confirms tears and tendinopathy. In foot drop, MRI can show denervation oedema of the anterior compartment. Compartment syndrome is diagnosed clinically and by pressure, not by imaging.

Clinical notes

Anterior compartment syndrome: pain on passive plantarflexion of the ankle and toes, a tense shin, weak dorsiflexion and numbness in the first web space (deep fibular nerve)
Foot drop from a common fibular nerve lesion at the fibular neck spares inversion (tibialis posterior, tibial nerve); an L5 root lesion weakens inversion too
Spontaneous rupture in older adults is often painless: foot slap, a lump in front of the ankle and loss of the tendon outline
A split transfer of its tendon to the lateral foot is used to balance a spastic varus foot

Anatomical variants

The tendon may split into two bands to the medial cuneiform and the first metatarsal, or insert on only one of them; insertions further away are rare

Development

A dorsal (extensor) muscle mass derivative, supplied by the deep fibular nerve; the medial rotation of the lower limb in the seventh week brings this extensor group to the front of the leg.

Memory aid

In front of the ankle, medial to lateral: "Tom Has Very Nice Dancing Pigs" (Tibialis anterior, extensor Hallucis longus, Vessels, Nerve [deep fibular], extensor Digitorum longus, Peroneus tertius).

Acute compartment syndrome

Test yourself

Think of the answer, then tap the question to see it.

What are the attachments and actions of the tibialis anterior?

From the lateral tibial condyle, upper lateral tibia and interosseous membrane to the medial cuneiform and first metatarsal base; it dorsiflexes the ankle and inverts the foot.

Which nerve supplies the tibialis anterior?

The deep fibular nerve (L4–L5); the tibialis anterior is the classic muscle for the L4 myotome.

What gait results from weakness of the tibialis anterior?

Foot drop, with a high-stepping gait and foot slap; heel walking is lost.

What are the signs of anterior compartment syndrome?

Pain on passive plantarflexion of the ankle and toes, a tense shin, weak dorsiflexion and numbness in the first web space (deep fibular nerve).

How does a common fibular nerve lesion differ from an L5 root lesion in foot drop?

A fibular neck lesion spares inversion (tibialis posterior, tibial nerve); an L5 root lesion weakens inversion too.

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Educational information, not medical advice. For any symptom, see a health professional.

Its names

Official Latin (TA2): musculus tibialis anterior TA2 2644
Official Spanish (DeCS): Músculo tibial anterior
English (TA2): Tibialis anterior muscle

Sources: Terminologia Anatomica (TA2); Anatomy, Bony Pelvis and Lower Limb: Tibialis Anterior Muscles; 8.5 Development of the Appendicular Skeleton (OpenStax (Rice University), 2022) · adapted, CC BY 4.0.

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Representative model, for educational purposes only.

Tibialis anterior highlighted on the Durgical 3D model