Muscles acting on the ankle joint, and their innervation.

Muscles Acting on the Ankle Joint

1. Muscles Acting on the Ankle Joint

The muscles acting on the ankle joint can be grouped by their functions into dorsiflexors, plantar flexors, evertors, and invertors. These muscles are divided into anterior, posterior, and lateral compartments of the leg:

Anterior Compartment (Dorsiflexion):

• Tibialis Anterior

  • Origin: Lateral condyle and superior two-thirds of the lateral surface of the tibia and interosseous membrane.

  • Insertion: Medial cuneiform and base of the 1st metatarsal.

• Extensor Digitorum Longus

  • Origin: Lateral condyle of the tibia, proximal three-quarters of the fibula, and interosseous membrane.

  • Insertion: Middle and distal phalanges of the lateral four digits.

• Extensor Hallucis Longus

  • Origin: Middle third of the anterior surface of the fibula and interosseous membrane.

  • Insertion: Base of the distal phalanx of the great toe.

• Fibularis Tertius

  • Origin: Inferior third of the anterior surface of the fibula and interosseous membrane.

  • Insertion: Base of the 5th metatarsal.

Posterior Compartment (Plantarflexion):

• Superficial Group:

  • Gastrocnemius

    • Origin: Medial and lateral femoral condyles.

    • Insertion: Posterior surface of the calcaneus via the Achilles tendon.

  • Soleus

    • Origin: Posterior aspect of the fibula and the soleal line of the tibia.

    • Insertion: Posterior surface of the calcaneus via the Achilles tendon.

  • Plantaris

    • Origin: Lateral supracondylar line of the femur.

    • Insertion: Posterior surface of the calcaneus.

• Deep Group:

  • Tibialis Posterior

    • Origin: Posterior surface of the tibia, fibula, and interosseous membrane.

    • Insertion: Navicular, cuneiforms, cuboid, and bases of the 2nd to 4th metatarsals.

  • Flexor Digitorum Longus

    • Origin: Posterior surface of the tibia.

    • Insertion: Bases of the distal phalanges of the lateral four digits.

  • Flexor Hallucis Longus

    • Origin: Inferior two-thirds of the posterior surface of the fibula and interosseous membrane.

    • Insertion: Base of the distal phalanx of the great toe.

Lateral Compartment (Eversion):

• Fibularis Longus

  • Origin: Head and superior two-thirds of the lateral surface of the fibula.

  • Insertion: Base of the 1st metatarsal and medial cuneiform.

• Fibularis Brevis

  • Origin: Inferior two-thirds of the lateral surface of the fibula.

  • Insertion: Base of the 5th metatarsal.

2. Blood Supply

• Arteries:

  • Anterior Compartment: Supplied by the anterior tibial artery, a branch of the popliteal artery.

  • Posterior Compartment: Supplied by the posterior tibial artery and the fibular artery.

  • Lateral Compartment: Supplied by branches of the fibular artery.

• Veins:

  • Accompanying veins (venae comitantes) of the arteries, which include the anterior tibial, posterior tibial, and fibular veins. These veins drain into the popliteal vein.

• Anastomoses:

  • Collateral circulation exists through the perforating branches of the anterior tibial and fibular arteries. The deep plantar arch forms connections between these vessels.

3. Innervation

• Anterior Compartment: Innervated by the deep fibular nerve (L4, L5).

• Posterior Compartment:

  • Superficial group: Tibial nerve (S1, S2).

  • Deep group: Tibial nerve (L4–S3).

• Lateral Compartment: Innervated by the superficial fibular nerve (L5, S1).

4. Functions

• Dorsiflexion: Performed by the anterior compartment muscles (e.g., tibialis anterior).

• Plantarflexion: Performed by the posterior compartment muscles (e.g., gastrocnemius, soleus).

• Eversion: Performed by the lateral compartment muscles (e.g., fibularis longus and brevis).

• Inversion: Performed by muscles like tibialis anterior and tibialis posterior.

5. Clinical Significance

• Anterior Compartment Syndrome: Compression of the deep fibular nerve and anterior tibial artery may occur due to increased compartmental pressure.

• Tibialis Posterior Tendon Dysfunction: A common cause of acquired flatfoot deformity.

• Achilles Tendon Rupture: Results in loss of plantarflexion strength, commonly affecting the gastrocnemius and soleus.

• Foot Drop: Weakness in dorsiflexion, commonly due to injury to the deep fibular nerve or L4–L5 radiculopathy.

• Peripheral Artery Disease (PAD): Impaired blood supply to the muscles of the leg and foot.

6. Innervation and Spinal Nerve Origins

• Deep Fibular Nerve: L4–L5 roots (anterior compartment).

• Tibial Nerve: L4–S3 roots (posterior compartment).

• Superficial Fibular Nerve: L5–S1 roots (lateral compartment).

Each nerve's root level is crucial for testing reflexes and muscle power in cases of nerve injury or radiculopathy.