Movement at the ankle is controlled by two joints. The ankle or talocrural joint is formed from the tibia and fibula of the lower leg and talus of the foot. Functionally, it acts as a hinge, allowing dorsiflexion (pulling the foot upwards towards the lower leg) and plantarflexion (pulling the foot downwards away from the lower leg). Eversion (tilting of the sole of the foot away from the midline) and inversion (tilting of the sole of the foot inwards towards the midline) is controlled by the subtalar joint formed between the talus and calcaneus bones of the foot.

The ankle joint is held in place by numerous strong ligaments that can be easily damaged when excessive force is placed on the ankle, particularly during strenuous inversion and eversion. Movement at the ankle is key for maintenance of posture and balance, but is most important in locomotion. Variation in muscle activation can control the movement of the ankle joint, allowing the foot to generate graduated force.

Muscles that generate movement at the ankle are generally found in the lower leg and can be split into three categories.

Anterior Compartment

Three muscles in the anterior compartment of the leg act to dorsiflex and invert the foot at the ankle joint.

Tibialis Anterior - The tibialis anterior muscle is located alongside the lateral surface of the tibia and is the strongest dorsiflexor of the foot.

• Attachments - Originates from the lateral surface of the tibia and attaches to the base of the big toe.
• Actions - Dorsiflexion and inversion of the foot.

Extensor Digitorum Longus - The extensor digitorum longus is a deep-lying extrinsic muscle that runs the length of the tibia.

• Attachments - Originates from the tibia and transitions into a tendon, passes into the foot, splits into four, and attaches to the toes.
• Actions - Extension of the toes and dorsiflexion of the foot.

Extensor Hallucis Longus - The extensor hallucis longus is a deep lying extrinsic muscle beneath the extensor digitorum longus.

• Attachments - Originates from the fibula and attaches to the big toe.
• Actions - Extension of the big toe, and dorsiflexion of the foot.

Anterior Compartment of the Leg

Anterior view of leg showing the muscles and tendons involved in ankle movement.

This image depicts the tibialis anterior, tibia, transcrural ligament, and cruciate crural ligament.

Posterior Compartment

Several muscles are located in the posterior compartment of the leg, typically grouped into superficial and basal groups. The majority of these muscles work to plantarflex the foot at the ankle.

Superficial Muscles

The superficial muscles give rise to the characteristic shape of the lower leg.

Gastrocnemius- The gastrocnemius, a two-headed muscle, is the most superficial of the muscles in the posterior compartment.

• Attachments – Both heads originate from the femur. The fibers converge to form the calcaneal tendon which attaches to the heel.
• Actions - Plantarflexes the foot, can also flex the lower leg at the knee but is not key in this movement.

Plantaris – The plantaris is a small muscle lying between the gastrocnemius and soleus. It is absent in 10% of people.

• Attachments - Originates from the femur and attaches to the heel via the calcaneal tendon.
• Actions - Plantarflexes the foot, can also flex the lower leg at the knee but is not key in this movement.

Soleus – The soleus is a large flat muscle which is the deepest lying of the superficial muscles.

• Attachments - Originates from the tibia and fibula and attaches to the heel via the calcaneal tendon.
• Actions - Plantarflexes the foot.

Deep Muscles

Tibialis Posterior - The tibialis posterior is the deepest lying of the muscles in the posterior compartment.

• Attachments - Originates from the tibia and fibula and attaches to the plantar surfaces of the toes.
• Actions - Inverts and plantarflexes the foot, maintains the arch of the foot.

Posterior Compartment of the leg

Posterior view of leg showing muscles and tendons involved in ankle movement.

This image depicts muscles of lower leg, including the soleus.

Lateral Compartment

Two muscles found in the lateral compartment function to control eversion of the foot. Physiologically, there is a preference for the foot to invert, so these muscles also prevent excessive inversion.

Fibularis Longus – The fibularis longus is the longer and more superficial of the two muscles.

• Attachments – Originates from the fibula and tibia. The fibers converge into a tendon which passes under the foot and attaches to the medial side of the foot.
• Actions - Eversion and plantarflexion of the foot.

Fibularis Brevis - The fibularis brevis muscles is the deeper and shorter of the two muscles.

• Attachments – Originates from the lateral surface of the fibula and attaches to the little toe.
• Actions - Eversion of the foot.

Key Movements

Eversion of the Foot (tilting of the sole of the foot away from the midline)

• Performed by the fibularis brevis and fibularis longus.

Inversion of the Foot (tilting of the sole of the foot inwards towards the midline)

• Performed by the tibialis posterior and tibialis anterior.

Dorsiflexion of the Foot (pulling the foot upwards towards the leg)

• Performed by the tibialis anterior, extensor hallucis longus and extensor digitorum longus.

Plantarflexion of the Foot (pulling the foot downwards away from the lower leg)

• Performed by the gastrocnemius, plantaris, soleus and fibularis longus.