Foot Function and Gait – The Lateral Compartment

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Functional and Kinematic Characteristics

All muscles in this group are positioned anterior to the axis of rotation of the talocrural joint, making them primary dorsiflexors. Due to its anatomical location, the tibialis anterior passes medially to the axis of rotation, allowing it to:
  • Induce inversion at the subtalar joint
  • Support the medial longitudinal arch
  • Contribute to inversion and adduction at the talonavicular joint
The extensor hallucis longus is primarily responsible for dorsiflexion at the talocrural joint and extension of the big toe, though its subtalar inversion effect is relatively minor. On the other hand, the extensor digitorum longus and fibularis (peroneus) tertius contribute not only to dorsiflexion but also assist in eversion of the foot.

Gait Function and Activation Patterns

The anterior muscle group is most active during:
  • Initial stance phase
  • Swing phase
Role in Initial Stance
During initial stance, these muscles perform eccentric contractions to regulate the speed of plantarflexion, ensuring a smooth landing. The tibialis anterior, in particular, controls medial longitudinal arch descent while modulating rearfoot pronation (eversion) during heel contact.
Role in Swing Phase
During the swing phase, this group works together to actively dorsiflex the ankle and extend the toes, preventing the foot from contacting the ground.

Muscle Coordination and Balance

For effective dorsiflexion in the sagittal plane, a precise balance of forces among the anterior muscles is essential:
  • The eversion and abduction force generated by the extensor digitorum longus and fibularis tertius
  • The inversion and adduction force produced by the tibialis anterior
If the tibialis anterior becomes paralyzed, the ankle can still dorsiflex, but foot movement will be biased toward eversion and abduction.

Muscles of the Lateral Compartment

The lateral compartment contains two primary muscles:
  1. Fibularis (Peroneus) longus
  1. Fibularis (Peroneus) brevis
Both muscles originate along the lateral fibula.
The fibularis longus, located more superficially, follows a complex distal course:
  • Passes behind the lateral malleolus
  • Traverses the groove of the cuboid bone
  • Enters the plantar surface of the foot
  • Finally attaches to the plantar-lateral surface of the first tarsometatarsal joint

Anatomical Features and Clinical Relevance of the Fibularis Brevis

The fibularis brevis tendon runs parallel to the fibularis longus behind the lateral malleolus, with both tendons housed within the same synovial sheath beneath the peroneal retinaculum.

After passing the retinaculum, the fibularis brevis tendon separates from the fibularis longus and attaches to the styloid process of the fifth metatarsal.

Clinically, this attachment site is prone to avulsion fractures, particularly in dancers and individuals who experience sudden, excessive inversion of the foot, leading to forceful contraction of the fibularis brevis and potential injury.