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Lateral Compartment of Leg

The lateral compartment of leg, or evertor compartment, is the smallest (narrowest) of the leg compartments. It is bounded by the lateral surface of the fibula, the anterior and posterior intermuscular septa, and the deep fascia of the leg.

The lateral compartment of leg ends inferiorly at the superior fibular retinaculum, which spans between the distal tip of the fibula and the calcaneus. Here, the tendons of the two muscles of the lateral compartment of leg (fibularis longus and brevis) enter a common synovial sheath to accommodate their passage between the superior fibular retinaculum and the lateral malleolus, using the latter as a trochlea as they cross the ankle joint.

Lateral Compartment of Leg Muscles

The lateral compartment of leg contains the fibularis longus and brevis muscles. These muscles have their fleshy bellies in the lateral compartment but are tendinous as they exit the compartment within the common synovial sheath deep to the superior fibular retinaculum. Both muscles are evertors of the foot, elevating the lateral margin of the foot.

Developmentally, the fibularis muscles are postaxial muscles, receiving innervation from the posterior divisions of the spinal nerves, which contribute to the sciatic nerve. However, because the fibularis longus and brevis pass posterior to the transverse axis of the ankle (talocrural) joint, they contribute to plantarflexion at the ankle – unlike the postaxial muscles of the anterior compartment (including the fibularis tertius), which are dorsiflexors. As evertors, the fibularis muscles act at the subtalar and transverse tarsal joints. From the neutral position, only a few degrees of eversion are possible.

In practice, the primary function of the evertors of the foot is not to elevate the lateral margin of the foot (the common description of eversion) but to depress or fix the medial margin of the foot in support of the toe off phase of walking and, especially, running and to resist inadvertent or excessive inversion of the plantarflexed foot (the position in which the ankle is most vulnerable to injury).

When standing (and particularly when balancing on one foot), the fibularis muscles contract to resist medial sway (to recenter a line of gravity, which has shifted medially) by pulling laterally on the leg while depressing the medial margin of the foot. To test the fibularis longus and brevis, the foot is everted strongly against resistance; if acting normally, the muscle tendons can be seen and palpated inferior to the lateral malleolus.

Fibularis Longus

The fibularis longus (FL) is the longer and more superficial of the two fibularis muscles, arising much more superiorly on the shaft of the fibula. The narrow FL extends from the head of the fibula to the sole of the foot. Its tendon can be palpated and observed proximal and posterior to the lateral malleolus

Distal to the superior fibular retinaculum, the common sheath shared by the fibular muscles splits to extend through separate compartments deep to the inferior fibular retinaculum. The FL passes through the inferior compartment – inferior to the fibular trochlea on the calcaneus – and enters a groove on the antero-inferior aspect of the cuboid bone. It then crosses the sole of the foot, running obliquely and distally to reach its attachment to the 1st metatarsal and 1st (medial) cuneiform bones. When a person stands on one foot, the FL helps steady the leg on the foot.

Fibularis Brevis

The fibularis brevis (FB) is a fusiform muscle that lies deep to the FL, and, true to its name, the FB is shorter than its partner in the lateral compartment of leg. Its broad tendon grooves the posterior aspect of the lateral malleolus and can be palpated inferior to it. The narrower tendon of the FL lies posterior to the tendon of the FB and does not contact the lateral malleolus.

The tendon of the FB traverses the superior compartment of the inferior fibular retinaculum, passing superior to the fibular trochlea of the calcaneus; it can be easily traced to its distal attachment to the base of the 5th metatarsal. The tendon of the fibularis tertius, a slip of muscle from the extensor digitorum longus, often merges with the tendon of the FB. Occasionally, however, the fibularis tertius passes anteriorly to attach directly to the proximal phalanx of the 5th digit.

Lateral Compartment of Leg muscles

Nerves in the Lateral Compartment of Leg

The superficial fibular (peroneal) nerve, a terminal branch of the common fibular nerve, is the nerve of the lateral compartment of leg. After supplying the FL and FB, the superficial fibular nerve continues as a cutaneous nerve, supplying the skin on the distal part of the anterior surface of the leg and nearly all the dorsum of the foot.

Lateral Compartment of Leg nerves

Blood Vessels in the Lateral Compartment of Leg

The lateral compartment of leg does not have an artery coursing through it. Instead, perforating branches and accompanying veins supply blood to and drain blood from the compartment.

Proximally, perforating branches of the anterior tibial artery penetrate the anterior intermuscular septum. Inferiorly, perforating branches of the fibular artery penetrate the posterior intermuscular septum, along with their accompanying veins (L. venae comitantes).

Lateral Compartment of Leg blood supply

References

  1. Khan IA, Mahabadi N, D’Abarno A, et al. Anatomy, Bony Pelvis and Lower Limb, Leg Lateral Compartment. [Updated 2022 Aug 8]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK519526/
  2. Hardin JM, Devendra S. Anatomy, Bony Pelvis and Lower Limb, Calf Common Peroneal (Fibular) Nerve. 2021 Oct 21. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan–. PMID: 30422563.
Last Reviewed
May 16, 2023
Contributed by
OrthoFixar

Orthofixar does not endorse any treatments, procedures, products, or physicians referenced herein. This information is provided as an educational service and is not intended to serve as medical advice.

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