Lateral and Medial Sides of Leg

Lateral Side of Leg

The lateral compartment of the leg is also known as the peroneal compartment. The word perone comes from the Greek language and means the pin of a brooch or buckle.

Boundaries of lateral compartment

The lateral compartment of the leg is enclosed by the following structures:

• Anteriorly: Anterior intermuscular septum
• Posteriorly: Posterior intermuscular septum
• Medially: Lateral surface of the fibula
• Laterally: Deep fascia and skin of the leg

Contents of lateral compartment

The lateral compartment contains the following structures:

• Muscles: Peroneus longus and peroneus brevis
• Nerve: Superficial peroneal nerve
• Artery: Branches of the peroneal artery
• Vein: Small veins that drain into the short saphenous vein

Peroneal Retinacula

The peroneal retinacula are two strong bands of deep fascia located on the lateral side of the ankle. They hold the tendons of the peroneus longus and peroneus brevis muscles in place and prevent them from slipping during ankle movements.

Superior peroneal retinaculum

The superior peroneal retinaculum is located just behind the lateral malleolus.

Attachments

• Anteriorly: Posterior border of the lateral malleolus
• Posteriorly: Lateral surface of the calcaneus and the superficial transverse fascial septum of the leg

Relations

The superior peroneal retinaculum encloses the tendons of both the peroneus longus and peroneus brevis muscles within a common synovial sheath.

Inferior peroneal retinaculum

The inferior peroneal retinaculum lies in front of and below the lateral malleolus.

Attachments

• Superiorly: Anterior part of the superior surface of the calcaneus
• Inferiorly: Lateral surface of the calcaneus

Relations

A fibrous septum extends from the deep surface of the inferior peroneal retinaculum to the peroneal trochlea. This septum divides the space beneath the retinaculum into two compartments:

• Upper compartment: Contains the tendon of the peroneus brevis muscle with its synovial sheath.
• Lower compartment: Contains the tendon of the peroneus longus muscle with its synovial sheath.

Muscles of Lateral Compartment of Leg

• The lateral compartment of leg contains two muscles:
  1. Peroneus longus
  2. Peroneus brevis

Peroneus Longus

The peroneus longus (also called fibularis longus) is a long, superficial muscle located in the lateral compartment of the leg.

Origin

The peroneus longus arises from the following areas:

1. Head of the fibula
2. Upper one-third and the posterior half of the middle one-third of the lateral surface of the fibular shaft
3. Anterior and posterior intermuscular septa

Course

The muscle fibers join to form a long, slender tendon. This tendon passes behind the lateral malleolus beneath the superior and inferior peroneal retinacula. It then changes direction, passes through a groove on the cuboid bone, and runs forwards and medially across the sole of the foot.

Insertion

The tendon is inserted into:

1. Lateral side of the base of the first metatarsal
2. Medial cuneiform bone

Nerve Supply

The peroneus longus is supplied by the superficial peroneal nerve.

Actions

The peroneus longus performs the following functions:

1. Everts the foot (main action)
2. Helps maintain the longitudinal arch of the foot
3. Helps maintain the transverse arch of the foot

Peroneus Brevis

The peroneus brevis (also called fibularis brevis) is a short, fusiform, bipennate muscle located in the lateral compartment of the leg. It lies deep to the peroneus longus muscle.

Origin

The peroneus brevis arises from:

1. Anterior half of the middle one-third and the entire lower one-third of the lateral surface of the fibula
2. Anterior and posterior intermuscular septa of the leg

Course

The muscle fibers pass vertically downward and form a tendon. The tendon runs behind the lateral malleolus, deep to the tendon of the peroneus longus, beneath the superior and inferior peroneal retinacula. It then passes forwards and laterally to reach the base of the fifth metatarsal.

Insertion

The tendon is inserted into the lateral side of the base of the fifth metatarsal.

Nerve Supply

The peroneus brevis is supplied by the superficial peroneal nerve.

Actions

The peroneus brevis performs the following functions:

• Everts the foot.
• Helps maintain the lateral longitudinal arch of the foot.

Superficial Peroneal Nerve

The superficial peroneal nerve is the main nerve of the lateral compartment of the leg.

Root Value

The superficial peroneal nerve is formed by the L5 and S1 spinal nerve roots.

Origin

The superficial peroneal nerve is the smaller terminal branch of the common peroneal nerve. It begins at the neck of the fibula within the substance of the peroneus longus muscle.

Course

The nerve starts on the lateral side of the neck of the fibula and passes through the peroneus longus muscle. It then descends between the peroneus longus and peroneus brevis muscles. Lower in the leg, it runs between the peroneus brevis and extensor digitorum longus muscles.

At the junction of the upper two-thirds and lower one-third of the leg, the nerve pierces the deep fascia. It then divides into medial and lateral terminal branches, which continue to the dorsum of the foot.

Branches and Distribution

Muscular Branches

The superficial peroneal nerve supplies:

• Peroneus longus
• Peroneus brevis

Cutaneous Branches

It provides sensory supply to:

• Lower one-third of the lateral side of the leg
• Most of the dorsum of the foot, except the areas supplied by the saphenous, sural, deep peroneal, and plantar nerves

Terminal Branches

Medial terminal branch gives two digital branches:

• Medial side of the great toe
• Adjacent sides of the second and third toes

Lateral terminal branch gives two digital branches:

• Adjacent sides of the third and fourth toes
• Adjacent sides of the fourth and fifth toes

Medial Side of Leg

• The medial side of the leg is located between the anterior and medial borders of the tibia. It mainly consists of the medial surface of the tibia, which is subcutaneous over most of its length and can be easily felt beneath the skin.
• The upper part of the medial surface of the tibia provides insertion to the following muscles:
  • Sartorius
  • Gracilis
  • Semitendinosus
• It also provides attachment to the tibial collateral ligament of the knee joint.

Features of medial side of leg

• The tibial collateral ligament is considered to represent the degenerated tendon of the adductor magnus muscle.
• The anserine bursa (also called the tibial intertendinous bursa) is located deep to the pes anserinus on the anteromedial aspect of the upper end of the tibia. It reduces friction between the tendons and the underlying bone.
• The pes anserinus (meaning goose’s foot) is formed by the combined tendons of the sartorius, gracilis, and semitendinosus muscles.
• These three muscles are known as the guy ropes of the pelvis because they arise from different parts of the hip bone and converge to a common insertion on the upper medial surface of the tibia. Together, they help stabilize the pelvis.
  1. Sartorius originates from the ilium and belongs to the anterior compartment of the thigh.
  2. Gracilis originates from the pubis and belongs to the medial compartment of the thigh.
  3. Semitendinosus originates from the ischium and belongs to the posterior compartment of the thigh.

• The saphenous nerve provides sensory supply to the skin on the medial side of the leg.
• The great saphenous vein ascends along the medial side of the leg. In the lower one-third of the leg, it passes obliquely behind the medial surface of the tibia.

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