Anterior & Lateral Compartments of the Leg

Anterior & Lateral Compartments of the Leg

• The leg is divided into three compartments by intermuscular septa, interosseous membrane, and bones.
• These compartments include: Anterior, Lateral, and Posterior.
• The muscles within each compartment share common functions and innervations.

Nerves Supply of Leg - From Sciatic Nerve

• The tibial nerve (purple) supplies the posterior compartment of the leg and sole of the foot.
• The common peroneal nerve divides into superficial and deep branches.
• The superficial peroneal nerve (blue) supplies the lateral compartment.
• The deep peroneal nerve (green) supplies the anterior compartment.

Muscles of the Anterior Compartment

• Key principles: muscles pass over the ankle joint, therefore are dorsiflexors.
• The long extensor muscles pass along the dorsal aspect of the toes.
• Deep peroneal nerve supplies dorsiflexors and toe extensors.
• Four muscles include: Tibialis Anterior, Extensor Hallucis Longus, Extensor Digitorum Longus, Peroneus (Fibularis) Longus.
• Kick motion THUd (medial to lateral).

Muscles of the Lateral Compartment

• Key principles: muscles pass lateral to the ankle joint.
• Thus, they evert the foot (pull the foot outwards).
• Superficial Peroneal Nerve supplies the muscles.
• Muscles: Peroneus Longus, Peroneus Brevis, Fibularis Tertius.

Tibialis Anterior

• Origin: Lateral condyle & superior half of lateral tibia & Interosseous membrane.
• Insertion: Medial & Inferior surface of medial cuneiform & 1st metatarsal.
• Action: Dorsiflexion and inversion of the foot.

Extensor Hallucis Longus

• Origin: Middle part of anterior surface of fibula & Interosseous membrane.
• Insertion: Dorsal aspect of base of distal phalanx of great toe.
• Action: Extends great toe (helps dorsiflexion of ankle).

Extensor Digitorum Longus

• Origin: Lateral condyle of the tibia & superior 3/4 of the medial surface of the fibula and interosseous membrane.
• Insertion: Middle & Distal phalanges of lateral 4 digits (extensor expansion).
• Action: Extends lateral 4 digits (helps dorsiflexion of ankle).

Peroneous Tertius

• A separated part of Extensor Digitorum Longus.
• Shares its origin and more distal fibers along the fibula.
• Insertion: 5th metatarsal (not a phalanx).
• Often absent.

Extensor Retinacula

• The deep fascia of the leg is called crural fascia.
• Two thickenings bind the tendons of the muscles before and after the ankle joint.
• Superior and inferior extensor retinaculum.

Blood Supply - Anterior Compartment

• Anterior tibial artery supplies the anterior compartment.
• A branch of the popliteal artery, it passes anteriorly through a gap in the interosseous membrane and descends (joined by the deep peroneal nerve).
• The neurovascular bundle (Nerve & Blood Vessels) has different characteristics.

Blood Supply - Lateral Compartment

• The lateral compartment does not have its own blood supply.
• Perforating arteries supply this compartment.
• Proximally - perforating arteries of anterior tibial artery.
• Distally - perforating arteries of peroneal (fibular) artery.

Dorsum of Foot - Blood Supply

• At the ankle joint, the Anterior Tibial Artery changes name to the Dorsalis Pedis muscle.
• The Extensor Hallucis Longus tendon crosses the Dorsalis Pedis.
• On the dorsum, the Dorsalis Pedis is located between the Extensor Hallucis Longus and the Extensor Digitorum Longus Tendons.

Dorsum of Foot - Blood Supply (Detail)

• Dorsalis Pedis enters the first interosseous space and divides into deep plantar artery and 1st dorsal metatarsal artery.
• Deep Planter artery anastomoses with lateral plantar artery to form deep planter arch.
• Dorsalis Pedis gives off branches: Lateral tarsal artery and arcuate artery.
• These arteries anastomose to form an arterial loop, which further divide to give off dorsal digital arteries.
• The metatarsal arteries are connected to the planter arch & plantar metatarsal arteries via perforating arteries.

Dissection Time

• Steps involve removing the skin over the leg, identifying anterior and lateral compartment muscles, locating the Neurovascular bundle (NVB) and continuing dissection over the dorsum of the foot, and locating the dorsalis pedis.