Anterior & Lateral Compartments of the Leg

Anterior & Lateral Compartments of the Leg

• The leg is divided into 3 compartments by intermuscular septa, interosseous membrane, and bones.
• Compartments include: Anterior, Lateral, and Posterior.
• Deep and superficial muscles within each compartment share common functions and innervations.

Nerves Supply of Leg - From Sciatic Nerve

• Tibial nerve (purple) supplies the posterior compartment of the leg and sole of the foot.
• Common Peroneal nerve branches into superficial and deep branches.
• Superficial Peroneal nerve (blue) supplies the lateral compartment.
• Deep Peroneal nerve (green) supplies the anterior compartment.

Muscles of Anterior Compartment

• Key principles: Pass over the ankle joint; therefore, they are dorsiflexors. Long extensors pass along the dorsal aspect of the toes.
• Key muscles include Tibialis Anterior, Extensor Hallucis Longus, Extensor Digitorum Longus, and Peroneus (Fibularis) Longus.
• If you kick something, it goes from medial to lateral (THUD).

Muscles of Lateral Compartment

• Key principles: Pass lateral to the ankle; therefore, they are evertors (pull the foot out).
• Key muscles include Fibularis (Peroneus) Longus and Fibularis (Peroneus) Brevis.

Peroneus (Fibularis) Longus

• Origin: Head & superior 2/3rds of lateral fibula.
• Inserts: Base of 1st Metatarsal and Medial cuneiform.
• Most Superficial.
• Passes posterior to lateral malleolus using it as a pulley.
• Enters a groove on the anterior inferior aspect of the cuboid bone.
• Runs obliquely & distally to its attachment.
• Like a Stirrup.

Peroneus (Fibularis) Brevis

• Origin: Inferior 2/3rds of lateral fibula.
• Inserts: Dorsal tuberosity of lateral side of base of 5th metatarsal.
• Deeper of the two muscles.
• Passes behind lateral malleolus (using it as a pulley).
• Works with the longus to evert foot (helps to prevent excessive inversion).

Tibialis Anterior

• Origin: Lateral condyle & superior half of lateral tibia & interosseous membrane.
• Inserts: Medial & inferior surface of medial cuneiform & 1st metatarsal.
• Action: Dorsiflexion & inverts the foot.

Extensor Hallucis Longus

• Origin: Middle part of anterior surface of fibula & interosseous membrane.
• Inserts: 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 tibial & superior 3/4 of medial surface of fibula and interosseous membrane.
• Inserts: Middle & Distal phalanges of lateral 4 digits (extensor expansion).
• Action: Extends lateral 4 digits (helps dorsiflexion of ankle).

Peroneous (Fibularis) Tertius

• Part of Extensor Digitorum Longus; it's origin is on the more distal fibres along fibula.
• Inserts into the 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 extensor retinaculum

• Strong, broad band of deep fascia.

Inferior extensor retinaculum

• Y-shaped band of deep fascia.

Blood Supply - Anterior Compartment

• Anterior Tibial Artery supplies the anterior compartment.
• The branch of the popliteal artery passes anteriorly through a gap in the interosseous membrane and descends.
• Joined with the deep peroneal nerve.
• Note: The neurovascular bundle has different vessels.

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.

Blood Supply - Dorsum of Foot

• Dorsalis Pedis passes into the first interosseous space, divides into deep plantar artery & 1st dorsal metatarsal artery.
• Deep plantar artery anastomoses with lateral plantar artery to form deep plantar arch.  

Dorsum of Foot - Blood Supply (cont.)

• Dorsalis pedis gives off 2 branches: Lateral tarsal artery & Arcuate artery.
• These anastomoses to form arterial loop and give off metatarsal arteries, which further divide to give off dorsal digital arteries. 

Dorsum of Foot - Blood Supply (cont.)

• Metatarsal arteries are also connected to the plantar arch & plantar metatarsal arteries via perforating arteries.
• The arch is usually hidden under extensor digitorum brevis.

Dissection Time

• Remove the skin over the leg.
• Identify & the muscles in anterior and lateral compartments.
• Try to find the neurovascular bundle (NVB).
• Dissection continues dorsally over the foot.
• Try to find dorsalis pedis.