ANTERIOR AND LATERAL

COMPARTMENT OF THE LEG

ANTERIOR COMPARTMENT OF THE LEGTibialis Anterior Muscle – paddle-shaped;

unipenniform.Origin: upper 2/3 of the lateral surface of the tibia and a

narrow adjacent surface of the fibula and interosseous membrane.

Insertion: superficial at the distal end near the medial malleolus. Beneath the extensor retinacula, it crosses the medial border of the foot to reach its insertion at the inferior surface of the first cuneiform and first metatarsal bones

Action: primarily a strong invertor of the foot; helps in adduction, internal rotation and dorsi-flexion of the foot.

Extensor Digitorum Longus Muscle Origin: upper 2/3 of the fibula and partly from the

interosseous membrane.Insertion: divides into 4 smaller tendons that are inserted

to the middle and distal phalanges of the 4 lateral toes.

These are joined by the small tendons of the extensor digitorum brevis, interosseous and lumbrical muscles, which form fibrous extensions that surround the bones to which they are attached.

Extensor Hallucis LongusOrigin: middle third of the fibula deep to the EDL.Insertion: its slender tendon emerges between the

tibialis anterior and EDL tendons. At the dorsum of the foot, it crosses medially to its insertion to the base of the distal phalanx of the big toe.

Peroneus Tertius Muscle – usually considered as a small slip of the EDL, which may be occasionally, present and distinguished by its fibers, which originate from the inferior third of the fibula. Its tendon may be mistaken as a 5th tendon of the EDL, but actually its tendon may be separated from the 4th or most lateral tendon of the EDL to its insertion at the tuberosity of the 5th metatarsal bone at the lateral border of the foot.

DORSUM OF THE FOOT

Extensor Digitorum Brevis – flat, sometimes fleshy muscle at the lateral surface of the dorsum of the foot.

Origin – upper surface of the calcaneus Insertion – the muscle divides into 3 muscular slips which

tendons that join corresponding tendons of the EDL for the 2nd, 3rd and 4th lateral toes.

Extensor hallucis brevis - distinguishing name for the most medial division of the EDB. Its tendon is inserted to the proximal phalanx of the hallux.

Dorsal Interosseous Muscles – 4 slips, each with two heads that arise from adjacent metatarsals. Their small tendons join the dorsal aponeurosis of the toes, formed by the extensor tendons.

Actions – they abduct the toes and help in flexing the metatarso-phalangeal joints. The deep branch of the lateral plantar nerve innervates them.

NEUROVASCULAR STRUCTURES

The neurovascular supply are located deep between the tibialis anterior and EDL muscles, bound by a common fascial sheath.

Anterior Tibial Artery – branches off from the popliteal artery at the inferior border of the popliteus muscle. It penetrates the upper end of the interosseous membrane to reach the anterior compartment where it descends vertically deep in the compartment on the anterior surface of the interosseous membrane down the ankle, where it surfaces beneath the superior extensor retinaculum between the tendons of the TA and EDL.

Branches:1.Anterior Tibial Recurrent – given off as the parent

trunk enters the anterior compartment. It joins the anastomoses around the knee joint.

2. Muscular and nutrient branches to the bones.3. Occassionally, a circumflex fibular artery. 4. Lateral and medial malleolar arteries that

participate in the malleolar and tarsal anastomoses with branches from the peroneal and dorsalis pedis.

Dorsalis Pedis Artery

Name given to the continuation of the anterior tibial artery after crossing the lower border of the inferior extensor retinaculum. Its pulsations may be felt very well as it lies on the navicular and cuneiform bones.

It courses forwards on the dorsum of the foot and ends by dividing into:

1. A transversely directed “arcuate artery” that curves laterally at the bases of the metatarsal bones, distributing digital branches for the toes, to end at the lateral border of the foot by anastomosing with the lateral tarsal artery.

2. A “deep plantar artery” which perforates the first interosseous space to anastomose with the plantar arch at the sole of the foot.

Deep Plantar Artery

2.2. It gives off lateral and medial tarsal branches that course deep to the tendons of the EDL, with anastomosing branches from the anterior tibial. Some branches reach the sole of the foot to communicate with branches from the plantar arteries.

2.3.A first dorsal metatarsal artery runs forwards to the first interosseous space, other dorsal metatarsal arteries for the interosseous spaces penetrate also to the sole and anastomose with plantar branches.

Accompanying veins drain into the anterior tibial vein, which joins the posterior tibial vein in the popliteal fossa to form the popliteal vein. Cutaneous veins unite to form a “dorsal venous arch” which is joined by veins from the hallux to form the long saphenous vein.

Muscle Origin Insertion ActionNerveSupply

Tibialis anterior

shaft of tibia and interosseous membrane

medial cuneiform and base of first metatarsal

extends the foot at ankle; inverts foot at subtalar and transverse tarsal jointshelps to maintain the medial longitudinal arch of foot

deep peroneal nerve

Extensor digitorum longus

shaft of fibula and interosseous membrane

extensor expansion of lateral four toes

extends toes; dorsiflexes (extends) foot

deep peroneal nerve

Peroneus tertius

shaft of fibula and interosseous membrane

base of fifth metatarsal

dorsiflexes (extends) foot; everts foot at subtalar and transverse tarsal joints

deep peroneal nerve

Extensor hallucis longus

shaft of fibula and interosseous membrane

base of distal phalanx of big toe

extends big toe; dorsiflexes foot; inverts foot at subtalar and transverse tarsal joints

deep peroneal nerve

Extensor digitorum brevis

calcaneus long extensor tendons to 2nd, 3rd, and 4th toes

extends big toe deep peroneal nerve

Extensor hallucis brevis

calcaneusproximal phalanx of big tow

extends big toedeep peroneal nerve

                                                                  

Muscle Origin Insertion ActionNerveSupply

Peroneus longus

shaft of fibula

base of first metatarsal andthe medial cuneiform

plantar flexes (flexes) foot; everts footat subtalar and transverse talar joints;supports lateral longitudinal arch and transverse arch of foot

superficial peroneal nerve

Peroneus brevis

shaft of fibula

base of fifth metatarsal bone

plantar flexes (flexes) foot: everts footat subtalar and transverse talar joints; holds up lateral longitudinal arch

superficial peroneal nerve

LATERAL COMPARTMENT OF THE LEG

Peroneus Longus – more superficial muscle of the two.Origin: lateral surface of the upper half of the fibula.Insertion: its tendon is covered by the peroneal retinaculum behind

the lateral malleolus winds around the lateral border of the foot to enter the sole, crossing to the medial side to be inserted at the medial cuneiform and base of the first metatarsal.

Peroneus Brevis – deeper muscle covered by the longus.Origin: lower half of the lateral surface of the fibulaInsertion: its short tendon deviates laterally to its attachment at the

dorso-lateral surface of the 5th metatarsal at the lateral border of the foot, near but inferior to the insertion of the longus.

These two muscles, innervated by the “superficial peroneal (or musculo-cutaneous) nerve of the leg are the primary evertors of the foot, with concomitant abduction. They also help in the plantar flexion of the foot and support/maintain its arches.

Lateral and Anterior Compartments

Common Peroneal Nerve – given off in the popliteal fossa. It courses along the border of the biceps tendon to the neck of the fibula where it divides into:– Superficial Peroneal (Musculo-cutaneous Nerve of the Leg),

which enters the lateral compartment between the peroneal muscles, innervates them. At about the middle of the leg, it continues obliquely downwards and anteriorly, supplying cutaneous branches to the skin at the lower part of the leg and dorsum of the foot.

– Deep Peroneal (Anterior tibial) Nerve – enters the anterior compartment after winding around the neck of the fibula. It is included in the fascial sheath of the anterior tibial vessels. After giving muscular branches to the muscles in the anterior compartment, it descends to the dorsum of the foot where it innervates the EDB, finally terminating as a cutaneous nerve to the skin between the first and second toes.