Superficial Structures

The short saphenous vein and the sural nerve course side by side in the superficial fascia along the middle of the back of the leg and lateral border of the foot.

At the anterior aspect of the ankle:

1. Superior extensor retinaculum [ligamentum transversum cruris]

Its fibers are directed transversely across the anterior surface of the distal end of the leg, attached to the distal ends of the tibia and lateral malleolus.

2. Inferior extensor retinaculum [ ligamentum cruciatum cruris ]

This is a Y-shaped band draped across the dorsum of the foot.

The stem of the Y is attached to the lateral surface of the calcaneus; one limb is extended and attached to the medial malleolus; the other dips down the medial border of the foot, attached to the plantar aponeurosis at the sole of the foot.

Lateral side of the ankle:3. Superior peroneal retinaculum - bridges

the gap between the lateral malleolus and calcaneus.

4. Inferior peroneal retinaculum - smaller reinforcing band attached to the peroneal tubercle of the calcaneus, extending over the tendons of the peroneal muscles to join the attachment of the inferior extensor retinaculum at the lateral surface of the calcaneus.

Medial side of the ankle:5. Flexor Retinaculum [ligamentum

laciniatum] - strong band that bridges the medial concavity of the calcaneus, attached to the medial malleolus and to the medial tubercle of the calcaneus.

Superficial Group “Triceps Surae Muscle”

Gastrocnemius – its two heads join to form a single belly which narrow to its tendon at about the middle of the leg.

Origins: medial and lateral head, from the corresponding femoral condyles.

Insertion: the “calcanean tendon” which is attached to a small area at the postero-inferior part of the calcaneus where a small bursa separates it from the bone.

Plantaris - small short muscle with a long tendon; arising from the lateral condyle of the femur, deep to the lateral head of the gastrocnemius and soleus muscles descending along the medial border of calcanean tendon joining it to its attachment.

Soleus – paddle-shaped muscle deep to the gastrocnemius; its fibers joining the calcanean tendon, which may also be called “ tendon of Achilles”.

Origins: popliteal [oblique] line of the tibia; and proximal third of the fibula.

[Note the passage of the tibial n.v.s. between the separated origins of this muscle; thus enabling them to descend deeper into the posterior compartment of the leg.]

The Triceps Surae or Calf Muscles are the principal plantar flexors of the foot [ankle].

This action is clearly demonstrated when one stands on tiptoe. Moreover, aside from the primary function, the gastrocnemius may also help in flexing the leg.

Intermediate LayerFlexor Digitorum Longus – the

medial [intermediate] muscle.Origin: posterior surface of the middle

third of the tibia.Insertion: its tendon of insertion is formed

behind the medial malleolus, positioned anterior to the tendon of the other intermediate muscle; and separated from the posterior n.v.s. The tendon proceeds to the sole of the foot where it divides into four tendons that are inserted to the distal phalanges of the four lateral toes.

Flexor hallucis longusOrigin: lateral fleshy muscle arising from

the posterior surface of the middle of the fibula.

Insertion: its tendon is positioned posterior to that of the FDL, to continue at the sole of the foot where it courses near the medial border of the foot to reach its insertion at the distal phalanx of the hallux.

Deep group

Popliteus – lies obliquely across the back of the knee, partly between the synovial membrane and the fibrous capsule of the joint.

Origin: the muscle fibers arise from the tendon attached to the popliteal sulcus (pit) at the lateral epicondyle, deep to the plantaris and lateral heal of the gastrocnemius.

Insertion: its fibers spread out towards their fleshy attachments at the soleal or oblique line at the back of the upper third of the tibia

Actions: helps in flexion and medial rotation of the leg

Tibialis Posterior – deepest muscle placed between the leg bones.

Origins: adjacent surfaces of the upper third of the tibia and fibula and the interosseous membrane.

Insertion: its fibers join a slender tendon which occupies the malleolar groove behind the medial malleolus, deep and anterior to the tendons of the intermediate muscles. The tendon continues to the sole of the foot where it spreads out to be attached to the tuberosity of the navicular, to the cuboid and to the bases of the 2,3, and 4 metatarsals.

Action: primarily an invertor of the foot, but it also helps in its adduction and plantar flexion

Neuro-vascular Structures in the Posterior Compartment of the Leg

Posterior Tibial ArteryCommencement: inferior border

of the popliteus muscle. It descends vertically between

the intermediate muscles behind the posterior tibialis muscle.

Behind the medial malleolus it lies between the FDL in front and the FHL behind.

As it emerges below the inferior border of the flexor retinaculum, it divides into terminal “medial and lateral plantar arteries” which are distributed to the tissues of the sole of the foot.

Branches:1. Peroneal artery – largest branch given off laterally near the

commencement of the parent trunk. It lies deep to the FHL, descending vertically to the ankle, where it gives off terminal “calcanean and malleolar branches” and a “perforating branch” that penetrates the interosseous membrane to reach the anterior compartment and descends to the dorsum of the foot where its last branches participate in the anastomoses around the ankle.

2. Posterior tibial recurrent – (may occasionally branch out from the anterior tibial artery). It participates in the anastomoses around the knee.

3. Circumflex fibular artery – (may also branch from the anterior tibial artery). It winds around the neck of the fibula to supply the lateral compartment of the leg.

4. Muscular and nutrient arteries to the bones. The parent trunk passes behind the lateral malleolus to the lateral

side of the foot where it ends by anastomosing with neighboring arteries.

5. Malleolar and calcanean branches – that anastomose with similar branches from the anterior tibial and peroneal arteries around the ankle joint, and with tarsal branches from those arteries.

Vena comites of these arteries unite to form veins that course with the posterior tibial artery to the popliteal region where they join with the anterior tibial veins to form the popliteal vein.

Superficial Group

Muscle Origin Insertion Action NerveSupply

Gastrocnemius medial and lateral condyles of femur

calcaneum plantar flexes (flexes) foot; flexes knee

tibial nerve

Plantaris lateral supracondylar ridgeof femur

calcaneum plantar flexes foot; flexes knee

tibial nerve

Soleus shafts of tibia and fibula

calcaneum with gastrocnemius, a powerful plantar flexor of ankle;main propulsive force in walking and running

tibial nerve

Deep Group

Muscle Origin Insertion Action NerveSupply

Flexor digitorum longus

shaft of tibia distal phalanges of lateral four toes

flexes distal phalanges of lateral four toes;plantar flexes foot; supports lateral longitudinal arch of foot

tibial nerve

Flexor hallucis longus

shaft of fibula

base of distal phalanx of big toe

flexes distal phalanx of big toe; plantarflexes foot; supports medial longitudinal arch of foot

tibial nerve

Tibialis posterior

shafts of tibia and fibula and interosseous membrane

tuberosity of navicular bone

plantar flexes foot; inverts foot at subtalar and transverse tarsal joints; supports medial longitudinal arch of foot

tibial nerve

The Plantar Region (Sole of the Foot)

Skin – thick, especially at the heel and beneath the heads of the metatarsals (termed metatarsal pad). It is adherent to the tough underlying fascia especially at the heel. In a live subject, observe that despite its thickness, the skin is discerningly sensitive as to differentiate objects felt at the sole of the foot, or to feel the pain caused by the penetration of a very tiny sliver of wood or any other sharp object.

Deep Fascia – strong, dense with a central shiny condensation called “plantar aponeurosis” which protects the deeper structures. It divides into 5 slips for the toes, which are reinforced by transverse fibers attached to the metatarsal ligaments of corresponding bones. Its posterior end is attached to the calcaneus. From its deep surface, fibrous septae separate the deeper layers of muscles and tendons.

Superficial First LayerComposed of 2 abductors at the

medial and lateral borders of the foot, and 1 flexor muscle in the middle of the sole.

Origin: Each muscle arises from the corresponding lateral and medial sides of the calcaneus.

Abductor Hallucis and Abductor Digiti Minimi Quinti

Insertion: base of the proximal phalanges of the corresponding digits.

(The tendon of the abductor hallucis is usually provided with a small sesamoid bone below the head of the first metatarsal bone).

Flexor Digitorum BrevisInsertion: divides into 4 tendons, one

for each of the four lateral toes. Each of those small tendons splits to be attached to the sides of the middle phalanx of the corresponding digit.

Second Layer 2 muscles and 2 tendons

Flexor Accessorius (or Quadratus Plantae)Origin: two heads from the lateral and medial sides of the

calcaneus. Insertion: tendon of the Flexor digitorum longus, thus helping its

action.LumbricalsOrigin: 4 small muscular slips each of which arise from a tendon

of the FDL. Insertion: each of the 4 small tendons joins the dorsally located

extensor tendon of the corresponding digit.

Tendon of the Flexor Digitorum Longus – from the medial border of the foot it proceeds forwards beneath (superior to) the belly of the flexor digitorum brevis; dividing into 4 tendons, each of which passes between the split tendons of insertion of the brevis towards its insertion at the tip of the distal phalanx of the corresponding digit.

Tendon of the Flexor Hallucis Longus – courses deep to the abductor hallucis at the medial border of the foot towards its insertion at the tip of the distal phalanx of the big toe.

Third layer2 flexors and one adductor

Flexor hallucis brevisOrigin: lateral cuneiform and cuboid bones. Insertion: sides of the base of the proximal

phalanx of the first digit.Flexor digiti minimiOrigin: base of the 5th metatarsalInsertion: base of the proximal phalanx of the

5th toe.Adductor hallucis – has two heads of origin:Origin: oblique head – bases of the 2nd ,

3rd, and 4th metatarsals.Insertion: base of the first phalanx of the big

toe at the middle of the sole.transverse head – deep

metatarsal ligaments, close to the heads of the 3rd –5th metatarsal bones.

Insertion: lateral side of the base of the first phalanx of the 1st digit .

Fourth layer 2 tendons and 2 sets of muscles

Tendon of the Peroneus Longus – enters at the lateral border of the sole, extending obliquely forwards and medially to its insertions at the medial cuneiform and base of the first metatarsal bone.

Tendon of the Tibialis Posterior – winds around the medial border of the foot towards its insertions at the navicular, cuneiforms and cuboid, and the bases of the metatarsals.

3 Plantar and 4 Dorsal Interosseous Muscles – located close to each other in the inter-metatarsal space. Generally, they arise from the adjacent sides of the metatarsal bones. Each of their slender tendons insert at the sides of the bases of the proximal phalanges of the 3 lateral toes.

The plantar interossei adduct the digits while the dorsal interossei abduct them. NS: lateral plantar nerve

Muscle Origin Insertion ActionNerveSupply

First Layer

Abductor hallucis

medial tubercle of calcaneum

medial side, base proximal phalanx big toe

flexes, abducts big toe. Supports medial longitudinal arch

medial plantar

Flexor digitorum brevis

medial tubercle of calcaneum

middle phalanx of four lateral toes

flexes lateral four toes. Supports medial and laterallongitudinal arches

medial plantar

Abductor digiti minimi

medial and lateral tubercles of calcaneum

lateral side base proximal phalanx fifth toe

flexes, abducts fifth toe. Supports lateral longitudinal arch

lateral plantar

Second Layer

accessory flexor (quadratus plantae)

medial and lateral sides of calcaneum

tendon flexor digitorum longus

aids long flexor tendon to flex lateral four toes

lateral plantar nerve

lumbricals tendons of flexor digitorum longus

dorsal extensor expansion of lateral four toes

extends toes at interphalangeal joints

first lumbrical-medial plantar; remainder-deep branch lateral plantar

Third Layer

Flexor hallucis brevis

cuboid, lateral cuneiform; tibialis posterior insertion

medial and lateral sides of base of proximal phalanx of big toe

flexes metatarso-phalangeal joint of big toe; supports mediallongitudinal arch

Medial plantar

Adductor hallucis, oblique head

bases second, third, fourth metatarsal bones

lateral side base proximal phalanx big toe

adducts big toe, supports transverse arch

deep branch lateral plantar

Adductor hallucis, transverse head

capsules 3, 4, 5 metatarsophalangeal joints

lateral side of base of proximal phalanx, big toe

adduct big toe deep branch lateral plantar

Flexor digiti minimi brevis

base of 5th metatarsal

lateral side base of proximal phalanx 5th toe

flexes little toe lateral plantar

Fourth Layer

Dorsal interossei (4)

adjacent sides of metatarsals

bases of phalanges and dorsal expansion of corresponding toes

abduct toes, using second toe as referenceflex metatarsophalangeal joints; extend interphalangeal joints

Lateral plantar

Plantar interossei (3)

3rd, 4th, 5th metatarsals

bases phalanges and dorsal expansion 3rd, 4th, 5th toes

adduct toes using second toe as referenceflex metatarso-phalangeal joints; extend interphalangeal joints

Lateral plantar

Neurovascular Structures at the Sole of the Foot

These structures enter the sole at the medial border of the foot. Their course is mostly between the first and second layers, the nerves being at the inner side of the vessels.– Medial Plantar Vessels – accompanied by a larger medial

plantar nerve. These structures course directly forwards, covered by the abductor hallucis. The nerve innervates the abductor and flexor hallucis brevis, flexor digitorum brevis and the first lumbrical muscles.

– Lateral Plantar Vessels – larger, and the accompanying nerve is smaller. They cross the middle of the sole to the lateral toes. At the level of the head of the metatarsals, the artery recurves towards the medial side as a “plantar arch”, giving digital branches. The nerve innervates the small muscles of the 5th digit including the flexor accessorius, adductor hallucis and 3 lateral lumbricals and all the interosseous muscles.

The veins join to form the posterior tibial vein at the flexor retinaculum.