The Foot

Ankle & foot joints | Main Anatomy Index | Femoral triangle

Deep Fascia of the Foot (pp. 463-4)

• This fascia is continuous with that of the ankle.
• It is thin on the dorsum of the foot, where it is continuous with the inferior extensor retinaculum.
• Over the lateral and posterior aspects of the foot, the deep fascia is continuous with the plantar fascia or deep fascia of the sole.

The Plantar Aponeurosis (pp. 463-3)

• This is the greatly thickened central part of the plantar fascia.
• It consists of a strong, thick central part and weaker and thinner medial and lateral portions.

• This plantar aponeurosis covers the entire length of the sole and consists of longitudinally arranged bands of dense fibrous connective tissue.
• It helps to support the longitudinal arches of the foot and hold the parts of the foot together.
• It arises posteriorly from the tuber calcanei and fans out over the sole, where it becomes broader and somewhat thinner.

• The plantar aponeurosis divides into five bands that split to enclose the digital tendons.
• They are attached to the margins of the fibrous digital sheaths and to the sesamoids of the great toe.
• From the margins of the central part of the plantar aponeurosis, vertical septa extend deeply to form three compartments of the sole of the foot: a medial compartment, a lateral compartment and a central compartment.

• The muscles, nerves and vessels may be described according to these compartments, but the muscles are usually described by layers.

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Muscles of the Foot

Muscles on the Dorsum of the Foot (p. 464)

• There are two closely connected muscles on the dorsum of the foot, the extensor digitorum brevis and extensor hallucis brevis. The latter muscle is part of the extensor digitorum brevis.

The Extensor Digitorum Brevis and Extensor Hallucis Brevis Muscles (p. 464)

• These broad thin muscles form a fleshy mass on the lateral part of the dorsum of the foot, anterior to the lateral malleolus, which can be seen in most feet and felt in all of them.

• Actions: the extensor digitorum brevis extends the second to fourth digits at the metatarsophalangeal joints, and the extensor hallucis brevis extends the first digit or great toe at the metatarsophalangeal joint.
• These muscles help the long extensor muscles extend the toes.

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Muscles in the Sole of the Foot

• There are four muscular layers in the sole of the foot.
• They are specialised to maintain the arches of the foot and to enable one to stand on uneven ground.
• These muscles have gross functions rather than delicate individual functions like those in the hand.

• There are two neurovascular planes in the foot: a superficial one between the first and second layer and a deep one between the third and fourth muscular layers.

First Layer of Plantar Muscles (p. 464)

• This superficial layer contains 3 short muscles.
• They all extend from the posterior part of the calcaneus to the phalanges.
• It contains the abductor of the great and small digits and the short flexors of the lateral four digits.

• These muscles act as a functional group that acts as an elastic spring for supporting the arches of the foot and maintaining the concavity of the foot.
• It contains abductor hallucis, flexor digitorum brevis, and abductor digiti minimi.

Second layer of Plantar Muscles (pp. 464-5)

• This layer, located deep to the first layer consists of the quadratus plantae and lumbrical muscles.

• The long tendons of flexor hallucis longus and flexor digitorum longus are also located on this layer.
• The tendon of the flexor hallucis longus crosses deep to the flexor digitorum longus as it passes to the first digit or the great toe.

• Quadratus plantae is from the calcaneus --> tendon of flexor digitorum longus.
• The lumbrical muscles are from tendons of flexor digitorum longus --> dorsal digital expansion.

Third Layer of Plantar Muscles (p. 465, 467)

• This layer has 3 short muscles of the great and small digits, which lie in the anterior half of the sole of the foot.
• Two act on the great digit and one on the small digit.

• Includes: flexor hallucis brevis, adductor hallucis and flexor digiti minimi.
• A sesamoid bone adheres to each of the tendons of the two heads of flexor hallucis brevis.

Fourth Layer of Plantar Muscles (p. 467)

• This layer consists of the interosseous muscles and the tendons of the fibularis (peroneus) longus and tibialis posterior muscles, which cross the foot to reach their distal attachments.

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