Muscles - Foot

Question 1

What are the functions of the intrinsic and extrinsic muscles of the foot?

Answer 1

Extrinsic muscles - arises from the anterior, lateral and posterior compartments of the leg. They are responsible for actions such as eversion, inversion, plantarflexion and dorsiflexion of the foot.

Intrinsic muscles - muscles are located within the foot and are responsible for fine motor actions of the foot, for example movement of individual digits.

Question 2

What are the intrinsic muscles of the dorsum of the foot?

Arterial supply?

Answer 2

These lie deep to the tendons of the extensor digitorum longus.

1) Extensor hallucis brevis
2) Extensor digitorum brevis

Arterial supply - branches of the dorsalis pedis.

Question 3

Extensor hallucis brevis

Answer 3

Origin - calcaneus, the interroseous talocalcaneal ligament and the inferior extensor retinaculum.

Insertion - base of the proximal phalanx of the great toe.

Innervation - deep fibular nerve

Actions - assists the extensor hallucis longus in extension of the great toe at the metatarsophalangeal joint.

Question 4

Extensor digitorum brevis

Answer 4

Origin - calcaneus, interroseous talocalcaneal ligament, inferior extensor retinaculum.

Insertion - extensor expansions of toes 2-4.

Innervation - deep fibular nerve.

Action - extends toes 2-4

Question 5

What are the intrinsic muscles of the plantar surface of each layer?

Answer 5

There are 10 intrinsic muscles in total.

1st layer - abductor hallucis, flexor digitorum brevis, abductor digiti minimi

2nd layer - quadratus plantae, lumbricals

Note that the flexor digitorum longus tendons pass through this layer.

3rd layer - flexor hallucis brevis, adductor hallucis, flexor digiti minimi brevis

4th layer - plantar interossei, dorsal interrossei

These muscles are either innervated by the medial or lateral plantar nerves.

Question 6

Abductor hallucis

Answer 6

Origin - medial tubercle of calcaneus, flexor retinaculum and plantar aponeurosis.

Insertion - medial base of the proximal phalanx of big toe.

Innervation - medial plantar nerve

Actions - abducts and flexes the great toe

Question 7

Flexor digitorum brevis

Answer 7

Origin - medial tubercle of the calcaneus and plantar aponeurosis.

Insertion - middle phlanges of the lateral four digits

Innervation - medial plantar nerve

Action - flexes the lateral four digit at the proximal interphalangeal joints

Question 8

Abductor digiti minimi

Answer 8

Origin - medial and lateral tubercles of the calcaneus and plantar aponeurosis.

Insertion - lateral base of the proximal phalanx of the 5th digit.

Innervation - lateral plantar nerve

Actions - abducts and flexes the 5th digit.

Question 9

Quadratus plantae

Answer 9

Origin - medial and lateral plantar surface of the calcaneus.

Insertion - tendons of the flexor digitorum longus

Innervation - lateral plantar nerve

Actions - assists flexor digitorum longus in flexing the lateral four digits.

Question 10

Lumbricals

Answer 10

Origin - tendons of the flexor digitorum longus.

Insertion - extensor hoods of the lateral four digits

Innervation - medial lumbrical by medial plantar nerve. Remaining by lateral plantar nerve.

Actions - flexes at the metatarsophalangeal joints, while extending the interphalangeal joints.

Question 11

Flexor hallucis brevis

Answer 11

Origin - plantar surfaces of cuboid and lateral cuneiforms, and from the tendon of the posterior tibialis.

Insertion - base of the proximal phalanx of the great toe.

Innervation - medial plantar nerve

Actions - flexes the proximal phalanx of the great toe at the metatarsophalangeal joint.

Question 12

Adductor hallucis

Answer 12

Located laterally to the flexor hallucis brevis. Consist of an oblique and transverse head.

Origin (oblique head) - bases of 2nd, 3rd, and 4th metatarsals.

Origin (transverse head) - plantar ligaments of the metatarsophalangeal joints.

Insertion (both heads) - lateral base of the proximal phalanx of the great toe.

Innervation - deep branch of lateral plantar nerve.

Actions - adducts the great toe. Assists in forming the transverse arch of the foot.

Question 13

Flexor digiti minimi brevis

Answer 13

It resembles the interrosei in structure.

Origin - base of 5th metatarsal.

Insertion - base of the proximal phalanx of the 5th digit.

Innevation - superficial branch of lateral plantar nerves.

Actions - flexes the proximal phalanx of the 5th digit.

Question 14

Plantar interrosei

Answer 14

Unipennate morphology.

Origin - medial side of metatarsals 3-5 digits.

Insertion - medial sides of phalanges 3-5 digits.

Innervation - lateral plantar nerve.

Actions - adducts digits 3-5 and flex at the metatarsophalangeal joints.

Question 15

Dorsal interossei

Answer 15

There are 4 dorsal interossei, which are located between metatarsals. Each arises from two metatarsals.

Origin - sides of metatarsals 1-5.

1st muscle - medial side of the proximal phalanx of 1st digit.

2-4th muscles - lateral sides of the proximal phalanxes of digits 2-4.

Innervation - lateral plantar nerve

Actions - abducts digits 2-4 and flex the metatarsophalangeal joints.

Question 16

Clinical relevance - contusion of extensor digitorum brevis

Answer 16

Tearing of this muscle will result in a haematoma. This produces characteristic swelling anteromedial to the lateral malleolus - differentiating it from a sprained ankle (for which it is more often confused).

Question 17

Clinical relevance - medial plantar nerve entrapment

Answer 17

The medial plantar nerve can become compressed and irritated as it passes deep to the abductor hallucis muscle.

This can cause aching, numbness and paraesthesia on the medial side of the sole of the foot. The muscle can become compressed during repetitive eversion of the foot, which may occur in some sports, such as gymnastics.