The muscles acting on the foot can be divided into two distinct groups; extrinsic and intrinsic muscles. Extrinsic muscles arise from the anterior, posterior and lateral compartments of the leg and are mainly responsible for actions such as eversion, inversion, plantarflexion and dorsiflexion of the foot. Intrinsic muscles, on the other hand, are located within the foot and are responsible for the fine motor actions of the foot, for example movement of individual digits. In this article, we shall examine the anatomy of the intrinsic muscles of the foot, which can be divided into those situated on the dorsum of the foot and those in the sole of the foot.
There are two intrinsic muscles situated within the dorsum of the foot: the extensor digitorum brevis and the extensor hallucis brevis. Both muscles are typically responsible for assisting the extrinsic muscles of the foot in extending the toes and are both innervated by the deep fibular nerve.
The extensor digitorum brevis is a small, thin muscle which lies underneath the long extensor tendons of the foot. It originates from the calcaneus and inferior extensor retinaculum, then attaches onto the long extensor tendons of the medial four toes. In terms of function, the extensor digitorum brevis is responsible for the extension of the lateral four toes. As previously mentioned, it is innervated by the deep fibular nerve.
The extensor hallucis brevis is often considered to be the medial part of the extensor digitorum brevis muscle, rather than a separate structure. It originates from the calcaneus and inferior extensor retinaculum and attaches to the base of the proximal phalanx of the great toe. As its name implies, the extensor hallucis brevis is responsible for the extension of the great toe and is also innervated by the deep fibular nerve.
There are ten intrinsic muscles located in the plantar aspect (sole) of the foot. They act collectively to stabilise the arches of the foot and individually to control movement of the digits, all of which are innervated by the medial or lateral plantar nerves, which are branches of the tibial nerve.
The muscles of the sole are arranged in four layers (superficial to deep):
In conclusion, understanding the intrinsic muscles of the foot can help us to better understand foot anatomy and movement, and to better diagnose and treat foot injuries.
The muscles acting on the foot can be divided into two distinct groups; extrinsic and intrinsic muscles. Extrinsic muscles arise from the anterior, posterior and lateral compartments of the leg. They are mainly responsible for actions such as eversion, inversion, plantarflexion and dorsiflexion of the foot. Intrinsic muscles are located within the foot and are responsible for the fine motor actions of the foot, for example movement of individual digits. In this article, we shall examine the anatomy of the intrinsic muscles of the foot. They can be divided into those situated on the dorsum of the foot, and those in the sole of the foot.
There are two intrinsic muscles located within the dorsum of the foot - the extensor digitorum brevis and extensor hallucis brevis. The extensor digitorum brevis originates from the base of the fifth metatarsal and attaches to the base of the distal phalanx of the second to fourth digits. The extensor hallucis brevis originates from the cuboid and lateral cuneiform and attaches to the bases of the distal phalanges of the great toe.Both muscles are responsible for extensor movement of the toes at the interphalangeal joints. They are innervated by the deep fibular nerve.
The muscles of the sole of the foot are divided into four layers:
The first layer of intrinsic muscles of the sole of the foot consists of the quadratus plantae, flexor digitorum brevis, abductor hallucis, and flexor hallucis brevis muscles. The quadratus plantae muscle originates from the plantar surfaces of the cuboid and calcaneus and inserts into the tendon of the flexor digitorum longus. It acts to assist the flexor digitorum longus in flexing the toes at the interphalangeal joints and is innervated by the deep fibular nerve.The flexor digitorum brevis muscle originates from the plantar aspect of the calcaneus and attaches to the bases of the proximal phalanges of the four lateral toes. It acts to flex the toes at the metatarsophalangeal joints and is innervated by the medial and lateral plantar nerves.The abductor hallucis muscle originates from the medial aspect of the calcaneus and the plantar aponeurosis. It inserts into the base of the proximal phalanx of the great toe and acts to abduct the great toe. It is innervated by the medial plantar nerve.The flexor hallucis brevis muscle originates from the plantar surfaces of the cuboid and lateral cuneiform and inserts into the base of the proximal phalanx of the great toe. It acts to flex the great toe at the metatarsophalangeal joint and is innervated by the medial plantar nerve.
The second layer of intrinsic muscles of the sole of the foot consists of the adductor hallucis, quadratus plantae, and four lumbricals. The adductor hallucis originates from the bases of the two, three and four metatarsals and inserts into the lateral aspect of the proximal phalanx of the great toe. It acts to adduct the great toe, and support the transverse arch of the foot. It is innervated by the deep branch of the lateral plantar nerve. The quadratus plantae is the same muscle as the one located in the first layer. It is located more posteriorly and assists in flexion of the toes at the interphalangeal joints.The lumbricals are four fan-shaped muscles. They arise from the tendon of the flexor digitorum longus and attach to the extensor expansion of the digits. They act to flex the metatarsophalangeal joints and extend the interphalangeal joints and are innervated by the medial and lateral plantar nerves.
The third layer of intrinsic muscles of the sole of the foot consists of the flexor hallucis brevis, adductor hallucis, and flexor digiti minimi brevis. The flexor hallucis brevis muscle has two heads of origin; the lateral head which originates from the plantar surfaces of the cuboid and lateral cuneiforms, and the medial head which originates from the tendon of the posterior tibialis tendon. It inserts into the base of the proximal phalanx of the great toe and acts to flex the great toe at the metatarsophalangeal joint. It is innervated by the medial plantar nerve.The adductor hallucis muscle is located laterally to the flexor hallucis brevis. It consists of an oblique and transverse head, with both heads attaching to the lateral aspect of the base of the proximal phalanx of the great toe. It acts to adduct the great toe, and support the transverse arch of the foot. It is innervated by the deep branch of the lateral plantar nerve. The flexor digiti minimi brevis muscle is located laterally on the foot. It resembles the interossei in structure and originates from the base of the fifth metatarsal and inserts into the base of the proximal phalanx of the fifth digit. It acts to flex the little toe at the metatarsophalangeal joint and is innervated by the superficial branch of the lateral plantar nerve.
The fourth and final layer of intrinsic muscles of the sole of the foot consists of the plantar and dorsal interossei. The plantar interossei are unipennate in shape and there are three of them. Each arises from a single metatarsal and attaches to the medial sides of the phalanges of digits three to five. They act to adduct the lateral three digits and flex the metatarsophalangeal joints and are innervated by the lateral plantar nerve.The dorsal interossei are bipennate in shape and there are four of them. Each arises from two metatarsals and attaches to the lateral sides of the proximal phalanges of digits two to four. They act to abduct the lateral four digits and flex the metatarsophalangeal joints and are innervated by the lateral plantar nerve.
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. It is therefore important for athletes and individuals engaging in activities that involve excessive movements of the foot to seek medical attention if they experience any symptoms relating to nerve entrapment.
The muscles of the foot can be divided into two main groups: extrinsic and intrinsic. The extrinsic muscles, located on the dorsal aspect of the foot, act upon the toes from a position outside the foot. The intrinsic muscles, on the other hand, are located on the plantar aspect of the foot and act upon the toes from a position inside the foot.
The muscles of the foot can be further divided into four layers on the plantar aspect. The first layer includes the Quadratus plantae and the Lumbricals, the second layer contains the Flexor digitorum brevis and Abductor digiti minimi, the third layer contains the Flexor hallucis brevis, Adductor hallucis, and Flexor digiti minimi, and the fourth layer contains the Plantar and Dorsal interossei.
The first layer, the most superficial, is located immediately underneath the plantar fascia. It features three muscles: the Quadratus plantae, the Lumbricals, and the tendons of Flexor digitorum longus.
The muscles of the foot are responsible for providing stability and enabling mobility. Collectively, they help to maintain the arches of the foot and control the movement of the toes. The various muscles and tendons of the foot, however, can be easily injured or strained, and it is important to take precautions to protect them.
The foot contains two categories of muscles, the extrinsic and the intrinsic muscles. The extrinsic muscles act on the foot from a distant origin, whilst the intrinsic muscles act solely on the foot itself. The muscles of the foot can be divided into four layers according to their location.
The first layer consists of the extensor digitorum brevis, extensor hallucis longus, and fibularis tertius. All of these muscles are responsible for dorsiflexion of the toes and the foot. This layer can be the source of a clinical problem in cases of overuse injury of the first layer muscles, which may lead to entrapment of the medial plantar nerve.
The second layer contains the extensor digitorum longus, fibularis longus, and fibularis brevis muscles. All of these muscles are responsible for aiding in the dorsiflexion of the foot and toes.
The third layer contains the tibialis anterior and the peroneus longus, both of which act to aid in plantar flexion of the foot. This layer also includes the Flexor hallucis brevis, which acts to flex the great toe at the metatarsophalangeal joint, and is innervated by the medial plantar nerve. Additionally, the Flexor digiti minimi brevis is also located in this layer. This muscle resembles the interossei in structure and acts to flex the little toe at the metatarsophalangeal joint. It is innervated by the superficial branch of the lateral plantar nerve.
The fourth layer contains the Plantar and Dorsal interossei, which act to adduct the lateral three digits and flex the metatarsophalangeal joints. These muscles are both innervated by the lateral plantar nerve. They also act to help in the plantarflexion of the foot and toes.
Clinically, the medial plantar nerve can become compressed and irritated as it passes deep to the abductor hallucis muscle, causing aching, numbness and paraesthesia on the medial side of the sole of the foot. This can occur with repetitive eversion of the foot, which may happen in some sports such as gymnastics. In order to prevent this kind of injury, it is important to perform exercises and stretching on a regular basis to keep the muscles flexible and strong.
The Adductor hallucis, also located in the third layer, has an oblique and transverse head and acts to adduct the great toe. It is innervated by the deep branch of the lateral plantar nerve. This muscle is important for proper alignment of the toes and should be included as part of a regular stretching routine.
To prevent the development of any problems associated with the intrinsic muscles of the foot, it is important to maintain proper stretching and strengthening exercises as part of an individual's regular exercise routine. Regular stretching of the first layer muscles, in particular, can help to prevent entrapment of the medial plantar nerve through a decrease in repetitive eversion of the foot. Additionally, proper strengthening of the adductor hallucis can help to prevent any misalignment of the toes.
