Sole of the Foot

This is the sole of the left foot. Start off by identifying the bones of the foot. When standing on the foot, the foot touches the ground mainly at the calcaneus bone and the heads of the metatarsals (H). Note two small bones, sesamoid bones (S) under the head of the 1st metatarsal. These small bones develop in the tendons of the flexor hallucis brevis muscle and probably serve as a fulcrum for the muscle to act more strongly. When we walk, our main lift off is at the big toe. Also note a shelf-like extension of the calcaneous, the sustentaculum tali, which supports the head of the talus when standing. One of the more important ligaments of the foot, the spring ligament, crosses under the head of the talus at this point, adding more support. This will be seen later.

Pay attention to two of the joint areas in the sole of the foot because they are the major joints for eversion and inversion of the foot:
  • subtalar joint (ST)
  • transverse talar joint (TT)
Once the skin of the sole of the foot has been removed, there is a very dense organized layer of deep fascia that runs down the middle of the sole; this is the plantar aponeurosis. There is also deep fascia covering the medial and lateral muscle groups but it has been removed in this image.

The plantar aponeurosis is thought to help maintain the medial longitudinal arch of the foot.
After the plantar aponeurosis has been removed you can see the muscles that make up the first layer of the sole of the foot and the arteries and nerves entering the foot.

The muscles of the first layer are:
  1. abductor hallucis
  2. flexor digitorum brevis
  3. abductor digiti minimi


The nerves are the:
  • medial plantar
  • lateral plantar


The arteries are branches of the posterior tibial artery and include the:
  • medial plantar
  • lateral plantar
The medial and lateral plantar nerves supply the muscles as well as the skin on the sole of the foot. They are branches of the tibial nerve.

The medial plantar nerve supplies the:
  • abductor hallucis muscle
  • flexor digitorum brevis
  • flexor hallucis brevis (in the third layer)
  • 1st lumbrical


The lateral plantar nerve supplies the remaining muscles in the sole of the foot. In a way, it is similar to the ulnar which supplies most of the small muscles of the hand. The muscles supplied are the:
  • abductor digiti minimi
  • accessory flexor (quadratus plantae)
  • adductor hallucis
  • flexor digiti minimi brevis
  • interossei
  • lumbricals 3, 4, 5
    When the flexor digitorum brevis is removed, the muscles of the second layer can be seen:
    1. accessory flexor (quadratus plantae)
    2. lumbricals
    3. tendons of the flexor digitorum longus from which the lumbricals arise
    The muscles of the third layer include the:
    1. flexor hallucis brevis
    2. adductor hallucis
      • oblique head
      • transverse head
    3. flexor digiti minimi brevis
    The fourth layer of muscles are the:
    1. dorsal interossei (dab) meaning dorsal abduct
    2. plantar interossei (pad) meaning plantar adduct


    At this level, you can also see the tendon of the peroneus longus crossing the sole of the foot.

    Nerves of the Sole of the Foot

    The medial and lateral plantar nerves supply muscles and skin of the sole of the foot.
    The medial plantar nerve gives rise to digital branches which then give rise to common digital branches and finally, the terminal branches. This nerve supplies the skin of the medial three and one half digits.

    The lateral plantar nerve gives rise to motor branches, a deep branch and finally branches to the skin of the lateral one and one-half digits.

    Arteries of the Sole of the Foot

    The arteries of the sole of the foot are derived from the posterior tibial artery. It splits into the medial and lateral plantar arteries.

    The medial plantar artery passes along the medial part of the sole of the foot and terminates by branching into digital branches.

    The lateral plantar artery becomes the plantar arterial arch which anastomoses by way of a perforating artery with the dorsal pedis artery. The arch gives rise to several metatarsal branches which split into digital branches.

    Ligaments of the Sole of the Foot

    The long plantar ligament and the plantar calcaneocuboid ligament lie deep to the muscles of the fourth layer. The long plantar ligament stretches from the calcaneum to the cuboid and to the bases of the second, third and fourth metatarsal bones.

    The plantar calcaneocuboid ligament, reaches the calcaneum to the cuboid on the deep aspect of the long plantar ligament.

    The plantar calcaneonavicular ligament extends from the calcaneus to the navicular bone and prevents the head of the talus from pushing down between the calcaneus and the navicular bones. This ligament is also know as the spring ligament since it is believed to give a spring-like action the the foot when walking.

    Arches of the Foot

    All of the bones of the foot are held together by ligaments but there are three that are strongly implicated in maintaining the arches of the foot:
    • long plantar ligament
    • calcaneocuboid ligament
    • calcaneonavicular ligament


    The muscles of the foot have two primary functions. They are responsible for the movement which is made during walking, and they also help to maintain the arches of the foot. The arches are arranged both longitudinally and transversely, and are caused primarily by the conformation of the bones of the foot and the ligaments which bind them together, and secondarily by the muscles which act upon the bones.

    The longitudinal arch of the foot is higher on the medial side, where it forms the instep as can be seen on a foot-print. It is made up of the 1st three digits and their metatarsals, the cuneiforms, the navicular bone and the talus.

    The lateral longitudinal arch is made up of digits 4 and 5 and their metatarsals, the cuboid and the calcaneum. It is much shallower than the medial arch.

    The transverse arch of the foot is primarily formed by the 5 metatarsal bones.


    Every ligament that connects the bones of the foot plays a part in the maintenance of the arches, but some which pass across two or more joints are especially important. Among these are the long plantar ligament, the plantar calcaneocuboid ligament and the plantar calcaneonavicular ligament, on which the head of the talus rests.

    While the normal tone of the small intrinsic muscles of the foot also plays an essential part in keeping the arches intact, the long muscles which are inserted by tendons into the bones of the foot have an even more important role. These are the tendon of the tibialis anterior muscle, the tendon of the tibialis posterior muscle, the tendon of the peroneus longus and the tendons of the flexor hallucis longus and flexor digitorum longus muscles.

    Finally, more superficially, the plantar aponeurosis also plays an important part in maintaining the medial longitudinal arch.

    Table of Muscles

    Muscle Origin Insertion Action Nerve
    Supply
    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 lateral
    longitudinal 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 metatarsophalangeal joint of big toe; supports medial
    longitudinal 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 fifth metatarsal lateral side base of proximal phalanx small 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 reference
    flex 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 reference
    flex metatarsophalangeal joints; extend interphalangeal joints
    lateral plantar


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