Medial Muscles of the sole of the Foot
The plantar muscles of the foot are traditionally studied in either layers or groups. If studying by layers, we can organise these muscles into four primary layers:
- 1st layer: abductor hallucis, flexor digitorum brevis, abductor digiti minimi
- 2nd layer: quadratus plantae, lumbricals
- 3rd layer: flexor hallucis brevis, adductor hallucis, flexor digiti minimi brevis
- 4th layer: plantar and dorsal interossei
The plantar muscles of the foot can alternatively be considered by medial, central and lateral groups. This article will discuss the medial plantar muscles.
Anatomy and supplyThe plantar fascia which surrounds all muscles of the sole of the foot consists of three chambers.
The muscles lying within the medial group form a bulge referred to as the 'ball' of the big toe. It contributes to the surface anatomy of the medial sole of the foot and is easy to palpate.
The medial plantar muscles are innervated by motor branches of the tibial nerve (L5-S2).
Abductor hallucis muscle
The abductor hallucis has its origin at the calcaneal tuberosity, plantar aponeurosis and the superficial layer of the flexor retinaculum. Its tendon runs distally to the medial sesamoid bone of the great toe and inserts into the base of the proximal phalanx of the big toe.
The muscle is innervated by the medial plantar nerve.
Adductor hallucis muscle
The adductor hallucis has two heads:
- The transverse head originates at the 3rd to 5th metatarsophalangeal joint and the deep transverse metatarsal ligament.
- The oblique head arises at the cuboid bone, the lateral cuneiform bone and the bases of the 2nd to 4th metatarsal bones. It may also/alternatively have an attachment to the sheath of the fibularis longus tendon. To be precise the oblique head does not lie within the medial but central group of the plantar fascia.
Both heads form a common tendon, which runs along the lateral sesamoid bone of the great toe, and inserts at the base of the proximal phalanx of the big toe.
The innervation is supplied by the lateral plantar nerve.
Flexor hallucis brevis muscle
The FHB originates at the lateral cuneiform bone and cuboid bone. It may also have attachments to the medial cuneiform bone, the plantar calcaneocuboid ligament and the tendon of tibialis posterior.
Its insertions are located at the base of the proximal phalanx of the great toe, via the the medial (medial head) and lateral (lateral head) sesamoid bones.
While the medial head is innervated by the medial plantar nerve, the lateral head is supplied by the lateral plantar nerve (double innervation).
In addition to the three above mentioned muscles there are more structures lying in the medial group of the plantar fascia e.g. the tendon of the flexor hallucis longus muscle; blood vessels and nerves of the medial foot sole (medial plantar artery and vein, medial plantar nerve).
The medial muscles of the foot sole have various tasks:
- First of all they act upon the metatarsophalangeal joint of the big toe, leading to the abduction (abductor hallucis muscle), adduction (adductor hallucis muscle) and flexion (both flexor hallucis brevis and adductor hallucis muscle) of the big toe.
- Furthermore they actively support the structure of the arches of the foot. While all three muscles stabilize the longitudinal arch, the transverse head of the adductor hallucis muscle is the only muscle securing the transverse arch.
The insufficiency of the ligaments and muscles of the foot sole often lead to foot deformities.
One of the most common is the bunion (hallux valgus), which characterized by a abnormal adduction of the metatarsal bone of the big toe. This results in a noticeable deviation of the great toe/hallux laterally towards the second toe.
Typical symptoms are callus formation around the first metatarsophalangeal joint, pain during stress and restriction of mobility. Obese women wearing inappropriate shoes (high-heeled, tight, pointy) and lacking physical exercise are particularly in risk of suffering from bunions.
Treatment for bunions usually begins by means of relatively conservative treatments such as rest, ice and mediacations for pain and inflammation. These interventions however, do not deal with the actual deformity involved, and function mainly to relieve discomfort and pain. In more serious cases, surgical intervention by means of an bunionectomy may be undertaken by a podiatric or orthopaedic surgeon.n