Lateral 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 lateral plantar muscles.
Anatomy and supply
The lateral chamber formed by the plantar fascia contains three muscles. Their muscle bellies form the surface of the lateral foot sole (ball of the little toe).
Abductor digiti minimi muscle
Flexor digiti minimi brevis muscle
The FDM runs from the metatarsal bone of the little toe and long plantar ligament to the base of the proximal phalanx of the little toe.
Opponens digiti minimi muscle
The opponens digiti minimi originates at the long plantar ligament, the base of the fifth metatarsal bone and the tendon sheath of the fibularis longus muscle. Thereupon it inserts again at the lateral border of the fifth metatarsal bone. This muscle is not found in all human bodies.
Besides the above mentioned muscles there are more structures lying within the lateral chamber of the plantar fascia supplying the lateral foot sole (lateral plantar artery, vein and nerve).
The lateral muscles of the foot sole move the little toe, or fifth digit of the foot through flexion (abductor digiti minimi and flexor digiti minimi brevis muscle), abduction (abductor digiti minimi muscle) and opposition (opponens digiti minimi muscle).
Furthermore they actively support the longitudinal arch of the foot. However in comparison to the medial muscles of the foot they are poorly developed and are relatively less important.
Although more commonly associated the big toe in the form of hallux valgus, a bunion can also develop at the metatarsophalangeal joint of the little toe. In this instance, they are generally referred to as a 'bunionette', or 'tailor's bunion'.
A bunionette occurs due to changes in the bony framework of the lateral foot, which causes the fifth metatarsal bone to protrude laterally, and the little toe proper to deviate medially towards the fourth digit. This results in a enlargement (sometime bony) on the outside of the foot which can cause discomfort, redness, swelling and pain.
Treatments most often are relatively conservative and involve the use of rest, ice, shoe modifications and padding, as well as medications for plain and inflammation. In severe cases, surgical intervention may be taken by an orthopaedic or podiatric surgeon, to remove the bony outgrowth.