Opponens digiti minimi muscle of foot

Origin and insertion

Opponens digiti minimi represents deep fibers of the flexor digiti minimi brevis muscle which slip off to the distal half of the fifth metatarsal bone. Opponens digiti minimi originates from three distinct sites; long plantar ligament, base of metatarsal bone 5 and tendon sheath of fibularis longus. The muscle travels for a short distance along the fifth metatarsal bone, inserting distally into its lateral border.

Relations

Plantar muscles of the foot can be organized anatomically in two distinct ways: 

• Vertically into three muscle compartments called medial, central and lateral.
• Horizontally into four muscle layers, which are simply numbered from superficial to deep.

Opponens digiti minimi occupies the lateral plantar compartment of foot. It is located lateral to flexor digiti minimi brevis and the fifth metatarsal bone. In addition, it is also one of the most lateral muscles located within the sole of the foot. Opponens digiti minimi also occupies the third layer, from superficial to deep. Here, it is located deep to abductor digiti minimi, which is situated in the first layer.

Innervation

Opponens digiti minimi is innervated by the superficial branch of the lateral plantar nerve, which originates from the S2 and S3 spinal nerves. The lateral plantar nerve is a branch of the tibial nerve.

Blood supply

Opponens digiti minimi shares a similar blood supply with flexor digiti minimi brevis. It is supplied by two branches of the dorsalis pedis artery, namely the arcuate and lateral tarsal arteries. In addition, the lateral plantar artery, which stems from the posterior tibial artery, sends a plantar digital branch to the opponens digiti minimi muscle.

Functions

Opponens digiti minimi acts on the fifth metatarsophalangeal joint, causing toe flexion and abduction. Toe flexion has important functional implications during walking, running and jumping. By pulling the fifth toe firmly towards the ground, opponens digiti minimi helps to maximize the grip of the foot onto the ground, facilitating thrust during the toe-off phase. When standing still, a strong grip onto the ground improves balance. Toe abduction is also important during these activities because opponens digiti minimi splays the fifth toe when weight is suddenly applied to the forefoot.

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Opponens digiti minimi also helps to support the lateral longitudinal arch of the foot. During running and jumping activities when the bodyweight is suddenly collapsed onto the foot, the muscle maintains the arch under stress by acting as a bowstring.