Plantar Interosseous Muscles – Anatomy, Nerve Supply

Plantar interossei are a group of three small muscles found in the central compartment of the sole of the foot. As the foot muscles can be divided either from lateral to medial into three groups or from superficial to deep into four layers, plantar interossei can be classified in two ways:

• They can be considered as part of the central plantar muscle group with the flexor digitorum brevis, quadratus plantae, lumbricals and dorsal interossei.
• Alternatively, they can be discussed as part of the fourth layer of plantar muscles (interosseous compartment), along with the dorsal interossei.

Plantar interossei are invested by the plantar interosseous fascia and accompanied by the dorsal interossei muscles. Plantar interossei are smaller than their dorsal counterparts and lie below the metatarsal bones.

Structure of Plantar Interosseous Muscle

The three plantar interosseous muscles are unipennate, as opposed to the bipennate structure of dorsal interosseous muscles, and originate on a single metatarsal bone. The three muscles originate on the medial aspect of metatarsals III-V. The muscles cross the metatarsophalangeal joint of toes III-V so the insertions correspond with the origin and there is no crossing between toes.^[rx] The muscles then continue distally along the foot and insert in the proximal phalanges III-V. The muscles cross the metatarsophalangeal joint of toes III-V so the insertions correspond with the origin and there is no crossing between toes.^[rx]

Plantar Interosseous

• The plantar interossei (3)
• Origin: medial aspect of the individual metatarsals of digits three through five
• Insertion: The proximal phalanges
• Action: Adduct the digits
• Blood Supply: Plantar metatarsal artery
• Innervation: Lateral plantar nerve

Origin and Insertion of Plantar Interosseous Muscle

Plantar interossei are the three fusiform, unipennate muscles, meaning that the fibers of each muscle are obliquely arranged and insert on one side of the tendon?. Each muscle arises from the medial plantar aspect of the 3rd to 5th metatarsal bones, respectively.

The muscle fibers course anteriorly, crossing the medial aspect of metatarsophalangeal joint to give off a tendon? at the level of the head of respective metatarsal bone. After passing deep to the deep transverse metatarsal ligament?, the tendon of each muscle inserts to the medial base of proximal phalanx and extensor expansion of the corresponding toe.

Recall that the extensor expansion of the foot is a hood-like, triangular aponeurosis of extensor digitorum longus muscle that provides a point of attachment for the extensor muscles. It is similar to but smaller than, the extensor expansion of the hand.

Nerve Supply

Plantar interossei are innervated by two branches of tibial nerve; the medial three muscles are supplied by the deep branch of lateral plantar nerve (S2-S3) while the most lateral plantar interosseous muscle (of the 4th interosseous space) is supplied by the superficial branch of this nerve.

All three plantar interosseous muscles are innervated by the lateral plantar nerve. The lateral plantar nerve is a branch from the tibial nerve, which originally branches off the sciatic nerve from the sacral plexus.^[rx]

Blood Supply

The blood supply of the plantar interossei arises from the posterior tibial artery, via the lateral plantar artery and its branches; deep plantar arch, plantar metatarsal, and dorsal metatarsal arteries.

Function

Since the interosseous muscles cross on the metatarsophalangeal joint, then they act on that specific joint and cause the adduction of toes III, IV, and V.^[rx]

Adduction itself is not of extreme importance to the toes, but these muscles work together with the dorsal interosseous muscles in flexion of the foot. They also work together to strengthen the metatarsal arch.^[rx]

References