Plantar interossei muscles
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.
This article will discuss the anatomy and function of plantar interossei muscles of the foot.
|Origin||Medial aspects of metatarsal bones 3-5|
|Insertion||Medial bases of proximal phalanges and extensor expansion of digits 3-5|
Metatarsophalangeal joints 3-5: Toe flexion, toes adduction;
Interphalangeal joints 3-5: Toes extension
|Innervation||Lateral plantar nerve (S2-S3)|
|Blood supply||Lateral plantar artery|
Origin and insertion
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.
Plantar interossei are located superficial to dorsal interossei and deep to muscles of the third layer of the sole; flexor hallucis brevis, adductor hallucis and flexor digiti minimi brevis. Plantar metatarsal arteries run parallel to the medial borders of plantar interossei.
There are a lot of structures to learn in foot anatomy. Get started by looking at the different muscle groups within the foot with the learning materials below.
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.
The blood supply of the plantar interossei arises from the posterior tibial artery, via lateral plantar artery and its branches; deep plantar arch, plantar metatarsal and dorsal metatarsal arteries.
Plantar interossei have three main actions; they flex and adduct the 3rd, 4th and 5th at the metatarsophalangeal joints and extend the 2nd to 4t toes at the interphalangeal joints. These activities are important during the push-off phase of running or walking as they maintain the position of 3rd to 5th toes and prevent them from thrusting apart once the body weight is applied to the forefoot.
Need a refresher course on the different types of body movements? Check out the following study unit to jog your memory!
Loss of function of the plantar (and dorsal) interossei will result in unopposed flexion of the toes. This is commonly described as a claw-toe deformity and is associated with denervation of the muscle. There are some denervation syndromes that should be considered when this deformity is seen.
One example is Charcot-Marie-Tooth disease, which is a hereditary sensorimotor neuropathy that affects the peripheral nervous system. It causes progressive muscular atrophy and sensory loss.