Muscles of the foot originate and insert in the foot as follows:
- The extensor digitorum brevis and extensor halluces brevis on the dorsal aspect of the foot or Dosrum of the foot;
- All the other muscles viz -the dorsal and plantar interossei, flexor digiti minimi brevis, flexor halluces brevis, flexor digitorum brevis, quadratus plantae (flexor accessorius), abductor digiti minimi, abductor hallucis, and lumbricals are on the plantar side of the foot in the sole where they are arranged in 4 layers.
Muscles primarily modify the actions of the long tendons and provide fine movements of the toes.
All muscles of the foot are innervated by the medial and lateral plantar branches of the tibial nerve except for the extensor digitorum brevis, which is innervated by the deep fbular nerve. The first two dorsal interossei also may receive part of their innervation from the deep fibular nerve.
Muscles of The Dorsum of The Foot or Dorsal of the foot
Extensor Digitorum Brevis
It’s a small muscle situated on the lateral part of the dorsum of the foot, deep to the tendons of extensor digitorum longus. It’s the only muscle on the dorsum of the foot and creates a fleshy swelling anterior to the lateral malleolus. The youthful beginner physicians sometime diagnose it as a contusion.
It originates from the anterior part of the superior surface of calcaneum, medial to the connection of the stalk of inferior extensor retinaculum.
- The muscle splits into 4 tendons for the medial 4 toes. The tendon to the big toe crosses in front of dorsalis pedis artery and inserts on the dorsal surface of the proximal phalanx of the big toe. The Lateral 3 tendons join the lateral side of the tendons of the extensor digitorum longus to the 2nd, third, and fourth toes.
- Medial most part of the extensor digitorum brevis, which creates the tendon for the big toe, splits or becomes different early. It’s called extensor hallucis brevis.
It’s by the lateral terminal branch of the deep peroneal nerve.
- Extensor hallucis brevis (EHB) stretches the metatarsophalangeal joint of the big toe.
- The other 3 tendons stretch the metatarsophalangeal and interphalangeal joints of 2nd, third, and fourth toes, especially when the foot is dorsiflexed.
Extensor Hallucis Brevis
The extensor hallucis brevis originates in conjunction with the extensor digitorum brevis. Its tendon attaches to the base of the proximal phalanx of the great toes. The muscle extends the metatarsophalangeal joint of the great toe and is innervated by the deep fbular nerve.
It arises from the calcaneus, the interosseous talocalcaneal ligament and the inferior extensor retinaculum and it connects to the base of the proximal phalanx of the great toe.
It helps the extensor hallucis longus in extending the great toe at the metatarsophalangeal joint.
It is innervated by Deep fibular nerve.
Plantar Side of The Foot (Muscles of The Sole of The Foot)
There are 18 intrinsic muscles and 4 extrinsic tendons in the sole of the foot. The muscles of the sole are described in 4 layers from superficial to deep (Table 30.1).
Muscle Layers of The Sole of The Foot
The muscles of the sole are primarily concerned with supporting the arches of the foot. The short and long muscles of the foot serve as synergists.
Neurovascular planes of the sole: There are 2 neurovascular planes between the muscle layers of the sole:
- Superficial neurovascular plane between the first and 2nd layers.
- Deep neurovascular plane between the 3rd and fourth layers.
In the superficial neurovascular plane is located the trunks of medial and lateral plantar nerves, and the arteries.
In the deep neurovascular plane is located the deep branches of the lateral plantar nerve and artery.
To understand the origin and insertion of the muscles of the foot the student must study the layout of the various bones on the plantar aspect of the skeleton of the foot.