Where is the muscle located and how is it structured?
The flexor digitorum brevis muscle (m. flexor digitorum brevis) originates from the medial process of the calcaneal tuberosity and the plantar aponeurosis. The muscle gives rise to four tendons that run toward the middle phalanges of digits II–V.
An anatomical feature of this muscle is the formation of the tendinous chiasm (chiasma tendinum). The tendons of the flexor digitorum brevis bifurcate and cross to allow the passage of the tendons of the flexor digitorum longus (m. flexor digitorum longus).
Topography and fascial compartments
The muscle is located on the plantar surface of the foot and belongs to the first layer of muscles in the tarsal region.
It lies superficially in the middle compartment of the sole. The flexor digitorum brevis and plantar aponeurosis are shown as sectioned structures of the deep layer of the sole. The muscle itself is covered by its own fascial layer.
Deep to the flexor digitorum brevis lies the tendon of the flexor digitorum longus. The quadratus plantae muscle (m. quadratus plantae) attaches to this tendon laterally.
Fascial spaces and clinical significance
In the metatarsal region of the middle plantar compartment, the superficial fascial space is identified. It is located between the tendons of the flexor digitorum brevis and the tendons of the flexor digitorum longus.
The middle plantar compartment has communications that are important for the spread of purulent infections. Infection can spread into the subcutaneous tissue of the sole along the plantar metatarsal and plantar digital vessels through the commissural openings in the plantar aponeurosis.
What is its function?
- Toe flexion: the muscle flexes the middle phalanges of digits II–V of the foot; flexion of the proximal interphalangeal joint of digits II–V of the foot is also noted.
- Longitudinal arch: the muscle forms the longitudinal arch of the foot.
Blood supply and innervation
- Blood supply (A): supplied by the medial and lateral plantar arteries (aa. plantares medialis et lateralis). The medial plantar artery runs within the medial intermuscular septum and branches to the muscles of the medial and middle fascial compartments.
- Innervation (Inn): provided by the medial plantar nerve (n. plantaris medialis). Innervation from S1–S3 is also indicated for the flexor digitorum brevis.
Class and exam questions
Which fascial compartment of the sole contains the flexor digitorum brevis?
The muscle lies superficially in the middle plantar compartment. It belongs to the first layer of foot muscles.
What is the "tendinous chiasm" (chiasma tendinum) in the foot?
This is an anatomical structure where the tendons of the flexor digitorum brevis bifurcate, allowing the tendons of the flexor digitorum longus to pass through.
Which nerves and segments innervate this muscle?
The flexor digitorum brevis is innervated by the medial plantar nerve (n. plantaris medialis). Innervation from S1–S3 is also specified for this muscle.
Which fascial space is related to the topography of this muscle?
Between the tendons of the flexor digitorum brevis and the tendons of the long flexor lies the superficial fascial space of the middle plantar compartment.
What else to study on this topic
- Plantar aponeurosis (aponeurosis plantaris)
- Flexor digitorum longus (m. flexor digitorum longus)
- Fascial and cellular spaces of the sole
- Medial plantar nerve (n. plantaris medialis)
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