Anatomy and Origin
The flexor digitorum brevis (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 course toward the middle phalanges of digits II–V.
A notable anatomical feature is the formation of the tendon chiasm (chiasma tendinum). The tendons of the flexor digitorum brevis split into two slips (bifurcation) to permit the passage of the tendons of the flexor digitorum longus.
Topography and Fascial Compartments
The muscle is located on the plantar aspect of the foot and represents the first layer of muscles in the tarsal region.
It lies superficially within the central compartment of the sole. The flexor digitorum brevis and the plantar aponeurosis overlie the deeper muscular layers. The muscle itself is covered by its own investing fascial layer.
Deep to the flexor digitorum brevis runs the tendon of the flexor digitorum longus. The quadratus plantae muscle (m. quadratus plantae) inserts into the lateral side of this long flexor tendon.
Fascial Spaces and Clinical Significance
Within the metatarsal region of the central plantar compartment lies the superficial fascial space. This space is located between the tendons of the flexor digitorum brevis and the tendons of the flexor digitorum longus.
The central plantar compartment communicates with pathways critical for the spread of purulent infections (plantar abscesses). Infections can spread into the subcutaneous tissue of the sole along the plantar metatarsal and plantar digital vessels through the gaps in the plantar aponeurosis.
Function
- Digital Flexion: The muscle flexes the middle phalanges of digits II–V of the foot, specifically acting on the proximal interphalangeal joints of the II–V digits.
- Longitudinal Arch: The muscle helps support the longitudinal arch of the foot.
Blood Supply and Innervation
- Blood Supply (A): Provided by the medial and lateral plantar arteries (aa. plantares medialis et lateralis). The medial plantar artery travels within the medial intermuscular septum and supplies branches to the muscles of the medial and central fascial compartments.
- Innervation (Inn): Supplied by the medial plantar nerve (n. plantaris medialis). Segmental innervation is typically attributed to S1–S3.