Flexor pollicis brevis

Location and compartment boundaries

The muscle is listed among the structures of the deep layer of the sole and topographically belongs to the medial fascial compartment of the sole.

The boundaries of this fascial space include:

• Inferiorly and medially — the fascia propria (fascia propria), which is a continuation of the thinned plantar aponeurosis.
• Laterally — the medial intermuscular septum (septum intermusculare mediale).
• Superiorly — at the tarsal level, the compartment is bounded by the navicular and medial cuneiform bones, and at the metatarsal level, by the first metatarsal bone.

Within this compartment at the metatarsal level (Metatarsus), the flexor hallucis brevis is located together with the abductor hallucis muscle (m. abductor hallucis).

Topography of the deep layer of the sole

The list of anatomical structures of the deep layer of the sole, along with m. flexor hallucis brevis, includes:

• Adductor hallucis muscle (m. adductor hallucis) — oblique (caput obliquum) and transverse (caput transversum) heads.
• Quadratus plantae muscle (m. quadratus plantae) and plantar interosseous muscles (mm. interossei plantares).
• Tendons of the flexor digitorum longus and brevis, flexor hallucis longus, and the peroneus brevis and longus muscles.
• Vessels and nerves: medial and lateral plantar arteries and nerves (a., n. plantaris medialis et lateralis), deep plantar arch (arcus plantaris profundus), plantar metatarsal arteries, and plantar metatarsal nerve.

Relationship with sesamoid bones and tendons

The sesamoid bones of the big toe are embedded in the tendons of m. flexor hallucis brevis and form a canal for the tendon of the flexor hallucis longus (tendo m. flexoris hallucis longi, FHL).

On the sole, the tendon of the flexor hallucis longus crosses with the tendons of the flexor digitorum longus at the level of the navicular/cuneiform bones: the FHL tendon passes deep to the FDL tendons toward the big toe.

Landmarks on anatomical specimens

In the topographic anatomy of the vessels and nerves of the medial surface of the leg and foot, the muscular landmarks include the abductor hallucis muscle (m. abductor hallucis), partially removed on the specimen, and the flexor hallucis brevis muscle (m. flexor hallucis brevis).

On the sole, the posterior tibial artery divides into the medial and lateral plantar arteries (a. plantaris medialis et a. plantaris lateralis).

Do not confuse with: flexor pollicis brevis

In upper extremity anatomy, there is a muscle with a similar Russian name — m. flexor pollicis brevis. It is located in the thenar compartment and acts on the thumb.

• Structure and origin: it has superficial and deep heads. The superficial head originates from the flexor retinaculum (retinaculum mm. flexorum), and the deep head originates from the trapezoid and capitate bones (os trapezoideum, os capitatum). The tendon of the flexor pollicis longus passes between the heads.
• Insertion: base of the proximal phalanx of the thumb laterally via the sesamoid bone.
• Function: flexes the proximal phalanx of the thumb; participates in opposition.
• Innervation: superficial head — by the median nerve (n. medianus), deep head — by the ulnar nerve (n. ulnaris).

Class and exam questions

What else to study on this topic

• Medial fascial compartment of the sole
• Flexor hallucis longus muscle (m. flexor hallucis longus)
• Thenar muscles
• Topography of the deep layer of the sole

Other topics in the "Anatomical Structures" section

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