Flexor Hallucis Brevis

The Flexor Hallucis Brevis (FHB) is one of the short muscles of the foot. It divides in front into two portions, which are inserted into the medial and lateral sides of the base of the first phalanx of the great toe. The detailed knowledge of its insertion into the proximal phalangeal base is decisive in any surgery involving the first metatarsophalangeal (MTP) joint, such as implant arthroplasty, resection arthroplasty or amputation. Complications resulting from injury to this insertion are commonly known. The aim of this study was to describe in detail the morphology of FHB insertion sites and to determine a safe extent of resection to be done at the base of the proximal phalanx.

Anatomy of Flexor Hallucis Brevis

It arises, by a pointed tendinous process, from the medial part of the undersurface of the cuboid bone, from the contiguous portion of the third cuneiform, and from the prolongation of the tendon of the Tibialis posterior which is attached to that bone.

It divides in front into two portions, which are inserted into the medial and lateral sides of the base of the first phalanx of the great toe, a sesamoid bone being present in each tendon at its insertion.

The medial portion is blended with the Abductor hallucis previous to its insertion; the lateral portion (sometimes described as the first plantar interosseus) with the Adductor hallucis. The tendon of the Flexor hallucis longus lies in a groove between the two.

Origin: The cuboid and the lateral cuneiform
Insertion: Proximal phalanx of the great toe
Action: Flex the great toe
Blood Supply: Medial plantar artery
Innervation: Medial plantar nerve

Origin and Insertion of Flexor Hallucis Brevis

The flexor hallucis brevis is a medial plantar muscle of the foot. It is composed of two muscle bellies that differ in origin due to the muscle arising from a bifurcate tendon. The lateral head arises from the medial part of the plantar surface of the cuboid bone, posterior to the groove for the fibularis longus tendon, and the adjacent surface of the lateral cuneiform bone. The medial head of flexor hallucis brevis arises from the lateral division of the tibialis posterior tendon and the middle band of the medial intermuscular septum.

The muscle also consists of lateral and medial bellies which run anteriorly and medially towards the great toe. The distal tendon of each belly terminates by inserting onto each side of the base of the proximal phalanx of the hallux. In the process, the tendon of the medial belly blends with the tendon of abductor hallucis muscle, while the tendon of the lateral belly blends with the tendon of adductor hallucis muscle.

Nerve Supply of Flexor Hallucis Brevis

The medial and lateral head of the flexor hallucis brevis is innervated by the medial plantar nerve. Both heads are represented by spinal segments S1, S2.
Flexor hallucis brevis is innervated by the medial plantar nerve (S1, S2), which is one of the terminal branches of the tibial nerve.

Blood Supply

Flexor hallucis brevis muscle receives arterial blood supply from the first metatarsal artery, which branches off the convexity of the plantar arch. The plantar arch is a semicircular anastomosis formed by the medial and lateral plantar arteries. Flexor hallucis brevis muscle is also supplied by the superficial branch of the medial plantar artery that arises from the posterior tibial artery.

Function

The primary function of the flexor hallucis brevis is flexion of the great toe at the metatarsophalangeal joint. This muscle aids the flexor hallucis longus in the toe-off phase of locomotion, increasing the final push-off from the ground during activities such as walking, running and jumping.

The fact that the flexor hallucis brevis tendons blend with the adductor hallucis and abductor hallucis signifies its importance in providing stability of the great toe during the aforementioned activities, ensuring maximum force translation during the thrust phase.

Flexor hallucis brevis also plays a role in the maintenance of the medial longitudinal arch by acting as a bowstring between the proximal phalanx of the hallux and tarsal bones. Muscular contraction brings the bones closer together, thereby raising the arch.

References

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Anatomy of Flexor Hallucis Brevis