Flexor Hallucis Brevis

Flexor Hallucis Brevis

The flexor hallucis brevis is a very small intrinsic foot muscle that is found deep within the medial portion of the sole. Sometimes if you feel pain in your toe during walking or dancing, it is usually caused by flexor hallucis brevis muscle.

Based on the location, plantar muscles can be classified in two ways; into one of the four muscular layers of the foot, or into the medial, central, or lateral group. The flexor hallucis brevis, together with the abductor and adductor hallucis muscles, belongs to the medial compartment in the horizontal plane.

While, in the vertical plane, it is grouped in the third layer of plantar muscles along with two additional muscles; the adductor hallucis and flexor digiti minimi. The tendons of the flexor hallucis brevis attach to the proximal phalanx of the toe.

At the joining position, two sesamoid bones develop that are implanted on each side of the tendons. This muscle flexed the great toe at the metatarsophalangeal joint. The flexor hallucis brevis, on the other hand, is responsible for preserving the medial longitudinal arch of the foot. 

Structure

The flexor hallucis brevis is a plantar flexor muscle located on the medial side of the foot. The muscle is made up of two bellies with separate origins that arise from a bifurcate tendon.

The lateral head of the flexor hallucis brevis is created by the neighboring surface of the lateral cuneiform bone and the medial part of the cuboid bone’s plantar surface, which is posterior to the fibularis longus tendon groove. While the medial head of the flexor hallucis brevis is formed by the lateral division of the tibialis posterior tendon and the middle band of the medial intermuscular septum. 

The muscle’s lateral and medial bellies run anteriorly and medially towards the great toe. On either side, the distal tendon of the belly joins to the base of the proximal phalanx of the hallux. The medial belly tendon connects to the abductor hallucis muscle’s tendon, while the lateral belly tendon connects to the adductor hallucis muscle’s tendon. 

Function

Flexion of the great toe at the metatarsophalangeal joint is the principal function of the flexor hallucis Brevis. During movements like walking, running, and jumping, this muscle assists the flexor hallucis longus in the toe-off phase of locomotion, boosting the final push-off from the ground. 

The tendons of the flexor hallucis brevis blend with the adductor hallucis and abductor hallucis, indicating their relevance in maintaining great toe stability during the aforementioned activities and guaranteeing maximum force translation during the thrust phase. Flexor hallucis brevis acts as a bowstring between the proximal phalanx of the hallux and the tarsal bones that helps to maintain the medial longitudinal arch. Muscle contraction elevates the arch and brings bones close to each other. 

Blood supply

The first metatarsal artery, which branches off the convexity of the plantar arch, supplies arterial blood to the flexor hallucis brevis muscle. The medial and lateral plantar arteries form a semicircular anastomosis ‘plantar arch’. The superficial branch of the medial plantar artery, which emerges from the posterior tibial artery, also supplies the flexor hallucis brevis muscle. 

What causes pain in Flexor Hallucis Brevis?

The anatomical diversity in the flexor hallucis brevis is significant, especially at the muscle’s origin. There are connective tissue slips extending from the calcaneus or the long plantar ligament. When the flexor hallucis brevis is injured, it causes pain in the big toe that might spread up the foot.

Pain in the ball of the foot or the big toe may indicate damage to the flexor hallucis brevis, and the muscle’s function should be assessed. People who have an injury in flexor hallucis brevis are often found trouble in walking and may favor their non-injured foot. 

Walking, running, or even standing on uneven or rough surfaces can all cause injury to the flexor hallucis brevis. Injuries can also be caused by ill-fitting shoes and high-heeled shoes. Many female ballet dancers adopt the technique of dancing en pointe or demi-pointe, which can result in foot and ankle injuries.

En pointe dancing necessitates a dancer’s physical strength, balance, and coordination to be developed over many years of training. Excessive plantarflexion of the ankle is used, which puts a lot of tension on the flexor hallucis longus (FHL), resulting in FHL tenosynovitis.

Tenosynovitis of the FHL is a rare occurrence in the general population, but it can affect ballet dancers due to the tension placed on the tendon during en pointe and demi-pointe dance. . Ligamentous laxity, poor en pointe technique, and foot pronation can predispose a patient to exert excessive stress on the FHL and producing injury.

The FHL runs posterior to the medial malleolus and deep to the flexor retinaculum. The FHL then passes through a groove in the posterior section of the talus between the medial and lateral tubercles. After that, the tendon goes through a plantar fibro-osseous tunnel to the sustentaculum tali before implantation into the plantar aspect of the hallux. 

Flexor Hallucis Brevis Treatment: For tenosynovitis of the FLS, you may use the following treatments;

  • Resting the region, lowering inflammation with ice, and non-steroidal anti-inflammatory drugs are used to treat the aforementioned injury. 
  • Stretching, strengthening, massage, ultrasound, and other techniques used in physical therapy can also assist reduce inflammation. 
  • Immobilization of the tendon with a cast or boot, depending on the severity of the symptoms, may be recommended to allow the tendon to rest. 
  • Corticosteroid injections should only be done on rare occasions due to the risk of weakening or rupturing the tendon. If you’re injecting corticosteroids into the FHL sheath, make sure the patient is immobilized to avoid rupturing the tendon. 
  • When symptoms persist despite conservative treatment, surgery may be necessary. The FHL tendon retinaculum is released posterior to the medial malleolus and continues down to the sustentaculum tali during surgery. Moreover, you should move the great toe to visualize the unconstrained motion of the tendon.

References:

  • https://www.hmpgloballearningnetwork.com/site/podiatry/treating-flexor-hallucis-longus-tendon-dysfunction-dancers retrieved on March 19, 2022.
  • https://www.rehabmypatient.com/toe/flexor-hallucis-brevis retrieved on March 19, 2022.
  • https://www.kenhub.com/en/library/anatomy/flexor-hallucis-brevis-muscle retrieved on March 19, 2022.
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