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21.07.2013.

Muscles flexing the toes





Flexor accessorius (quadratus plantae)
Flexor digitorum brevis
Flexor hallucis brevis

Flexor accessorius (quadratus plantae)

Flexor accessorius lies deep to flexor digitorum brevis, arising by two heads from the medial and lateral tubercles of the calcaneus and the adjacent long plantar ligament. A flattened muscular band is formed by the merging of the two heads which inserts into the tendon of flexor digitorum longus in the midpoint of the sole, proximal to the origin of the lumbricals.



Nerve supply

Flexor accessorius is supplied by the lateral plantar nerve, root value S2, 3. The skin over the region is supplied by root S1.

Action

It helps the long flexor tendons flex all the joints of the lateral four toes. By pulling on the lateral side of the tendon of flexor digitorum longus, it changes the direction of pull so that the toes flex towards the heel and not towards the medial malleolus.

Functional activity

Flexor accessorius has an important role to play in gait when flexor digitorum longus is already shortened because of plantarflexion of the ankle joint. This muscle exerts its action on the long flexor tendons so that the toes can be flexed to grip the ground giving support and thrust during the propulsive phase. This action essentially means that flexor digitorum longus can be considered to act powerfully across two joints at the same time – an unusual phenomenon.

Palpation

Lying deep in the sole of the foot, flexor accessorius cannot be palpated.

Flexor digitorum brevis

Flexor digitorum brevis is situated in the sole of the foot lying just deep to the central part of the plantar aponeurosis between abductor hallucis medially and abductor digiti minimi laterally. Arising from the medial tubercle of the calcaneus, the deep surface of the central portion of the plantar aponeurosis and the muscular septa either side, the fibres pass forwards in the middle of the sole, and separate into four tendons, which pass to the lateral four toes. Just distal to the metatarsophalangeal joint, within their respective fibrous flexor sheaths, each tendon splits into two for the passage of the flexor digitorum longus tendon, which passes from deep to superficial. After rotating through almost 180° the outer margins of the slips of each tendon rejoin, leaving a shallow groove along which the flexor digitorum longus tendon slides. After passing over the proximal interphalangeal joint, the tendon again splits to insert into the sides of the base of the middle phalanx.

Nerve supply

Flexor digitorum brevis is supplied by the medial plantar nerve, root value S2, 3. The skin covering this area is supplied by roots L5, S1.

Action

Flexor digitorum brevis primarily flexes the proximal interphalangeal joint of the lateral four toes, followed by flexion of the metatarsophalangeal joints.

Functional activity

Flexor digitorum brevis is obviously concerned, as is flexor digitorum longus, in producing the thrust from the toes when the demand arises.

Palpation

This muscle is almost impossible to palpate as it is covered with some of the thickest fascia in the body and its tendons lie deep within the foot.

Flexor hallucis brevis

Flexor hallucis brevis is a short muscle situated deep in the sole of the foot, appearing between abductor hallucis medially and flexor digitorum brevis laterally. It arises from the medial side of the plantar surface of the cuboid bone, behind the groove for peroneus longus, and the adjacent surface of the lateral cuneiform and from the tendon of tibialis posterior.
The muscle fibres run forwards and medially towards the great toe, separating into two fleshy bellies to lie either side and deep to the tendon of flexor hallucis longus. From each belly arises a tendon which inserts onto the appropriate side of the base of the proximal phalanx. The medial tendon unites with that of abductor hallucis, while the lateral tendon unites with the tendon of adductor hallucis, thereby giving common insertions. Small sesamoid bones, which run in shallow grooves on the head of the first metatarsal, develop in each tendon.

Nerve supply

Flexor hallucis brevis is supplied by the medial plantar nerve, root value S1, 2. The skin covering the area is supplied by root L5.

Action

The action of flexor hallucis brevis is to flex the metatarsophalangeal joint of the great toe.



Functional activity

Flexor hallucis brevis will, of course, aid flexor hallucis longus in the final push-off from the ground during activity. Being accompanied at its insertion by abductor and adductor hallucis suggests that the steadying of the great toe during propulsion must be of great importance, probably to ensure the generation of maximum force. When the great toe is deformed as in hallux valgus, where the tip points laterally and the base medially, this thrust is lost and the patient finds it difficult to run or sometimes walk, even at slow speeds.
It is interesting to note that it is not uncommon for injuries to occur to the sesamoid bones, particularly in individuals who put considerable strain on the great toe. Such injuries produce an inflamed region where the sesamoid bone slides against the metatarsal. This can cause considerable pain and altered function.

Palpation

This muscle is set so deep in the plantar surface of the foot that it is not possible to palpate. Only the sesamoid bones found within its tendons can be felt, and then only with considerable practice.

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