Sesamoiditis is painful inflammation of the sesamoid apparatus, which is located in the forefoot. It is a common condition that typically affects physically active young people. Sesamoiditis causes pain in the ball of the foot, especially on the inner (medial) side. The pain may be constant, or it may occur with or be aggravated by, movement of the big toe joint. It may be accompanied by swelling (edema) throughout the bottom (plantar aspect) of the forefoot.
The forefoot consists of the five toes and their connecting long bones, the metatarsals . Each toe (phalanx) is made up of several small bones called phalanges . The phalanges of all five toes are connected to the metatarsals by metatarsophalangeal joints at the ball of the foot. The forefoot bears half the body's weight and balances pressure on the ball of the foot.
The big toe, or hallux, has two phalanges and two joints (interphalangeal joints); it also has two tiny, round, sesamoid bones that enable it to move up and down. On an x-ray of the foot, they appear as a pair of distinctive oval dots near the first metatarsal head (front end of the first long bone of the forefoot). The other four toes each have three phalanges, two joints, and no sesamoid bones.
The sesamoid bones closest to the inner side of the foot are called medial sesamoid bones; the ones closest to the outside of the foot are called lateral sesamoid bones. The sesamoids are embedded in the flexor hallucis brevis tendon, one of several tendons that exert pressure from the big toe against the ground and help initiate the act of walking. The sesamoid bones have two principal functions.
They absorb impact forces in the forefoot during walking through a series of attachments to other structures in the forefoot. Although they are separated by a bony ridge called the crista at the bottom (plantar aspect) of the first metatarsal head, they are connected to one another by an intersesamoid ligament. They also are attached to other tendons and ligaments in the forefoot (e.g., tendons of the abductor and abductor hallucis muscles, sesamophalangeal ligament, metatarsosesamoid ligament). This array of attachments enables the sesamoids to disperse some of the impact of the foot striking the ground during walking.
The connecting ligaments, the first metatarsophalangeal joint capsule, and the sesamoid bones (known collectively as the sesamoid apparatus ) act as a fulcrum, providing the flexor tendons a mechanical advantage as they pull the big toe down against the ground during walking.
Sesamoiditis is usually caused by repetitive, excessive pressure on the forefoot. It typically develops when the structures of the first metatarsophalangeal joint are subjected to chronic pressure and tension. The surrounding tissues respond by becoming irritated and inflamed. This is a common problem among ballet dancers and people who play the position of catcher in baseball. Any activity that places constant force on the ball of the foot - even walking - can cause sesamoiditis.
Damage to the sesamoid bone may also result in sesamoiditis. Stress fractures (microscopic tears in the bone structure due to repetitive abuse) can produce this condition.
Signs and Symptoms
Sesamoiditis typically can be distinguished from other conditions that cause pain in the forefoot by its gradual onset. The pain usually begins as a mild ache and increases gradually if the aggravating activity is continued. It may build to an intense throbbing. In most cases, there is little or no bruising or redness. Pain and swelling can limit the ability of the first metatarsophalangeal joint to flex upward (dorsiflexion) or downward (plantarflexion), causing a loss of range of motion in the big toe and difficulty walking.
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