Sesamoiditis is a painful foot condition affecting the sesamoid bones and the surrounding tissues. The sesamoid bones are a pair of tiny bones whose function is to aid the mechanical action of the tendons. They vary in size from individual to individual, but are usually about the size of a jelly bean, and their function is to act as a fulcrum to hold the tendons further away from the joint.
Most bones in the body are connected to each other by joints; however the sesamoid bones are not, and are embedded in tendons or muscles. They help to prevent the tendon from flattening to help achieve a more consistent pull when flexing. In the foot, the sesamoid bones are embedded in the flexor hallucis brevis muscle and associated tendons, whose function is to flex the big toe downwards.
Sesamoiditis is the inflammation of the sesamoid bones, along with the surrounding tissues. As with any inflammation of tissue and bone, it can cause intense pain. In the case of sesamoiditis, pain it is felt directly below the first metatarsal joint in the big toe, in the ball of the foot. The pain usually gets worse over a period of time, helping with the diagnosis and differentiating it from other ball of foot problems. The sudden onset of pain is possible however, when the condition is caused by trauma such as a stress fracture to the sesamoid bones. Due to the small size of the bones, it is sometimes difficult to diagnose the condition with an x-ray, and a bone scan is the most reliable way of getting an accurate diagnosis, and also determining the severity of the condition.
The most common sesamoiditis symptom is pain experienced when walking, although any load bearing exercise is likely to cause pain. The pain is strongest during the “toe off” when walking, as the body weight transfers onto the toes. Pain is felt directly underneath the first metatarsal head in the ball of the foot, at the base of the big toe.
Sesamoiditis is usually accompanied by tenderness of the surrounding tissues, and intensifies when direct pressure is applied. The pain is usually only felt during activity, and whilst the pain may persist for a short time when the weight is taken off the feet, it usually rapidly subsides. As the condition deteriorates, the pain persists for longer, and in severe cases, pain is present most of the time. Sesamoiditis also can cause a small degree of swelling under the first metatarsal joint.
There are a number of causes of sesamoiditis, although the age of patients can indicate which is most likely. In the older age ranges the condition is most commonly due to arthritic changes to the sesamoid bones, usually at the point where they articulate with the head of the first metatarsal.
Osteoarthritis of the sesamoid bones is the most likely cause in older patients, and may involve the formation of additional bone in the form of a bone spur. This bone fragment can cause inflammation of the surrounding muscles and tendons as well as the sesamoid bones themselves becoming inflamed. Osteoporosis is another factor, which weakens the bones, reducing their ability to cope with the forces from walking. Whilst this is common with older patients, it can also be a cause of sesamoiditis in younger women, especially those with a history of eating disorders or irregular menstruation.
For most healthy young to middle aged adults the condition is usually the result of a single trauma to the sesamoid bones, or repeated stresses over time. Women who frequently wear high heels place an increased stress on the forefoot, as do athletes and dancers. Any job which requires squatting or carrying heavy loads can also trigger the condition over time.
Some people can be prone to develop sesamoiditis due to abnormalities of the bones themselves, and those people with large sesamoid bones are particularly prone to the condition. The larger the bones, the greater the force they have to take, and the result of injury is far more likely. People with high arches also place a greater strain on the forefoot, and runners who overpronate – excessive roll their feet inwards when running – are more likely to develop the condition.
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