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Sesamoiditis occurs when the tendons surrounding the sesamoid bones become irritated and inflamed. So, what exactly is a sesamoid bone? In short, a sesamoid is a bone embedded in a tendon. In your foot, the sesamoids are two pea-shaped bones located in the ball of the foot, beneath the big toe joint.

Acting as a pulley for tendons, the sesamoids help the big toe move normally and provide leverage when the big toe pushes off during walking and running.

Sesamoid bones are unique because they are the only bones in the body that are not connected to other bones via joints. Instead, they are connected to other bones by tendons, or they are embedded in muscles in the body.

The sesamoids also serve as a weight-bearing surface for the first metatarsal bone (the long bone connected to the big toe), absorbing the weight placed on the ball of the foot when walking, running and jumping.

Sesamoid injuries can involve the bones, tendons and/or surrounding tissue in the joint. They are often associated with activities requiring increased pressure on the ball of the foot, such as running, basketball, football, golf, tennis and ballet.

In addition, people with high arches are at risk for developing sesamoid problems. Frequent wearing of high-heeled shoes can also be a contributing factor.

Types of Sesamoid Injuries in the Foot

There are three types of sesamoid injuries in the foot:

• Sesamoiditis. This is an overuse injury involving chronic inflammation of the sesamoid bones and the tendons involved with those bones. Sesamoiditis is caused by increased pressure on the sesamoids. Often, sesamoiditis is associated with a dull, longstanding pain beneath the big toe joint. The pain comes and goes, usually occurring with certain shoes or certain activities.
• Turf toe. This is an injury of the soft tissue surrounding the big toe joint. It usually occurs when the big toe joint is extended beyond its normal range. Turf toe causes immediate, sharp pain and swelling. It usually affects the entire big toe joint and limits the motion of the toe. Turf toe may result in an injury to the soft tissue attached to the sesamoid or a fracture of the sesamoid. Sometimes a “pop” is felt at the moment of injury.
• Fracture. A fracture (break) in a sesamoid bone can be either acute or chronic.
  • An acute fracture is caused by trauma—a direct blow or impact to the bone. An acute sesamoid fracture produces immediate pain and swelling at the site of the break but usually does not affect the entire big toe joint. A chronic fracture is a stress fracture (a hairline break usually caused by repetitive stress or overuse).
  • A chronic sesamoid fracture produces longstanding pain in the ball of the foot beneath the big toe joint. The pain, which tends to come and go, generally is aggravated with activity and relieved with rest.
• Older adults with osteoarthritis can also experience sesamoiditis because osteoarthritis can weaken bones and lead toinflammation.The sesamoid bones are subject to breakage (fracture) as well as sesamoiditis. Sometimes, it can be difficult to tell the difference between the two conditions.