A sesamoid is a small bone (about the size of a small pea) that’s connected only to tendons or is embedded in muscle. Two very small sesamoids are located in the underside of the foot near the big toe - one on the outer side of the foot and the other closer to the middle.

Their function is to provide a smooth surface for the tendons to slide over, helping the tendons to transmit muscle forces. In the foot, sesamoids also help to support weight and elevate the bones of the big toe.

If the tendons surrounding the sesamoids become irritated or inflamed, the result is called sesamoiditis and is a form of tendonitis. Sesamoiditis is a common condition among people such as runners because of the pressures placed on their feet.

Symptoms of sesamoiditis include:

  • Swelling and/or bruising.
  • Pain under the big toe or on the ball of the foot.
  • Difficulty and/or pain in bending and straightening the big toe.

Surgery is usually not required to treat sesamoiditis. Treatments generally include:

  • Discontinuation of the activity causing  discomfort.
  • Applying ice to the sole of the foot.
  • Wearing shoes that are soft-soled and low-heeled.
  • Over-the-counter pain medications and anti-inflammatories, such as ibuprofen and aspirin.  
  • Using cushioning in shoes.
  • Injection of a steroidal medication to reduce swelling.

 If symptoms persist, it may be necessary to wear a removable brace on the leg for a month or so, until the inflammation reduces.