Unbeknownst to most people, there are two small pea-shaped bones that sit underneath the big toe joint. These bones, like the knee cap, sit within a tendon, and are known as sesamoid bones. Inflammation of these bones is known as sesamoiditis.
The purpose of these small bones is to sit within the tendon (flexor hallucis longus) and assist in providing a mechanical advantage to propulsion provided by the big toe joint.
However, for various reasons, these small delicate bones are prone to injury and can become inflamed, fractured or go on to irreversible bone necrosis.
The most common activities to cause sesamoid inflammation (sesamoiditis) are usually running, aerobics, netball and any other activities which require lots of jumping and having weight on the front of the foot. If there is a biomechanical issue which causes overload of the 1st MTP joint, this can also cause sesamoiditis.
Sometimes sesamoiditis can progress to a sesamoid fracture when there is no reduction in the amount of pressure going through these small bones, or if there is reduced bone density (osteoporosis). This is more common with over-training situations, heavy landing after a jump, or if there are unremitting occupations demands on the foot.
Treatments for sesamoiditis range from rest, antiinflammatories and icing, through to orthotics, and sometimes an immobilisation brace (CAM walker / moon boot). In some instances where a sesamoid injury fails to heal, a condition called avascular necrosis may occur, leading to bone death. This often requires surgical intervention to reduce ongoing pain.