One of the most common questions we get as a podiatrist, is what are those two little round spots on my x-rays? These round spots, which lie under the ball of your foot, are called sesamoids. A sesamoid is a bone that lives inside a tendon. For example, the largest sesamoid is the patella, also known as the knee cap.
Why Does it Hurt?
These two bones can become inflamed or injured during certain activities. When the bones become inflamed the condition is called sesamoiditis. Sesamoiditis is due to an excessive force applied to them. To be exact, these bones lie under the first metatarsal (see diagram). Patients with a very high arch are prone to this condition because the bones are pressing against the ground more so than if the arch was flatter.
Now, these bones are very prone to injury if the patient has a high arch foot and does activities that require jumping, like basketball and volleyball. Running provides excessive forces and pressure along these bones as well, and can occur in people whose feet are flat but have excessive pronation during their gait.
Diagnosing the Problem:
If too much force is applied to these bones, they can fracture. X-rays are necessary to rule out a fracture to these bones. X-rays must be taken on both feet even if the symptoms are only on one foot. This is because the sesamoids could have a natural partition. What I mean is instead of two bones there can be three or four bones. This occurred at birth and is a normal variant of the bones. Taking X-rays on both feet can help differentiate between the normal separation and a fracture.
Treatment for sesamoiditis is to off-load the area. This can be done with padding, and proper shoes. In addition, to eliminate the excessive forces in the area, a custom orthotic is necessary. Sometimes a cortisone injection is needed to reduce the inflammation. In addition, laser therapy with the MLS-laser helps treat this condition by bringing in new cells to reduce the swelling.
If the bone is fractured, then applying a cast might be needed or sometimes just a walking boot for three to four weeks. These fractures are hard to heal and if this is the case, surgical removal of the bone is required. Either way, the cause of the fracture or inflammation must be treated in order to prevent a recurrence and this is done with custom orthotics.
Injuries to the sesamoid are very common and should not be overlooked. So, if you are having pain at the ball of your foot, you should call your local podiatrist to check it out.