Sesamoids

What are sesamoid bones

The two oval-shaped bones under the big toe joint are called the medial and lateral sesamoids. They measure approximately 1 x 1.5 cm and lie within the two tendons that move the big toe (flexor hallucis brevis FHB). They work in the same way as the knee cap acts to straighten the knee. Therefore, the surface of the bones should be very smooth (covered with articular cartilage) to allow the bones to glide smoothly over the head of the first metatarsal bone (see diagram).

How are they damaged

These two bones obviously take a great amount of force through them during normal walking. Repetitive injury to them may cause inflammation with roughening of the articular surface (sesamoiditis) and pain. The bones may also fracture. This is usually an over-use injury and is more common in runners/sprinters/jumpers.

What are the symptoms

Pain under the big toe joint is the predominant symptom. This may be constant and cause a limp following an acute injury. More chronic symptoms may occur in atheletes who may have few symptoms during normal walking but pain may prevent return to sporting activities.

How is it diagnosed

Careful examination of the foot may pin-point the pain and exclude other causes of pain around the big toe. Specific x-rays may demonstrate abnormalities and a bone scan or MRI scan are often helpful.The scan below has the normal medial sesamoid identified with a green arrow and the inflamed lateral sesamoid circled with a white arrow.

How can it be treated

Initial modification of the exercise regime will be necessary to allow the sesamoids to recover and heel but preventing stiffening of the toe joint. During this period a specialised insert can be made to off-load the affected bone, distributing the forces across the foot. Once the initial acute episode has settled a progressive return to previous sporting activities may commenced.

Most people do not require surgery. Those patients who fail to settle despite carefully supervised rehabilitation may need repair of the fracture with bone graft and a tiny screw or careful removal of the affected sesamoid bone. If removal of the sesamoid is necessary it is important to repair the FHB tendon to ensure good function and push-off strength. This generally gives good relief of symptoms and most athletes are able to return to their previous sporting activities.