What are Sesamoid Bones?
Sesamoids are bones in the body that are located within a tendon, such as the knee cap. There are two sesamoid bones beneath the main joint of the big toe, the metatarsophalangeal (MTP) joint.
These sesamoid bones have several functions. First, they act like pulleys for the tendons that help to flex the toe for strong push-off and propulsion during walking or running. Additionally, they bear weight or absorb shock as the foot hits the ground, dissipating stress. Their name derives from Latin, due to their similar appearance to a sesame seed.
What Types of Injuries Can Occur with the Sesamoid Bones?
There are several different conditions or injuries that can cause pain in the sesamoid bones of the big toe. It is possible to fracture one of these bones, often due to landing on the foot while jumping or playing sports. The patient may notice a cracking sensation and often has rapid onset of severe pain and swelling.
The sesamoids also have very limited circulation and are prone to a condition called avascular necrosis, in which the bone actually dies due to poor blood supply. Ultimately the bone may crumble and fragment leading to worsened pain and difficulty with weight bearing.
Stress fracture of a sesamoid is another common condition caused by repetitive exercise or running. This can be seen in runners who are rapidly increasing their mileage such as training for an upcoming race. Some patients are born with one of the sesamoid bones in two or more pieces that never fused together during childhood, a condition called a bipartite sesamoid. These can become sore due to overuse or impact.
Since the sesamoids do have a joint surface against the overlying metatarsal bone, it is possible to develop cartilage problems of that small joint or even full-blown arthritis. Sesamoiditis is a generic term to describe pain in a sesamoid bone that is not caused by a clearly identifiable factor but nonetheless leads to pain and difficulty walking or running.
Symptoms of Sesamoid Injuries
Patients with sesamoid problems may experience:
• Difficulty with walking and daily activities
• Difficulty running or playing sports
• Swelling in the area of the toe
• Difficulty with fitting a shoe
Very flexible shoes or shoes with a high heel concentrate more force in that area which also worsens sesamoid pain. Sesamoids bear a large amount of force with walking or running, so engaging in those activities may rapidly cause symptoms.
The orthopedic surgeon will examine the patient and typically identify tenderness with pressure over one of the sesamoid bones beneath the toe. There may also be a grinding sensation with motion of the toe. Due to the pain, the toe joint can be stiff and any attempt to stretch it causes pain. In some cases, irritation of one of the sesamoid bones may cause irritation to a nearby nerve on the bottom of the toe leading to numbness and tingling sensations.
X-rays are typically used to evaluate the toe for other sources of pain such as arthritis. The sesamoids themselves can be seen on X-rays, although special views to clearly look at them are sometimes necessary. The orthopedic doctor may also recommend obtaining an MRI or CT scan to look for fragmentation, arthritis, or bone bruising. These scans can also be helpful to look at adjacent structures such as the toe tendons to rule out other problems.