Sesamoiditis is an irritation and inflammation of the sesamoid bones and the tendons surrounding them, typically affecting the ball of the foot just beneath the big toe joint. This condition is a form of tendonitis, caused when the small bones embedded within the tendons become stressed and inflamed due to repetitive pressure. It is a common source of chronic forefoot pain that can make walking and bearing weight uncomfortable.
The Location and Function of Sesamoids
The sesamoid bones are two small, pea-shaped bones located on the underside of the forefoot, directly beneath the head of the first metatarsal. Like the kneecap, these bones are unique because they are embedded within a tendon rather than connecting directly to other bones at a joint. They sit within the tendons that help control the movement of the big toe.
The primary function of the sesamoids is to act as a pulley system, providing leverage for the flexor tendons of the big toe. This mechanical advantage increases the force the tendons can exert, which is crucial for pushing off the ground during movement. The sesamoids also help absorb the shock and weight distributed to the ball of the foot.
Physical Signs and Subjective Symptoms
The presentation of sesamoiditis involves subtle physical signs and a distinct pattern of subjective pain. Visible signs can include mild redness and slight swelling around the big toe joint. Significant bruising or swelling is less common unless the condition is severe or accompanied by a fracture. The most telling physical sign is tenderness directly beneath the big toe joint when pressure is applied.
The subjective experience typically begins as a dull ache that develops gradually over time, often lasting for months. This pain is focused under the ball of the foot where the sesamoids are located. The discomfort tends to intensify during weight-bearing activities, such as standing, walking, or running, and is particularly noticeable when the foot pushes off the ground. People often alter their gait or begin to limp to shift weight away from the painful area.
Common Causes and Risk Factors
Sesamoiditis develops primarily from chronic overuse and repetitive stress that continuously loads the forefoot. Activities involving repeated push-off movements or prolonged pressure on the ball of the foot are common triggers for the condition. Runners, ballet dancers, and athletes requiring frequent jumping or quick changes in direction often experience this mechanical stress.
Footwear choices also contribute to the condition. Frequently wearing high-heeled shoes places excessive pressure on the forefoot, directly loading the sesamoid bones. Shoes with very thin, flexible soles that offer little cushioning or support can increase the impact on the area. Certain foot structures, such as a high arch or a very flat foot, can also increase susceptibility by altering the biomechanics and weight distribution.
Confirmation and Next Steps
A healthcare provider confirms sesamoiditis through a physical examination and diagnostic imaging. The physical assessment involves palpating the area to pinpoint localized tenderness and checking the range of motion of the big toe joint. Pain often increases with passive upward bending of the toe. Symptoms alone are not sufficient to confirm the diagnosis, as other conditions can mimic the pain.
Imaging studies are necessary to rule out a more serious injury, such as a stress fracture or avascular necrosis (a disruption of blood supply to the bone). Standard X-rays are typically ordered to visualize the bones and check for fractures. If X-rays are inconclusive, a bone scan, CT scan, or Magnetic Resonance Imaging (MRI) may be used to look for subtle bone irritation or soft tissue inflammation.