The Sesamoid Bones

The sesamoid bones are small, round bones embedded within tendons. They are found in locations where a tendon passes over a joint, serving to protect the tendon and increase its mechanical effect. The most well-known sesamoid bones are the patellae, commonly referred to as the kneecaps, but there are several other sesamoid bones located throughout the body.

Anatomy

Sesamoid bones are typically found in the hands, feet, and knees. In the human body, the largest sesamoid bone is the patella, which is located in the knee. Other sesamoid bones are found in the metacarpophalangeal joint of the thumb and the metatarsophalangeal joint of the big toe.

Knee

• Patella: The patella is the largest sesamoid bone in the body. It is located in the quadriceps tendon and articulates with the femur. The patella protects the knee joint and improves the leverage of the quadriceps muscle.

Hand

• Pisiform: The pisiform bone is a sesamoid bone found in the wrist. It is located within the tendon of the flexor carpi ulnaris muscle.
• Thumb: Sesamoid bones are often found in the tendons of the adductor pollicis and flexor pollicis brevis muscles at the base of the thumb.

Foot

• Hallux: The big toe, or hallux, typically has two sesamoid bones located in the tendons of the flexor hallucis brevis muscle. These bones help bear the weight of the body during walking and running.

Function

Sesamoid bones serve several important functions:

• Protection: They protect tendons from stress and wear.
• Mechanical Advantage: By altering the direction of muscle forces, sesamoid bones increase the mechanical advantage of the muscles they are associated with.
• Weight Bearing: In the foot, sesamoid bones help bear the weight of the body, especially during activities such as walking, running, and jumping.

Clinical Significance

Sesamoid bones can be involved in various medical conditions, including:

• Sesamoiditis: Inflammation of the sesamoid bones, often due to repetitive stress or trauma. It is commonly seen in athletes and dancers.
• Fractures: Sesamoid bones can fracture due to acute trauma or chronic stress.
• Osteoarthritis: Degenerative changes can occur in the joints associated with sesamoid bones, leading to pain and dysfunction.

Diagnosis and Treatment

Diagnosis of sesamoid bone conditions typically involves physical examination and imaging studies such as X-rays, MRI, or CT scans. Treatment may include rest, ice, anti-inflammatory medications, physical therapy, and in some cases, surgical intervention.

See Also

• Bone
• Tendon
• Joint
• Muscle