Sesamoid bones are small bones that are usually embedded in a muscle or most often in a tendon near the joint surfaces. The functions of these bones are to modify pressure, reduce friction which protects the tendons, change the direction of muscle pull and help with muscle actions. The largest and best-known sesamoid bone in the body is the patella. The patella serves to transfer the force of the quadriceps femoris muscle to the lower leg so that it enables the extension of the lower leg and also serves to protect and stabilize the knee joint. The sesamoid bones of the hand and foot are also common. In the foot, the highest presence is recorded in the area of the first metatarsal joint. In the hand, there are regularly two sesamoid bones on the articular junction of the metacarpal bone and the proximal phalanx of the thumb, and they can also appear on other metacarpal bones. A rarer anatomical variation of the sesamoid bones are cyamella and fabella, which most often occur as a result of increased load on the tendons. In athletes, the most common injuries related to the sesamoid bones affect the patella and the sesamoid bones of the foot. Injuries occur as a result of overloading and high-intensity activities, less often as a result of direct trauma. The most common injuries are stress fractures of the medial sesamoid bone of the big toe and fracture and instability of the patella.