The paracarpal bone of the foot is a congenital anomaly of the second ossification center of the navicular tuberosity, forming an independent paracarpal bone at the navicular tuberosity. The paracarpal is mostly bilateral and there are three types: one is round with no contact surface with the navicular bone, growing on the posterior tibial tendon like a patella, and its base is a cartilaginous surface composed of hyaline cartilage that slides along the canal of the posterior tibial tendon, and this type usually does not produce symptoms. Another type is round or triangular in shape and is part of the navicular bone but is separated from the navicular tuberosity by fibrocartilage, and this type is more likely to produce symptoms. The third type is where the paravicular bone has fused with the navicular bone, producing an enlarged navicular tuberosity that may rub against the shoe surface and cause pain. Normally, 10% to 14% of people have a paracarpal bone in their feet. The paracarpal bone is a defect in the foot structure that affects the stability of the foot. Under normal circumstances, the posterior tibial tendon passes under the medial end of the navicular bone and ends at the bottom surface of the second and third medial cuneiform bones and the bottom surface of the second and third metatarsals. In the presence of the paracone, the posterior tibial tendon travels above the medial surface of the paracone and stops at the paracone in a relatively fixed manner. This change in the direction of travel and stopping point destroys the inherent role of the posterior tibial tendon in raising the longitudinal arch of the foot and causing the foot to turn inward. As a result, it is very easy to cause flat feet, and easy to strain and cause symptoms. In some patients, although there is no paronychium, the navicular tuberosity is excessively enlarged and the attachment point of the posterior tibial muscle is abnormal, which can also cause similar functional disorders and symptoms. In addition, the medial projection of the longitudinal arch of the foot during walking, the hypertrophy of the navicular tuberosity rubbing against the edge of the shoe, local bursitis, and tenosynovitis of the posterior tibial muscle can also occur, producing symptoms such as swelling and pain. Patients with this disease are more common in young women, and often have flat feet. When standing for a long time or walking for a long time, the pain is felt on the medial side of the bottom of the foot. The medial navicular bone is elevated and there is pressure pain. The pain on the medial side of the foot is increased when the resistance foot is turned inward. Localized bursitis may be present. Sometimes there is also pressure pain in the posterior tibial tendon. X-rays show small bony blocks with neat edges in the posterior part of the navicular bone, with the same density as the navicular bone, and some irregularities or osteosclerosis and cystic changes in the joint with the navicular bone. The diagnosis can be confirmed based on the clinical symptoms and signs of elevation and pressure pain at the medial navicular bone on the plantar surface of the foot, combined with the paraphyseal bones in the posterior part of the navicular bone on the X-ray plain film. Children with mild symptoms can reduce activities appropriately, or wear orthopedic shoes with arches or fixation with plaster to reduce symptoms. If bursitis or posterior tibial tendonitis is present, local closure with hormones may be used. If the symptoms are severe and non-surgical treatment is ineffective, surgical treatment can be performed to remove the paracarpal bone and refix the posterior tibial tendon stop. However, removal of the pars plana does not restore the normal arch of the foot, and some patients may still have the symptoms of flat feet.