Fractures of the coccyx may involve the peripheral end of one or both forearm bones (radius or ulna) or, less commonly, one of the wrist bones. The pigeon carpus consists of the two long bones of the forearm (radius and ulna) and the eight small bones of the wrist, which are located between the forearm bones and the bones of the distal hand.
Fractures of the clavicle usually involve the largest bone of the forearm, namely the radius. Coccyx fractures are usually caused by a fall in the hand. Typically, a pigeon carpal fracture occurs when people fall on an outstretched arm, with the wrist bent backwards. As a result, the radius breaks near the wrist and the broken end of the radius is displaced upward toward the back of the hand. This type of fracture is called a Colles fracture. A fracture of the ulna is often present. Colles fractures are common in older people, especially if they have osteoporosis, which weakens the bones. Less commonly, the wrist is broken when people fall with the arm bent forward or when the back of the wrist is hit. The broken end of the radius is displaced downward, toward the side of the palm. This type of fracture is called a Smith fracture. Often the median nerve can also be injured.
The clinical picture includes pain, swelling and tenderness of the pectus carpi. If the median nerve is damaged, the tip of the index finger is numb and people may have difficulty moving the thumb. In the long term, and if left untreated, pigeon carpal fractures can lead to stiffness, persistent pain and/or osteoarthritis, especially if the fracture extends into the wrist joint.
Diagnosis is made with plain radiographs of the pheocephaly, and rarely a CT scan may be needed.
Coccygeo-carpal fractures, if displaced, should be reduced by manipulation and then held in place with a cast or splint. Reduction is performed under local anaesthesia at the site of the fracture. The plaster remains in place for 4-6 weeks, and the patient is re-examined radiologically to determine the progress of the fracture closure. If the fracture is overwhelming or extends intra-articularly, surgery (open reduction and internal osseointegration) may be performed, especially in active adults who should be able to fully use their wrist. Alternatively, external osseointegration may be performed. After surgery, the previous function of the coccyx is restored at 6 to 12 months after the fracture.