#Dislocation of Carpal Bones.#--The two rows of carpal bones may be separated from one another, or any one of the individual bones may be displaced. These injuries are rare, and result from severe forms of violence, usually from a fall on the extended hand. Pain, deformity, and loss of function are the ordinary symptoms. The treatment consists in making direct pressure over the displaced bone, while traction is made on the hand, which is alternately flexed and extended. Of these injuries that most frequently observed is displacement of the _head of the capitate bone_ (_os magnum_) from the navicular (scaphoid) and lunate (semilunar) bones. Frequently these bones are fractured, and fragments accompany the displaced os magnum. In full palmar flexion of the wrist the displaced head of the os magnum forms a prominence on the dorsum opposite the base of the third metacarpal, which temporarily disappears when the hand is dorsiflexed. There is an increase in the antero-posterior diameter of the wrist, situated on a lower level than that which accompanies fracture of the lower end of the radius; flexion and extension of the wrist are limited; and in some cases there are symptoms referable to pressure on the median nerve. By keeping the hand in the dorsiflexed position for a week or ten days, the bone may become fixed in its place and the function of the wrist be restored, but it is often necessary to excise the bone. The _lunate_ may be displaced forward by forcible dorsiflexion of the hand, and forms a projection beneath the flexor tendons; there is usually loss of sensibility in the distribution of the ulnar nerve in the hand. The most satisfactory treatment is removal of the bone. In a few cases the _navicular_ has been displaced (Fig. 51), and has had to be subsequently replaced by operation. Separation of any of the other bones is rare. [Illustration: FIG. 51.--Radiogram showing Forward Dislocation of Navicular (Scaphoid) Bone.] #Carpo-metacarpal Dislocations.#--Any or all of the metacarpal bones may be separated from the carpus by forced movements of flexion or extension. The commonest displacement is backward. The thumb seems to suffer oftener than the other digits. These injuries, however, are so rare, and the deformity is so characteristic, that a detailed description is unnecessary. #Sprain of the wrist# is a common injury, and results from a fall on the hand, a twist of the wrist, or from the back-firing of a motor-crank dorsiflexing the hand. The marked swelling which rapidly ensues may render it difficult to distinguish a sprain from the other injuries that are liable to result from similar causes--Colles' fracture, separation of the lower radial epiphysis, dislocation of the wrist, and fractures and dislocations of the carpal bones.