(5) Impacted fracture occurs at the end of long bones when the shaft is driven up into the head of the bone. In such a case some of the signs of fracture are absent. There will be no unnatural degree of movement, for example.
Mode of Union.—The first step in the pro cess of repair consists in the pouring out from the blood-vessels of the bone and its outer and inner lining membranes of a fluid and cells capable of forming a consistent tissue. This tissue becomes at first fibrous, then cartilaginous, and finally is transformed into bone. The ma terial which thus unites fractures is called cal lus. When the fragments have not separated from one another, but remain in their proper position, the callus is formed only between the two ends, where it is called permanent callus, and, as internal callus, in the marrow cavity, which it completely fills up. But when the bones have separated, and have not been pro perly replaced, the repairing material is exuded from the blood-vessels in sufficient quantity to fill up the gap between the two fragments, and to surround the two ends completely so as to form a clasp. When this has become converted into bone a bridge of new bone connects the fragments, and a ring of new bone encircles them for some distance above and below the place of fracture. The portion that acts the part of ring does not remain permanently. It exists for the purpose of keeping the broken bone at rest until a union has been accom plished between the ends. When that has been effected much of the encircling callus is ab sorbed. For this reason it has been called pro visional, external, or sheathing callus. The time which elapses before complete union has taken place varies according to the age and strength of the person, and also according to the size of the bone, the accuracy of the ad justment of the fragments, and the degree of perfectness of rest permitted to the part. The usual time, however, is from four to ten weeks. But the process does not end here. As soon as rigidity has been obtained the sharp edges of the bone begin to be smoothed away, and any bone that has been formed in excess of what is necessary for purposes of union is slowly ab sorbed. By absorption also the inner layers of new bone change from dense to spongy bony tissue, and the marrow cavity is cleared of its internal callus. The last stage may be com pleted in from six to twelve months.
Non-union.—Some bones do not readily unite at all by bony union. They arc generally bones which, from the position they occupy, and owing to the action of the muscles attached to them, do not get sufficient rest to permit of the repara tive process going on in all its stages. As a result the callus never reaches the stage of true bone, but stops short at the fibrous or gristly stage. This is specially liable to occur in repair of the neck of the thigh-bone, the olecranon process of the ulna, the processes of the shoul der-blade, and very particularly the knee-pan. In the union of any bone, however, such an arrest of development may take place. It may be that the person is not in vigorous health, and therefore the repair is tedious or incomplete. Frequent meddling by the attendant, or con stant movement by the patient, will produce a like result. The occurrence of suppuration or death of a portion of the bone, a thing likely enough to occur in a compound or comminuted fracture, would also interfere with perfect repair. In such cases ligamentous may take the place of bony union, or the ends of the bone, remaining separate, may become rounded off, covered with a glistening fibrous tissue, and inclosed within a kind of fibrous sheath, so that a false joint is formed, which permits of free movement.
Signs. ----Naturally the first signs of fracture are pain and loss of function—the person use the broken limb. In a short time there will also be swelling and discoloration, due, first of all, to the blood from the torn blood-vessels, and, next, to the material that exudes from the vessels for repair. It is of great value to be able to examine the limb before the swelling sets in, as it may mask some of time most im portant distinguishiug signs of fracture. The most important signs are—(1) unnatural capa city of movement at the site of the fracture; (2) a peculiar crackling sensation called ccepitation, which may be felt by the hand placed over the fracture, when the opposed surfaces of the broken bone grate upon each other; (3) defor mity, caused by the displacement of one of the fragments. (1) The unnatural power of motion is most generally present, though when the break is near a joint it may be difficult to dis tinguish it from the ordinary movement of the bone in the joint. It is one of the main distin guishing features between fracture and disloca tion, the limb being, in the latter case, deprived of its natural power of movement. (2) Crepita tion is obtained by trying to move one end of the broken bone on the other, and conveys a sense of rough, coarse grating to the hands. It cannot be discovered if there be any degree of swelling; it may not be obtained when the broken bone is alongside of another, which supports it and prevents the necessary move ments. For instance, if, in the forearm, the radius were broken, the support of the ulna would prevent crepitation. (3) Deformity is, above all others, the most important sign. Deformity is due to displacement, generally of the more remote of the two fragments. The displacement may have been effected at the moment of fracture by the violence which caused it. It is frequently produced by the muscles attached to the bone, the natural ten sion of the muscles causing them to pull away the lent, and making it project in some unusual manner. The weight of the fractured limb, beyond the injured part, is also a frequent cause. Thus, if the thigh-bone be broken, the foot will act as a lever, displacing the lower fragment outwards. The displacement may be of different kinds : (a) Displacement by riding, in which one end lies over the other. (b) An gular displacement, where the two ends are not in the same straight line, but form an angle. (c) Displacement by turning. Au instance of this has been given already, viz., in fracture of the thigh-bone the weight of the foot turns the lower fragment outwards. There is, therefore, rotation of the lower fragment. (d) Lateral dis placement, in which one fragment moves to the side of the other, keeping parallel with it, and without losing its grip of the other fragment. Most of these displacements can be conjoined. Thus riding can coexist with rotation, &c. Besides the signs already mentioned, another may be noted, viz. shortening of the fractured limb. This is not always present. When it does occur it is due to displacement, one frag ment overriding the other and so causing the apparent shortening. To detect this, as well as to detect swelling and deformity, a comparison must be instituted between the sound limb and the limb supposed to be broken, and measure ments taken to determine any difference in length.