8. Involvement of nerves by pressure of callus, most often seen about the elbow.
9. Thrombosis leading to obliteration of the deeper and enlargement of the more superficial veins.
10. Edema, also the result of venous obstruction by pressure of callus.
11. Chronic hydrarthrosis.
12. Arthritis deformans traumatica. This is usually a remote result of fractures, and manifests itself by slow changes in shape and position, with deformity and disability. It occurs most often in the aged.
13. Necrosis, which may be the result of failure in the process of repair and will probably necessitate operation.
14. Malignant changes. These have to do with the occurrence of sarcoma in bone callus, a complication which is known to occasionally arise. (See [Sarcoma].) It also refers to primary sarcoma, by which bone is weakened, or secondary carcinoma, which produces the same result.
15. Syphilis. Chronic syphilitic disease is well known to weaken bones by atrophic processes as well as by the deposition of gumma. It is known also to delay, or sometimes almost prevent, the process of callus formation, ossification, and later absorption. Syphilitic patients with fractures need to be kept under antispecific medicines.
REPAIR OF FRACTURES.
The immediate consequence of a fracture is outpour of blood both from the broken-bone surfaces and from whatever other tissues may have been lacerated. This produces, first, a hematoma, which is followed by a certain degree of local edema, perhaps even of general edema of the distal parts. The latter will subside with a rapidity proportionate to the promptness of suitable treatment and the nature of the injury. The blood begins to coagulate within a short time, while with the disappearance of the more fluid portion granulations begin to form from the periosteum, as well as bone surfaces, externally and internally, and even from the marrow. The clot loses its original characteristics and is permeated more or less rapidly by granulations. With the site of the injury wrapped in a mass of granulation tissue we speak of the so-called provisional callus, whose amount will depend upon the severity of the injury and the accuracy of the replacement of the parts. If laceration has been but trifling and the bones are accurately apposed the amount of callus will be small, otherwise it may be large; so large, in fact, as to be easily palpated and even to cause edema and pain by pressure. Repair of the fracture is effected by the gradual conversion of this callus into cartilaginous tissue and then into bone. So much of it, at least, as lies on the outer side of the bone and is known as external callus goes through this change. The internal callus, i. e., that within the marrow cavity, undergoes a more direct transformation, which amounts to immediate ossification. The internal callus usually ossifies completely, and then forms a medullary plug that serves as an internal splint and affords support and strength. In time it completely disappears, this time varying in different cases.