1. The mechanism of non-union of fractures of the tibia, common to all clinical circumstances of this condition, is fibrinoid degeneration of connective tissue in the interior of the callus. Fibrinoid forms when the bone injury has been extensive, has been complicated by infection, or has been difficult to immobilize. The process appears to be similar to that seen in chronic adventitious bursitis. If motion and friction are not controlled, fibrinoid degeneration continues indefinitely, and a permanent pseudarthrosis may develop. Immobilization acts as a deterrent to the formation of fibrinoid and permits the refilling of the defect with new fibrocartilaginous callus.
2. Fibrinoid is not a simple barrier to osteogenesis; it indicates a defective callus. Fibrinoid fails to draw osteogenesis from the periosteum and endosteum across the fracture gap. According to interpretations of the newer theory of osteogenesis, it lacks the ability of cartilage and fibrocartilage to promote new-bone formation by induction.
3. The effect of open operations on fresh fractures is to increase the volume of damaged bone which has to be absorbed and replaced before the fracture can unite and permit full weight-bearing on the leg. Comminuted fractures of the shaft of the human adult tibia should be considered non-operable fractures during the first six months of healing, because the trauma added by surgery exceeds the normal capacity for bone regeneration in this area of the skeleton.
4. Bone-grafting, without excision of the fibrocartilaginous callus, may be applied successfully in ununited fractures of the tibia before eighteen months of healing. Excision of the pseudarthrosis, osteotomy of the fibula, and telescoping of the fracture ends are advisable in ununited fractures after eighteen months. All of the standard surgical procedures of onlay, inlay, or intramedullary bone grafts are capable of producing union with the aid of one additional year of immobilization of the fracture, but the success of the operation is determined by the proliferative reaction of the bone ends, not the bone graft. If the bone ends are in close contact, the function of the graft appears to be that of an inductor.
5. Recurrence of sepsis is the chief cause of failure of all types of bone-graft operations. Roentgenograms which show a diffuse increase in density of bone tissue three or four centimeters above and below the fracture line indicate latent sepsis. In such cases six months, or even two years, without drainage is not a safe period of waiting to permit a bone-graft operation. Only synostosis operations which avoid the fracture site are free of risks of further damage to the bone ends by infection.
6. Radical leg-shortening procedures are an alternative to amputation and may be applicable in old ununited fractures with large soft-tissue defects after repeated failure of bone-grafting operations.