[Pathophysiology of disrupted bone healing]

There are three immediate causes of disturbance in fracture healing. In order of significance, these are: (1) lack of vascularization and concomitant bone necrosis, (2) instability at the wrong moment, and (3) lack of contact amongst fragments. Bone necrosis arises as a result of the actual trauma or through destruction of vessels caused by implantation: the medullary vessels by marrow nailing and the periosteal vessels by plate osteosynthesis applying conventional techniques. Thus, the injury's triggering impulse and interfragmentary movement are unable to reach vital receptors. In the case of spontaneous bone healing, there should be no unpredictable excessive strain on the bone during the vulnerable phase of callus formation; otherwise, callus fracture and pseudarthrosis may occur. A lack of contact amongst fragments, caused by interposition of muscle, blocks the flow of information. Direct fracture healing can also be defined as "necrosis healing" and may be disturbed, to a considerable extent, by bone necrosis, excessive strain preceding actual osseous bridging as well as by bone defects. The alternative - bridge healing - tends to refracture. In spongy bones, a lack of fragment contact leads to healing defects, necessitrating early spongiosa transplantation.