The biology of fracture healing. An overview for clinicians. Part II.

Bone healing problems can be divided into: technical failures, when treatment problems have impaired normal biologic potential; biologic failures, when biologic malfunctions have made the correct treatment ineffective; and combinations of the two. Biologic failures include inadequate callus formation or lack of a normal regional acceleratory phenomenon (RAP), normal modeling or remodeling, or maldifferentiation of the healing tissues, plus combinations. The most common biologic failures involve the inability to form callus and/or a normal RAP. When an inadequate RAP combines with inadequate callus production, then chronic infection, nonunion, multiple failed bone grafts and fixation procedures, and even amputation can ensue. Accumulating evidence suggests that most biologic failures stem from problems attributable to mitogens, differentiating and priming agents, growth factors, and other labile biochemical and biophysical messengers and signals in the region of the fracture itself. The ability of bone to heal can differ in different parts of the bony skeleton at a given moment. Until the basic causes of such problems can be corrected, present-day clinicians must manage them by presently available treatments while conducting research that might resolve them. The causes of most biologic failures probably act within the first weeks after the fracture, although it may take months for clinical roentgenograms to show their effects.