Fracture healing: fracture healing understood as the result of a fascinating cascade of physical and biological interactions. Part I. An Attempt to Integrate Observations from 30 Years AO Research.

The choice of best procedure in fracture treatment relies on a proper understanding of tissue reactions to the prevailing mechanical and biological conditions. Investing time and effort is rewarding as it opens up access to a fascinating world and improves fracture treatment based on logical decision making. An intact bony skeleton enables mechanical functions of the human body such as locomotion. This function of the bone is made possible by its stiffness and strength, which allows bone to carry load without undergoing major deformation while remaining intact even under heavy loads. The shortcoming of bone as a strong and stiff material is its brittleness. Its brittleness prevents bone from bridging a fracture under unstable conditions. In spontaneous healing or healing under flxible fiation, a cascade of repair tissues stabilizes the fracture and allows for solid bony union. Excessive load fractures the bone. Disrupted bone loses its stiffness. Loss of stiffness and, consequently, loss of skeletal support disables the function of the limb. fracture healing is a ubiquitous and spontaneous process which restores stiffness as a prerequisite for mechanical function. Restoration of mechanical integrity requires that bone bridges and/or remodels the fracture site. If there is high initial tissue deformation (strain) at the fracture site, bone as a brittle material cannot bridge the gap. In spontaneous healing or healing under flxible fiation a cascade of consecutive phases of tissue differentiation are required to overcome this shortcoming of bone. The cascade increases tissue stiffness at the expense of tolerance to deformation until a low value of interfragmental strain is reached that then allows bone to form a solid bridge. The cascade of differentiation is impressive as a "reasonable" process with a goal. Therefore, bone healing is often considered as a rational process where the repair tissues are expected "to think and to act in order to achieve". we propose the observation of bone reactions without assuming that these reactions are guided by goal-oriented intelligence because the latter is non-existent. Observing the unexpected without having a preconceived opinion is a precondition for new insight. This approach avoids being misled into projecting one's own thinking into tissues that react without goal orientation. fracture healing is a repair process which requires induction and must be enabled. To get a feel for the problem we will fist address the mechanical properties of bone as the prerequisites for its mechanical functions. Then we will discuss which conditions induce and which enable the repair process. The following paper addresses a fascinating interplay between physical and biological processes that enable fractured bone to bridge solidly and remodel to regain its "pre-fracture" function and structure. no one of the different treatment modalities or healing patterns is best on its own. for a given situation the goal is to recover the function of the bone, limb and patient early and permanently by choosing the optimal procedure and implant. Understanding bone reactions permits a rational choice and replaces subjective predilection and monomania. The stability of the fiation and the blood supply are priority considerations, which must often be weighed against each other.