The healing of a fracture is one of the most remarkable of all the repair processes in the body since it results, not in a scar, but in the actual reconstitution of the injured tissue in something very like its original form. It is not to be expected therefore that the mechanisms controlling such a process will be easily elucidated and indeed they involve problems of cellular homeostasis which are among the most fundamental in biology. If it is not quite the “cunning’st pattern of excelling nature” then it is something quite close to it and a great deal of that pattern at present stands unrevealed.

However, this review is primarily concerned with those features which have direct clinical relevance and it is fortunately possible to treat fractures successfully without a complete understanding of the cellular mechanisms involved without at the same time relying entirely on empiricism. A number of factors influence the healing which can be identified from both clinical and experimental work and may be taken into consideration to put treatment on a more rational basis. It is with these observations that we shall be particularly concerned and cellular mechanisms will be discussed only if they appear to have clinical implications. Such an account must necessarily include details of the healing process as it is modified by contemporary methods of treatment but first it is necessary to consider the events that occur in the healing of a simple fracture in an unsplinted long bone.