[Illustration: FIG. 4.--Excess of Callus after compound fracture of Bones of Forearm.]
#Absorption of Callus.#--It sometimes happens that when an acute infective disease, especially one of the exanthemata, supervenes while a fracture is undergoing repair, the callus which has formed becomes softened and is absorbed. This may occur weeks or even months after the bone has united, with the result that the fragments again become movable, and it may be a considerable time before union finally takes place.
#Tumours of Callus.#--Tumours, such as chondroma and sarcoma, and cysts which are probably of the same nature as those met with in osteomyelitis fibrosa, are liable to occur in callus, or at the seat of old fractures, but the evidence so far is inconclusive as to the causative relationship of the injury to the new-growth. They are treated on the same lines as tumours occurring independently of fracture.
#Badly United Fracture--Mal-Union.#--Union with marked displacement of the fragments is most common in fractures that have not been properly treated--as, for example, those occurring in sailors at sea; and in cases in which the comminution was so great that accurate apposition was rendered impossible. It may also result from imperfect reduction, or because the apparatus employed permitted of secondary displacement. Restlessness on the part of the patient from intractability, delirium tremens, or mania, is the cause of mal-union in some cases; sometimes it has resulted because the patient was expected to die from some other lesion and the fracture was left untreated.
Whether or not any attempt should be made to improve matters depends largely on the degree of deformity and the amount of interference with function.
When interference is called for, if the callus is not yet firmly consolidated, it may be possible, under an anæsthetic, to bend the bone into position or to re-break it, either with the hands or by means of a strong mechanical contrivance known as an osteoclast. In the majority of cases, however, an open operation yields results which are more certain and satisfactory. When the deformity is comparatively slight, the bone is divided with an osteotome and straightened; when there is marked bending or angling, a wedge is taken from the convexity, as in the operation for bow-leg. To maintain the fragments in apposition it may be necessary to employ pegs, plates, bone-grafts, or other mechanical means. Splints and extension are then applied, and the condition is treated on the same lines as a compound fracture.