The presence of these three signs in association is sufficient to prove the existence of a fracture, but the absence of one or more of them does not negative this diagnosis. There are certain fallacies to be guarded against. For example, a fracture may exist and yet unnatural mobility may not be present, because the bones are impacted into one another, or because the fracture is an incomplete one. Again, the extreme tension of the swollen tissues overlying the fracture may prevent the recognition of movement between the fragments. Deformity also may be absent--as, for instance, when there is no displacement of the fragments, or when only one of two parallel bones is broken, as in the leg or forearm. Similarly, crepitus may be absent when impaction exists, when the fragments completely override one another, or are separated by an interval, or when soft tissues, such as torn periosteum or muscle, are interposed between them. A sensation simulating crepitus may be felt on palpating a part into which blood has been extravasated, or which is the seat of subcutaneous emphysema. The creaking which accompanies movements in certain forms of teno-synovitis and chronic joint disease, and the rubbing of the dislocated end of a bone against the tissues amongst which it lies, may also be mistaken for the crepitus of fracture.
It is not advisable to be too diligent in eliciting these signs, because of the pain caused by the manipulations, and also because vigorous handling may do harm by undoing impaction, causing damage to soft parts or producing displacement which does not already exist, or by converting a simple into a compound fracture.
It is often necessary for purposes of diagnosis to administer a general anæsthetic, particularly in injuries of deeply placed bones and in the vicinity of joints. Before doing so, the appliances necessary for the treatment of the injury should be made ready, in order that the fracture may be reduced and set before the patient regains consciousness.
_Radiography in the Diagnosis of Fractures._--While radiography is of inestimable value in the diagnosis of many fractures and other injuries, particularly in the vicinity of joints, the student is warned against relying too implicitly on the evidence it seems to afford.
