h chiefly in the humerus and in the
clavicle.

_Failure of Union--"Un-united Fracture."_--As the time taken for union
varies widely in different bones, and ossification may ultimately
ensue after being delayed for several months, a fracture cannot be
said to have failed to unite until the average period has been long
overpassed and still there is no evidence of fusion of the fragments.
Under these conditions failure of union is a rare complication of
fractures. In adults it is most frequently met with in the humerus,
the radius and ulna (Fig. 6), and the femur; in children in the bones
of the leg and in the forearm.

[Illustration: FIG. 6.--Radiogram of Un-united Fracture of Shaft of
Ulna of fifteen years' duration.]

In a radiogram the bones in the vicinity of the fracture, particularly
the distal fragment, cast a comparatively faint shadow, and there may
even be a clear space between the fragments. When the parts are
exposed by operation, the bone is found to be soft and spongy and the
ends of the fragments are rarefied and atrophied; sometimes they are
pointed, and occasionally absorption has taken place to such an extent
that a gap exists between the fragments. The bone is easily penetrated
by a bradawl, and if an attempt is made to apply plates, the screws
fail to bite. These changes are most marked in the distal fragment.

The want of union is evidently due to defective activity of the
bone-forming cells in the vicinity of the fracture. This may result
from constitutional dyscrasia, or may be associated with a defective
blood supply, as when the nutrient artery is injured. Interference
with the trophic nerve supply may play a part, as cases are recorded
by Bognaud in which union of fractures of the leg failed to take place
after injuries of the spinal medulla causing paraplegia. The condition
has been attributed to local causes, such as the interposition of
muscle or other soft tissue between the fragments, or to the presence
of a separated fragment of bone or of a sequestrum following
suppuration. In our experience such factors are seldom present.

If the treatment recommended for delayed union fails, recourse must be
had to operation, the most satisfactory procedure being to insert a
bone graft in the form of an intra-medullary splint. In certain cases
met with in the bones of the leg in children, the degree of atrophy of
the bones is such that it has been found necessary to amputate after
repeated attempt