the dead bone may cause complications, as when a
sequestrum derived from the trigone of the femur perforates the
popliteal artery or the cavity of the knee-joint, or a sequestrum of the
pelvis perforates the wall of the urinary bladder.

The extent to which bone which has been lost is reproduced varies in
different parts of the skeleton: while the long bones, the scapula, the
mandible, and other bones which are developed in cartilage are almost
completely re-formed, bones which are entirely developed in membrane,
such as the flat bones of the skull and the maxilla, are not reproduced.

[Illustration: FIG. 119.--Femur and Tibia showing results of Acute
Osteomyelitis affecting Trigone of Femur; sequestrum partly surrounded
by new case; backward displacement of lower epiphysis and implication of
knee-joint.]

It may be instructive to describe _the X-ray appearances of a long bone
that has passed through an attack of acute osteomyelitis_ severe enough
to have caused necrosis of part of the diaphysis. The shadow of the dead
bone is seen in the position of the original shaft which it represents;
it is of the same shape and density as the original shaft, while its
margins present an irregular contour from the erosion concerned in its
separation. The sequestrum is separated from the living bone by a clear
zone which corresponds to the layer of granulations lining the cavity in
which it lies. This clear zone separating the shadow of the dead bone
from that of the living bone by which it is surrounded is conclusive
evidence of a sequestrum. The medullary canal in the vicinity of the
sequestrum being obliterated, is represented by a shadow of varying
density, continuous with that of the surrounding bone. The shadow of the
new case or involucrum with its wavy contour is also in evidence, with
its openings or cloacae, and is mainly responsible for the increase in
the diameter of the bone.

The skiagram may also show separation and displacement of the adjacent
epiphysis and destruction of the articular surfaces or dislocation of
the joint.

_Sequelae of Acute Suppurative Osteomyelitis._--The commonest sequel is
the presence of a sequestrum with one or more discharging sinuses; owing
to the abundant formation of scar tissue these sinuses have rigid edges
which are usually depressed and adherent to the bone.

_The Recognition and Removal of Sequestra._--So long as there is dead
bone there will be suppuration from the granulation