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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 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.
Necrosis is the term applied to the death of a tangible portion of bone, and the dead portion when separated is called a sequestrum. The term exfoliation is sometimes employed to indicate the separation or throwing off of a superficial sequestrum.
These procedures may be carried out at the same time as the sequestrum is removed, or after an interval. In all of them, asepsis is essential for success. The deformities resulting from osteomyelitis are more marked the earlier in life the disease occurs.
The opening in the skin persists as a sinus, or develops into a typical ulcer with irregular, crescentic margins; in either case a probe reveals the presence of carious bone or of a sequestrum. The health may be impaired as a result of mixed infection, and the absorption of toxins and waxy degeneration in the viscera may ultimately be induced.
In cases of thickening of the bone with persistent and severe pain, if relief is not afforded by the repeated application of blisters, the thickened periosteum should be incised, and the bone opened up with the chisel or trephine. In cases attended with suppuration, the swelling is incised and drained, and if there is a sequestrum, it must be removed.
Displacement or partial extrusion of 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 first change is due to the deposit of new bone on the periosteal surface; later, there is the shadow of the sequestrum. Healing does not take place until the sequestrum is extruded or removed by operation. In compound fractures, if a fragment dies and forms a sequestrum, it is apt to be walled in by new bone; the sinuses continue to discharge until the sequestrum is removed.
The extrusion of a sequestrum may occur, provided there is a cloaca large enough to allow of its escape, but the surgeon has usually to interfere by performing the operation of sequestrectomy.
Finally, the sequestrum lies loose in a cavity lined by tuberculous granulation tissue, and is readily identified in a radiogram. This type of sclerosis preceding death of the bone is highly characteristic of tuberculosis. [Illustration: FIG.
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