[Illustration: FIG. 124.--Tuberculous Osteomyelitis of Os Magnum,
excised from a boy aet. 8. Note well-defined caseous focus, with several
minute foci in surrounding marrow.]
Sometimes the tuberculous granulation tissue spreads in the marrow,
assuming the characters of a diffuse infiltration--diffuse tuberculous
osteomyelitis. The trabecular framework of the bone undergoes erosion
and absorption--rarefying ostitis--and either disappears altogether or
only irregular fragments or sequestra of microscopic dimensions remain
in the area affected. Less frequently the trabecular framework is added
to by the formation of new bone, resulting in a remarkable degree of
sclerosis, and if, following upon this, there is caseation of the
tubercle and death of the affected portion of bone, there results a
sequestrum often of considerable size and characteristic shape, which,
because of the sclerosis and surrounding endarteritis, is exceedingly
slow in separating. When the sequestrum involves an articular surface it
is often wedge-shaped; in other situations it is rounded or truncated
and lies in the long axis of the medullary canal (Fig. 125). 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.
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