of the joint (Fig. 156).

[Illustration: Fig. 126.--Diffuse Tuberculous Osteomyelitis of Right
Tibia.

(Photograph lent by Sir H. J. Stiles.)]

#Diffuse Tuberculous Osteomyelitis in the shaft of a long bone# is
comparatively rare, and has been observed chiefly in the tibia and the
ulna in children (Fig. 126). It commences at the growing extremity of
the diaphysis, and spreads along the medulla to a variable extent; it is
attended by the formation of vascular and porous bone on the surface,
which causes thickening of the diaphysis; this is most marked at the
ossifying junction and tapers off along the shaft. The infection not
only spreads along the medulla, but it invades the spongy bone
surrounding this, and then the cortical bone, and is only prevented from
reaching the soft parts by the new bone formed by the periosteum. The
bone is replaced by granulation tissue, and disappears, or part of it
may become sclerosed and in time form a sequestrum. In the macerated
specimen, the sequestrum appears small in proportion to the large cavity
in which it lies. All these changes are revealed in a good skiagram,
which not only confirms the diagnosis, but, in many instances,
demonstrates the extent of the disease, the presence or absence of a
sequestrum, and the amount of new bone on the surface. Finally the
periosteum gives way, and an abscess forms in the soft parts; and if
left to itself ruptures externally, leaving a sinus. The most
satisfactory _treatment_ is to resect sub-periosteally the diseased
portion of the diaphysis.

_In cancellous bones, such as those of the tarsus_, there is a similar
caseous infiltration in the marrow, and this may be attended with the
formation of a sequestrum either in the interior of the bone or
involving its outer shell, as shown in Fig. 127. The situation and
extent of the disease are shown in X-ray photographs. After the
tuberculous granulation tissue erupts through the cortex of the bone, it
gives rise to a cold abscess or infects adjacent joints or tendon
sheaths.

[Illustration: FIG. 127.--Advanced Tuberculous Disease in region of
Ankle. The ankle-joint is ankylosed, and there is a large sequestrum in
the calcaneus.

(Specimen in Anatomical Museum, University of Edinburgh.)]

If an exact diagnosis is made at an early stage of the disease--and this
is often possible with the aid of X-rays--the affected bone is excised
sub-periosteally or its interior is cleared out with the sharp