With few exceptions, tuberculous disease in the interior of a bone does not reveal its presence until by extension it reaches one or other of the surfaces of the bone.  In the shaft of a long bone its eruption on the periosteal surface is usually followed by the formation of a cold abscess in the overlying soft parts.  When situated in the articular ends of bones, the disease more often erupts in relation to the reflection of the synovial membrane or directly on the articular surface—­in either case giving rise to disease 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 spoon and gouge, the latter procedure being preferred in the case of the calcaneus to conserve the stability of the heel.  When several bones and joints are simultaneously affected, and there are sinuses with mixed infection, amputation is usually indicated, especially in adults.