Tuberculous disease in bone is characterised by its insidious onset and slow progress, and by the frequency with which it is associated with disease of the adjacent joint.

#Periosteal tuberculosis# is met with in the ribs, sternum, vertebral column, skull, and less frequently in the long bones of the limbs.  It may originate in the periosteum, or may spread thence from the marrow, or from synovial membrane.

In superficial bones, such as the sternum, the formation of tuberculous granulation tissue in the deeper layer of the periosteum, and its subsequent caseation and liquefaction, is attended by the insidious development of a doughy swelling, which is not as a rule painful, although tender on pressure.  While the swelling often remains quiescent for some time, it tends to increase in size, to become boggy or fluctuating, and to assume the characters of a cold abscess.  The pus perforates the fibrous layer of the periosteum, invading and infecting the overlying soft parts, its spread being influenced by the anatomical arrangement of the tissues.  The size of the abscess affords no indication of the extent of the bone lesion from which it originates.  As the abscess reaches the surface, the skin becomes of a dusky red or livid colour, is gradually thinned out, and finally sloughs, forming a sinus.  A probe passed into the sinus strikes carious bone.  Small sequestra may be found embedded in the granulation tissue.  The sinus persists as long as any active tubercle remains in the tissues, and is apt to form an avenue for pyogenic infection.

In deeply seated bones, such as the upper end of the femur, the formation of a cold abscess in the soft parts is often the first evidence of the disease.

Diagnosis.—­Before the stage of cold abscess is reached, the localised swelling is to be differentiated from a gumma, from chronic forms of staphylococcal osteomyelitis, from enlarged bursa or ganglion, from sub-periosteal lipoma, and from sarcoma.  Most difficulty is met with in relation to periosteal sarcoma, which must be differentiated either by the X-ray appearances or by an exploratory incision.

X-ray appearances in periosteal tubercle:  the surface of the cortical bone in the area of disease is roughened and irregular by erosion, and in the vicinity there may be a deposit of new bone on the surface, particularly if a sinus is present and mixed infection has occurred; in syphilis the shadow of the bone is denser as a result of sclerosis, and there is usually more new bone on the surface—­hyperostosis; in periosteal sarcoma there is greater erosion and consequently greater irregularity in the contour of the cortical bone, and frequently there is evidence of formation of bone in the form of characteristic spicules projecting from the surface at a right angle.

The early recognition of periosteal lesions in the articular ends of bones is of importance, as the disease, if left to itself, is liable to spread to the adjacent joint.