The most common is an osteomyelitis commencing in the marrow exposed in a wound infected with pyogenic organisms.  In amputation stumps, fungating granulations protrude from the sawn end of the bone, and if necrosis takes place, the sequestrum is annular, affecting the cross-section of the bone at the saw-line; or tubular, extending up the shaft, and tapering off above.  The periosteum is more easily detached, is thicker than normal, and is actively engaged in forming bone.  In the macerated specimen, the new bone presents a characteristic coral-like appearance, and may be perforated by cloacae (Fig. 122).

[Illustration:  FIG. 122.—­Tubular Sequestrum resulting from Septic Osteomyelitis in Amputation Stump.]

Like other pyogenic infections, it may terminate in pyaemia, as a result of septic phlebitis in the marrow.

The clinical features of osteomyelitis in an amputation stump are those of ordinary pyogenic infection; the involvement of the bone may be suspected from the clinical course, the absence of improvement from measures directed towards overcoming the sepsis in the soft parts, and the persistence of suppuration in spite of free drainage, but it is not recognised unless the bone is exposed by opening up the stump or the changes in the bone are shown by the X-rays.  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.  Even after healing has taken place, relapse is liable to occur, especially in gun-shot injuries.  Months or years afterwards, the bone may become painful and tender.  The symptoms may subside under rest and elevation of the limb and the application of a compress, or an abscess forms and bursts with comparatively little suffering.  The contents may be clear yellow serum or watery pus; sometimes a small spicule of bone is discharged.  Valuable information, both for diagnosis and treatment, is afforded by skiagrams.

[Illustration:  FIG. 123.—­New Periosteal Bone on surface of Femur from Amputation Stump.  Osteomyelitis supervened on the amputation, and resulted in necrosis at the sawn section of the bone. (Anatomical Museum, University of Edinburgh.)]

TUBERCULOUS DISEASE

The tuberculous diseases of bone result from infection of the marrow or periosteum by tubercle bacilli conveyed through the arteries; it is exceedingly rare for tubercle to appear in bone as a primary infection, the bacilli being usually derived from some pre-existing focus in the bronchial glands or elsewhere.  According to the observations of John Fraser, 60 per cent. of the cases of bone and joint tubercle in children are due to the bovine bacillus, 37 per cent. to the human variety, and in 3 per cent. both types are present.