PART II. PRACTICE OF SURGERY

SECTION III. DISEASES

Part 12. 2. Diseases of Bone

Attention has already been directed to one form of injury to a Bone bone, viz., fracture. A word may now be said about inflammation diseases, of a bone and its results. As a typical instance we will take a long bone, consisting of a shaft and two extremities. The walls of the shaft consist of dense bone, the extremities of cancellated tissue. The shaft of the bone is hollow, and filled with medullary tissue. In the fully developed bone the extremities alone are tipped with cartilage ; in the extremities of the bones of a growing person there are also layers, termed the epiphyseal cartilages. The bone-is surrounded by a fibrous membrane termed the periosteum. This membrane is richly supplied with blood-vessels, which ramify through it and pass, along with lymphatic vessels and nerves, from it into the Plaversian canals in the dense bone forming the shaft. The deeper layers of the periosteum consist of osteoblastic cells, which also line the Haversian canals. In the undeveloped condition these cell elements take an active part in the growth of the bone as regards its breadth, the epiphyseal cartilages taking an active part in its growth as regards its length. The medullary tissue la-the cavity of the bone is supplied by the nutrient artery ; the cancellated tissue forming the extremities receives its blood-supply partly from the nutrient artery and partly from vessels passing in-directly from the periosteum. When a bone is injured—as happens, for example, in a severe bruise—the blood-vessels in the periosteum and in the Haversian canals become congested, effusion of liquor sanguinis and migration of the white blood corpuscles take place, and a severe gnawing pain is felt at the seat of the bruise. The pain is severe because the effusion cannot escape. It collects under the periosteum and in the Haversian canals. The cell elements in these situations are irritated, and cell proliferation takes place. The periosteum becomes thickened, and if the tension continues suppuration may occur between the periosteum and the bone. The periosteum is raised from the bone ; the blood-vessels passing into the Haversian canals are obliterated or torn across ; and the outer layers of the hard dense bone, their sources of nutriment being cut off, die. The extent of the necrosed tissue will depend upon the extent of the suppurating area ; if the suppurating area includes the nutrient artery within its range, nutriment being then cut off from the medullary tissue from which in part the deeper layers of the shaft of the bone are supplied with blood, death of the whole thickness of the shaft of the bone may occur. As already stated, the most acute forms of suppurative periostitis and suppurative osteomyelitis are infective diseases, the suppuration in them being due to the presence of a micrococcus. If after an injury the primary inflammation is relieved by fomentations, leeching, or incisions, suppuration may be prevented; or even if, after suppuration has occurred, free incisions are made to allow the pus to escape, the periosteum may assume its normal position, and the area of necrosis be limited or necrosis be prevented altogether. After a portion of the shaft of the bone dies, the necrosed area is gradually absorbed; but, if the area is of considerable size, and more particularly if sepsis occurs, the dead part is gradually separated from the living, and after a time it becomes loose, and as a rule has to be removed by operation. If the inflammation, acute in the first in-stance, becomes sub-acute, or if it is sub-acute from the first, then, instead of suppuration, the effusion under the periosteum coagu-lates, whereupon lymph is formed, the proliferating osteoblastic cells in the lymph take up their normal function, anil new bone is made. This mass of new bone is termed a node. In the Haversian canals the osteoblasts there forming bone will render the bone tissue more dense and ivory-like in consistence, to which the term sclerosis is applied. In some cases the osteoblastic cells in the Haversian canals, instead of forming bone, feed upon the original bony tissue which constitutes the walls of the canals. The Haversian canals becoming enlarged, the result is a lessening of the amount of inorganic matter in the area affected, and a cancellation of the hard bone takes place. This condition is called rarefying ostitis. The rarefaction of the dense bone may persist, or the process may stop, the osteoblasts again forming bone and the rarefied area becoming sclerosed. In the cancellated tissue in the extremities of the long bones, and in that which forms the mass of the short bones, such as the vertebrae, the tarsal and the carpal bones, the inorganic matter compared with the hard bone is relatively in smaller amount than the organic matter filling the cancellse. Here as a result of injury the thin lamellfe of bone may be cut off from their blood-supply, and death take place. If the process is acute, an area of cancellated tissue will die, and be separated from the surrounding living tissue as in the hard bone. In consequence, however, of the quantity of organic matter, death may take place in a molecular form, more nearly allied to the process of ulceration in the soft parts. This condition is known as caries. If the inflammatory process in cancellated tissue is sub-acute, instead of a molecular death, sclerosis of the cancellated tissue occurs. When the cancellated tissue is the seat of inflammation, in con-sequence of its close connexion and intimate anatomical relations with the articular cartilages, they in their turn become implicated, and we have then to deal with disease of the joint. In all cases in which incisions are made to relieve tension under the periosteum, or in which portions of bone are removed to relieve tension in the shaft or in the medullary cavity of a bone, or in which incisions are made to check the progress of inflammatory action in the can-cellated tissue, strict antiseptic precautions must be taken to pre-vent sepsis occurring in the wound.






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