The distinction between hypertrophy of bone and chronic inflammation is sometimes a difficult one to draw. In the former there is a new-formation, as in the latter, and it may be only the absence of a definite inflammatory irritant which may determine the distinction.

In true hypertrophy new bone is formed of a strictly noraial character, and the result is a general or local enlargement of the bone. A general enlargement of a bone is called Hyperostosis, while a partial enlargement is Periostosis.

The Causation is in many cases obscure. It may be determined, as already mentioned (Fig. 68, p. 194), by a prolonged hyperemia, which gives rise to increased nutritive activity. In other cases it is Compensatory, as where the fibula undergoes hypertrophy in consequence of an ununited fracture of the tibia. In other cases we have to do with a gradual enlargement of unknown cause.

A General hyperostosis, in which the bones generally are enlarged, has been described by Paget under the designation Osteitis deformans. As the name implies, Paget regards the condition as the result of inflammation. The disease usually affects in the first place the bones of the lower limb and the cranium. These undergo great enlargement, while at the same time their tissue is opened out as by a rarefying ostitis. The bones are also softened, so that various curvatures are produced. The enlarged medullary spaces are filled as in inflammation with a tissue which is abundantly cellular. The name Osteoporosis is also given.

A peculiar feature in this disease is the frequent co-existence of tumours, which may be either sarcomatous, cancerous, or lymphatic (as in a case of Goodhart's), but are not always seated in the bones.

A hyperostosis affecting single bones has been observed chiefly in the skull and face. These bones may be enormously enlarged, and the face in particular may take on characters which have suggested Yirchow's name of Leontiasis ossea.

Periostosis is more unusual apart from inflammatory enlargement, but partial enlargements of the processes of bones occur.

Literature

Paget, Med. chir. trans., vol. lx., 1876; Treves, Path, trans., xxxii.. 1881; Silcock, ibid., xxxvi., 1885; Robinson, ibid., xxxviii., 1887; Goophart, mid., xxxix., 1888; Clutton, ibid.; Hutchinson, Paget, and others, Illust. Med. News, vol. ii., 1889, pp. 169-189; Gilles de la Tourette et Marinesco, Nouv. Iconograph. d. 1. Salpetriere, 1895.