734 



THE BONES AND JOINTS. 



mation of the joint may follow. The walls of the shafts of the long 

 bones may be converted into spongy tissue. If, as is sometimes the case, 

 an ossifying periostitis occurs at the same time, the bone is thickened but 

 spongy ; or sometimes there are concentric layers of compact bone tissue, 

 separated by rarefied bone. 



Condensing Osteitis (Osteo-Sclerosis). This lesion is characterized by 

 the new formation of bone in the walls of the marrow cavities or Haver- 

 sian canals. The bone is formed under the influence of the blood-vessels 

 and osteoblasts, as in normal bone formation, but with less regularity. 

 It may result in the conversion of cancellous tissue into compact bone, 

 in the filliug-up of the medullary cavity of long bones with more or less 

 dense bone tissue. The compact bone, owing to the filling of its Haver- 

 sian canals, may become very dense and ivory-like. When the medullary 



PIG. 486. CONDENSING OSTEITIS, OR OSTEO-SCLEROSIS, IN ULNA OF CHILD. 



a, Fragment of old bone with roughened, sinuous edges ; b, old Howship's lacunae covered with more re- 

 cently formed bone lamella- ; c, d, new Haversian canals. 



cavities of long bones are involved the yellow marrow is converted into 

 red marrow by the absorption of fat and increased vascularity. 



Osteo-sclerosis is frequently associated with ossifying periostitis. It 

 often follows rarefying osteitis, and then the Howship's lacunae resulting 

 from the original absorption process may be filled and covered in with 

 new bone lamellae (Fig. 486). It is apt to occur in connection with 

 necrosis or chronic inflammation of adjacent soft parts, but it sometimes 

 occurs independently under unknown conditions. 



Suppurative Osteitis (Abscess of Bone). This process occurs usually in 

 the ends of the long bones, and is associated with rarefying osteitis. As 

 the bone tissue is absorbed, a circumscribed cavity may be formed in the 

 bone, filled with pus and lined with granulation tissue. 



Less frequently abscesses are formed in the shaft of a long bone by 

 circumscribed suppuration of the medulla. Such abscesses may occur in 



