DISEASES OF THE JOINTS 423 



of granulation tissue which entirely alter the appearance of 

 the membrane as we know it normally. 



In the early stages the contents of the joint are composed 

 of thin pus and synovia. Later, as destruction of the 

 synovial membrane proceeds, the Mow of synovia is stopped, 

 while the pus formation goes on until finally nothing but 

 pus and dead tissue products fill the cavity. 



If the suppurative process has commenced from within, 

 the pus that is formed is, as a rule, thick and creamy, com- 

 paratively unstained, and free from marked odour. If, 

 on the other hand, air has gained access to the joint, or the 

 suppurative process has started from the materials intro- 

 duced by a foreign body, the joint contents are thin, blood- 

 stained, and stinking. 



The inflammatory changes in the joint soon spread to the 

 ligaments, and to the soft structures in contact with them. 

 This means that the ligaments become infiltrated with in- 

 flammatory exudate, that the fibrous bundles composing 

 them become separated, and that the ligaments are weakened 

 and easily stretched. As a consequence, a certain amount 

 of displacement or dislocation of the bones is allowed. 



In like manner the inflammatory changes keep spreading 

 until we have the periosteum next the ends of the bones 

 affected. The periostitis thus set up invariably takes the 

 osteoplastic form, and as a result of this we have growths 

 of new bone in the near neighborhood of the joint. It is in 

 the later stages of the disease — that is, when the pus has 

 been evacuated and reparative changes commenced — that 

 this osteoplastic periostitis is most marked, and it plays 

 a large part in bringing about the condition of anchylosis, 

 which we shall afterwards describe. 



Grave changes also occur in the articular cartilages. 

 They quickly lose their peculiar glistening polish, their 

 semitransparency is lost, and the natural tint of a pearl-like 

 blue gives way to a dirty yellow. Later this is followed by 

 erosion of the cartilages at such points as they happen to 

 be in greatest contact. The ends of the bones are thus 

 exposed, and their medullary cavities exposed to infection. 



