DISEASES OF THE JOINTS 423 



In the early stages the contents of the jomt are composed 

 of thm pas and synovia. Later, as destruction of the synovial 

 membrane i3roceeds, the flow 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, 

 comparatively 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 

 introduced 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 

 inflammatory 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 neighbourhood 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. As a 

 result we get in them the changes we have already described 

 under Ostitis. 



