re commonly of
the marrow in osteomyelitis fibrosa.

CHAPTER XXI

DISEASES OF JOINTS

Definition of terms--Ankylosis. DISEASES: Errors of
development--Bacterial diseases: _Pyogenic_; _Gonorrhoeal_;
_Tuberculous_; _Syphilitic_; _Acute rheumatism_--Diseases
associated with certain constitutional conditions: _Gout_; _Chronic
articular rheumatism_; _Arthritis deformans_;
_Haemophilia_--Diseases associated with affections of the nervous
system: _Neuro-arthropathies_; _Charcot's disease_--Hysterical or
mimetic affections of joints--Tumours and cysts--Loose bodies.

#Definition of Terms.#--The term _synovitis_ is applied to any reaction
which affects the synovial membrane of a joint. It is usually associated
with effusion of fluid, and this may be serous, sero-fibrinous, or
purulent. As the term synovitis merely refers to the tissue involved, it
should always be used with an adjective--such as gouty, gonorrhoeal, or
tuberculous--which indicates its pathological nature.

The terms _hydrops_, _hydrarthrosis_, and _chronic serous synovitis_ are
synonymous, and are employed when a serous effusion into the joint is
the prominent clinical feature. Hydrops may occur apart from
disease--for example, in the knee-joint from repeated sprains, or when
there is a loose body in the joint--but is met with chiefly in the
chronic forms of synovitis which result from gonorrhoea, tuberculosis,
syphilis, arthritis deformans, or arthropathies of nerve origin.

_Arthritis_ is the term applied when not only the synovial membrane but
the articular surfaces, and it may be also the ends of the bones, are
involved, and it is necessary to prefix a qualifying adjective which
indicates its nature. When effusion is present, it may be serous, as in
arthritis deformans, or sero-fibrinous or purulent, as in certain forms
of pyogenic and tuberculous arthritis. Wasting of the muscles,
especially the extensors, in the vicinity of the joint is a constant
accompaniment of arthritis. On account of the involvement of the
articular surfaces, arthritis is apt to be followed by ankylosis.

The term _empyema_ is sometimes employed to indicate that the cavity of
the joint contains pus. This is observed chiefly in chronic disease of
pyogenic or tuberculous origin, and is usually attended with the
formation of abscesses outside the joint.

_Ulceration of cartilage_ and _caries of the articular surfaces_ are
common accompaniments