oose body of other than tuberculous origin.

(3) _Cold abscess_ or _empyema_ of the knee is a rare condition, in
which the joint becomes filled with pus. It usually results from a
primary tuberculosis of the synovial membrane occurring in children
reduced in health and the subject of tuberculosis elsewhere.

(4) _Diffuse Thickening of the Synovial Membrane--White Swelling._--So
long as this form of the disease remains confined to the synovial
membrane, the chief feature is that of an indolent elastic swelling in
the area of the joint. The swelling tapers off above and below, so
that it acquires a fusiform shape, and from the wasting of the muscles
it appears greater than it really is. The range of movement is
moderately restricted.

At first the patient limps, keeps the knee slightly flexed, and
complains of tiredness and stiffness after exertion. As the articular
surfaces become affected, there is pain, which is readily excited by
jarring of the limb, or by any attempt at movement; the joint is held
rigid, and there may be startings at night. If untreated, flexion
becomes more pronounced--it may be to a right angle--the leg and foot
are everted, and, in children, the tibia may be displaced backwards
(Fig. 124). The wasting of muscles continues, the part becomes hot to
the touch, the swelling increases, and may show areas of softening or
fluctuation from abscess formation.

[Illustration: FIG. 124.--Advanced Tuberculous Disease of Knee, with
backward displacement of Tibia.]

White swelling is to be differentiated from peri-synovial gummata,
from myeloma and sarcoma of the lower end of the femur, and from
bleeder's knee. In the first of these the swelling is nodular and less
uniform, and there may be tertiary ulcers or depressed scars in the
neighbourhood of the patella. In tumours the swelling is more marked
on one side of the joint, it is uneven or nodular, it does not
correspond to the shape of the synovial membrane, and may extend
beyond the limits of the joint, and it involves the bone to a greater
extent than is usual in disease of the joint. Skiagrams show expansion
of the bone in central tumours, or abundant new bone in ossifying
sarcoma. The diagnosis of bleeder's knee is to be made from the
history.

(5) _Primary Tuberculous Disease in the Bones of the Knee._--So long
as the foci are confined to the interior of the bone, it is impossible
to recognise their existence, unless they are of sufficient size to