junction instead of at the hip. While
rigidity is usually absolute as regards rotation, it may sometimes be
possible with care and gentleness to obtain some increase of flexion.
For diagnostic purposes most stress should therefore be laid on the
presence or absence of rotation.

If the sound limb is flexed at the hip and knee until the lumbar spine
is in contact with the table, the real flexion of the diseased hip
becomes manifest, and may be roughly measured by observing the angle
between the thigh and the table (Fig. 113). This is known as "Thomas'
flexion test," and is founded upon the inability to extend the
diseased hip without producing lordosis.

[Illustration: FIG. 113.--Thomas' Flexion Test, showing angle of
flexion at diseased (left) hip.]

_Swelling_ is seen on the anterior aspect of the joint; it may fill up
the fold of the groin and push forward the femoral vessels. It is
doughy and elastic, but may at any time liquefy and form a cold
abscess. Swelling about the trochanter and neck of the bone may be
estimated by measuring the antero-posterior diameter with callipers,
and comparing with the sound side. Swelling on the pelvic aspect of
the acetabulum can sometimes be discovered on rectal examination.

_Third Stage._--This probably corresponds with caries of the articular
surfaces, since pain is now a prominent feature, and there are usually
startings at night. The attitude is one of adduction, inversion,
flexion, and apparent or real shortening of the limb (Fig. 114). The
_flexion_ is usually so pronounced that it can no longer be concealed
by lordosis, so that when the patient is recumbent, although the spine
is arched forwards, the limb is still flexed both at the hip and at
the knee; with the spine flat on the table, the flexion of the thigh
may amount to as much as a right angle. The _adduction_ varies greatly
in degree; when it is slight, as is most often the case, the toes of
the affected limb rest on the dorsum of the sound foot. When moderate,
it is compensated for by raising the pelvis on the affected side, with
_apparent shortening_ of the limb, this being the result of an effort
on the part of the patient to restore the normal parallelism of the
limbs, the sound limb being abducted to the same extent as the
affected limb is adducted. It is important to recognise the cause of
this shortening, as it can be corrected by treatment. As a result of
the obliquity of the pelvis, the patient, when erec