locating the knee entailed no
disability. When the child begins to walk, an apparatus which will
prevent hyper-extension and lateral motion should be fitted to the
limb.

#Congenital absence of the patella# usually complicates other
abnormalities of the knee-joint. The tubercle of the tibia is
prominent and the extensor tendon unusually thick. In flexion the
tendon rises on to the lateral condyle of the femur.

#Congenital Dislocation of the Patella Laterally.#--This may be
persistent or intermittent. In the _persistent form_ the dislocation
is present from birth; the patella rests on the trochlear surface of
the lateral condyle, and when the knee is flexed may pass farther
outwards and become completely dislocated, lying against the lateral
aspect of the condyle.

In _the intermittent_ or _recurrent_ form the patella lies in its
normal place, but is liable to be displaced outwards when the joint is
flexed; the displacement occurs suddenly and unexpectedly in walking,
and the patient may fall to the ground, suffering intense pain. The
knee-cap is readily replaced on extending the joint, but the sprain of
the joint is followed by effusion, and the patient is usually disabled
for a day or two. It is met with chiefly in girls, and there may be a
history that the child was late in walking and learned with
difficulty. On examination, the patella is found to have an abnormal
range of movement outwards, although it cannot be completely
dislocated without considerable pain. If the child is brought for
advice when there is fluid in the joint, the condition is liable to be
mistaken for tuberculous synovitis. The observation that the undue
mobility of the knee-cap is present in both knees is of assistance in
arriving at a diagnosis, and also the history that the girl has
repeatedly hurt her knee in falling.

The cause of the abnormal mobility of the patella varies in different
cases; in some there is congenital laxity of the ligaments, in others
a faulty formation of the lower end of the femur. Bade has observed
families in which several children were affected, and although there
was nothing abnormal in the shape of the bones, the knee was slender
and delicately formed.

The use of a strong knee-cap may prevent falling, but as a rule an
operation is required, and there is quite a number to choose from, the
principle of them all being to prevent displacement of the bone
without unduly restricting flexion of the joint. That d