ven farther outwards.
The capsular and other ligaments are slack, so that the joint is
unstable and easily hyper-extended. There is often some effusion into
the joint.

[Illustration: FIG. 137.--Female child with Rickety deformities of
upper and lower extremities.

(Mr. D. M. Greig's case.)]

_Radiograms_ reveal the changes in the bones (Fig. 138); the shaft of
the femur or tibia, or both, which may also be curved, is set
obliquely on its epiphysis; and the clear zone, corresponding to the
epiphysial cartilage, is uneven and broader than normal. There are
also less obvious changes in the density of the shadow and in the
arrangement of the trabecular structure of the bones.

[Illustration: FIG. 138.--Radiogram of case of Double Genu Valgum in a
child aet. 4.]

_Clinical Features._--In the infantile form (Fig. 139) the knock-knee
is commonly associated with rickets in other parts of the skeleton,
and especially with bending of the tibia and femur, and in extreme
cases the child may be unable to walk.

[Illustration: FIG. 139.--Genu Valgum in a child aet. 4. Patient
standing.]

The deformity is about as frequently bilateral as unilateral. There
may be knock-knee on the one side and bow-knee on the other. If, as is
usually the case, the deformity is due to obliquity of the femur, it
disappears on flexing the joint (Fig. 140), because in flexion the
tibia glides behind the projecting median condyle; if the deformity
affects the tibia only, the influence of flexion in disguising it is
not so marked. It is usually possible to hyper-extend the joint, and,
in the extended position, to rotate the leg outwards to a greater
extent than is normal. In unilateral knock-knee, the affected limb is
a little shorter than its fellow, but the patient compensates for this
by depressing the pelvis on the affected side.

[Illustration: FIG. 140.--Genu Valgum. Same patient as Fig. 139.
Sitting, to show disappearance of deformity on flexion of knee.]

_Prognosis._--In children below the age of six, the bones naturally
tend to straighten if the child is kept off its feet. After this age,
there is no such prospect.

The _treatment of knock-knee in children_ is directed towards curing
the rickets and preventing the child from putting its feet to the
ground. If it cannot have the services of a nurse and the use of a
perambulator, a light padded splint is applied on the lateral side of
the limb, extending from the iliac crest to 3 inche