29); sometimes increased--_coxa
valga_. There is also a variable degree of torsion of the neck,
ante-torsion being of practical importance as it increases the
difficulty of retaining the head in the socket. The capsule is lax and
admits of the head passing upwards for a variable distance on to the
dorsum ilii. In unilateral cases the ligamentum teres is elongated and
thickened; in bilateral cases it is frequently absent.

[Illustration: FIG. 128.--Radiogram of Double Congenital Dislocation
of Hip in a girl aet. 4.]

[Illustration: FIG. 129.--Innominate Bone and upper end of Femur from
a case of Congenital Dislocation of Hip.]

In _children who have walked_, the head of the femur is pushed farther
upwards on the dorsum ilii; the capsule becomes lengthened by
supporting the weight of the body. That part of the capsule which
arises from the lower margin of the acetabulum stretches across the
socket and partly shuts it off from the rest of the joint cavity. In
course of time the capsule becomes greatly thickened, and may present
an hour-glass constriction about its middle, which may prove a serious
obstacle to reduction. The socket becomes small and triangular, and
there is almost no ledge against which the head of the femur can rest.
A superficial depression may form on the ilium where it is pressed
upon by the head of the femur, covered by the capsule; and in the
course of years, as the head changes its position, several secondary
sockets may be formed. No proper new bony socket forms like that in
traumatic dislocations that remain unreduced because in the congenital
variety the thickened capsule intervenes between the head of the bone
and the dorsum ilii. The displacement of the head is most frequently
backwards (dorsal luxation), and as the point of support thus falls
behind the acetabulum the pelvis tilts forwards, and the lumbar spine
becomes unduly concave (lordosis). The muscles of the hip and thigh
alter in consequence of the changed relations; the gemelli,
obturators, and piriformis are lengthened, the adductors, hamstrings,
and ilio-psoas are shortened, while the glutei and quadriceps are but
little altered. In rare cases the head is displaced upwards and lies
immediately above the acetabulum.

[Illustration: FIG. 130.--Congenital Dislocation of Left Hip in a girl
aet. 8. The patient is putting the whole weight on the dislocated
limb.]

_Clinical Features._--The condition rarely attracts attention until
th