Congenital Dislocation of the Hip
This is the commonest of all congenital dislocations. Its frequency varies in different countries, being greater on the continent of Europe than in this country. It is more often unilateral than bilateral (about 4 to 1), and is about three times more common in girls than in boys.
The dislocation takes place in the early months of intra-uterine life, and may be associated with deficiency of the liquor amnii.
Pathological Anatomy.—In the infant, the anatomical changes in the joint are less marked than they are after the child has borne its weight on the limb. The acetabulum, never having been occupied by the head of the femur, is imperfectly developed; it remains flat and shallow, is partly filled with fibro-fatty tissue derived from the synovial membrane, and is always too small for the head of the femur. The cotyloid ligament being broader and thicker than usual, makes the osseous portion of the socket appear deeper than it really is. In unilateral cases the affected half of the pelvis is contracted, so that the pelvic basin is narrowed and oblique. The head of the femur is small, flattened, and, in some cases, conical; and the angle formed by the neck with the shaft is altered, sometimes diminished, it may be to a right angle—coxa vara ([Fig. 129]); 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.
Fig. 128.—Radiogram of Double Congenital Dislocation of Hip in a girl æt. 4.
Fig. 129.—Innominate Bone and upper end of Femur from a case of Congenital Dislocation of Hip.