Morphological variants in the human fetal hip joint. Their significance in congenital hip disease.

In a study of 280 hips in 140 normal fetuses, sixty-five of the ninety-two hips of forty-six fetuses between the ages of twelve weeks and term showed morphological variants, yet they were neither subluxated nor dislocated and showed no statistically significant morphological differences from normal joints. The vazriants observed included flattening (fourteen hips) or rounding-off of the rim of the labrum (nine hips), localized dips in the labrum (twenty hips), folding of the labrum (six hips), capsular folds (four hips), extension of the pulvinar pad between the joint surfaces (six hips), and kinking of the ligament of the head of the femur (seven hips). The localization of these variants in the anterosuperior quadrant of the acetabulum was highly significant (p < 0.001), but there was no significant relationship to sex or side of involvement. A significant relationship to age, on the other hand, was evident since the frequency of these minor morphological variations in the fetal hip joint appeared to increase with age. Considering all 140 fetuses, the ones with variant hips formed 55 per cent of all of those older than twenty-eight weeks and only 23 per cent of those younger than twenty-eight weeks (p = 0.007). I suggest that some of these variants are subclinical manifestations of congenital hip disease.