Acetabular growth potential in congenital dislocation of the hip and some factors upon which it may depend.

The factors which determine the rate and amount of acetabular growth in congenital dislocation of the hip are ill-understood. A prospective radiological study has been devised in order to assess the influence of the age of congruity, femoral anteversion and neck/shaft angles on acetabular growth. To be included, the children must have reached at least 8 years of age. Those with associated congenital abnormalities and subluxation were excluded, as were those who had operations for acetabular reconstruction. Seventy-four hips were suitable for analysis, and the age range at follow-up was from 8 to 17 years. The acetabular angle was used as an index of acetabular growth. Measurement of this angle, and the anteversion and neck/shaft angles were made before, and each year after reduction of the hip. Congruity was assessed from a radiograph with the legs in the functional position. A satisfactory acetabulum was obtained in 44 hips and the mean age of congruity was 33 months; the acetabulum was unsatisfactory in 30 hips, with a mean age of congruity of 48 months. Four years is the critical age, for if congruity is obtained later, the risk of producing a moderate or severely dysplastic acetabulum is more than doubled. If congruity is obtained under four years of age, growth of the acetabulum with continue in most patients up to 8 and in some to 11 YEARS OF age; the resulting acetabulum was normal or mildly dysplastic. Fifty-nine per cent of the satisfactory hips at follow-up had a normal anteversion angle, and 6 per cent a normal neck/shaft angle. Correction of these angles by themselves, seems not to be a major importance for promoting acetabular growth.