Hip dysplasia and osteoarthrosis: a survey of 4151 subjects from the Osteoarthrosis Substudy of the Copenhagen City Heart Study.

INTRODUCTION: Hip dysplasia (HD) is assumed to be an etiological factor in the development of premature hip osteoarthrosis (OA). We established the prevalences of HD and OA in adults according to qualified radiographic discriminators, and investigated the relationship between HD and OA.
METHODS: Wiberg's CE angle (CE), Sharp's angle, the femoral head extrusion index, the acetabular depth ratio (ADR), the radiographic OA discriminators of Croft, and of Kellgren and Lawrence, and also minimum joint space width (JSW) < or = 2 mm were applied to the standing, standardized pelvic radiographs of 1429 men (22-93 years), and 2430 women (22-92 years).
RESULTS: The 4 HD discriminators were interrelated. A negligible sex-related difference in acetabular morphology was found, male acetabulae being slightly more dysplastic than female acetabulae. However, differences between the sexes for right and left CE angles were within 1.0 degree, and within 1.4 degrees for right and left Sharp's angles. There were no cases of hip subluxation (breakage of Shenton's line > or = 5 mm). Average CE angle was 34 degrees in men (SD 7.3 degrees), and 35 degrees in women (SD 7.6 degrees). Applying a CE cut-off value of 20 degrees for designation of definite hip dysplasia, we found a prevalence of hip dysplasia of 3.4%. Approximately 2% of cases were unilateral and 1.4% of cases were bilateral. We found significant relationships between radiographic OA discriminators and the CE angle, femoral head extrusion index and ADR. Odds ratios ranged from 1.0 to 6.2. Compared to subjects with OA in morphologically normal hips, a trend towards younger age in subjects with HD and OA was noted, but this was not strictly significant.
INTERPRETATION: We found that HD is not uncommon in the general population. The assumption that HD is an etiological factor in the development of hip OA was confirmed.