Radiographic measurements of hip dysplasia at skeletal maturity-new reference intervals based on 2,038 19-year-old Norwegians

Normative references for radiographic measurements commonly used in the diagnosis of developmental dysplasia of the hip at skeletal maturity are incomplete. The present study therefore aimed to establish new gender-specific standards for measurements reflecting the acetabular morphology, namely Sharp's angle, the acetabular roof angle of Tonnis (AA) and the acetabular depth-width ratio (ADR), and measurements reflecting the position of the femoral head related to the acetabulum, namely the center-edge (CE) angle of Wiberg, the refined CE angle of Ogata, and the femoral head extrusion index (FHEI). The joint space width (JSW) is also reported. The population-based 1989 Bergen Birth Cohort (n = 3,935) was invited at age 19 years to a follow-up during 2007-09, of which 2,038 (52 %) attended. A standardized antero-posterior radiograph was assessed. The normative references are presented as mean +/- standard deviation (SD) and 2.5-97.5 percentiles with 95 % confidence intervals. A total of 2,011 (841 males, 1,170 females, mean age 18.6 (SD 0.6)) radiographs were analyzed. Sharp's angle was 38.8A degrees aEuro parts per thousand A +/- aEuro parts per thousand 3.5A degrees in males and 40.7A degrees aEuro parts per thousand A +/- aEuro parts per thousand 3.5A degrees in females, with 97.5 percentiles of 46A degrees and 47A degrees, respectively. The CE angle was 32.1A degrees aEuro parts per thousand A +/- aEuro parts per thousand 6.1A degrees in males and 31.0A degrees aEuro parts per thousand A +/- aEuro parts per thousand 6.1A degrees in females, with 2.5 percentiles of 21A degrees and 20A degrees, respectively. The FHEI was 86.0 % A +/- 6.3 % in males and 85.6 % A +/- 6.6 % in females, with 2.5 percentiles of 74A degrees and 73A degrees, respectively. Updated gender-specific reference ranges for radiographic measurements commonly used for hip dysplasia at skeletal maturity are reported, similar to or slightly wider than those described in the literature. Statistically significant gender differences have been confirmed for most of the measurements.