The acetabulum in Perthes’ disease: a prospective study of 123 children

Abstract

Purpose We assessed the radiographic changes of the acetabulum during the course of Perthes’ disease and investigated whether they were associated with femoral head sphericity 5 years after diagnosis. Methods We studied 123 children with unilateral Perthes’ disease, femoral head necrosis more than 50 % and age at diagnosis 6 years or older. Pelvic radiographs were taken at onset, 1 year and 5 years after diagnosis. Sharp’s angle, acetabular depth-to-width ratio (ADR) and lateral acetabular inclination were measured. Results Compared to the unaffected hips, the Perthes’ hips developed significantly higher Sharp’s angles (p < 0.001) and a higher proportion with an upward-sloping lateral acetabular margin (Perthes’ hips: 49 %, unaffected hips 1 %). The mean ADR values were significantly lower on the affected side at all stages (p < 0.001). ADR values at diagnosis were associated with a more spherical femoral head at the 5-year follow-up [odds ratio (OR) 1.012, 95 % confidence interval (CI) 1.002–1.022, p = 0.016]. None of the other acetabular parameters were significantly associated with the femoral head shape 5 years after diagnosis. Conclusion The acetabulum developed an increasingly dysplastic shape in the course of Perthes’ disease. Early dysplastic changes of the acetabulum were not associated with a poor radiological outcome 5 years after diagnosis. Routine measurement and monitoring of acetabular changes in plain radiographs were of little prognostic value and can, therefore, hardly be recommended in clinical practice.