Radiographic threshold values for hip screening in cerebral palsy

Purpose To analyse the consequences of using different radiographic measurements and different threshold values for hip screening in children with cerebral palsy (CP). Methods In a total sample of children with CP a standardised radiological follow-up of the hips was carried out as a part of a hip prevention programme. Acetabular index (AI) and migration percentage (MP) were measured on all radiographs. In this study, 1,067 radiographs of 272 children born 1992–1998 were analysed. Results Lateral displacement of the femoral head was common without acetabular dysplasia, and acetabular dysplasia occurred at a later stage than femoral head lateralisation. Hip dysplasia without lateral displacement of the femoral head was rare. In 16 of the 56 hips (29%) with AI ≥ 27° and in 23 of the 71 (32%) hips with MP ≥ 33% the values decreased below the threshold value without operative treatment. In hips with AI ≥ 30° only 2 of 31 hips (6%) and in hips with MP ≥ 40% only 5 of 44 hips (11%) decreased below the threshold values without operative treatment. Conclusions Radiographic follow-up with only measurement of the MP seems sufficient in screening for dislocation in children with CP. MP ≥ 33% is recommended as threshold for reaction or intensified observation. In children with MP ≥ 40%, the lateral displacement increased over time in most hips, thus indicating the need for operative intervention. In children with MP 33–40%, treatment should be based on other clinical signs and the progression of MP over time.