Hip dysplasia in bilateral cerebral palsy: incidence and natural history in children aged 18 months to 5 years

Children with bilateral cerebral palsy (CP) born during 1989 to 1992 (n=346 ) to a geographically defined population were ascertained and followed up t o age 5 years. The aims of the study were to monitor hip development by ser ial X-rays; to record gross locomotor development, aspects of physical mana gement, and any hip-related orthotics or surgery; to learn more of the natu ral history of hip development in this condition; and to provide guidelines for a surveillance protocol for those clinically managing children with bi lateral CP. Children were X-rayed at 18, 24, 30, 48, and 60 months. X-rays were taken in a standardized position and measured to record migration perc entage, acetabular index, Sharp's angle, and Smith's diaphyseal ratios. Rel ationships between the measures were investigated and a natural history of the children's hip development suggested. At as early as 18 months, migrati on percentages were significantly greater than in the normally developing p opulation, although no measured CP factor could be identified to be the cau se of this early change. Two possible factors affecting early hip developme nt are described, neither of which is clinically apparent: the first separa tes the bilateral CP population as a whole from the normal population; but there is an additional presdisposing factor affecting some children only wh ich in the presence of the motor disorder, has a significant influence on e arly hip development and subsequent dysplasia. The study confirms that, whe n measured correctly, migration percentage is the best guide to hip surveil lance and the need for treatment. It is suggested that all children with bi lateral CP should be X-rayed in a standardized position at 30 months (corre cted for gestational age).