Hip pain in children with cerebral palsy: a population-based registry study of risk factors.

BACKGROUND: Hip pain is prevalent in children with cerebral palsy (CP). Hip displacement is a known risk factor for hip pain. However, many children do not have displaced hips but still have hip pain and the aetiologies are poorly understood. The aims of this study were to investigate: 1. the prevalence of hip pain related to age, gender, gross motor function, degree of hip displacement and 2. the associations between hip pain and age, gender, gross motor function, degree of hip displacement, ranges of hip and knee motion (ROM) and degree of spasticity in the muscles around the hip.

METHODS: This was a cross-sectional retrospective register study based on data from the Swedish follow-up programme and national healthcare registry CPUP, which includes > 95% of children with CP in Sweden. The participants were born in 2000 or later and 4-16 years of age. Data from the latest examination were used. In Aim 1, the prevalence of hip pain was calculated using frequencies and crosstabs. Differences between groups were calculated using chi-square tests and independent samples t-tests. In Aim 2, associations between hip pain and the variables were analysed using logistic regression.

RESULTS: The overall prevalence of hip pain was 7%. No significant gender difference was found. Hip pain prevalence increased with age, lower gross motor function and higher degree of hip displacement. The median migration percentage (MP) in painful hips was 26%, compared to 21% in hips where pain was not reported. In the multivariable analysis, significant associations with hip pain were found for MP > 30% and decreased ROM in abduction, flexion and inwards rotation of the hip (p < 0.05).

CONCLUSION: Hip displacement was associated with hip pain. However, hip displacement was not present in the majority of painful hips. In addition to hip displacement, decreased ROM was also associated with hip pain.