Aims. The Uppföljningsprogram för cerebral pares (CPUP) Hip Score distinguishes between children with cerebral palsy (CP) at different levels of risk for displacement of the hip. The score was constructed using data from Swedish children with CP, but has not been confirmed in any other population. The aim of this study was to determine the calibration and discriminatory accuracy of this score in children with CP in Scotland. Methods. This was a total population-based study of children registered with the Cerebral Palsy Integrated Pathway Scotland. Displacement of the hip was defined as a migration percentage (MP) of > 40%. Inclusion criteria were children in Gross Motor Function Classification System (GMFCS) levels III to V. The calibration slope was estimated and Kaplan-Meier curves produced for five strata of CPUP scores to compare the observed with the predicted risk of displacement of the hip at five years. For discriminatory accuracy, the time-dependent area under the receiver operating characteristic curve (AUC) was estimated. In order to analyze differences in the performance of the score between cohorts, score weights, and subsequently the AUC, were re-estimated using the variables of the original score: the child’s age at the first examination, GMFCS level, head shaft angle, and MP of the worst hip in a logistic regression with imputation of outcomes for those with incomplete follow-up. Results. The discriminatory accuracy of the score in the new population of 367 children was high (AUC 0.78 (95% confidence interval (CI) 0.71 to 0.86)). The calibration of the score was insufficient (slope 0.48 (95% CI 0.31 to 0.65)), and the absolute risks of displacement of the hip in this population were overestimated. The AUC increased with re-estimated weights (0.85 (95% CI 0.79 to 0.91)). Conclusion. The
Hip displacement, defined in this study as a
migration percentage (MP) of more than 40%, is a common, debilitating complication
of cerebral palsy (CP). In this prospective study we analysed the
risk of developing hip displacement within five years of the first
pelvic radiograph. . All children with CP in southern and western Sweden are invited
to register in the hip surveillance programme CPUP. Inclusion criteria
for the two groups in this study were children from the CPUP database
born between 1994 and 2009 with Gross Motor Function Classification
System (GMFCS) III to V. Group 1 included children who developed
hip displacement, group 2 included children who did not develop
hip displacement over a minimum follow-up of five years. A total
of 145 children were included with a mean age at their initial pelvic
radiograph of 3.5 years (0.6 to 9.7). The odds ratio for hip displacement was calculated for GMFCS-level,
age and initial MP and head-shaft angle. A risk score was constructed
with these variables using multiple logistic regression analysis.
The predictive ability of the risk score was evaluated using the
area under the receiver operating characteristics curve (AUC). . All variables had a significant effect on the risk of a MP >
40%. The discriminatory accuracy of the
