The head shaft angle is associated with hip displacement in children at GMFCS levels III-V - a population based study

Background: An increased Head Shaft Angle (HSA) has been reported as a risk factor for hip displacement in children with cerebral palsy (CP) but opinions differ in the literature. The purpose of this study was to re-evaluate the relationship between HSA and hip displacement in a different population of children with CP. Methods: The Cerebral Palsy Integrated Pathway Scotland surveillance programme includes 95% of all children with CP in Scotland. The pelvic radiographs from 640 children in GMFCS levels III-V were chosen. The most displaced hip was analysed and the radiographs used were those taken at the child's first registration in the database to avoid the potential effects of surveillance on subsequent hip centration. A logistic regression model was used with hip displacement (migration percentage [MP] >= 40%) as outcome and HSA, GMFCS, age and sex as covariates. Results: The MP was >= 40% in 118 hips with a mean HSA of 164 degrees (range 121-180 degrees) and < 40% in 522 hips with a mean HSA of 160 degrees (range 111-180 degrees). The logistic regression analysis showed no significant influence of age and sex on MP in this population but a high GMFCS level was strongly associated with hip displacement. An increased HSA was also associated with hip displacement, a 10 degrees difference in HSA for children adjusted for age, sex, and GMFCS gave an odds ratio of 1.26 for hip displacement equal or above 40% (p = 0.009) and hips with HSA above 164.5 degrees had an odds ratio of 1.96 compared with hips with HSA below 164.5 degrees (p = 0.002). Conclusion: These findings confirm that HSA is associated with hip displacement in children in GMFCS levels III-V.