THE INFLUENCE OF HEAD SHAFT ANGLE ON HIP DISPLACEMENT IN 640 GMFCS III TO V CHILDREN: A POPULATION-BASED STUDY

Purpose This study re-examined the influence of the head shaft angle (HSA) on hip dislocation in a large cohort of children with cerebral palsy (CP). Method The radiographs of GMFCS Level III – V children from a surveillance programme database were analysed and migration percentage (MP) and HSA measured. The first radiograph of each patient was taken to remove the effect of the surveillance programme. The most displaced hip in each child, by MP, was used for analysis and the corresponding HSA measured. Hip displacement was defined as MP u003e40% and logistic regression was used to adjust for HSA, GMFCS, age and sex. Results 640 children were eligible (271 female (42.3%), 369 male (57.7%), mean age 8.2 years, GMFCS III: 160 (25%), GMFCS IV: 184 (28.75%), GMFCS V: 296 (46.25%). 118 children (18.44%) had a MP u003e40% and mean HSA was 160° (range 111 – 180°). Statistical analysis showed that an increasing HSA was associated with hip displacement (odds ratio of 1.02 for a 1° change). A 10° difference in HSA between two patients of the same age, sex and GMFCS gave odds of 1.26 of the patient with the higher HSA having hip displacement. Age and sex had no influence in this model, while a high GMFCS-level was a strong risk factor. Conclusion Chougule et al found no correlation between HSA and hip migration in children with CP using linear regression analysis. However, the relationship between these variables is not linear. The present study independently confirms an earlier study that HSA is a risk factor for hip displacement in GMFCS III-V children.