The Femoral Head-Shaft Angle Is Not a Predictor of Hip Displacement in Children Under 5 Years With Cerebral Palsy: A Population-based Study of Children at GMFCS Levels III-V

The aim of this study was to evaluate whether the femoral head-shaft angle (HSA) is a predictor of hip displacement in children with cerebral palsy (CP). METHODS: The patients were recruited from a population-based hip surveillance program. Inclusion criteria were age under 5 years, bilateral CP, Gross Motor Function Classification System (GMFCS) levels III-V, and migration percentage (MP) of both hips <40% at the primary radiograph. With these criteria, 101 children (61 boys) were included. GMFCS was level III in 26 patients, level IV in 23, and level V in 52. An anteroposterior radiograph of the pelvis was taken at diagnosis and at the last follow-up. Only the worst hip of each patient (the hip with the largest MP) was used for the analyses. RESULTS: The mean age at the primary radiograph was 2.4 years (range, 0.8 to 4.9 y). The mean primary HSA was 171.0 degrees (range, 152 to 190 degrees). The mean follow-up time was 4.3 years (range, 0.9 to 11.8 y). The mean MP at the primary radiograph was 17.5% (range, 0% to 39%) and at the last follow-up 41.9% (range, 0% to 100%). At that point, MP was <40% in 54 hips and ≥40% in 47 hips. There was no significant difference in primary HSA between patients with final MP<40% and those with final MP≥40% (170.8 and 171.3 degrees, respectively; P=0.761). At the last follow-up, the mean HSA was significantly larger in hips with final MP≥40% than in hips with final MP<40% (171.1 vs. 167.4 degrees; P=0.029). CONCLUSIONS: There was a markedly increased valgus position of the proximal femur in nonambulatory children with CP. However, the primary HSA in children below 5 years of age was not a predictor of later hip displacement, defined as MP≥40%. CLINICAL RELEVANCE: Measurement of HSA is not necessary in routine hip surveillance in children below 5 years. LEVEL OF EVIDENCE: Level I—investigating a diagnostic test.