Hip displacement in relation to age and gross motor function in children with cerebral palsy

Purpose: Hip dislocation in cerebral palsy (CP) is a serious complication. By radiographic screening and prophylactic surgery of children at risk most dislocations can be prevented. CPUP, the Swedish CP registry and follow-up program, includes annual radiographic examinations of children at Gross Motor Function Classification System (GMFCS) levels III-V. Data from CPUP were analysed to assess the risk of hip displacement in relation to GMFCS levels and age. Methods: All children at GMFCS levels III-V (N = 353) whose first radiographic screening occurred before 3 years of age were followed between the ages 2-7 years. Migration percentages (MPs) were recorded annually (1,664 pelvic radiographs) and analysed using discrete time survival analysis. Results: The risk of hip displacement between 2 years and 7 years of age was significantly (p < 0.05) higher for children at GMFCS level V during the entire study period. The risk was highest at 2-3 years of age and decreased significantly (p < 0.001) with each year of age (OR = 0.71, 95 % CI 0.60-0.83). The cumulative risk at age 7 years for those at GMFCS V for MP ≥ 40 % was 47 % (95 % CI 37-58). The corresponding risk at GMFCS IV was 24 % (16-34) and at GMFCS III 23 % (12-42). Conclusions: Children at GMFCS V have a significantly higher risk of hip displacement compared with children at GMFCS III-IV. The risk is highest at 2-3 years of age. The results support a surveillance program including radiographic hip examinations as soon as the diagnosis of severe CP is suspected.