Radiological Assessment of Inter- and Intra-observer Reliability in Hip Migration Measurements in Children With Cerebral Palsy at a Tertiary Referral Center.

Background Hip migration is a common deformity in children with cerebral palsy (CP). Although children with CP often have anatomically normal hips at birth, progressive spasticity can lead to hip subluxation, dislocation, and acetabular dysplasia over time. Early recognition of hip migration is crucial because timely intervention can significantly change the prognosis and reduce morbidity. The aim of this study was to evaluate the inter- and intra-observer reliability of radiographic hip migration measurements in children with CP. Materials and methods We conducted a prospective observational study from 2020 to 2022 to determine inter- and intra-observer variation in the diagnosis of hip migration among children with CP. Eligible participants were recruited from the clinic and followed up for a period of two years. They underwent serial supine AP pelvic radiographs at six-month intervals. The radiographic parameters evaluated were Reimer's migration percentage (MP) and the acetabular index (AI). Four observers with varying levels of clinical experience independently assessed the radiographs. Inter- and intra-observer agreement was analyzed using intraclass correlation coefficients (ICCs) and standard statistical methods. Results Eighteen children (mean age 12.2 years, range 2-18 years, SD 7.72) with spastic CP were included in the study. To ensure consistency and avoid inter-hip variability in the same patient, the hip showing greater displacement served as the unit of analysis. Based on the Gross Motor Function Classification System, nine were classified as level IV, seven as level III, and two as level V. The MP demonstrated consistently high inter- and intra-observer reliability, with ICCs and 95% CIs of 0.999 (0.988-1.000) at baseline and 0.999 (0.999-1.000) at endline. Similarly, the AI also showed excellent inter- and intra-observer reliability, with ICCs and 95% CIs of 0.992 (0.984-0.997) at baseline and 0.998 (0.997-0.999) at endline. These findings indicate strong reproducibility for both measurements across observers and time points. MP analysis showed a significant increase from baseline to endline (Wilcoxon Z = -3.724, p = 0.0002), indicating progression of hip migration. AI also increased significantly over time (paired t = -3.944, p = 0.0010), reflecting the progression of acetabular dysplasia. Both represent secondary outcomes of the study. Conclusions This study demonstrates that both MP and AI provide comparable and clinically acceptable levels of inter- and intra-observer reliability, with a slight advantage for MP. These results underscore the value of MP as a primary surveillance metric while reaffirming AI as a reliable adjunct for evaluating acetabular morphology in children with CP. By contributing additional evidence on the reproducibility of these measurements, our study supports their continued use within structured hip surveillance programs. Further multicenter, prospective studies are needed to validate these findings in broader populations and to strengthen the foundation for standardized, universally applicable surveillance protocols.