Incidence and risk factors of hip dislocation in children with cerebral palsy: A systematic review and pooled analysis

Background: Hip displacement and dislocation are among the most disabling musculoskeletal sequelae of cerebral palsy (CP) yet reported incidence and risk-factor estimates vary widely across studies. We undertook a systematic review and pooled analysis to quantify cumulative incidence across Gross Motor Function Classification System (GMFCS) strata and identify reproducible clinical and radiographic predictors. Methods: A protocol was registered in PROSPERO (CRD420251026860). MEDLINE (PubMed), Embase, CINAHL and CENTRAL were searched from inception to March 30, 2025. Eligible longitudinal studies enrolled ≥30 children with CP aged 2–18 years, provided ≥2 years’ follow-up without confounding hip-directed intervention, and reported migration percentage (MP) data or equivalent permitting derivation. Hip displacement and dislocation were harmonized as MP >30 % and >50 %, respectively. Study quality was appraised with ROBINS I. Proportions were stabilized with the Freeman–Tukey double-arcsine transformation and pooled in random-effects (REML) models; odds ratios (ORs) for candidate predictors were combined using inverse-variance random-effects methods. Heterogeneity (I2, τ2), prediction intervals, influence diagnostics, Hartung–Knapp sensitivity and Egger tests were performed. Certainty was graded with adapted GRADE. Results: Nineteen studies met inclusion; nine natural-history cohorts (n = 1556; median follow-up 5.1 y) contributed extractable incidence data. The pooled cumulative incidence of hip displacement/dislocation was 38.2 % (95 % CI 31.7–45.1 %; I2 = 77 %; prediction interval 6.0 53.8 %). Incidence was 17.1 % in ambulant children (GMFCS I–III) and 71.9 % in non-ambulant children (IV–V), yielding an OR 3.72 (95 % CI 2.56–5.40) for non-ambulant vs ambulant groups. A baseline MP ≥ 30 % quadrupled subsequent risk (OR 4.48, 95 % CI 2.66–7.54; I2 = 0 %). Pelvic obliquity ≥10° was associated with increased risk in a single cohort (OR 2.70, 95 % CI 1.34–5.46) and should be regarded as suggestive pending replication. No consistent effects were found for sex, gestational age or CP subtype. Conclusions: Approximately four in ten children with CP, and more than two thirds of those in GMFCS IV–V, develop clinically important hip displacement without targeted intervention. GMFCS IV–V status and an early MP ≥ 30 % are robust, actionable triggers for intensifying hip surveillance to six-monthly radiography; pelvic obliquity ≥10° may further stratify risk but requires confirmation. Uniform MP thresholds, time-to-event analyses and reporting of modifiable exposures are needed in future multicenter cohorts to refine preventive care.