Purpose: This study aims to assess the incidence of hip displacement and dislocation (denominated as hip migration) among ambulant and non-ambulant Danish children with cerebral palsy (CP) by estimating their cumulative incidence of migrated hips. A secondary objective is to compare the prevalence across different Danish regions. Methods: Data were obtained from the Danish Cerebral Palsy Follow-Up Program (CPOP) from the years 2008 to 2021. This population-based cohort study included 1388 children with CP (58% male; 42% female) as subjects; aged 0–15 years; with an average age of 5.4 years at their last follow-up. The children were categorized according to their Gross Motor Function Classification System (GMFCS) level into ambulators (GMFCS I–III) and non-ambulators (GMFCS IV–V). The Kaplan–Meier estimator was employed to calculate the cumulative incidence of migrated hips from birth until the date of their last radiographic follow-up. Differences between ambulatory and non-ambulatory children and regional differences were assessed with the Log-rank test. Results: Median radiological follow-up for ambulators was 51 months and 94 months for non-ambulators. The cumulative incidence of hip dislocation was 0.3% (95% CI: 0–0.8%) and 22.0% (95% CI: 9.2–34.8%) for ambulators and non-ambulators, respectively (p < 0.0001), whereas the incidence of hip displacement was 21.1% (95% CI: 16.3–25.9%) and 76.7% (95% CI: 68.6–84.7%) for ambulators and non-ambulators, respectively (p < 0.0001). There were no significant regional differences in the incidence of hip dislocation among ambulators, but there were significant differences for non-ambulators. Moreover, significant regional differences were detected in hip displacement for both ambulators and non-ambulators. Conclusions: The prevalence of hip migration in Danish children with CP is significantly higher among non-ambulators, who are at an increased risk of hip migration compared to their ambulant counterparts. However, the low frequency of radiographic follow-up for ambulators might cause the incidence of hip migration to be underestimated. This study highlights the necessity of continued targeted surveillance and interventions in Danish non-ambulators.

Aims: The aim of this study was to investigate whether a hip-related tenotomy is associated with a lower risk of severe hip outcomes in nonambulant children with cerebral palsy and established displacement of the hip. Methods: This nationwide register-based cohort study included children classified as Gross Motor Function Classification System (GMFCS) level IV or V who were enrolled in the Danish Cerebral Palsy Follow-Up Program (CPOP) between 1 January 2008 and 31 December 2023. Hips with a baseline migration percentage (MP) of between 30% and 49% were included and followed until the first occurrence of a severe hip outcome, defined as a MP of ≥ 50% or osteotomy of the hip. Death was treated as a competing event. The cumulative incidence was estimated using the Aalen-Johansen estimator. Associations were analyzed using Fine-Gray competing-risk regression with cluster-robust standard errors. Results: A total of 259 children, contributing 406 hips, were included, of which 110 underwent a tenotomy. At ten years, the cumulative incidence of a severe hip outcome was 34.7% (95% CI 28.8 to 40.7) without tenotomy, and 20.4% (95% CI 12.4 to 28.5) with tenotomy. In adjusted competing-risk regression, tenotomy was associated with a significantly lower risk of a severe hip outcome (sub-distribution hazard ratio (sHR) 0.53 (95% CI 0.34 to 0.84); p = 0.006). GMFCS-specific Fine-Gray analyses showed a significant association in GMFCS level IV (sHR 0.35 (95% CI 0.16 to 0.78); p = 0.010), whereas the association did not reach significance in GMFCS level V (sHR 0.68 (95% CI 0.40 to 1.19); p = 0.180). Spasticity, as classified according to the Modified Ashworth Scale (MAS) 1 and ≥ 3, was independently associated with a significantly increased risk of a severe hip outcome. Conclusion: A hip-related tenotomy was associated with a significantly lower incidence of the subsequent development of a severe hip outcome among nonambulant children with established displacement of the hip, particularly in GMFCS level IV. In GMFCS level V, progression remained substantial irrespective of the soft-tissue release, emphasizing the importance of careful patient selection and continued surveillance. Cite this article: Bone Joint J 2026;108-B(11):1379–1384.

Background and purpose: Hip migration is a common complication in children with cerebral palsy (CP). Although spasticity has long been considered a contributing factor, muscle-specific associations with hip migration remain unclear. We aimed to investigate whether assessed hip spasticity was associated with hip displacement risk in non-ambulant children with CP.Methods: In this population-based cohort study using Danish Cerebral Palsy Follow-Up Program (CPOP) data, children classified as Gross Motor Function Classification System (GMFCS) levels IV–V with at least 1 hip radiograph were included. Pathological hip migration was defined as migration percentage (MP) ≥ 30%. Spasticity was assessed using the Modified Ashworth Scale (MAS) for hip adductors, flexors, and extensors. Overall hip spasticity was defined as summed MAS (0, 1–3, 4–6, 7–9). Cumulative incidence was estimated with death as a competing event, and associations were evaluated using Fine–Gray regression adjusted for GMFCS level.Results: 422 children (786 hips) were included; 374 hips (48%) reached MP ≥ 30%, and death occurred as a competing event in 16 patients (25 hips). Higher overall hip spasticity was associated with increased risk of hip migration, with subdistribution hazard ratios (sHRs) of 1.46 (CI 1.05–2.01), 1.77 (CI 1.22–2.58), and 2.53 (CI 1.59–4.02) for MAS 1–3, 4–6, and 7–9, respectively, compared with MAS 0. Adductor spasticity showed the most consistent association with sHRs ranging from 1.44 to 1.97 across MAS categories.Conclusion: In children with CP classified as GMFCS levels IV–V, higher clinically assessed hip spasticity—particularly of the hip adductors—was associated with development of a hip at risk for displacement.