Association between spasticity of the hip and development of hip displacement in children: a cohort study of 786 hips.

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.