Background: Hip displacement is considered to be common in children
with cerebral palsy but the reported incidence and the proposed risk factors
vary widely. Knowledge regarding its overall incidence and associated risk
factors can facilitate treatment of these children.
Methods: An inception cohort was generated from the Victorian
Cerebral Palsy Register for the birth years 1990 through 1992, inclusive, and
multiple data sources pertaining to the cohort were reviewed during 2004.
Gross motor function was assessed for each child and was graded according to
the Gross Motor Function Classification System (GMFCS), which is a valid,
reliable, five-level ordinal grading system. Hip displacement, defined as a
migration percentage of >30%, was measured on an anteroposterior radiograph
of the pelvis with use of a reliable technique.
Results: A full data set was obtained for 323 (86%) of 374 children
in the Register for the birth years 1990 through 1992. The mean duration of
follow-up was eleven years and eight months. The incidence of hip displacement
for the entire birth cohort was 35%, and it showed a linear relationship with
the level of gross motor function. The incidence of hip displacement was 0%
for children with GMFCS level I and 90% for those with GMFCS level V. Compared
with children with GMFCS level II, those with levels III, IV, and V had
significantly higher relative risks of hip displacement (2.7, 4.6, and 5.9,
Conclusions: Hip displacement is common in children with cerebral
palsy, with an overall incidence of 35% found in this study. The risk of hip
displacement is directly related to gross motor function as graded with the
Gross Motor Function Classification System. This information may be important
when assessing the risk of hip displacement for an individual child who has
cerebral palsy, for counseling parents, and in the design of screening
programs and resource allocation.
Level of Evidence: Prognostic Level II. See Instructions
to Authors for a complete description of levels of evidence.