Aim: To identify the prevalence of knee contracture and its association with gross motor function, age, sex, spasticity, and muscle length in children with cerebral palsy (CP).
Method: Cross-sectional data for passive knee extension were analysed in 3 045 children with CP (1 756 males, 1 289 females; mean age 8y 1mo [SD 3.84]). CP was classified using the Gross Motor Function Classification System (GMFCS) levels I (n=1 330), II (n=508), III (n=280), IV (n=449), and V (n=478). Pearson's χ2 test and multiple binary logistic regression were applied to analyse the relationships between knee contracture and GMFCS level, sex, age, spasticity, hamstring length, and gastrocnemius length.
Results: Knee contracture greater than or equal to 5 degrees occurred in 685 children (22%). The prevalence of knee contracture was higher in older children and in those with higher GMFCS levels. Odds ratios (ORs) for knee contracture were significantly higher for children at GMFCS level V (OR=13.17), with short hamstring muscles (OR=9.86), and in the oldest age group, 13 years to 15 years (OR=6.80).
Interpretation: Knee contracture is associated with higher GMFCS level, older age, and shorter muscle length; spasticity has a small effect. Maintaining muscle length, especially of the hamstrings, is important for reducing the risk of knee contracture.
What this paper adds: Knee contracture occurs in children with cerebral palsy at all Gross Motor Function Classification System (GMFCS) levels. Knee contracture in children is associated with short hamstring muscles, higher GMFCS level, and older age. Short hamstring muscles present a greater risk for knee contracture than spasticity.
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