Kinematic determinants of anterior knee pain in cerebral palsy: a case-control study.

OBJECTIVE To quantify the role patellofemoral and tibiofemoral kinematics may play in development of anterior knee pain (AKP) in individuals with cerebral palsy (CP). DESIGN Case-control. SETTING Clinical research center. PARTICIPANTS Knees from individuals with diagnosed CP (n=20) and control knees (n=40) were evaluated. Controls were matched for sex and age based on the group average. Matching by height and weight was a secondary priority. Subjects in the control cohort were asymptomatic with no history of lower leg abnormalities, surgery, or major injury. Only individuals who were physically capable of sustaining slow, cyclic knee flexion-extension for 2.5 minutes and had no contraindications to magnetic resonance imaging were enrolled. Both groups were samples of convenience. INTERVENTIONS Not applicable. MAIN OUTCOME MEASURES Three-dimensional patellofemoral and tibiofemoral joint kinematics, acquired during active leg extension, under volitional control. RESULTS Participants with CP and AKP (n=8) demonstrated significantly greater patellofemoral extension, valgus rotation, and superior and posterior displacement relative to controls and to the subgroup of participants with CP and no AKP (n=12). Patellofemoral extension discriminated AKP in individuals with CP with 100% accuracy. CONCLUSIONS In quantifying the 3-dimensional, in vivo knee joint kinematics during a volitional extension task, kinematic markers that discriminate AKP in individuals with CP were identified. This provides an ability to predict which individuals with CP are most likely to develop AKP and could enable aggressive conservative treatment, aimed at reducing patella alta and excessive patellofemoral extension, to be prescribed before considering surgical options. The current findings will likely lead to improved clinical diagnostics and interventions for individuals with CP, with the ultimate goal of helping maintain, if not improve, functional mobility throughout the lifespan.