Joint moment contributions to swing knee extension acceleration during gait in individuals with spastic diplegic cerebral palsy.

The mechanisms contributing to swing phase knee acceleration in individuals with spastic diplegic cerebral palsy (CP) are not well understood, but evidence suggests that selective voluntary motor control (SVMC) may play a role. The purpose of this study was to examine the relationship between lower limb SVMC, measured using Selective Control Assessment of the Lower Extremity (SCALE), and joint moment contributions to swing knee extension acceleration in participants with spastic diplegic CP. Eighteen participants were recruited (mean age=13.8 years, range=6-30 years, Gross Motor Function Classification System Levels I-III). Induced acceleration analysis was performed during the swing phase of gait. Average joint moment contributions to swing knee extension acceleration were calculated. Contributions from stance limb and swing limb joint moments were correlated with SCALE scores using Pearson's correlations. A strong correlation was found (p<0.0001, r=0.85) between SCALE score and the total swing joint moment contributions to swing knee extension acceleration. As SCALE score increased, swing joint moments provided less resistance to knee extension acceleration. No relationship (p=0.18) was found between stance moment contributions to swing knee acceleration and stance limb SCALE scores. Excessive contributions from swing limb joint moments appear to be the factor limiting swing knee extension in spastic diplegic CP gait. Interventions that address negative contributions due to spasticity may not be effective in patients who cannot generate adequate knee extension due to poor SVMC.