2025 Theses Doctoral

The Influence of Selective Voluntary Motor Control on Terminal Swing Phase in Ambulatory Children with Cerebral Palsy

Jezequel, Jennifer

Background
The ability to walk and keep up with peers is an important goal amongst children with cerebral palsy (CP) and their caregivers. Factors associated with decreased walking speed are of interest amongst clinicians and researchers. Decreased knee extension during the terminal swing phase of gait is one of a variety of factors that contributes to inadequate step length and ultimately, to walking speed. The aim of this study was to examine factors associated with the magnitude of knee extension during terminal swing phase, including a task-specific measure of selective voluntary motor control (SVMC), such as the Walking Dynamic Motor Control Index (walk-DMC). It was hypothesized that impaired SVMC of the swing limb, as measured by walk-DMC, and decreased stance phase stability, as measured by single limb support time of the stance limb, would be significant predictors of decreased magnitude of knee extension during terminal swing phase in the group with diplegia. It was hypothesized that impaired SVMC of the swing limb would be a significant predictor of decreased knee extension during terminal swing phase in the group with hemiplegia, whereby stability in stance phase of the uninvolved limb was less impaired.

Methods
The study involved a retrospective analysis of instrumented gait data, inclusive of surface electromyography (sEMG), from an accredited motion analysis laboratory between 2015 and 2024. Participants between the ages of 7-18 years with a diagnosis of diplegic or hemiplegic CP, Gross Motor Function Classification System (GMFCS) levels I and II were included. A forward stepwise multiple linear regression model was used to predict the magnitude and the timing of knee extension during terminal swing phase. Predictors of interest included SVMC, as measured by walk-DMC, knee extension and ankle dorsiflexion joint range of motion (ROM), hamstring muscle spasticity, measures of knee extensor strength, and hamstring muscle-tendon lengthening characteristics of the swing limb, as well as single limb support time of the stance limb. GMFCS level and history of prior surgery were included as covariates.

Results
The final dataset used in the analysis included 90 individuals with diplegic CP (GMFCS level I, n = 35; GMFCS level II, n = 55) and 105 individuals with hemiplegic CP (GMFCS level I, n = 59; GMFCS level II, n = 46). SVMC, as measured by the walk-DMC, demonstrated a negative correlation with the magnitude of knee extension during terminal swing phase in both the group with diplegia (r = -.39, p < .001) and the group with hemiplegia (r = -.31, p = .001), such that better SVMC was associated with increased knee extension at terminal swing phase. Stance phase stability, as measured by single limb support time of the contralateral limb, was not significantly correlated with the magnitude of knee extension during terminal swing phase in the group with diplegia (r = .01, p = .892), while a positive correlation was observed in the group with hemiplegia (r = .33, p < .001). For the group with diplegia, the stepwise multiple regression model populated with walk-DMC, knee extension ROM, ankle dorsiflexion ROM, and extensor lag in the group with diplegia was statistically significant, R2 = .324, F(4, 85) = 10.195, p < .001, adjusted R2 = .292. The addition of GMFCS level and history of prior surgery, as covariates, led to a statistically significant increase in R2 of .111, F(2, 83) = 8.163, p < .001. For the group with hemiplegia, the stepwise multiple regression model populated with walk-DMC, single limb support time of the contralateral limb, and ankle dorsiflexion ROM in the group with hemiplegia was statistically significant, R2 = .251, F(3, 101) = 11.308, p < .001, adjusted R2 = .229. The model including the covariates of GMFCS level and history of prior surgery was not statistically significant (R2 of .006, F(2, 99) = .418, p = .660).

Conclusion
Decreased knee extension in terminal swing phase in individuals with CP is multifactorial and is not simply the result of tight hamstrings or weak knee extensors. Impaired SVMC, as measured by walk-DMC, is a significant predictor of decreased knee extension during terminal swing phase. Including task-specific measures of SVMC, such as the walk-DMC, is essential when using instrumented gait analysis (IGA) in assessing gait pathology to inform clinical decision-making and predict outcomes following treatment.