Evaluation of gait function in children with cerebral palsy: New insights into commonly used methods

• Main Author: Gagnat, Yngvild
• Format: Dissertation
• Language: English

Walking is an essential motor skill for daily living and social participation. The neuromuscular system is vital in achieving support, stability, and progression during walking. Motor disorders, such as cerebral palsy (CP) may cause deviations in gait pattern, asymmetry, and altered muscle activity with excessive muscle co-activation, affecting gait function. In children with CP, impaired gait function may be seen through increased energy cost of walking compared to typically developing children, which in turn may limit activity level and participation. Evaluation of factors related to both typical and pathological gait function is important for clinical decision making. For such, objective and quantitative methods are needed. A 3-dimensional gait analysis (3DGA) describes the gait pattern by providing kinetic, kinematic, and spatiotemporal information. Global measures, such as the gait deviation index (GDI), may be extracted from the 3DGA data, providing an overall score of gait pathology. Surface electromyography (sEMG) provide information about muscle activity and muscle coactivation during walking. However, there are unwanted factors affecting the sEMG signal, and various ways to deal with this, which complicates the interpretation. Moreover, various methods are used to calculate the co-activation index. Energy cost of walking represents the overall gait function and may be presented as total (gross energy cost) or in addition to resting energy expenditure (net energy cost). Gross energy cost is considered more reliable, while net energy cost is reported less affected by between-subject variations in speed and growth-related subject characteristics. However, the effect of the within-subject variation in speed on energy cost is less established. Additionally, to what extent energy cost is affected by a deviating and more asymmetric gait with increased muscle co-activation, is still deficient. Therefore, this thesis aimed to gain further insight into commonly used methods for evaluating gait function in ambulant children with CP. Paper I evaluated how the interpretation of muscle activity and co-activation was affected by the normalisation of the sEMG-amplitudes, and compared two methods of calculating the coactivation index. The findings showed that the overall muscle activity pattern did not change after normalisation, but the between-subject variation was reduced. However, relevant physiological variation may have also been eliminated. The children wi