Impact Peak, Knee Muscle Cocontraction, and Knee Angle during Early Contact of Running in Children with Diplegic Cerebral Palsy

Abstract

Purpose: Some children with ambulatory diplegic cerebral palsy (CP) are able to run. Running can enjoyable and a simple form of exercise for children with CP to stay physically active. However, they may be at risk for lower extremity injuries due to atypically high impact force. Excessive knee muscle cocontraction and the inability to modify knee angle during early contact phase of running may contribute to ineffective force attenuation, resulting in atypical high impact peak and load rates during running. The purpose of this study was to compare impact peak, load rates, knee stiffness, knee muscle cocontraction and knee contact angle during early stance phase of running between children with CP and children with typical development (TD). Method: Six children with CP and eight with TD participated in this study. Because of difference in strike patterns during running in children with CP that had not been anticipated in the initial research plan. Therefore, kinetic and knee angle data of four identified children with TD were included from unpublished database and were used to compare those with children with CP who contacted the ground with midfoot and rearfoot from this study. After static trials were collected in all children, children ran at a comfortable speed in the motion analysis laboratory equipped with eight video - camera, three force plates and a wireless surface electromyography (EMG). Three acceptable trials of running in which leg hitting the middle of the force plates were required for data analysis. Kinetics and knee contact angle we re post - processed, analyzed and computed at a period of initial contact (IC) to impact peak (IP) of vertical ground reaction force (GRF). Impact peak, average and instantaneous load rates, knee stiffness, knee muscle cocontraction, and knee contact angle at IC and at IP as well as knee excursion from IC to IP were dependent variables of this study. Mann - Whitney U test were used to compare dependent variables between children with CP and children with TD. Effect sizes (ES) of r of all variables were also reported. Results: Impact force and load rates were significantly higher in the more involved and the less involved legs of children with CP, compared to those with TD although children with CP and children with TD ran at similar running speeds. No other variables were different between the two groups. Conclusion: Due to very small sample size, the findings from this study still need further investigation. The key finding suggests that children with CP have atypically high impact peak and load rates despite slow running speeds, when compared with children with TD. High impact peak and load rates may be used to determine children with CP who may be at risk for lower extremity injuries. Parents, teachers and health professionals such as physical therapists, who work with children with CP should consider atypically high impact force and load rates if children demonstrate any pain and/or musculoskelatal discomfort during and after running. Proper footwear, orthoses, and…