Muscle weakness impacts negatively upper limb movement patterns in children with unilateral cerebral palsy

Background and Objective(s) Upper limb three-dimensional motion analysis (UL-3DMA) in children with unilateral CP (uCP) has thus far been investigated using various tasks, vastly challenging the comparison between studies. Based on Statistical Parametric Mapping (SPM1d), we previously highlighted the value of reach-to-grasp a vertical cylinder (RGV), hand-to-head (HTH) and hand-to-shoulder (HTS) to study UL movement pathology in uCP. SPM1d takes into account the dependency between the time points of the waveform, by using random field theory, which allows identifying areas in the waveform where the differences are present or where a specific parameter may interfere. Muscle weakness has been shown to impact negatively on activity measures of UL function in children with uCP, though it remains unknown to what extent this motor impairment impacts on UL movement pathology. The aim of this study was to examine the role of elbow and wrist muscle weakness on kinematic waveforms during three tasks (RGV, HTH and HTS). Study Design Cross-sectional Study Participants & Setting Sixty children with uCP (mean age 10y4m (SD 2y5m), 25 girls, 29 right-hemiplegia, n=18 MACS I, n=28 MACS II, n=14 MACS III) participated in this study. Children were recruited via the CP-care program from University Hospitals Leuven. Materials/Methods The affected UL was measured using a 3DMA during the execution of three tasks: RGV, HTH and HTS. Manual Muscle Testing (score 0-5) was used to evaluate muscle strength in elbow and wrist extensors and elbow supinators. Individual muscle scores were summed to calculate the overall score (range 0-25). SPM1d was used to perform a linear regression analysis between the kinematic waveforms and muscle weakness (overall score). Statistical significance was set at alpha < 0. 01. Results Elbow and wrist weakness significantly explained the increased elbow flexion and pronation during RGV in 44% and 75% of the curve, respectively (flexion, z=3. 21, p=0. 0012; pronation, z=3. 21, p < 0. 0001). Muscle weakness also accounted for increased pronation during more than half of the movement of HTH (64%, z=3. 26, p < 0. 0001) and HTS (60%, z=3. 23, p < 0. 0001). Also, muscle weakness explained increased wrist flexion of the entire movement for all three tasks (RGV, z=3. 35, p < 0. 0001; HTH, z=3. 29, p=0. 0001; HTS, z=3. 24, p < 0. 0001). Last, increased shoulder elevation was also explained by muscle weakness for all tasks (RGV, z=3. 25, p=0. 003; HTH, z=3. 24, p=0. 006; HTS, z=3. 28, p < 0. 0001), though weakness did not contribute to shoulder rotation and elevation plane movement pathology. Conclusions/Significance We used a linear regression in SPM1d to identify for the first time the adverse impact of muscle weakness on the kinematic waveforms of the elbow, wrist and shoulder during three different UL tasks. The results show that SPM1d could be of clinical relevance to increase our understanding of the relation between UL impairments and movement pathology. In the long run, such insights will contribute to further optimization of UL rehabilitation in uCP.status: Published onlin