Foot Weight-Bearing in Supported Standing: Influence of Verticalization Angles and Hip/Knee Flexion in Children and Adolescents with Cerebral Palsy (GMFCS IV-V)

<b>Background:</b> Supported standing is commonly prescribed for children and adolescents with cerebral palsy (CP) to support musculoskeletal health and participation. However, objective data on plantar loading under different positioning conditions are limited, particularly in individuals with severe motor impairment (GMFCS IV-V). This study quantified plantar loading as an operational measure of foot weight-bearing during supported standing across combinations of verticalization angle and hip/knee flexion. <b>Methods</b>: Twenty-six children and adolescents with CP (GMFCS IV-V; 6-17 years) were assessed using a standardized back-supported standing system. Plantar loading was measured with two calibrated force plates at six verticalization angles (0°, 30°, 45°, 60°, 75°, 90°) combined with four hip/knee flexion angles (0°, 15°, 30°, 45°). Loading was expressed as a percentage of body weight (% BW). Effects were analyzed using repeated-measures analysis of variance. <b>Results:</b> Plantar loading increased progressively with increasing verticalization angles across all hip/knee flexion conditions. Clinically relevant loading levels (>70% BW) were achieved at a verticalization angle of 60° in most flexion conditions. Maximum plantar loading was observed at 90° verticalization combined with 30° hip/knee flexion (96.4% BW). At 90° verticalization, plantar loading remained substantial even with 45° hip/knee flexion (81.4% BW). Increasing hip/knee flexion did not result in a linear reduction in plantar loading; a significant decrease was observed only at 45° flexion. <b>Conclusions</b>: Verticalization angle is the primary determinant of plantar loading during supported standing in children and adolescents with severe CP. Clinically meaningful plantar loading-and thus effective foot weight-bearing-can be achieved at moderate verticalization angles despite hip and knee flexion, supporting flexible positioning strategies.