Toddler Lower Extremity Posture in Child Restraint Systems

Abstract

The postures of 28 toddlers 18 to 36 months old were analyzed in conditions simulating rear-facing and forward facing child restraints. Rear-facing conditions included a narrow and wide child restraint configuration, while the forward-facing conditions used a shorter and longer cushion length. Data collected include 3D coordinates of key body landmarks as well as surface scans focusing on the lower extremities. In addition, standard anthropometry measures and full body scans in standing and seated postures were collected for each subject. An overhead photo of each child’s posture was taken at one-second intervals throughout the test session. The number of different postures for each subject was tabulated and categorized. For rear-facing test conditions, the most common lower-extremity postures were legs relaxed, feet together with knees bent outward, knees pulled back towards torso, and both legs straight and elevated. For the forward-facing test conditions, the most common lower extremity postures were legs relaxed, feet together with knees bent and rotated outward, one leg bent and one leg straight, and legs crossed. There were no distinct trends with selected posture and the subjects’ age or size. Analysis of the measured subject postures showed variations in lower-extremity posture with child restraint condition. The narrow rear-facing condition more often had subjects with lower extremities in a relaxed posture, while the wide condition had more children with their feet flat together or their legs extended. For forward-facing, there was less variation in posture with the shorter cushion length; more children chose the frog leg or extended leg postures with the longer cushion length. Distribution of measured lower-extremity postures varied with age group. An attempt was made to position the lower extremities of the HIII 3YO and 18MO ATDs in the most common rear facing configurations chosen by the subjects. Although the more limited range of motion of the ATDs did not allow them to be placed in the most extreme positions chosen by subjects, the ATD posture could be adjusted to several postures commonly chosen by subjects without modifications to the ATD.