Existing neck scale factors to determine Injury Assessment Reference Values (IARV) for the paediatric one, three and six year old, and the 5th percentile female populations are based on extrapolations from the adult 50th percentile male and from the calcaneal tendon tensile strength data. The research question addressed in this study is: What are the scale factors and resulting neck tolerances for these age-specific populations if data from human spinal components and neck geometry are used? The analysis included the determination of scale factors under extension, tension, compression, and flexion loading modes as a function of age, namely one, three and six year old, and the 5th percentile female groups. Variations in the biomechanical properties of each spinal component were determined from human cadaver studies. Active spinal components were identified under each of the four loading modes and relationships were established for each component to obtain material-based scale factors. Combining material scaling with neck geometrical data yielded the scale factors for the three paediatric groups under all four loading modes. The age-dependent scale factors in extension, tension, compression, and flexion were respectively: 0.14, 0.25, 0.24, 0.14 for the one year old; 0.19, 0.30, 0.29, 0.18 for the three year old; and 0.25, 0.37, 0.36, 0.24 for the six year old. It appears that scale factors, and hence, resulting injury tolerance values based on spine component material properties, are more appropriate than the values extrapolated from the calcaneal tendon tensile test data.
Abstract