Diaphyseal long bone fractures have been identified in very young children (1-3 years) due to accidental and non-accidental trauma. Failure to diagnose a child’s fracture as non-accidental upon first presentation is associated with an increased likelihood of repeat injury and death. Computational modeling may be used to diagnose if a fracture was caused by accidental or non-accidental trauma. Due to differences in composition, microstructure, and mechanical behavior, the properties of mature bone cannot be scaled and applied to immature bone. The objective of this dissertation was to investigate the evolution of composition, microstructure, tissue-level and whole-bone mechanical behavior of cortical bone in porcine long bones as a function of early maturation (newborn, 1 month, 3 months). Tissue-level elastic modulus, fracture stress, and energy absorption increased as a function of maturation at a quasistatic rate. Fracture stress increased as a function of maturation at a faster rate and increased as a function of increasing displacement rate. Fracture strain decreased with increasing displacement rate. Carbonate-to-phosphate ratio was linearly related to elastic modulus. Fracture stress was related to carbonate-to-phosphate ratio and matrix maturation ratio.

Second moment of area and flexural rigidity increased from newborn to 1 month. Second moment of area increased between 1 and 3 months. Whole bone stiffness, fracture load, energy absorption, and maximum bending moment increased from newborn to 1 month. Fracture displacement decreased between 1 and 3 months. Qualitative assessment of fracture pattern suggested that jagged fracture patterns and partial fractures arise with maturation.

Mathematical relationships between Hounsfield Units and density, and between density and elastic modulus were determined. These relationships were used to configure finite element models. The models using elastic moduli intended for immature bone underestimated the experimental 3-point bending conditions at each age, whereas the load-displacement behavior was overestimated when mature elastic moduli were applied. Taken together, these studies indicate that the mechanical behavior of immature bone differs from mature bone, and that immature bone must be studied independently. This dissertation serves as a basis to motivate future work to further understand the mechanical behavior of immature bone in response to traumatic loading scenarios.