The Material Properties of Human Tibia Cortical Bone in Tension and Compression: Implications for the Tibia Index

The risk of sustaining tibia fractures as a result of a frontal crash is commonly assessed by applying measurements taken from anthropometric test devices to the Tibia Index. The Tibia Index is an injury tolerance criterion for combined bending and axial loading experienced at the midshaft of the leg. However, the failure properties of human tibia compact bone have only been determined under static loading. Therefore, the purpose of this study was to develop the tensile and compressive material properties for human tibia cortical bone coupons when subjected to three loading rates: static, quasistatic, and dynamic. This study presents machined cortical bone coupon tests from 6 loading configurations using four male fresh frozen human tibias. A servo-hydraulic Material Testing System (MTS) was used to apply tension and compression loads to failure at approximately 0.05 s⁻¹, 0.5 s⁻¹, and 5.0 s⁻¹ to cortical bone coupons oriented along the long axis of the tibia. Although minor, axial tension specimens showed a decrease in the failure strain and an increase the modulus with increasing strain rate. There were no significant trends found for axial compression samples, with respect to the modulus or failure strain. Although the results showed that the average failure stress increased with increasing loading rate for axial tension and compression, the differences were not found to be significant. The average failure stress for the static, quasi-static, and dynamic tests were 150.6 MPa, 159.8 MPa, and 192.3 MPa for axial tension specimens and 177.2 MPa, 208.9 MPa, and 214.1 MPa for axial compression specimens. When the results of the current study are considered in conjunction with the previous work the average compressive strength to tensile strength ratio was found to range from 1.08 to 1.36.