MECHANICAL-BEHAVIOR OF HUMAN MORSELIZED CANCELLOUS BONE IN TRIAXIAL COMPRESSION TESTING

Despite its widespread use as graft material in orthopaedic surgical p rocedures, morselized cancellous bone has not yet been well characteri zed from the standpoint of its mechanical properties. To accommodate t he noncohesive nature of this loose particulate form of bone, a triaxi al compression test apparatus commonly used in engineering soil mechan ics was adapted for the testing of fresh-frozen human morselized cance llous bone specimens. Triaxial compression tests were run to 30% axial strain at five different levels of confining pressure ranging from 0. 276 to 8.552 MPa. The measured axial stress versus axial strain behavi or was bimodal, characterized initially by relatively stiff linear beh avior, then by a rapid transition to a much more compliant (but, again , approximately linear) domain until test cessation. The apparent axia l moduli of both response regions were found to be nearly linear funct ions of the transverse confining pressure. As typically prepared surgi cally, the distribution of particle size was found to have approximate ly 80% of the bone graft, by weight, encompassed in particles 0.43-3.2 mm in size. Triaxial tests of samples segregated by size showed that particle size had no appreciable effect on apparent material propertie s. The nominal Young's modulus and Poisson's ratio of morselized cance llous bone were 100 MPa and 0.2, respectively.