Effect of Synthetic Marrow on Synthetic Open-Cell Foam Vertebrae

Abstract

The intended purpose of this research is to further supplement the first generation of the Analogue Spine Model (ASM) by introducing a bone marrow component. Currently the ASM does not include a bone marrow component. While not mechanically relevant, bone marrow does have an effect on bone cement intrusion. Techniques such as brushing (removing surface debris) and pressurized lavage (removing marrow from bone interstices) used in preparation for the bone-cement interface during surgical procedures have been shown to improve cement intrusion into the cancellous bone. This indicates that marrow may play a key role in bone cements' contribution to anchoring bone screws. The addition of a bone marrow component to the analogue spine model will create a more realistic testing platform for medical devices employing bone screws. Preliminary work has identified glycerin as a candidate for use as a yellow marrow substitute due to its viscosity and availability. Four point bending was utilized as a rapid, preliminary assessment of the synthetic marrow's effect on the resins used to produce cancellous and cortical bone. Specimens produced by Pacific Research Laboratories (PRL) were soaked in the synthetic marrow for durations of two and four weeks and compared to a control group. Results showed significant difference between the groups in modulus and ultimate stress. Synthetic marrow's effect on analogue cancellous bone was then assessed by compression testing and bone screw pullout testing. Specimens produced by PRL were soaked for four weeks in the synthetic marrow and compared to a control. Modulus, yield stress, ultimate stress, and pullout strength were all found to be significantly decreased by the synthetic marrow. The change in material properties was significant in terms of statistics; however, values for these properties were still in the range of reported literature values. Further testing is necessary to ensure properties do not continue to decrease in longer soaking durations.