Does Patient-Specific Implant Design Reduce Subsidence Risk in Lumbar Interbody Fusion? A Bottom Up Analysis of Methods to Reduce Vertebral Endplate Stress

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PROQUEST: 2198656190

Abstract

This research focused on the analysis of vertebral endplate stresses due to varying designs of lumbar interbody fusion cages utilizing novel polymeric materials and patient specific properties and geometry. It was hypothesized that customizing the material properties of the implant body by varying the porosity of a cage made from poly(para-phenylene), stresses on the vertebral endplate could be reduced. First a thorough study of endplate material properties was conduced to devlelop a predictive model for apparent endplate properties based on demographic and radiographic data. It was found that it was possible to successfully predict endplate stiffness and Brinell Hardness using various indices. It was found that additional information was needed to build a predictive model for apparent modulus of the endplate, likely needing a higher resolution CT scan of the vertebral body. Further, the endplate moduli measured in this study was far below those previously reported and utilized in models. As such, it provided a useful tool in analysis of endplate stresses. Next, the biological response of porous PPP was analyzed by implanting porous and solid PPP and polyetheretherketone (PEEK) implants in rat tibia. After 8 weeks, radiographic imaging revealed that porous PPP implants permitted significantly more bone ingrowth compared to PEEK (76% vs 49%). Further, modelling of pushout testing revealed substantial increase in pushout force required for porous PPP implants compared to PEEK implants, highlighting PPP’s potential as an orthopedic biomaterial. Finally, utilizing the endplate material properties measured in the first study, a systematic analysis of endplate stresses under loading for various implant designs with varying geometric design, material properties, and patient bone contouring was conducted. This study revealed that increased contact area with the bone provides the largest reduction in endplate stresses while material variation with porosity provides negligible reductions in implants with relatively high contact areas. Though the results did not demonstrate a significant result for patient specific implants, this research provides valuable insight into the mechanics of porous materials in addition to overall implant design. These results can be used to guide development in novel surgical implants for lumbar interbody fusions as the field continues to mature.

Cited Works (10)

Year	Entry
2003	Liebschner MAK, Kopperdahl DL, Rosenberg WS, Keaveny TM. Finite element modeling of the human thoracolumbar spine. Spine. March 15, 2003;28(6):559-565.
2001	Grant JP, Oxland TR, Dvorak MF. Mapping the structural properties of the lumbosacral vertebral endplates. Spine. April 15, 2001;26(8):889-896.
2008	Zhang J, Niebur GL, Ovaert TC. Mechanical property determination of bone through nano- and micro-indentation testing and finite element simulation. J Biomech. 2008;41(2):267-275.
1992	Oliver WC, Pharr GM. An improved technique for determining hardness and elastic modulus using load and displacement sensing indentation experiments. J Mater Res. 1992;7(6):1564-1583.
2005	Karageorgiou V, Kaplan D. Porosity of 3D biomaterial scaffolds and osteogenesis. Biomaterials. September 2005;26(27):5474-5491.
1997	Rho J-Y, Tsui TY, Pharr GM. Elastic properties of human cortical and trabecular lamellar bone measured by nanoindentation. Biomaterials. 1997;18(20):1325-1330.
2004	Oliver WC, Pharr GM. Measurement of hardness and elastic modulus by instrumented indentation: advances in understanding and refinements to methodology. J Mater Res. January 2004;19(1):3-20.
2001	Homminga J, Weinans H, Gowin W, Felsenberg D, Huiskes R. Ostehoporosis changes the amount of vertebral trabecular bone at risk of fracture but not the vertebral load distribution. Spine. July 2001;26(14):1555-1560.
1999	Zysset PK, Guo XE, Hoffler CE, Moore KE, Goldstein SA. Elastic modulus and hardness of cortical and trabecular bone lamellae measured by nanoindentation in the human femur. J Biomech. October 1999;32(10):1005-1012.
2012	Dall’Ara E, Pahr D, Varga P, Kainberger F, Zysset P. QCT-based finite element models predict human vertebral strength in vitro significantly better than simulated DEXA. Osteoporos Int. February 2012;23(2):563-572.

Cited By (1)

Year	Entry
2021	Fernandes RJR. Biomechanical Strategies to Reduce Subsidence in Posterior Lumbar Interbody Fusion Procedures [Master's thesis]. University of Western Ontario; 2021.