Bone Grafting for Femoral Head Osteonecrosis: Automated Creation of Patient-Specific Finite Element Models

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Abstract

The treatment goal in early femoral head osteonecrosis is to prevent progression to structural collapse. A promising surgical procedure employed is cortical bone grafting, in which a canal is drilled through the femoral neck, in to the necrotic lesion. A bone graft is press fit into the canal to provide mechanical reinforcement until healing can restore structural integrity.

Finite element (FE) modelling has shown that the structural efficacy of this procedure is sensitive to graft placement. Appropriately placed grafts afford considerable stress relief of vulnerable necrotic bone, whereas inappropriately placed grafts may increase the risk of collapse. To foster the use of such models in surgical planning, new techniques were developed to speed their construction.

In conjunction with FE model development, experimental validation was performed. A pressure vessel applied hydrostatic compressive loading to the surface of a cadaveric femoral head mounted inside the vessel. Linear variable differential transformers measured deformation at 72 sites on the head surface.

Measurements made for normal and necrotic femoral heads were in agreement with FE model predictions. This serves as evidence that the finite element model stiffness matrix reasonably represents the structural stiffness of the femoral heads.

To create an FE model of an actual grafted femur, patient radiographs and MRIs were used to determine the graft position and the extent of the necrotic lesion. A new coordinate system was created, aligned with the graft axis, and a finite element mesh constructed within this system. This technique, termed graft based meshing, greatly simplifies construction of an o rd erly mesh. Existing test data were used to generate a realistic material property distribution; the strength and stiffness of necrotic bone elements were appropriately attenuated. Using this method, models were created and analyzed, both of an actual g ra ft configuration obtained surgically, and a possible alternative graft orientation. In terms of the necrotic bone stress to strength ratio, this alternative graft orientation was more favorable than the actual, provided that the graft was advanced to very near the subchondral plate.

Cited Works (13)

Year	Entry
1975	Reilly DT, Burstein AH. The elastic and ultimate properties of compact bone tissue. J Biomech. 1975;8(6):393-405.
1991	Baker KJ. The Influence of Mechanical Stress on Collapse Propensity in MRI-Delineated Femoral Head Osteonecrosis [PhD thesis]. University of Iowa; December 1991.
1982	Brown TD, Mutschler TA, Ferguson AB. A non-linear finite element analysis of some early collapse processes in femoral head osteonecrosis. J Biomech. 1982;15(9):705-715.
1984	Brown TD, Vrahas MS. The apparent elastic modulus of the juxtarticular subchondral bone of the femoral head. J Orthop Res. 1984;2(1):32-38.
1983	Brown TD, Shaw DT. In vitro contact stress distributions in the natural human hip. J Biomech. 1983;16(6):373-384.
1977	Carter DR, Hayes WC. The compressive behavior of bone as a two-phase porous structure. J Bone Joint Surg. 1977;59A(7):954-962.
1990	Odgaard A, Andersen K, Melsen F, Gundersen HJG. A direct method for fast three-dimensional serial reconstruction. J Microsc (Oxford). September 1990;159(pt 3):335-342.
1994	Skinner HB, Kim AS, Keyak JH, Mote CD Jr. Femoral prosthesis implantation induces changes in bone stress that depend on the extent of porous coating. J Orthop Res. July 1994;12(4):553-563.
1987	Afoke NY, Byers PD, Hutton WC. Contact pressures in the human hip joint. J Bone Joint Surg. August 1987;69B(4):536-541.
1990	Keyak JH, Meagher JM, Skinner HB, Mote CD Jr. Automated three-dimensional finite element modelling of bone: a new method. J Biomed Eng. 1990;12(5):389-397.
1993	Keyak JH, Fourkas MG, Meagher JM, Skinner HB. Validation of an automated method of three-dimensional finite element modelling of bone. J Biomed Eng. November 1993;15(6):505-509.
1992	Keyak JH, Skinner HB. Three-dimensional finite element modelling of bone: effects of element size. J Biomed Eng. 1992;14(6):483-489.
1980	Brown TD, Ferguson AB Jr. Mechanical property distributions in the cancellous bone of the human proximal femur. Acta Orthop Scand. 1980;51(1):429-437.

Cited By (1)

Year	Entry
1998	Pedersen DR. MRI-Based Finite Element Models of Surgically Achieved Fibular Graft Placement for Osteonecrosis of the Femoral Head [PhD thesis]. University of Iowa; May 1998.