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2 Acta of Bioengineering and Biomechanics

2 2013

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Mock-up in hip arthroplasty pre-operative planning

Zanetti E. M., Bignardi C.

Acta of Bioengineering and Biomechanics

2013

Vol. 15, no. 3

123--128

The correct estimation of stem boundary conditions in hip arthroplasty cannot be performed simply by subtracting the prosthesis volume from the bone volume: the stem implant path needs to be taken into account. Digital mock-up is a technique commonly applied in the automotive field which can be used for this aim. Given a certain femur, a stem, and an implantation path, the volume of the removed bone stock can be evaluated, as well as the final contact area between the bone and the stem, and, section by section, the residual cortical bone thickness. The technique proved to be useful: if the stem implant path is not considered, the removed bone stock volume can be underestimated up to 6%, while the contact area extension can be overestimated up to 28%. On the whole, a new methodology has been set up and tested, which can be usefully employed to accurately establish stem boundary conditions in the pre-operative planning stage, and in order to perform a reliable structural stress analysis. The methodology implemented here by experienced researchers can be made available to surgeons, setting up an apposite software suite.

Analysis of the influence of a metha-type metaphysical stem on biomechanical parameters

Pozowski A., Ścigała K., Kierzek A., Paprocka-Borowicz M., Kuciel-Lewandowska J.

Acta of Bioengineering and Biomechanics

2013

Vol. 15, no. 2

13--20

The full postoperative loading of the limb is possible if patients are properly selected and qualified for hip arthroplasty and the requirements as to the proper position of the metaphysial stem are met. The lack of precision, and patient qualification which does not satisfy the fixed criteria may result in stem setting inconsistent with the assumptions. An analysis based on the finite element method (FEM) will enable one to find out how to plan the magnitude of operated joint loading on the basis of the position of the stem in the postoperative radiograph. By analyzing the distribution of bone tissue deformations one can identify the zones where the spongy bone is overloaded and determine the strain level in comparison with the one determined for a model of the bone with the stem in proper position. On the basis of the results obtained one can estimate the range of loads for the operated limb, which will not result in the loss of the stem’s primary stability prior to obtaining secondary stability through osteointegration. Moreover, an analysis of the formation of bone structures around the stem showed that the incorrect setting of a Metha-type stem may lead to the initiation of loosening.