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2 Acta of Bioengineering and Biomechanics

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Biomechanical criterion for selecting cancellous bone screws: arthrodesis in the hindfoot

Reihsner R., Huber W. O., Beer R.

Acta of Bioengineering and Biomechanics

2007

Vol. 9, nr 2

27-33

The aim of the paper was to compare primary biomechanical stability of different arthrodesis screws (7.3 mm AO screw with and without washer, 6.5 mm Herbert screw and 6.5 mm Ideal Compression Screw (I.CO.S)). The work necessary to achieve an adequate compressive force with them was compared to the measurement with the AO screw with washer, because this method is for the time being the most commonly used one and is called the golden standard. Compressive force was measured indirectly, via screw tension measurement, with strain gauges method. From the measurements we calculated the work to reach a limit of 60 N and the ratios corresponding to the value of the golden standard: I.CO.S (35.2%), Herbert (89.0%), AO-screw without washer (116%). The I.CO.S showed superior results. Only in the case of extremely poor bone quality, a clear advantage of I.CO.S could be expected in practice.

Photoelastic investigation of mechanical problems in applying acetabulum cups to hip prosthesis

Beer R., Eberhardsteiner J., Kodvani J., Jecic S.

Acta of Bioengineering and Biomechanics

2006

Vol. 8, nr 1

47-54

Acetabulum cups are the counterparts of endoprostheses, which are mounted in the pelvis. There are different designs of such cups. They differ in their form and in the way of mounting. This paper deals with the threaded acetabulum cups with conical shape mounted in the pelvis. In general, one has to distinguish between stresses caused by the mounting process and lifetime stresses of the mounted cup. Stresses remaining of the mounting must ensure the so-called primary stability; however, they will disappear to some degree due to rheological properties of bone. The question arises whether the mounting stresses are responsible for local plastic deformations and the corresponding residual stresses or not. In this paper, mostly loading stresses and their dependence on the contact properties between pelvis and cup or between cup and polyurethane inlay are considered.