Article
Biomechanical comparison of two anglestable retrograde interlocked femur nails and the LISS in a human 33A3 osteotomy model
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Authors
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P. Höhle
- Klinik und Poliklinik für Unfallchirurgie, Klinikum der Johannes Gutenberg Universität Mainz, Mainz, Germany
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W. Sternstein
- Biomechanisches Labor der Abteilung für Unfallchirurgie, Klinikum der Johannes Gutenberg Universität Mainz, Mainz, Germany
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J. Blum
- Klinik und Poliklinik für Unfallchirurgie, Klinikum der Johannes Gutenberg Universität Mainz, Mainz, Germany
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A. Prescher
- Anatomisches Institut, RWTH Aachen, Aachen, Germany
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P.M. Rommens
- Klinik und Poliklinik für Unfallchirurgie, Klinikum der Johannes Gutenberg Universität Mainz, Mainz, Germany
| Published: | September 28, 2006 |
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Outline
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Purpose: Do new interlocking modalities of retrograde nails show higher torsional and axial stiffness in instable distal femur fractures compared to the LISS ? A biomechanical study was performed to compare three plane screw locking in the distal fragment and a broad spiral blade and one bolt interlocking in one direction distally to anglestable internal fixation through the LISS in one direction with 9 screws.
Methods: Two nail types and the LISS were used in a total of 18 pairs of human femur 33A3 osteotomy models:
A) 9 pairs with 1. DFN (Synthes) with a spiral blade and one bolt distally; 2. LISS (Synthes) with 9 locking screws;
B) 9 pairs with 1. DFN with a spiral blade and one bolt distally; 2. SCN (Stryker) with two condyle screws and nuts and two oblique screws distally. Proximal locking in the nails was double. The femora were fixed with PMMA at both ends in a 6° valgus position, connected to a kardan shaft and dynamically loaded in a servo pneumatic testing machine with axial (10-500 N) and torsional (0,1-12 Nm) loading. In the test 100 cycles of sinuswavy applied alternating axial and torsional load were measured.
Results: Axial stiffness after DFN implantation was 33.5 % (median) of the intact femora; axial stiffness after SCN implantation was 49.8 % (median) of the intact femora; axial stiffness after LISS implantation was 41.25 % (median) of the intact femora (DFN-SCN p:0.68; DFN-LISS p:0.86). Torsional stiffness after DFN implantation was 45.6 % (median) of the intact femora; torsional stiffness after SCN implantation was 59.0 % (median) of the intact femora; torsional stiffness after LISS implantation was 62.4 % (median) of the intact femora (DFN-SCN p:0.26; DFN-LISS p:0,066).
Conclusion: No significant differences in axial and torsional stiffness were detected between the DFN and SCN and the DFN and LISS. The 33A3 gap osteotomy fixation with the three plane interlocking and use of condyle screws with nuts of the SCN in the distal fragment shows higher axial and torsional stiffness than in the DFN (statistical striking but not significant). The use of LISS shows the highest torsional stiffness (statistical striking but not significant after 4 cycles); its reversible deformation under axial force is the highest of the three implants going along with a low plastic subsidence which causes overproportional movement in the gap at higher axial loads.
