[Evaluating the stability of fracture fixation systems: mechanical device for evaluation of 3-D stiffness in vitro].
Different fixation systems are used for fracture and defect treatment. A prerequisite for complication free healing is sufficient mechanical stability of the osteosynthesis. In vitro investigations offer the possibility of both analysing and assessing the pre-clinical fixation stability. Due to the complex loading environment in vivo, stiffness analysis should include a complete determination of the stiffness under standardised conditions. Based on a mathematical procedure to calculate the 3-D stiffness, a mechanical testing device for the 3-D loading of fixation systems was designed and integrated in the existing test set-up. The set-up consisted of a material testing machine to produce the necessary loads and an optical measurement device to detect the resulting inter-fragmentary movements. To validate the testing device, the 3-D stiffness matrices of different Ilizarov fixator configurations were determined and compared. The good reproducibility of the test was reflected in the small intra-individual variability of the stiffness components. A distinct direction dependence of the fixator stiffness was observed. Increasing the number of rings led to a stiffness increase of up to 50%, especially in bending. The presented testing device allows a complete standardised determination of the stiffness of different fixation systems. It considers the direction dependence of the stiffness and creates a prerequisite for a more direct implant comparison.
Kassi
J P
JP
Unfall- und Wiederherstellungschirurgie, Charité, Campus Virchow-Klinikum, Humboldt Universität zu Berlin.
Hoffmann
J E
JE
Heller
M
M
Raschke
M
M
Duda
G N
GN
D001696:Biomechanical Phenomena; D004867:Equipment Design; D019544:Equipment Failure Analysis / Q000295:instrumentation*; D006801:Humans; D018889:Ilizarov Technique / Q000295:instrumentation; D016474:Weight-Bearing