Abstract
The stability of an external ring fixator using trans-osseous wires is determined by the number of wires per ring, their tension and their configuration. Ideally a crossing angle of 90° in the centre of the bone provides the greatest stability. This is however rarely possible due to the restrictions imposed by safe anatomical corridors. The Taylor Spatial Frame is a hexapod structure which relies on 6 connecting struts attached to fixed tabs on the ring; the Ilizarov system allows connecting rods to be placed in any available spaces.
The aim of this study was to identify differences in wire placement using the TSF compared with the standard Ilizarov ring.
Method: Cross-sectional anatomical diagrams of the tibia were taken from 3 levels. Lines representing wires were drawn crossing at the centre of the bone. The maximum crossing angles for an Ilizarov ring using safe anatomical corridors were calculated. A TSF ring was then superimposed on the image and angles recalculated taking into account impedance caused by the strut tabs. The angles were compared using a Students t-test taking p=0.05 as significant.
Results: The average maximum crossing angle of the Ilizarov wires was 61° compared with 36° for the TSF. At all 3 levels the angles were found to be significantly different (p=0.002).
Discussion: Limitations in the trans-osseous wire placement has implications for construct stability and therefore function. This may force the surgeon to make greater use of half pins, or more wires. We have shown significant differences in pin placement using the TSF which should be taken into consideration when using the system.
Theses abstracts were prepared by Professor Roger Lemaire. Correspondence should be addressed to EFORT Central Office, Freihofstrasse 22, CH-8700 Küsnacht, Switzerland.
