[Axis and rotationally correct positioning of bicondylar femoral prosthesis: preoperative planning and intraoperative...

Clinical outcome and durability of a bicondylar knee endoprosthesis depend on a correct positioning of the femoral prosthesis which should be implanted perpendicularly to the mechanical femoral axis and parallel to the transepicondylar axis to guarantee a harmonic balance of ligaments..

Neither the mechanical axis nor the transepicondylar axis can be correctly defined intraoperatively without an instrumental device. Using the method presented here these axes can be determined indirectly using distal and dorsal femoral condyle tangents. Both tangents can be properly defined preoperatively as well as operatively. An x-ray of the whole femur is necessary for the mechanical femoral axis and a thin-layer computed tomography (CT) scan is necessary for the transepicondylar axis. Plug-in sleeves for the 4-in-1 block from 0-13° and a special angle measurement device are required for the operative transfer.

This method has been used on 783 patients of whom 38 have been examined in a follow-up study. The deviation of the perpendicular to mechanical axis was on average 0.32° and the average deviation from the parallel to transepicondylar axis was 1.04°.

The presented procedure is safe and economical and saves operating time.