[Drilling with 3D fluoroscopic navigation in osteonecrosis of the femoral condyle].

The primary goal of drilling procedures for the treatment of osteonecrotic lesions is revascularisation of the defect area. In the literature good results are reported for this technique in 70% of cases. Precise drilling of the necrosed area as part of a minimally invasive technique does, however, require unequivocal intraoperative identification of the region visually, either by arthroscopy or by fluoroscopy. In the case of inadequate imaging, as in our case, there is no longer any guarantee of precise drilling.Computer-assisted navigation system have already improved the precision of drilling procedures performed for various indications. Basically, however, a navigation is only as accurate as the underlying imaging. The use of preoperative data sets assumes an invasive and/or elaborate intraoperative recording procedure. For a procedure not requiring recording to be possible, image diffusion of the MRI and ISO-C(3D) data sets during the surgery would be necessary. In the present case a preoperative MRI data set was first combined with the ISO-C(3D) data set acquired intraoperatively. To this end, following application of the reference base a 3D scan was performed, and the data ascertained were transferred to the navigation system and in addition to the planning software. After fusion of the images the drilling canals were planned and implemented on the basis of the additional information emerging from the combination of the data. To be sure of success postoperatively, this was also merged with the preoperative MRI. The example shows that combining data sets makes it possible to improve the precision and safety of drilling in target areas that cannot be adequately imaged. In future, we hope it will prove possible to transfer the image data back into the navigation system after they have been merged. At present this is only possible with CT and MRI images. A comparative clinical trial is needed to find to what extent the success rate is improved over that achieved with conventional techniques.