Core decompression by exact drilling into ischemic lesions of the femoral condyle stays a challenging procedure, particularly in obese patients. The precision of fluoroscopically-based drilling compared to conventional drilling was evaluated in an in-vitro model for obesity. 40 sawbones were prepared mimicking osteonecrosis in obese patients. 20 sawbones were drilled by guidance of an intraoperative navigation system VectorVision® (BrainLAB, Munich, Germany); the other 20 sawbones were conventionally drilled by fluoroscopic control only. Regarding the distance to the desired mid-point of the lesion, a statistically significant difference with 0.55 mm in the navigated group and 1.19 mm in the control group could be stated (p<0.001). Significant differences were further found for the number of drilling corrections (p<0.001) and radiation time needed (p<0.001). Even in difficult circumstances as in obese patients, the drilling guided by the VectorVision®-navigation system shows high precision with simultaneous enormous reduction of radiation time.