[CT-free image guided acetabulum navigation in clinical routine].
After experimental and preclinical evaluation (HAP Paul Award 2001) of the CT-free image-guided surgical navigation system for acetabular cup placement (SurgiGATE C-arm cup" by Medivision, Switzerland), the system was introduced into clinical routine. The computation of the angular orientation of the cup is based on reference coordinates from the anterior pelvic plane concept. A hybrid strategy for pelvic landmark acquisition has been introduced involving percutaneous pointer-based digitization with the noninvasive biplanar landmark reconstruction using multiple registered fluoroscopy images. From January 2001 to December 2002, a total of 256 consecutive patients with primary osteoarthrosis (mean age 69 years, 161 male, 95 female, 132 left, and 124 right hip joints) were operated on with the hybrid CT-free navigation system. During each operation the angular orientation of the inserted implant was recorded. To determine the placement accuracy of the acetabular components, 50 consecutive patients underwent a CT scan 7-10 days postoperatively to analyze the cup position related to the anterior pelvic plane. This was all done blinded by the same investigator with the planning software of the CT-based navigation system of Medivision. There was no significant learning curve observed for the use of the system. The mean value for postoperative inclination was 43 degrees (SD 3.0, range: 37 degrees -49 degrees ) and for anteversion 19 degrees (SD 3.9, range: 10 degrees -28 degrees ). The resulting system accuracy, i.e., the difference between intraoperatively calculated cup orientation and postoperatively measured implant position showed a mean error of 1.5 degrees for the inclination (maximum 5 degrees, SD 1.1) and 2.4 degrees for the anteversion (maximum 6 degrees, SD 1.3). An accuracy of better than 5 degrees inclination and 6 degrees anteversion was achieved under clinical conditions, which implies that there is no significant difference in performance from the established CT-based navigation methods. Image-guided CT-free cup navigation provides a reliable solution for future THA.