Abstract
Objectives/Background: Long-term outcome in THR is multifactorial influenced. Malpositioning leads to complications as early loosening, leg length difference or dislocation of the artificial joint. A proven factor for early losening is a misplacment of the center of rotation or varusposition of the stem. A higher luxation risk results out of high inclination and anteversion angles an reduced soft tissue tension.
Aim of this study was to prove the image free navigation software in the modular Navitrack-System to check the implant position based on anatomical intraoperative acquired data.
Design/Methods: In 35 consecutive cases we implantet the ACA screwcup and the Optan anatomical stem with use of the Navitrack navigation System. The software calculates al relevant data out of intraopertive probed landmarks. Intraoperative the shifting of the center of rotation, the cup anteversion and inclination, the stem inclination and torsion and the leglength shift is shown in real time. Intraoperative data were compared with postoperative position measurement in plain X-rays and in 15 patients in postoperative CT scans.
Results: In all cases navigated implantpositioning was possible. In 3 cases stem positioning was not possible cause of refference loosening. Mean inclination of the cup as shown in the Navigation System was 52 (range 45 – 58 ), mean anteversion was 11 (range -5 – 27). Mean postoperative inclination measured on postoperative X-Ray was 53,8 (range 49 – 60). The difference between the shown values from the CAS System to the postoperative X Ray for the inclination was 1,8 (range -9 – 6). The leg length difference on postoperative X-ray was in mean 3,1 mm, on screenshots 2,8 mm. The difference between screenshot and X ray was in mean 0,83 mm.
Conclusions: This study shows, that with the CT free software for the Navitrack-System reliable cup and stem navigation is possible. Whenever the hip joint allows to probe a spherical segment in the femoral head or acetabulum navigated THR is possible without the need of intraoperative fluoroscopy or preoperative CT scan. For leg length control and cup Inclination the data are still promising. Further investigation is necessary for stem axis and cup anteversion according to the navigation based reference coordinate system. Whenever no geometric sphere existent, e.g. severe hip dysplasia, the system must be developed as a hybrid system with CT (NMR) based cup and image-less stem navigation.
Theses abstracts were prepared by Professor Roger Lemaire. Correspondence should be addressed to EFORT Central Office, Freihofstrasse 22, CH-8700 Küsnacht, Switzerland.
