Abstract
Acetabular component malpositioning increases the risk of impingement, dislocation, and wear. The goal of computer-assisted techniques is to improve the accuracy of component positioning, in particular optimizing the orientation of the acetabular cup.
The goal of the current study was to measure accuracy of cup placement in a large clinical series of hips that underwent CT-based computer-assisted THA.
146 hips in 140 patients underwent CT-based computer-assisted THA between 2006 and 2008. In all cases cup orientation was planned according to the individual preoperative CT and the anterior pelvic plane with an inclination of 41° and anteversion of 30°. For the procedure, all patients were placed in the lateral position and the cup was implanted using angled instruments. Intra-operatively all cases were navigated using an optoelec-tronic camera and tracked instruments (Vector Vision prototype, BrainLab, Germany).
Post-operatively, cup orientation was measured using a previously validated technique of 2D/3D-matching using the preoperative CT and post-operative radiographs. This technique allows for accurate measurement of cup position from plain radiographs corrected for individual pelvic orientation.
The mean accuracy for inclination was −2.5° ± 4.0° (−12° – 10°) and for anteversion it was 0.7° ± 5.3° (−11° – 15°). In 2 hips (1.4%) a deviation of more then 10° in inclination and in 4 hips (2.7%) a deviation of more then 10° in anteversion were found.
The current study demonstrates that the acetabular component can routinely be implanted with the assistance of CT-based navigation with reasonable agreement between the navigation measurements of component orientation at the time of surgery. Nonetheless, outliers still occasionally occur. These might be due to unrecognized loosening of the pelvic reference base, inaccurate registration or the use of the ipsilateral surface-based registration algorithms which rely heavily on points near the center of rotation of the hip.
Correspondence should be addressed to Diane Przepiorski at ISTA, PO Box 6564, Auburn, CA 95604, USA. Phone: +1 916-454-9884; Fax: +1 916-454-9882; E-mail: ista@pacbell.net
