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The Rationale for Tilt-Adjusted Acetabular Cup Navigation
Jürgen W. Babisch, MD1; Frank Layher, PhD1; Louis-Philippe Amiot, MD, MSc, FRCSC2
1 Department of Orthopaedics, Friedrich Schiller University Jena at the Rudolf-Elle-Hospital Eisenberg, Klosterlausnitzer Strasse 81, 07607 Eisenberg, Germany
2 Department of Orthopaedics, Hopital Maisonneuve-Rosemont, Universite de Montreal, 5345 Boul de l'Assomption Bureau 55, Montreal, Quebec H1T 4B3, Canada
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Disclosure: The authors did not receive any outside funding or grants in support of their research for or preparation of this work. One or more of the authors, or a member of his or her immediate family, received, in any one year, payments or other benefits of less than $10,000 or a commitment or agreement to provide such benefits from a commercial entity (ORTHOsoft). No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, division, center, clinical practice, or other charitable or nonprofit organization with which the authors, or a member of their immediate families, are affiliated or associated. The present study is part of a larger project supported by the DFG (Deutsche Forschungsgemeinschaft, project BA 2229/1-1 and 1-2, Gait Analysis After Hip Navigation). However, the grant was used only for gait analysis and was not connected with the present study.
Investigation performed at the Department of Orthopaedics, Friedrich-Schiller University Jena at the Rudolf-Elle-Hospital Eisenberg, Eisenberg, Germany

The Journal of Bone and Joint Surgery, Inc.
J Bone Joint Surg Am, 2008 Feb 01;90(2):357-365. doi: 10.2106/JBJS.F.00628
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Background: When performing total hip arthroplasty without computer navigation, surgeons align the acetabular component with landmarks such as the plane of the operating table and the presumed position of the pelvis. In contrast, first-generation computer navigation systems rely on the pelvic anterior plane, defined by the anterior superior iliac spines and the pubic tubercle. We sought to study the effect of patient positioning on the tilt of the pelvis as measured in the pelvic anterior plane and its effect on cup alignment angle values.

Methods: In forty patients, the supine pelvic anterior plane tilt angle was measured with use of computed tomographic scans made before and after total hip arthroplasty (Group A). In thirty other patients undergoing total hip arthroplasty, preoperative supine pelvic anterior plane tilt angle was measured with a computed tomographic scan and the preoperative standing pelvic anterior plane tilt angle was measured on a lateral radiograph (Group B). From these data, we used hip navigation planning software to develop a nomogram providing tilt-adjusted cup angles that would align the cup in a target range of 40° ± 10° of abduction and 15° ± 10° of anteversion. A third group of ninety-eight patients (Group C) then underwent total hip arthroplasty with computer navigation with use of our nomogram to provide tilt-adjusted values for cup alignment. Postoperative computed tomography scans were made to evaluate cup alignment, and the patients were followed for at least one year.

Results: In Group A, the mean preoperative supine pelvic tilt angle (and standard deviation) was -8.9° ± 6.8° (forward rotation of the pelvis) and the mean postoperative angle was -10.9° ± 7.6° (p < 0.05). In Group B, the mean preoperative supine pelvic tilt angle was -10.4° ± 7.4° and the mean preoperative standing pelvic tilt angle was -5.0° ± 9.4° (p < 0.001). In the group of ninety-eight patients who underwent navigated total hip arthroplasty (Group C), there were no dislocations at one year of follow-up. Seventy-two patients underwent postoperative computed tomography scans; 99% of cup anteversion values and 97% of cup abduction values were in the target range.

Conclusions: For navigation systems that rely on the pelvic anterior plane, cup alignment values can be converted to familiar target values with our nomogram with good accuracy and reproducibility. The next generation of navigation systems should be able to measure the pelvic tilt for each individual patient and automatically adjust alignment values.

Level of Evidence: Diagnostic Level II. See Instructions to Authors for a complete description of levels of evidence.

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    These activities have been planned and implemented in accordance with the Essential Areas and policies of the Accreditation Council for Continuing Medical Education (ACCME) through the joint sponsorship of the American Academy of Orthopaedic Surgeons and The Journal of Bone and Joint Surgery, Inc. The American Academy of Orthopaedic Surgeons is accredited by the ACCME to provide continuing medical education for physicians.
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