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Averaging Different Alignment Axes Improves Femoral Rotational Alignment in Computer-Navigated Total Knee Arthroplasty

Siston, Robert A. PhD; Cromie, Melinda J. MS; Gold, Garry E. MD; Goodman, Stuart B. MD, PhD; Delp, Scott L. PhD; Maloney, William J. MD; Giori, Nicholas J. MD, PhD

Journal of Bone & Joint Surgery - American Volume: 01 October 2008 - Volume 90 - Issue 10 - p 2098–2104
doi: 10.2106/JBJS.G.00996
Scientific Articles

Background: Computer navigation systems generally establish the rotational alignment axis of the femoral component on the basis of user-defined anatomic landmarks. However, navigation systems can also record knee kinematics and average alignment axes established with multiple techniques. We hypothesized that establishing femoral rotational alignment with the use of kinematic techniques is more accurate and precise (repeatable) than the use of anatomic techniques and that establishing femoral rotational alignment by averaging the results of different alignment techniques is more accurate and precise than the use of a single technique.

Methods: Twelve orthopaedic surgeons used three anatomic and two kinematic alignment techniques to establish femoral rotational alignment axes in a series of nine cadaver knees. The axes derived with the individual anatomic and kinematic techniques as well as the axes derived with six combination techniques—i.e., those involving averaging of the alignments established with two of the individual techniques—were compared against a reference axis established with computed tomography images of each femur.

Results: The kinematic methods were not more accurate (did not have smaller mean errors) or more precise (repeatable) than the anatomic techniques. The combination techniques were accurate (five of the six had a mean error of <5°) and significantly more precise than all but one of the single methods. The percentage of measurements with <5° of error as compared with the reference epicondylar axis was 37% for the individual anatomic techniques, 30% for the individual kinematic techniques, and 58% for the combination techniques.

Conclusions: Averaging the results of kinematic and anatomic techniques, which is possible with computer navigation systems, appears to improve the accuracy of rotational alignment of the femoral component. The number of rotational alignment outliers was reduced when combination techniques were used; however, they are still a problem and continued improvement in methods to accurately establish rotation of the femoral component in total knee arthroplasty is needed.

1Departments of Mechanical Engineering and Orthopaedics, Ohio State University, E305 Scott Laboratory, 201 West 19th Avenue, Columbus, OH 43210

2Department of Mechanical Engineering, Stanford University, Building 530, 440 Escondido Mall, Stanford, CA 94305-3030

3Department of Radiology, Stanford University School of Medicine, 300 Pasteur Drive, Stanford, CA 94305-5105

4Department of Orthopaedic Surgery, Stanford University School of Medicine, 300 Pasteur Drive, Edwards R109, Stanford, CA 94305-5335

5VA Palo Alto Health Care System, 3801 Miranda Avenue, Surgical Services-MC 112, Palo Alto, CA 94304. E-mail address: ngiori@stanford.edu

Copyright 2008 by The Journal of Bone and Joint Surgery, Incorporated
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