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Scientific Articles   |    
Averaging Different Alignment Axes Improves Femoral Rotational Alignment in Computer-Navigated Total Knee Arthroplasty
Robert A. Siston, PhD1; Melinda J. Cromie, MS2; Garry E. Gold, MD3; Stuart B. Goodman, MD, PhD4; Scott L. Delp, PhD2; William J. Maloney, MD4; Nicholas J. Giori, MD, PhD5
1 Departments of Mechanical Engineering and Orthopaedics, Ohio State University, E305 Scott Laboratory, 201 West 19th Avenue, Columbus, OH 43210
2 Department of Mechanical Engineering, Stanford University, Building 530, 440 Escondido Mall, Stanford, CA 94305-3030
3 Department of Radiology, Stanford University School of Medicine, 300 Pasteur Drive, Stanford, CA 94305-5105
4 Department of Orthopaedic Surgery, Stanford University School of Medicine, 300 Pasteur Drive, Edwards R109, Stanford, CA 94305-5335
5 VA Palo Alto Health Care System, 3801 Miranda Avenue, Surgical Services-MC 112, Palo Alto, CA 94304. E-mail address: ngiori@stanford.edu
View Disclosures and Other Information
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 in excess of $10,000 or a commitment or agreement to provide such benefits from a commercial entity (Wright Medical). 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.
Investigation performed at Stanford University, Stanford, California

The Journal of Bone and Joint Surgery, Inc.
J Bone Joint Surg Am, 2008 Oct 01;90(10):2098-2104. doi: 10.2106/JBJS.G.00996
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Abstract

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.

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    Accreditation Statement
    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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