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Effect of Postoperative Mechanical Axis Alignment on the Fifteen-Year Survival of Modern, Cemented Total Knee Replacements
Sebastien Parratte, MD, PhD1; Mark W. Pagnano, MD1; Robert T. Trousdale, MD1; Daniel J. Berry, MD1
1 Department of Orthopedic Surgery, Mayo Clinic, 200 First Street S.W., Rochester, MN 55905. E-mail address for M.W. Pagnano: pagnano.mark@mayo.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 (DePuy).

A commentary by Michael A. Mont, MD, and Ormonde M. Mahoney, MD, is available at www.jbjs.org/commentary and as supplemental material to the online version of this article.
Investigation performed at the Mayo Clinic, Rochester, Minnesota

Copyright © 2010 by The Journal of Bone and Joint Surgery, Inc.
J Bone Joint Surg Am, 2010 Sep 15;92(12):2143-2149. doi: 10.2106/JBJS.I.01398
A commentary by Ormonde M. Mahoney, MD, is available here
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Abstract

Background: 

One long-held tenet of total knee arthroplasty is that implant durability is maximized when postoperative limb alignment is corrected to 0° ± 3° relative to the mechanical axis. Recently, substantial health-care resources have been devoted to computer navigation systems that allow surgeons to more often achieve that alignment. We hypothesized that a postoperative mechanical axis of 0° ± 3° would result in better long-term survival of total knee arthroplasty implants as compared with that in a group of outliers.

Methods: 

Clinical and radiographic data were reviewed retrospectively to determine the fifteen-year Kaplan-Meier survival rate following 398 primary total knee arthroplasties performed with cement in 280 patients from 1985 to 1990. Preoperatively, most knees were in varus mechanical alignment (mean and standard deviation, 6° ± 8.8° of varus [range, 30° of varus to 22° of valgus]), whereas postoperatively most knees were corrected to neutral (mean and standard deviation, 0° ± 2.8° [range, 8° of varus to 9° of valgus]). Postoperatively, we defined a mechanically aligned group of 292 knees (with a mechanical axis of 0° ± 3°) and an outlier group of 106 knees (with a mechanical axis of beyond 0° ± 3°).

Results: 

At the time of the latest follow-up, forty-five (15.4%) of the 292 implants in the mechanically aligned group had been revised for any reason, compared with fourteen (13%) of the 106 implants in the outlier group (p = 0.88); twenty-seven (9.2%) of the 292 implants in the mechanically aligned group had been revised because of aseptic loosening, mechanical failure, wear, or patellar problems, compared with eight (7.5%) of the 106 implants in the outlier group (p = 0.88); and seventeen (5.8%) of the 292 implants in the mechanically aligned group had been revised because of aseptic loosening, mechanical failure, or wear, compared with four (3.8%) of the 106 implants in the outlier group (p = 0.49).

Conclusions: 

A postoperative mechanical axis of 0° ± 3° did not improve the fifteen-year implant survival rate following these 398 modern total knee arthroplasties. We believe that describing alignment as a dichotomous variable (aligned versus malaligned) on the basis of a mechanical axis goal of 0° ± 3° is of little practical value for predicting the durability of modern total knee arthroplasty implants.

Level of Evidence: 

Therapeutic Level III. 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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