0
Commentary and Perspective   |    
Commentary on an Article by Sebastien Parratte, MD, PhD, et al.: “Effect of Postoperative Mechanical Axis Alignment on the Fifteen-Year Survival of Modern, Cemented Total Knee Replacements”
Michael A. Mont, MD1; Ormonde M. Mahoney, MD2
1 Sinai Hospital of Baltimore, Baltimore Maryland
2 Athens, Georgia
View Disclosures and Other Information
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 (Stryker Orthopaedics, Wright Medical, and TissueGene) and less than $10,000 (Magnifi) or a commitment or agreement to provide such benefits from these commercial entities.

Copyright © 2010 by The Journal of Bone and Joint Surgery, Inc.
J Bone Joint Surg Am, 2010 Sep 15;92(12):e16 1-2. doi: 10.2106/JBJS.J.00937
The main article is available here
5 Recommendations (Recommend) | 3 Comments | Saved by 3 Users Save Case
It has been a long-held tenet of total knee replacement that the restoration of a neutral mechanical axis promotes improved durability and function following this surgery. Observational data from over ten series have led to this belief and have in fact been corroborated by in vitro testing, in which increased wear and premature failure of components can occur if the total knee replacements are mechanically aligned in a varus position1-14. This concept is further reinforced by the advances in computerized navigation and other imaging systems that aim for this "ideal" coronal plane alignment to enhance knee replacement survival rates.
The report by Parratte and associates entitled "Effect of Postoperative Mechanical Axis Alignment on the Fifteen-Year Survival of Modern, Cemented Total Knee Replacements" challenges these assertions by finding that total knee replacements placed outside of a few degrees from the mechanical axis in the coronal plane had equal survival rates when compared with knees placed within ±3° of the mechanical axis. The authors analyzed the fifteen-year survival for 398 primary total knee arthroplasties that had been performed with cement in 280 patients between 1985 and 1990. Patients were stratified into two groups: those with knees that were aligned well in the mechanical axis (292 knees with a mechanical axis of 0° ± 3°) and those with knees that were not as well aligned (106 knees with a mechanical axis beyond 0° ± 3°). Survival of the knee replacements was analyzed according to three end points: (1) revision for any reason, including revision for septic and aseptic complications, (2) revision because of mechanical failure, aseptic loosening, radiographic wear, or patellar complications, and (3) revision because of mechanical failure, aseptic loosening, or radiographic wear, with exclusion of patellar complications. There was no difference in survival between the mechanically aligned group and the outlier group in terms of any of these end points. The authors concluded that this postoperative coronal plane mechanical axis dichotomous variable did not influence outcome. They did not assert that this alignment variable is completely irrelevant, but rather that it might not be as important a factor in terms of outcome as previously thought. The authors found that patient age and body-mass index had an effect on outcome and postulated that other factors such as gait may have an impact on total knee survival.
This is a well written evaluation of the observed effect of alignment on the durability of total knee replacements and is the only published series involving the use of modern cemented total knee designs with both preoperative and postoperative full-length radiographs available for 95% of the patients. Long-term follow-up (fifteen years) was available through chart review and telephone interviews conducted with patients without recent clinic visits. The statistical analysis was conducted in an appropriate fashion, and the conclusion is reasonable.
The importance of this work is that surgeons as well as companies that propagate the belief that simply achieving coronal plane alignment within a few degrees will lead to the best survival of total knee replacements may be incorrect. In addition, the use of computerized navigation systems to achieve ideal coronal plane alignment can be more expensive and time-consuming and may not necessarily improve the survival of total knee replacements.
We do, however, question the premise that both varus and valgus knees could be treated equally in this observational study. It is our opinion that patients whose knees are in varus alignment postoperatively are at higher risk for failure than patients whose knees have valgus alignment. This could be equated with an analysis of the health risks of obesity in which patients of "normal weight" are compared with patients of "abnormal weight," with underweight and overweight patients being combined in the "abnormal" group, thus diluting the well-recognized health risks seen in overweight individuals. In this case, the authors do not reveal what the failure rates were within the subgroups, potentially leading to a misinterpretation of the result. For example, in the most extreme case, there could have been fourteen revisions in the varus alignment group (32%) and zero revisions in the valgus alignment group (0%). Recognition of this limitation may have prompted the authors’ closing statement: "a neutral mechanical axis remains a reasonable target and should be considered as the standard for comparison if other alignment targets are introduced."
This report challenges previously held beliefs regarding the desirability of achieving a neutral mechanical axis in every patient undergoing total knee reconstruction and underscores the importance of exploring this and other total knee alignment or positioning issues. We do believe that to look at the multitude of other factors such as different degrees of outliers, varus or valgus outliers, rotational and translational positioning, and patient demographics would require a much larger study to be statistically valid and to draw major conclusions.
In summary, the authors found that total knee replacements in the outlier group had similar survival to those in the mechanically aligned group. This is an extremely important study that challenges previously accepted notions about the importance of coronal plane alignment, which may not be true. It also should foster further work on larger groups of patients in terms of the analysis of optimal total knee alignment for individual patients as well as other factors (i.e., gait) that might influence implant survival as well as functionality.
We did not receive any outside funding or grants in support of this research.
Berend  ME;  Ritter  MA;  Meding  JB;  Faris  PM;  Keating  EM;  Redelman  R;  Faris  GW;  Davis  KE. Tibial component failure mechanisms in total knee arthroplasty. Clin Orthop Relat Res.  2004;428:26-34.[PubMed][CrossRef]
 
Brouwer  RW;  Jakma  TS;  Brouwer  KH;  Verhaar  JA. Pitfalls in determining knee alignment: a radiographic cadaver study. J Knee Surg.  2007;20:210-5.[PubMed]
 
Cooke  TD;  Sled  EA;  Scudamore  RA. Frontal plane knee alignment: a call for standardized measurement. J Rheumatol.  2007;34:1796-801.[PubMed]
 
D'Lima  DD;  Chen  PC;  Colwell  CW  Jr. Polyethylene contact stresses, articular congruity, and knee alignment. Clin Orthop Relat Res.  2001;392:232-8.[PubMed]
 
Eckhoff  DG;  Bach  JM;  Spitzer  VM;  Reinig  KD;  Bagur  MM;  Baldini  TH;  Flannery  NM. Three-dimensional mechanics, kinematics, and morphology of the knee viewed in virtual reality. J Bone Joint Surg Am.  2005;87  Suppl 2:71-80.[PubMed]
 
Hvid  I;  Nielsen  S. Total condylar knee arthroplasty. Prosthetic component positioning and radiolucent lines. Acta Orthop Scand.  1984;55:160-5.[PubMed]
 
Jeffery  RS;  Morris  RW;  Denham  RA. Coronal alignment after total knee replacement. J Bone Joint Surg Br.  1991;73:709-14.[PubMed]
 
Lotke  PA;  Ecker  ML. Influence of positioning of prosthesis in total knee replacement. J Bone Joint Surg Am.  1977;59:77-9.[PubMed]
 
Matsuda  S;  Miura  H;  Nagamine  R;  Urabe  K;  Harimaya  K;  Matsunobu  T;  Iwamoto  Y. Changes in knee alignment after total knee arthroplasty. J Arthroplasty.  1999;14:566-70.[PubMed]
 
Mont  MA;  Fairbank  AC;  Yammamoto  V;  Krackow  KA;  Hungerford  DS. Radiographic characterization of aseptically loosened cementless total knee replacement. Clin Orthop Relat Res.  1995;321:73-8.[PubMed]
 
Ritter  MA;  Faris  PM;  Keating  EM;  Meding  JB. Postoperative alignment of total knee replacement. Its effect on survival. Clin Orthop Relat Res.  1994;299:153-6.[PubMed]
 
Sparmann  M;  Wolke  B;  Czupalla  H;  Banzer  D;  Zink  A. Positioning of total knee arthroplasty with and without navigation support. A prospective, randomised study. J Bone Joint Surg Br.  2003;85:830-5.[PubMed]
 
Spencer  BA;  Mont  MA;  McGrath  MS;  Boyd  B;  Mitrick  MF. Initial experience with custom-fit total knee replacement: intra-operative events and long-leg coronal alignment. Int Orthop.  2009;33:1571-5.[PubMed]
 
Werner  FW;  Ayers  DC;  Maletsky  LP;  Rullkoetter  PJ. The effect of valgus/varus malalignment on load distribution in total knee replacements. J Biomech.  2005;38:349-55.[PubMed]
 

Submit a comment

References

Berend  ME;  Ritter  MA;  Meding  JB;  Faris  PM;  Keating  EM;  Redelman  R;  Faris  GW;  Davis  KE. Tibial component failure mechanisms in total knee arthroplasty. Clin Orthop Relat Res.  2004;428:26-34.[PubMed][CrossRef]
 
Brouwer  RW;  Jakma  TS;  Brouwer  KH;  Verhaar  JA. Pitfalls in determining knee alignment: a radiographic cadaver study. J Knee Surg.  2007;20:210-5.[PubMed]
 
Cooke  TD;  Sled  EA;  Scudamore  RA. Frontal plane knee alignment: a call for standardized measurement. J Rheumatol.  2007;34:1796-801.[PubMed]
 
D'Lima  DD;  Chen  PC;  Colwell  CW  Jr. Polyethylene contact stresses, articular congruity, and knee alignment. Clin Orthop Relat Res.  2001;392:232-8.[PubMed]
 
Eckhoff  DG;  Bach  JM;  Spitzer  VM;  Reinig  KD;  Bagur  MM;  Baldini  TH;  Flannery  NM. Three-dimensional mechanics, kinematics, and morphology of the knee viewed in virtual reality. J Bone Joint Surg Am.  2005;87  Suppl 2:71-80.[PubMed]
 
Hvid  I;  Nielsen  S. Total condylar knee arthroplasty. Prosthetic component positioning and radiolucent lines. Acta Orthop Scand.  1984;55:160-5.[PubMed]
 
Jeffery  RS;  Morris  RW;  Denham  RA. Coronal alignment after total knee replacement. J Bone Joint Surg Br.  1991;73:709-14.[PubMed]
 
Lotke  PA;  Ecker  ML. Influence of positioning of prosthesis in total knee replacement. J Bone Joint Surg Am.  1977;59:77-9.[PubMed]
 
Matsuda  S;  Miura  H;  Nagamine  R;  Urabe  K;  Harimaya  K;  Matsunobu  T;  Iwamoto  Y. Changes in knee alignment after total knee arthroplasty. J Arthroplasty.  1999;14:566-70.[PubMed]
 
Mont  MA;  Fairbank  AC;  Yammamoto  V;  Krackow  KA;  Hungerford  DS. Radiographic characterization of aseptically loosened cementless total knee replacement. Clin Orthop Relat Res.  1995;321:73-8.[PubMed]
 
Ritter  MA;  Faris  PM;  Keating  EM;  Meding  JB. Postoperative alignment of total knee replacement. Its effect on survival. Clin Orthop Relat Res.  1994;299:153-6.[PubMed]
 
Sparmann  M;  Wolke  B;  Czupalla  H;  Banzer  D;  Zink  A. Positioning of total knee arthroplasty with and without navigation support. A prospective, randomised study. J Bone Joint Surg Br.  2003;85:830-5.[PubMed]
 
Spencer  BA;  Mont  MA;  McGrath  MS;  Boyd  B;  Mitrick  MF. Initial experience with custom-fit total knee replacement: intra-operative events and long-leg coronal alignment. Int Orthop.  2009;33:1571-5.[PubMed]
 
Werner  FW;  Ayers  DC;  Maletsky  LP;  Rullkoetter  PJ. The effect of valgus/varus malalignment on load distribution in total knee replacements. J Biomech.  2005;38:349-55.[PubMed]
 
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.
CME Activities Associated with This Article
Submit a Comment
Please read the other comments before you post yours. Contributors must reveal any conflict of interest.
Comments are moderated and will appear on the site at the discretion of JBJS editorial staff.

* = Required Field
(if multiple authors, separate names by comma)
Example: John Doe





David Biau
Posted on June 17, 2011
statistical analysis allows us to put limits on our uncertainty, but not to prove anything.
Dpt Biostat, Hopital Saint Louis, Paris, France

Dear Editor, I read with interest the article By Parratte et al. and commend the authors for providing long-term data on the association between alignment and survival in total knee arthroplasty. Contrary to previous data and common belief they did not find a statistical association between the two. However, I think the answer to this conundrum is not mechanical but statistical [1]: In a Neyman-Pearsonian perspective (to whom we owe the theory of hypotheses testing), this is what we would call a type II error [2]. In a randomized trial when we do not find a difference that exists we call it a type II error, namely we did not reject the null hypothesis of no difference when it was in fact false. However, this is a retrospective study where patients were not randomized so we should interpret their study from a Fisherian (Ronald Fisher, who popularized the P value) standpoint [3]. The authors test the null hypothesis of no effect of +/- 3 degrees postoperative mechanical axis malalignment on total knee survival and the P value is not significant (P<0.05). Their conclusion should be that there is no difference in survival between knees outside the range of +/- 3 degrees and those within that range. But they are not willing to make that conclusion and state “a neutral mechanical axis remains a reasonable target and should be considered as the standard ”. The reason is that Fisher taught us that the P value is only a measure of a chance finding under the null hypothesis and that the results of an experiment should first be interpreted in the light of previous data. Numerous biomechanical and clinical studies have demonstrated the detrimental effect of poor alignment on knee replacement survival. So one may just conclude that the effect observed in their study is a chance finding. If they repeated the “experiment again” (namely if they operated again on 398 patients and misaligned 27% of the knees) they would probably find a larger difference. There is no power calculation or type II error in Fisher's theory but there is something else we can use: the precision of the estimates. The Journal of Bone and Joint Surgery guidelines to authors is that “ninety-five percent confidence intervals are required for any estimate appearing in the text or graphs”. However, the authors do not provide a confidence interval for the estimated hazard ratio of revision for any reason (HR=1.05) which would help us to make more sense of their findings [4]. [1] Biau DJ et al. P value and the theory of hypothesis testing: an explanation for new researchers. CORR, 2010. [2] Neyman J, Pearson E. On the problem of the most efficient tests of statistical hypotheses. Philos Trans R Soc Lond A. 1933. [3] Fisher RA. Statistical Methods for Research Workers. Edinburgh, UK; 1925. [4] Biau DJ et al. Statistics in brief: the importance of sample size in the planning and interpretation of medical research. CORR, 2008

Mark W. Pagnano, MD
Posted on June 14, 2011

The data requested by Dr. Stiehl has been available to him and all readers of The Journal online, under the Supplementary material associated with this paper, since the time of original publication. A bar graph in that supplementary material includes the exact number of patients at each postoperative alignment value.

James B Stiehl, Md
Posted on June 14, 2011
jbstiehlmd.com

These authors offer an appropriate and judicious evaluation of this timely publication. They draw a most important conclusion that the data may deceive if not organized appropriately. The obvious possibility of the Parratte paper is that the alignment target of +/-3 degrees may not be correct. I would challenge the Editors to allow the readership to see the exact alignment details of the cohorts, as the numbers are slight. This was my challenge to the authors when I first heard this work.

Related Content
The Journal of Bone & Joint Surgery
JBJS Case Connector
Topic Collections
Related Audio and Videos
PubMed Articles
Clinical Trials
Readers of This Also Read...
JBJS Jobs
01/08/2014
Pennsylvania - Penn State Milton S. Hershey Medical Center
02/05/2014
Oregon - The Center - Orthopedic and Neurosurgical Care and Research
03/19/2014
Virginia - VIRGINIA COMMONWEALTH UNIVERSITY MEDICAL CENTER