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Commentary and Perspective   |    
The Definitive Answer: Fixed-Bearing Versus Mobile-Bearing TKACommentary on an article by Young-Hoo Kim, MD, et al.: “Long-Term Comparison of Fixed-Bearing and Mobile-Bearing Total Knee Replacements in Patients Younger Than Fifty-one Years of Age with Osteoarthritis”
James A. Shaw, MD
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The author received no payments or services, either directly or indirectly (i.e., via his institution), from a third party in support of any aspect of this work. Neither the author nor his institution has had any financial relationship, in the thirty-six months prior to submission of this work, with any entity in the biomedical arena that could be perceived to influence or have the potential to influence what is written in this work. Also, the author has not had any other relationships, or engaged in any other activities, that could be perceived to influence or have the potential to influence what is written in this work. The complete Disclosures of Potential Conflicts of Interest submitted by authors are always provided with the online version of the article.


Copyright © 2012 by The Journal of Bone and Joint Surgery, Inc.
J Bone Joint Surg Am, 2012 May 16;94(10):e69 1-2. doi: 10.2106/JBJS.K.01725
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The authors are to be congratulated on their long-term study comparing fixed-bearing and mobile-bearing total knee prostheses in patients who have osteoarthritis. Like most prior studies, the clinical and radiographic results and complication rates were similar in both groups, with no evidence to prove superiority of one design over the other.
Unlike most prior studies, this study is exemplary in every way. The authors have no conflicts of interest referable to prosthetic design or royalties. Both types of prostheses were manufactured by the same company at the same time interval using the same polyethylene preparation. The patients were all fifty years or younger, representing a physically demanding patient population with regard to total knee prostheses. The mean follow-up was 16.8 years (range, fifteen to eighteen years), which is a long enough interval for subtle advantages or disadvantages to manifest themselves. The study design was prospective and randomized. In addition, and, most importantly, each of the 108 patients served as an internal control in that all patients had simultaneous bilateral knee replacements performed by the same surgeon: one knee received a fixed-bearing component and the other knee received a mobile-bearing component. From a clinical study design perspective, it simply doesn't get any better than that.
Mobile-bearing designs were introduced in the United States by DePuy (Warsaw, Indiana) in the 1980s, first with the meniscal-bearing concept, then followed shortly thereafter with the rotating platform design. (Both designs were preceded by several years by the Oxford unicompartmental meniscal-bearing design [Biomet, Warsaw, Indiana].) The two DePuy products were championed by Buechel and Pappas, who hold joint patents (patent numbers 4,340,978 and 5,171,283) on both designs. Reported problems with bearing dissociation and edge wear led to design modifications, which were followed by diminishing use of the meniscal concept in favor of the rotating platform design.
The purported advantage of the dual-surface articulation was the maintenance of low rotational constraint while gaining lower tibiofemoral contact stresses. The former is important for the durability of component fixation, while the latter is important for polyethylene wear concerns. A polished tibial articulating surface was believed to lessen the probability of back-side wear, as well. Clinical results reported by Buechel et al.1 and others2 were favorable, leading most manufacturers to introduce mobile-bearing knee designs of their own as patent constraints expired.
The literature is replete with articles comparing the two design concepts, with an occasional small study that made use of the matched-pair design mentioned above3. Virtually all arrive at the same conclusions that were expressed in the current study. Two large randomized multicenter studies4,5 presented at the 2011 American Academy of Orthopaedic Surgeons annual meeting in San Diego failed to confirm any of the hypothetical design benefits of mobile-bearing prostheses, while at the same time identifying no detrimental aspects, with the possible exception of greater cost for mobile-bearing designs. The choice appears to boil down to surgeon preference.
An unassailable fact is that this topic has been beaten to death in the arthroplasty literature. With the publication of the current study, I consider the subject closed. A very important article was recently published by Sheth et al.6 in The Journal of Bone and Joint Surgery, titled “Poor Citation of Prior Evidence in Hip Fracture Trials.” In their opening paragraph, the authors state: “Critical appraisal of prior evidence, especially prior randomized trials evaluating issues similar to the one of interest, should act as a starting point for researchers who wish to conduct a new trial or study. Prior evidence informs the need for additional research and facilitates interpretation of the results of a new study. Ultimately, this due diligence should discourage researchers from conducting trials for which well-established conclusions already exist, preventing redundancy within the literature, avoiding inefficient use of research time and funding, and eliminating the potential harm to patients involved in unnecessary surgical trials.”
Many topics within the realm of total knee arthroplasty seem to fall into the category of needless redundancy. Every year there are new articles published, or “point-counterpoint” symposia presented, addressing age-old topics like meniscal-bearing versus fixed-bearing total knee arthroplasty, posterior-stabilized versus cruciate-retaining total knee arthroplasty, patellar resurfacing versus nonresurfacing total knee arthroplasty, drains versus no drains, or continuous passive motion versus no continuous passive motion, with no significant additions to already published literature or previously presented symposia. Perhaps, if we give credence to the admonitions of Sheth et al., we will all be better off.
Buechel  FF  Sr;  Buechel  FF  Jr;  Pappas  MJ;  D'Alessio  J. Twenty-year evaluation of meniscal bearing and rotating platform knee replacements. Clin Orthop Relat Res.  2001;388:41-50.
 
Sorrells  RB;  Stiehl  JB;  Voorhorst  PE. Midterm results of mobile-bearing total knee arthroplasty in patients younger than 65 years. Clin Orthop Relat Res.  2001;390:182-9.
 
Chiu  KY;  Ng  TP;  Tang  WM;  Lam  P. Bilateral total knee arthroplasty: One mobile-bearing and one fixed-bearing. J Orthop Surg (Hong Kong).  2001;9:45-50.
 
Mahoney  OM;  Kinsey  T;  D'Errico  T;  Shen  J.  Comparable clinical outcomes of fixed versus mobile bearing posteriorly stabilized TKA [abstract]. In: AAOS 2011 Annual Meeting Proceedings; 2011 Feb 15-19. San Diego: American Academy of Orthopaedic Surgeons; 2011. p 518. Abstract no. 003.
 
Murray  DW.  Five year results of an RCT comparing mobile and fixed bearing total knee replacement [abstract]. In: AAOS 2011 Annual Meeting Proceedings; 2011 Feb 15-19. San Diego: American Academy of Orthopaedic Surgeons; 2011. p 518. Abstract no. 001.
 
Sheth  U;  Simunovic  N;  Tornetta  P;  Einhorn  TA;  Bhandari  M. Poor citation of prior evidence in hip fracture trials. J Bone Joint Surg Am.  2011;93:2079-86.
 

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References

Buechel  FF  Sr;  Buechel  FF  Jr;  Pappas  MJ;  D'Alessio  J. Twenty-year evaluation of meniscal bearing and rotating platform knee replacements. Clin Orthop Relat Res.  2001;388:41-50.
 
Sorrells  RB;  Stiehl  JB;  Voorhorst  PE. Midterm results of mobile-bearing total knee arthroplasty in patients younger than 65 years. Clin Orthop Relat Res.  2001;390:182-9.
 
Chiu  KY;  Ng  TP;  Tang  WM;  Lam  P. Bilateral total knee arthroplasty: One mobile-bearing and one fixed-bearing. J Orthop Surg (Hong Kong).  2001;9:45-50.
 
Mahoney  OM;  Kinsey  T;  D'Errico  T;  Shen  J.  Comparable clinical outcomes of fixed versus mobile bearing posteriorly stabilized TKA [abstract]. In: AAOS 2011 Annual Meeting Proceedings; 2011 Feb 15-19. San Diego: American Academy of Orthopaedic Surgeons; 2011. p 518. Abstract no. 003.
 
Murray  DW.  Five year results of an RCT comparing mobile and fixed bearing total knee replacement [abstract]. In: AAOS 2011 Annual Meeting Proceedings; 2011 Feb 15-19. San Diego: American Academy of Orthopaedic Surgeons; 2011. p 518. Abstract no. 001.
 
Sheth  U;  Simunovic  N;  Tornetta  P;  Einhorn  TA;  Bhandari  M. Poor citation of prior evidence in hip fracture trials. J Bone Joint Surg Am.  2011;93:2079-86.
 
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