Scientific Article   |    
Comparison of Simultaneous Bilateral with Unilateral Total Knee Arthroplasty in Terms of Perioperative Complications
Daniel P. Bullock, BA; Scott M. Sporer, MD, MS; Thomas G. ShirreffsJr., MD
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Investigation performed at the Department of Orthopaedic Surgery, Dartmouth Hitchcock Medical Center, Lebanon, New Hampshire

Daniel P. Bullock, BA
Scott M. Sporer, MD, MS
Thomas G. Shirreffs Jr., MD
Department of Orthopaedic Surgery, Dartmouth Hitchcock Medical Center, One Medical Center Drive, Lebanon, NH 03756

The authors did not receive grants or outside funding in support of their research or preparation of this manuscript. They did not receive payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, educational institution, or other charitable or nonprofit organization with which the authors are affiliated or associated.

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J Bone Joint Surg Am, 2003 Oct 01;85(10):1981-1986
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Background: Previous studies have demonstrated an increased rate of perioperative complications and morbidity following simultaneous bilateral total knee arthroplasty compared with the rate following unilateral total knee arthroplasty. The purpose of this study was to compare the rate of perioperative complications and morbidity associated with simultaneous bilateral total knee arthroplasty with that associated with unilateral total knee arthroplasty.

Methods: The records on all bilateral total knee arthroplasties performed between January 1994 and June 2000 and unilateral total knee arthroplasties performed between January 1995 and June 2000 were retrospectively reviewed. The records on 514 unilateral total knee arthroplasties and 255 bilateral total knee arthroplasties were analyzed to determine demographic information, preoperative comorbidities, perioperative complications, and thirty-day and one-year mortality rates.

Results: The rates of some perioperative complications, including myocardial infarction, postoperative confusion, and the need for intensive monitoring, were greater after the bilateral arthroplasties. However, the thirty-day and one-year mortality rates and the risks of pulmonary embolism, infection, and deep venous thrombosis were similar for the two groups.

Conclusions: The risk of perioperative complications associated with bilateral simultaneous total knee arthroplasty was slightly increased compared with that associated with unilateral total knee arthroplasty, but the mortality rates were similar. Ultimately, the decision to proceed with simultaneous knee replacement should depend on patient preference through informed choice.

Level of Evidence: Therapeutic study, Level III-2 (retrospective cohort study). 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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    Daniel P. Bullock
    Posted on December 22, 2003
    Dr. Bullock responds
    Department of Orthopaedic Surgery, Dartmouth Hitchcock Medical Center, Lebanon, New Hampshire

    We thank Drs. Bezwada, Ettiene, and Mont for their interest in our study and their comments regarding our research.

    Concerning the question of comparability of the two patient populations, we agree that establishing similarity between study groups is paramount in any study that does not utilize randomization. In our study, the majority of patients undergoing unilateral total knee arthroplasty did not have bilateral gonarthrosis. That is why we took great care to establish the equivalence of the two groups prior to the surgery. The analysis, including age, sex, surgical indication, and pertinent medical co-morbidities, was reported in the JBJS web site publication in the appendix of the study. With the exception of body mass index and rates of smoking, no statistically significant differences were noted. Therefore, we were confident that a comparison of the two groups was valid.

    As Dr. Bezwada and colleagues correctly point out, it is reasonable to compare rates of mortality and morbidity after first doubling the rates from the unilateral group. Any patient from the unilateral group would require a second surgery to achieve the same knee replacement status as a patient from the bilateral group. If unilateral rates are doubled, any statistical differences between the two groups would certainly diminish. In those categories with small absolute differences or relative risks less than 2.0, differences might even disappear or reverse. While we demonstrated this phenomenon for length of stay, a formal analysis for each category was not performed since it would have been based on purely extrapolated data. On the other hand, the statistical difference for myocardial infarction and intensive care admission had relative risks of 5.13 and 6.61, respectively. Given these higher values, it is unlikely that they would equilibrate with doubled unilateral rates. It is for the above reasoning that we feel the simultaneous bilateral procedure does not subject patients to an unacceptable level of risk, but that in patients greater than 70 years old (no patients under 70 had myocardial infarction) cardiac risk should be considered in making a decision.

    At the same time, comparing unilateral rates directly to bilateral rates is a useful tool. Any time a physician and patient are choosing between a simultaneous bilateral procedure and a staged unilateral procedure, in reality the choice is between a single unilateral procedure and a simultaneous procedure. The decision to proceed with the second stage is never made until a patient successfully recovers from the first stage. If a major complication were to occur in the first stage then the second procedure would likely be cancelled. We believe that the physician and patient should consider both interpretations of the risks. Direct comparison of unilateral and bilateral rates is worthy of consideration. However, doubling unilateral rates and comparing to simultaneous rates provides a pertinent overview of the risk profiles.

    With respect to the interpretation of mortality rates in the greater than 80 year old population, the small number of patients in this group limits the ability to draw conclusions from the age specific data. Our inclusion of the data for age specific deaths was primarily to illustrate the ages of the patients who died following the respective procedures. Regarding the analysis of statistical significance for mortality rates, the p values were calculated using the Fisher Exact test since occurrences were less than 5. The two tailed P values were greater than 0.05 and thus the differences were not statistically significant(1).

    The primary intent of our study was to compare outcomes between the two groups of unselected, consecutive patients, at a single institution. We agree that risk stratification with regard to bilateral vs. unilateral total knees is an important concept; however, our study did not attempt to capture this characteristic. We feel our study has shown that the simultaneous bilateral procedure is a relatively safe procedure when compared to unilateral total knee arthroplasty. We did identify myocardial infarction as a specific outcome that is greater in the bilateral simultaneous population and that infarction occurred only in those over the age of 70.

    With regard to clinical practice, we feel that bilateral simultaneous total knee arthroplasty should be offered to patients as a reasonable alternative to staged bilateral total knee arthroplasty, but that specific attention must be made to cardiac risk factors, particularly in those over the age of 70.

    References: 1. Zar, Jerrold H. Biostatistical Analysis. Third Edition. New Jersey: Prentice Hall. 1996. p 540-549.

    Hari P. Bezwada, M.D.
    Posted on November 17, 2003
    Comparison Between Bilateral and Unilateral Total Knee Arthroplasty
    Rubin Institute for Advanced Orthopaedics, Sinai Hospital of Baltimore

    November 12, 2003

    To the Editor:

    We read “Comparison of Simultaneous Bilateral with Unilateral Total Knee Arthroplasty: Perioperative Complications” by Bullock et al with great interest, but were concerned with the message that is being delivered.

    Their study compares the rate of perioperative complications between simultaneously performed bilateral total knee arthroplasties and unilateral total knee arthroplasty. It may not be appropriate to compare unilateral total knee arthroplasty to simultaneous bilateral total knee arthroplasty. A more appropriate comparison would compare staged bilateral total knee arthroplasties to simultaneous bilateral total knee arthroplasties.

    Did the patients undergoing unilateral total knee arthroplasty have bilateral gonarthrosis? We would submit that patients with bilateral gonarthrosis undergoing unilateral total knee arthroplasty or bilateral total knee arthroplasty may be different from patients with unilateral gonarthrosis undergoing unilateral total knee arthroplasty. For example,patients undergoing simultaneous bilateral total knee arthroplasty have a greater chance of surviving ten years when compared to patients undergoing unilateral total knee arthroplasty(1).

    The decision for staged bilateral total knee arthroplasty versus simultaneous bilateral total knee arthroplasty may be driven by both patient preferences and physician preferences. However, this should be tempered by the rate of complications in particular patient subgroups.

    Additionally, the presence and incidence of medical comorbidities are not clear from our reading of this manuscript. The rate of post-operative medical complications appears to be related to the degree of pre-operative cardiovascular morbidity (2,3,4). We believe that proper analysis of the data would require that the rate of complications in patients undergoing unilateral total knee arthroplasty be doubled in order to more appropriately compare them to complications in patients undergoing bilateral total knee arthroplasty.

    We also question the validity of the statistical analysis? There are only 26 patients in the >80 yr old group undergoing bilateral TKA. This may adversely affect the outcome and make interpretation using percentages invalid. If the numbers are correct and appropriately interpreted, then a one-year mortality rate of 8% in patients over the age of 80 would be very high and not be a “slightly increased perioperative risk.” This is markedly different than the 4.08% noted by Lynch et al., (3).

    The question we would like answered from a paper such as this regards risk stratification. Perhaps a multiple regression analysis should be performed to identify risk factors and then appropriately stratify them, rather than using a chi-square analysis or Fisher exact test. Finally, we are unsure of the lack of statistical significance in the mortality rates as interpreted by the authors. It would appear that the differences between 0.0% and 0.78% as well as 0.63% and 2.1% are likely to be statistically significant.

    We realize that not everyone will be candidates for bilateral total knee arthroplasty, which is why these issues need to be clarified.

    References: 1) Ritter MA, Harty LD, Davis KE, Meding JB, Berend M. Simultaneous Bilateral, Staged Bilateral, and Unilateral Total Knee Arthroplasty. A Survival Analysis. J Bone Joint Surg Am. 2003; 85:1532-1537. 2) Adili A, Bhandari M, Petruccelli D, De Beer J. Sequential Bilateral Total Knee Arthroplasty Under 1 Anesthetic in Patients > or = 75 years old: Complications and Functional Outcomes. J Arthroplasty. 2001; 16:271 -278. 3) Lynch NM, Trousdale RT, Ilstrup DM. Complications After Concomitant Bilateral Total Knee Arthroplasty in Elderly Patients. Mayo Clin Proc. 1997; 72:799-805. 4) Parvizi J, Sullivan TA, Trousdale RT, Lewallen DG. Thirty-Day Mortality After Total Knee Arthroplasty. J Bone Joint Surg Am. 2001; 83:1157-1161.


    Michael A. Mont, MD

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