Published 3/1/2012
Peter Pollack

Safety of Simultaneous Bilateral vs. Unilateral TKA

Massive dataset offers insight into complication rates

What factors are associated with complication rates after simultaneous total knee arthroplasty (TKA)?” asked Bryan D. Springer, MD, who presented his study, “Factors Associated with Perioperative Complication Rates after Unilateral vs. Simultaneous TKA,” at the AAOS Annual Meeting.

Dr. Springer and Susan M. Odum, MS, drew data from the Nationwide Inpatient Sample (NIS), a national claims database.

“We looked back over a 4-year period, from 2004 through 2007,” said Dr. Springer. “Part of the data compares simultaneous bilateral TKA with unilateral TKA, but we also examined other factors that put patients at risk for complications after knee replacement.”

“A lot of studies comparing bilateral TKA to unilateral TKA have looked at only one or two complications at a time,” said Ms. Odum. “We tried to identify all possible complications following a TKA and grouped them as major complications, minor complications, or mortality.”

What are the odds?
The potential benefits of simultaneous bilateral TKA include decreased overall length of hospitalization, shorter anesthesia time, and decreased rehabilitation time in addition to a decreased cost to both the patient and the institution. These benefits may be offset, however, by the potential increase in morbidity and mortality that is associated with simultaneous bilateral TKAs.

During the 2004–2007 period, 407,070 TKAs were performed, based on the NIS dataset—24,574 simultaneous bilateral TKAs and 382,496 unilateral TKAs. Complications were determined using ICD-9 codes, and covariates included comorbidities, demographics, payer type, and hospital type.

The research team found that patients who underwent simultaneous bilateral TKAs had significantly increased odds for all types of complications. Of the 24,574 simultaneous TKAs, minor complications (such as peripheral vascular complications, phlebitis, or nonhealing surgical wounds) were reported in 1,682 cases (6.84 percent); minor complications were reported in 4.6 percent (17,582) of the 382,496 unilateral TKAs.

The proportion of major complications such as septic pulmonary embolisms or central nervous system complications was 1.49 percent for simultaneous TKAs and 1.19 percent for unilateral TKAs. The in-hospital mortality rate was 0.2 percent for simultaneous TKAs and 0.09 percent for unilateral TKAs.

In addition, a greater number of comorbidities were associated with complication rates in simultaneous bilateral TKAs than in unilateral TKAs.

Overall, African Americans and Native Americans had significantly higher odds of incurring minor complications than Caucasians did, and women had significantly lower odds of incurring any type of complication than men. The patients younger than 45 years of age were the most likely to incur a major in-hospital complication.

One unexpected outcome involved the relative risk of complications among various hospital types. Rural and urban non-teaching hospitals had lower complication rates overall than urban teaching hospitals, even though rural hospitals were associated with increased risk of mortality.

“Our assumption was that surgeries in an urban teaching hospital would have a reduced risk of complication,” said Dr. Springer, “but that wasn’t the case.”

According to Ms. Odum, the higher risk of complications in teaching hospitals could have been driven by higher risk patients, who might have been referred or sought treatment at these hospitals.

Interpreting the data
Dr. Springer cautioned that, despite the large patient population involved in the study, a lack of patient-specific data made it difficult to quantitatively determine if patients who need both knees replaced would face a lower risk of complications in a simultaneous or a staged scenario.

In addition, he noted that the study was limited to in-hospital complications, which may mean that overall complications are underestimated. Surgical issues—such as the complexity of the case, blood loss, and surgical time—could not be determined but might have an impact on overall complication rates. Coding errors and misclassification of complications are other database study limitations.

“We want to be careful in interpreting these data,” he cautioned. “I tell my patients that the risk of complications increases if both knee replacements are performed at the same time, compared to having a single knee replaced. One of those complications is an increased risk of dying.

“It’s important to identify higher risk patients and treat them appropriately. I would rarely perform a bilateral knee replacement on a patient who is older than age 70 and has any type of coronary or pulmonary disease, simply because their risk is greater.”

“Patients who have bilateral knee arthritis and who need both knees replaced in 3 or 6 months, or even a year, are undergoing the risk of complication twice,” said Ms. Odum. “In the future, we would like to be able to use this large dataset to compare the overall risks of simultaneous bilateral TKA to staged bilateral TKA and to unilateral TKA.”

Disclosure information: Dr. Springer—DePuy, A Johnson & Johnson Company; Stryker, Convatec Surgical. Ms. Odum reported no conflicts.

Peter Pollack is a staff writer for AAOS Now. He can be reached at ppollack@aaos.org

Additional Resources
Factors Associated with Perioperative Complication Rates after Unilateral vs. Simultaneous TKA