Obesity Alone May Not Affect TKR Outcome or Increase Complication Risk

Obesity alone may not diminish outcomes or increase the risk of complications in total knee replacement (TKR) patients, according to two research studies. However, TKR patients may face significantly longer hospital stays and related costs. TKR in obese patients previously has been associated with increased postoperative complications and lower clinical function scores in multiple research studies.

In one study, Hilal Maradit-Kremers, MD, MSc, Associate Professor of Epidemiology at Mayo Clinic in Rochester, Minnesota, and colleagues reviewed the records of more than 8,000 patients who had undergone single primary or revision TKR procedures between 2000 and 2008. They collected data on clinical and surgical characteristics, complications and hospital costs. Patients were classified into 8 groups based on body mass index (BMI) and comorbidities, including diabetes and hypertension.

Length-of-hospital-stay and direct medical costs were lowest for patients with a BMI of 25-30. Greater BMI was associated with significantly longer hospital stays after adjusting for age, sex, type of surgery, and comorbidities. Every 5 unit increase in BMI beyond 30 was associated with approximately $250 to $300 higher hospitalization costs in primary knee arthroplasty, and $600 to $650 higher hospitalization costs in revision procedures. Although increasing BMI was not associated with an overall increase in complication risk during the 90-day window, there was a higher rate of infections in obese patients.

"The costs associated with obesity are believed to be largely those that come from managing comorbid medical conditions linked to obesity, such as diabetes," said lead study author Maradit-Kremers. "We attempted to tackle this problem by restricting the analysis to patients without comorbid conditions," he explained. "Even in the absence of comorbidities, obesity was still associated with longer stays and higher hospital costs."

"The bottom line is that obesity is increasingly common among patients undergoing joint replacement and it creates a myriad of technical and medical challenges, and likely contributes to the financial burden of the surgery," added senior author David G. Lewallen, MD, an Orthopaedic Surgeon, also from Mayo Clinic.

In a related study, Chin Tat Lim, MBBS, from Singapore, and colleagues analyzed the outcomes of 301 total knee arthroplasty patients between December 2008 and April 2010 and grouped them according to BMI. The authors found no difference in surgical time between obese and nonobese patients, although the obese patients had a longer hospital stay following TKR (7.77 days vs 6.29 days, respectively).

Patient outcomes were recorded preoperatively and at 2 years after TKR using Knee Society Score (KSS), Short Form 36 Health Survey (SF36), and Western Ontario and McMaster Universities Arthritis Index (WOMAC) outcomes. The nonobese patients achieved superior postoperative flexion and range of movement. The absolute improvements in WOMAC scores among the obese patients postsurgery also were deemed statistically superior and comparable to those of nonobese patients.

"[TKR is a] safe and efficacious operation in obese patients with no significantly greater risk of complication," the investigators concluded. "Obesity does not negate good surgical outcome in [total knee arthroplasty]," added lead author Lim.