Weight Loss Before TKA Improves Outcomes for Morbidly Obese Patients

    With the prevalence of obesity rising to nearly 40% among American adults, [1] orthopaedic surgeons are facing a serious issue: Should they perform elective total knee arthroplasty (TKA) on patients with a high body mass index (BMI) – knowing that obesity can put patients at risk for complications of surgery – or should they require them to lose weight first?

    A 2013 statement from a work group of the American Association of Hip & Knee Surgeon suggests that delaying the procedure, especially in obese patients with comorbidities, may be appropriate. [2] The problem is, the literature shows that only about 20% of patients with a high BMI will be able to lose enough weight to bring their BMI under 40 before surgery – and that they won’t necessarily lose the weight after TKA either. [3]

    There’s some good news, though: A study presented at the 2019 Annual Meeting of the American Academy of Orthopaedic Surgeons found that significant weight loss may not be necessary. Morbidly obese patients who lost at least 20 pounds before TKA had shorter hospital stays and lower odds of being discharged to a nursing facility even if they remained morbidly or severely obese.

    “There isn’t a standard practice for how much weight needs to be lost prior to surgery, nor is there a standard definition for clinically significant weight loss,” said lead author Benjamin Keeney, PhD, an instructor in orthopaedics at Dartmouth Geisel School of Medicine. “With this paper, we tried to find the justification for losing 5, 10, or 20 pounds. It’s hard to find where it explicitly states this is the amount of weight you need to lose for meaningful change, especially in the context of total knee arthroplasty.”

    In the study, Dr. Keeney and his colleagues wanted to determine how much weight loss would be necessary in morbidly obese patients (BMI over 40) to achieve:

    • Reduction in operative time
    • Decreased length of stay
    • Fewer discharges to a nursing facility
    • Improvements in physical function

    They retrospectively reviewed prospectively collected data from 2011 to 2016 at a single tertiary care hospital, identifying 203 patients who were morbidly obese at least 90 days prior to surgery. Before undergoing TKA.:

    • 41% of patients lost at least 5 pounds
    • 29% lost at least 10 pounds
    • 14% lost at least 20 pounds

    After the weight loss, 27 patients were no longer considered morbidly obese, although 23 were still considered severely obese (BMI of 35 to 40).

    Patients with morbid obesity who lost 20 pounds before TKA had lower odds of being discharged to a nursing facility, lower odds of an extended length of stay of at least 4 days, and an absolute shorter length of stay compared to patients who did not lose 20 pounds. The researchers found no differences in operative time or physical function improvement. Benefits were seen even in patients who remained morbidly or severely obese.

    “While we don’t have a full understanding of the minimal weight loss necessary to improve outcome from a physiologic standpoint, our study supports even small increments of weight loss in patients undergoing knee replacement,” said senior author David S. Jevsevar, MD, MBA, chair of orthopaedics at Dartmouth-Hitchcock Medical Center and the Geisel School of Medicine. “Our work may also reflect weight loss as being a surrogate for patient activation and engagement, which have been shown to have significant impact on outcomes in this patient population.”

    “Because length of stay and facility discharge are primary drivers of cost, quality of life, and satisfaction, [the study findings have] immense implications,” Dr. Keeney said. “If you lose at least 20 pounds before surgery, your outcomes are going to be much better, even if you are still a physically large patient at the time of surgery.

    “This is a concrete goal instead of telling patients we won’t operate on you unless you get below a BMI of 40, which for some patients, can be 50 or 100 pounds.”


    Keeney B, Austin D, Jevsevar DS. How Much Preoperative Weight Do Morbidly Obese Patients Undergoing Total Knee Arthroplasty Need to Lose to Meaningfully Improve Outcomes? (Poster P0090) Presented at the 2019 Annual Meeting of the American Academy of Orthopaedic Surgeons, March 12-16, Las Vegas, Nevada.


    1. Centers for Disease Control and Prevention. Adult Obesity Facts. Available at https://www.cdc.gov/obesity/data/adult.html. Accessed March 12, 2019. 
    2. Workgroup of the American Association of Hip and Knee Surgeons Evidence Based Committee. Obesity and total joint arthroplasty: a literature based review. J Arthroplasty. 2013 May;28(5):714-21. doi: 10.1016/j.arth.2013.02.011. Epub 2013 Mar 19.
    3. Ast MP, Abdel MP, Lee YY, Lyman S, Ruel AV, Westrich GH. Weight changes after total hip or knee arthroplasty: prevalence, predictors, and effects on outcomes. J Bone Joint Surg Am. 2015 Jun 3;97(11):911-9. doi: 10.2106/JBJS.N.00232.