Common modifiable risk factors in total joint arthroplasty: a 2021 update—obesity

In a 2019 clinical practice guideline published by the American Academy of Orthopaedic Surgeons, it was stated that, among all risk factors evaluated, only obesity could be deemed as having reached the level of moderate strength evidence as a risk factor for periprosthetic joint infection (PJI) [1]. In the guideline, all three moderate-quality studies used body mass index (BMI) as a global measure of obesity, and all three determined that a statistically significant increase in adverse outcomes was associated with a BMI greater than 35 kg/m2. Is BMI the best indicator of obesity and surgical difficulty? Are there other ways to determine if an obese patient is suitable for an arthroplasty? What does the proper management of obese patients look like? Michael A Mont, MD, Orthopaedic Surgeon, Rubin Institute for Advanced Orthopedics, introduces the evidence on this topic and shares his experience with us.


Michael A Mont

Rubin Institute for Advanced Orthopedics
Baltimore, United States

High BMI: a cause for delaying or denying obese patients of arthroplasty?

As patients who have BMIs ≥ 40–50 kg/m2 (ie, morbidly obese and super obese patients) are increasingly among the arthroplasty patients, more evidence is now available that these patients are at risk for increased complications and worse outcomes [2–6]. Various reasons have been theorized for the cause for unfavorable outcomes in obese patients, and these include underdosing of preoperative antibiotics, thicker subcutaneous adipose tissue at the surgical site (leading to poor perfusion and lower oxygen tension in tissues, technical difficulties during surgery, as well as longer surgical times), and more frequent nasal Staphyloccocus aureus colonization [2, 7].

The exact BMI cutoff that marks a significant rise of worse outcome after TJA is still controversial [2, 8, 9]. While the balance of benefits and risks in delaying or denying patients with BMIs is still being debated, institutional (or individual) restrictions have already been applied to some obese patients in their access to TJA. In fact, other weight risk factors, such as patients who have BMI lower than 18 kg/m2 may sometimes be at a greater risk of negative outcomes due to malnutrition and low albumin [7, 10–12].


Evolving BMI thresholds of increased adverse outcomes after total joint arthroplasty

Before 2011, comparisons of BMI above and below 30 kg/m2 were frequently made in studying these relationships and the occurrence of infection after TJA [13–15]. Since then, much effort has been made in finding a BMI value that can serve as a clear threshold above which a significant increase of negative outcomes, whether it be PJI, readmission, reoperation, or a long list of other complications, can be expected. A few examples from recent publications are given below:

  • For the purpose of prophylactic antibiotic dosing for patients undergoing TJA, Lübbeke et al [2] conducted a study in a prospective, hospital-based cohort (9,061 patients) of primary TJA patients to investigate the influence of obesity on the incidence of PJI. Dividing the patients into five BMI categories according to the World Health Organization (WHO) definition, the adjusted incidence rate ratio (IRR) of PJI was calculated using patients who had normal BMI as the reference for the four other BMI categories. As can be seen in Table 1 below, while the IRR of PJI in the overweight and Class I obese patients remained similar to the patients who had normal BMI, it was clearly higher in Class II and III obese patients. 
    Lübekke et al [2] concluded that after primary TJA, patients who had a BMI of ≥ 35 had more than double the rate of PJI than patients who had a BMI < 35.


Abbreviations: BMI, body mass index; IRR, incidence rate ratio; CI, confidence interval.
* Cox regression analyses performed with adjustments for covariates such as age, sex, smoking status, diabetes, and use of antibiotic-laden cement.

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  • Do obese patients benefit from arthroplasties as much as patients who have normal BMI?
  • Central versus peripheral obesity
  • A patient-centered approach: allowing and motivating patients to invest in their own medical future
  • Conclusion

Part 1 | Diabetes

Part 3 | Smoking

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Contributing experts

This series of articles was created with the support of the following specialists (in alphabetical order):

Matthew P Abdel

Mayo Clinic
Rochester, United States

Steven MacDonald

University of Western Ontario
London, Canada

Michael A Mont

Rubin Institute for Advanced Orthopedics
Baltimore, United States

This article was compiled by Maio Chen, Senior Project Manager Medical Writing, AO Foundation, Switzerland.


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