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Weighing in on Body Mass Index and Infection After Total Joint Arthroplasty

Is There Evidence for a Body Mass Index Threshold?

Shohat, Noam, MD; Fleischman, Andrew, MD; Tarabichi, Majd, MD; Tan, Timothy L., MD; Parvizi, Javad, MD

Clinical Orthopaedics and Related Research®: October 2018 - Volume 476 - Issue 10 - p 1964–1969
doi: 10.1007/s11999.0000000000000141

Background Although morbid obesity is considered a modifiable risk factor for periprosthetic joint infection (PJI), there is no consensus regarding an appropriate threshold for body mass index (BMI) above which a high risk for infection may outweigh the benefits of surgery.

Questions/purposes (1) Is there a BMI cutoff threshold that is associated with increased risk for PJI? (2) Is the risk of PJI increased in higher obesity classes?

Methods A retrospective study was conducted of all primary THAs and TKAs performed at one institution between 2006 and 2015. Overall 19,226 patients were eligible to be included in the study; 1053 patients were excluded as a result of incomplete data, resulting in a final cohort of 18,173 patients (8757 TKAs and 9416 THAs). PJI was defined using the International Consensus Meeting criteria. To ensure accurate followup, and because there is evidence to support the association between obesity and early infection, we identified PJI within 90 days of the index surgery. This relationship was examined separately for BMI as a continuous variable and for each BMI category as defined by the Centers for Disease Control and Prevention (underweight ≤ 18.49 kg/m2; normal 18.5-24.9 kg/m2; overweight 25-29.9 kg/m2; obese class I 30-34.9 kg/m2; obese class II 35-39.9 kg/m2; obese class III ≥ 40 kg/m2). Analyses were performed with logistic regression, accounting for both patient and surgical risk factors. A BMI threshold was evaluated with a receiver operating characteristic (ROC) curve and the Youden index.

Results The area under the ROC curve for BMI and risk of PJI within 90 days was only 0.58 (confidence interval [CI], 0.52-0.63) suggesting such a cutoff was not much better than random chance. Among the BMI classes, patients with class III obesity (≥ 40 kg/m2) were the only ones showing a higher risk for PJI within 90 days (odds ratio [OR], 3.09 [1.46-6.54]; p = 0.003). The risk of developing PJI was not greater for overweight (OR, 0.72; 95% CI, 0.38-1.4), class I obese (OR, 1.06; 95% CI, 0.57-2.0), or class II obese (OR, 1.08; 95% CI, 0.52-2.2) patients. Underweight patients also demonstrated no increased risk for PJI (OR, 1.80; 95% CI, 0.23-13.9).

Conclusions The risk for infection increases gradually throughout the full range of BMI, but no threshold exists. Weight reduction before surgery may mitigate risk for infection for all patients with a BMI above normal. Of note, patients with a BMI > 40 kg/m2 carried a threefold higher risk for PJI and for these patients, the risks of surgery must be carefully weighed against its benefits.

Level of Evidence Level III, therapeutic study.

N. Shohat, A. Fleischman, M. Tarabichi, T. L. Tan, J. Parvizi, The Rothman Institute at Thomas Jefferson University, Philadelphia, PA, USA

N. Shohat, Sackler Faculty of Medicine, Tel Aviv University, Ramat Aviv, Israel

J. Parvizi, The Rothman Institute, 125 S 9th Street, Suite 1000, Philadelphia, PA 19107, USA, email:

Each author certifies that neither he, nor any member of his immediate family, has funding or commercial associations (consultancies, stock ownership, equity interest, patent/licensing arrangements, etc) that might pose a conflict of interest in connection with the submitted article.

All ICMJE Conflict of Interest Forms for authors and Clinical Orthopaedics and Related Research® editors and board members are on file with the publication and can be viewed on request.

Clinical Orthopaedics and Related Research® neither advocates nor endorses the use of any treatment, drug, or device. Readers are encouraged to always seek additional information, including FDA approval status, of any drug or device before clinical use.

Each author certifies that his institution approved the human protocol for this investigation and that all investigations were conducted in conformity with ethical principles of research.

This work was performed at The Rothman Institute at Thomas Jefferson University, Philadelphia, PA, USA.

Received August 01, 2016

Received in revised form April 01, 2017

Accepted November 13, 2017

© 2018 Lippincott Williams & Wilkins LWW
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