Overview:
Honestly, how well does the BMI statistic capture clinically relevant information for obese patients?
Honestly, how well does the body mass index (BMI) statistic capture clinically relevant information for obese patients?
A group of researchers from the Miami Orthopaedic Research Foundation and the Larkin Hospital Department of Orthopedic Surgery, both in Miami, Florida, put that question to the acid test in a new study, “Body Mass Index is Not an Appropriate Proxy for the Condition of Peri-Incisional Adiposity in Primary Total Joint Arthroplasty Patients,” which appears in the February 25, 2025 edition of The Journal of Arthroplasty.
“I felt that it was extremely discriminatory that the American Academy of Orthopaedic Surgeons (AAOS) had published a blanket statement that patients with a BMI greater than 40 should not have a total hip or total knee arthroplasty,” stated co-author Arturo Corces, M.D. to OTW. “Patients who are overweight struggle with the weight and in my opinion, there is no place for strict cutoffs such as the AAOS has prescribed.”
“I had often seen in my practice patients who appear to be extremely overweight and yet had extremely thin lower extremities. Conversely there are patients who are technically not obese and have extremely thick thighs and knees.”
BMI Is Inconsistent
According to the study authors, who had found an inconsistent association between BMI and complications following total joint arthroplasty (TJA), “BMI is ubiquitously used as a proxy for obesity due to its simplicity of attainment and calculation. However, the utility of BMI to represent the state of adipose tissue is unclear. The quantity of skeletal muscle further complicates the binary application of BMI as a metric for access to care.”
Study Methodology
For this study, the team preoperatively evaluated 370 patients set to undergo total knee arthroplasty or total knee arthroplasty (n=271) and total hip arthroplasty (n=99). The mean age was 67 years, the mean BMI was 31.7, 59% were women, and 80% were Latin American.
For the 99 total hip arthroplasties (THA), mean age was 67 years and mean BMI 30.5. For the 271 TKAs, mean age was 69 years and mean BMI 32.8.
According to the authors, in THA patients, the Pearson’s correlation coefficient was r = 0.436, which indicates a moderate correlation between BMI and adiposity.
Using radiography, the TKA patients showed an r = 0.395 for femoral peri-incisional adiposity and r = 0.249 for tibial peri-incisional adiposity, which indicates a weak correlation between BMI and adiposity.
Using ultrasounds, the TKA patients showed an r = 0.560 for femoral peri-incisional adiposity and r = 0.544 for tibial peri-incisional adiposity, which indicates a moderate correlation between BMI and adiposity.
Dr. Corces told OTW, “Our most important result is the fact that we have not been able to show a direct correlation between BMI and peri-incisional adiposity. We believe that the high rate of infection and wound complications seen in overweight patients is more closely related to the adiposity that is overlying the extremity and through which the incision will be made than the BMI. We have several new papers that we are working on that show that with certain techniques improvement on infection rates etc. can occur.”
