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Body mass index found to not be a factor in knee arthroplasty postoperative pain
The new findings contradict earlier assumptions that BMI is directly associated with poor results.
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Though previous reports have labeled high body mass index as being a factor in developing postoperative knee pain, research shows that these associations may be erroneous.
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The new findings were presented by Jasvinder A. Singh, MD, MPH, at the American Academy of Orthopaedic Surgeons 76th Annual Meeting. Singh’s study focused on the association between a high preoperative body mass index (BMI) and the prevalence of moderate to severe knee pain in the short to intermediate postoperative follow-up of total knee arthroplasty (TKA) patients.
“Our objective was to examine whether preoperative BMI is a significant independent predictor of more pain at both 2 and 5 years after primary TKA and 2 and 5 years after revision TKA,” he said.
Primary and revision
Singh and his team identified a cohort of patients who underwent either primary or revision TKA from 1993 to 2005 and responded to follow-up questionnaires at the 2- and 5-year postoperative periods. Multivariable logistic regression compared the odds of moderate to severe knee pain by BMI category, adjusting for age, gender, diagnosis, comorbidity, implant fixation (for primary TKA), distance from the medical center of choice and American Society of Anesthesiologists (ASA) score.
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The survey involved 7,137 primary TKA patients at the 2-year postoperative point and 4,211 at 5-years, as well as 1,532 revision TKA patients at the 2-year postoperative point and 875 at 5-year follow-up.
Analysis
Multivariable-adjusted odds ratios of moderate to severe knee pain by BMI (in kg/m2) in primary TKA at 2 years and 5 years were: 25-29.9 – 1.02 and 1.28; 30-39.9 – 1.00 and 1.18; and 40 or greater – 1.26 and 1.19. None of the odds ratios were significant, Singh told Orthopedics Today.
Similarly, the odds ratios of moderate to severe knee pain in revision TKA patients at 2 years and 5 years were: 25-29.9 – 1.00 and 1.45; 30-39.9 – 1.17 and 1.18; and 40 or greater– 1.22 and 1.19. Again, none of these reached statistical significance, he said.
BMI was not associated with moderate to severe pain at 2 or 5 years post-primary TKA or post-revision TKA, he reported.
“There is no significant difference in BMI categories with regards to the risk of moderate to severe pain,” Singh said.
Singh cited several strengths of the study, including a large sample size enabling greater accuracy. Though there is more work to be done on the subject, Singh feels the evidence presented should allow physicians and their patients to focus on the more important aspects of preparation for – and recovery from – a TKA procedure.
“High BMI did not alter the risk of moderate to severe pain, and this should reassure both patients and surgeons that BMI does not impact pain outcomes post-TKA,” he said.
For more information:
- Jasvinder A. Singh, MD, MPH, is an assistant professor of medicine at the University of Minnesota. He can be reached at Rheumatology/111R VA Medical Center, One Veterans Drive, Minneapolis, MN 55417; 612-7467-4195; e-mail: Jasvinder.md@gmail.com. He has no direct financial interest in any products or companies mentioned in this article.
Reference:
- Singh, JA, Gabriel SE, Lewallen D. Pain relief following TKA is not affected by the body mass index (BMI). Paper #153. Presented at the American Academy of Orthopaedic Surgeons 76th Annual Meeting. Feb. 25-28, 2009. Las Vegas.