What’s worse, obesity or malnutrition in patients undergoing multi-level posterior lumbar instrumentation?

Background: Obesity and malnutrition are both associated with worse outcomes after spine surgery, but their relative risks remain unclear. This study compared postoperative complications and reoperation rates after multilevel posterior lumbar instrumentation in malnourished and obese patients. Methods: Adult patients undergoing multi-level posterior lumbar instrumentation for lumbar spinal stenosis or spondylolisthesis were identified in the TriNetX Research Network. Malnutrition was defined as serum albumin <3.5 g/dL and body mass index (BMI) <30 kg/m 2 . Obesity was defined as BMI of 30 kg/m 2 or greater and serum albumin of 3.5 g/dL or greater. Morbid obesity was defined as BMI of 40 kg/m 2 or greater with normal albumin. Propensity score matching adjusted for age, sex, race, and comorbidities. Outcomes within 90 days included surgical site infection (SSI), wound dehiscence (WD), and reoperation. Results: In our study, we evaluated 646 malnourished patients who were matched to 646 morbidly obese patients. Malnourished patients had higher odds of SSI or WD than obese/morbidly obese patients, although these differences were not statistically significant. However, malnourished patients had significantly higher odds of reoperation within 90 days than both groups. Conclusion: Malnutrition was associated with similar wound complication rates but higher reoperation risk than obesity and morbid obesity after multi-level posterior lumbar instrumentation. Poor nutritional status appeared to be a stronger predictor of adverse postoperative outcomes than elevated BMI alone.