Does the obesity paradox apply to early postoperative complications after hip surgery? A retrospective chart review

Background There is evidence that very obese patients (body mass index [BMI] > 40 kg/m²) undergoing hip replacement have longer average hospital stays, as well as higher rates of complications and readmission compared with patients with normal BMI. However, there are sparse data describing how overweight and obese patients fare in the period immediately after hip replacement surgery compared with patients with low or normal BMI. In this study, we sought to explore the association of BMI with the rate of early postoperative complications in patients undergoing total hip arthroplasty. Methods A proprietary hospital software program, Clinical Looking Glass was used to query the Montefiore Medical Center database and create a list of patients with International Classification of Diseases, Ninth Revision code 81.51 (hip replacement) from the period of January 1, 2010, through December 31, 2012. The medical records of patients with length of stay 5 or more days were reviewed to evaluate the reason for the extended stay. The primary outcome studied was the association between BMI and occurrence of early complications in patients who had undergone total hip replacement surgery. Logistic regression was used to calculate adjusted odds ratio (OR) and 95% confidence interval (CI) for the association of BMI and early postoperative complications. Results Of the 802 patients undergoing hip replacement surgery within our time frame, 142 patient medical records were reviewed due to their length of stay of ≥ 5 days. Overall complication rate in the analyzed patients demonstrated a J-curve distribution pattern, with the highest morbidity being 23.5% in the underweight group, the second highest in the normal-weight group (17.3%), and decreasing to nadir in the overweight (8.0%) and obese class I (10.0%) and then higher again in classes II (14.3%) and III (16.7%). Adjusted ORs demonstrated the same J distribution pattern similar to the pattern observed in the univariate analysis. Of the variables studied, Charlson score (OR, 1.1; 95% CI, 1.1-1.2; P =.03), diagnosis of hip fracture (OR, 5.2; 95% CI, 2.8-9.8; P =.01), normal weight (OR, 1.9; 95% CI, 1.1-3.8; P =.04), and obese class III (OR, 2.5; 95% CI, 1.1-6.3; P =.04) were the factors associated with the highest odds of early complications after hip replacement surgery. Conclusions In this retrospective review of hip replacement surgery patients, BMI classification was a predictor of early postoperative complications. Although the exact underlying mechanisms are still not clear, these results are consistent with the obesity paradox, in which obesity or its correlates provide some form of protection.