Beyond Body Mass Index: A Systematic Review and Meta-Analysis of Adiposity Measures Versus Body Mass Index in Predicting Infection Risk Following Elective Spinal Surgery

Postoperative infections are among the most frequent complications following elective spinal surgery, often leading to reoperations, prolonged hospitalisation, and increased healthcare burden. Body mass index (BMI), although widely used to assess obesity-related surgical risk, lacks anatomical specificity and fails to capture regional fat distribution relevant to wound healing and operative exposure. This systematic review adhered to Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines and evaluated observational studies comparing BMI with site-specific adiposity metrics in predicting surgical site infections (SSI) following elective spinal fusion procedures. Searches were conducted across five databases using predefined terms related to spinal surgery, adiposity, BMI, and infection outcomes. Inclusion criteria targeted studies reporting postoperative SSI alongside a comparative analysis of BMI and regional fat measures. Data extracted included sample size, adiposity definitions, infection outcomes, and statistical effect sizes. A subgroup meta-analysis was performed using a random-effects model to pool odds ratios (ORs) from studies evaluating subcutaneous fat thickness. Seven studies met the eligibility criteria. Across all studies, localised adiposity measures showed stronger associations with postoperative SSI than BMI. In a subgroup meta-analysis of three studies reporting subcutaneous fat thickness, the pooled OR was 1.09 (95% CI: 1.01-1.17; p=0.0193), indicating a statistically significant increased odds of infection among patients with greater regional fat burden. Significant statistical heterogeneity was observed (I²=84%). Site-specific adiposity metrics, particularly subcutaneous fat thickness, are more reliable predictors of postoperative infection than BMI in spinal surgery populations. Their integration into preoperative risk assessment tools could enhance surgical planning and infection prevention. Future research should focus on standardising adiposity measurement protocols and validating threshold values across diverse spinal procedures.