Early revision rate after posterior spinal fusion surgery increases with every additional BMI point.

Purpose: Revision surgery has a profound impact on patient outcomes and is a crucial consideration in the assessment of healthcare burden following spine surgery. In this context, obesity is a significant factor influencing the rate of revision surgery. To elucidate the impact of obesity on the risk of early revision surgery after posterior fusion of the thoracic and lumbar spine, we conducted a prospective single-institution cohort study.

Methods: Over a 24-month period a total of 227 consecutive patients who underwent posterior thoracolumbar spinal fusion surgery involving up to four segments were included in the analysis. The objective was to identify factors associated with early revision surgery occurring within three months. The impact of demographic data, comorbidities, intraoperative variables, and follow-up data on the incidence of revision surgery were evaluated through univariate and multivariate statistical analysis. The revision rate was examined according to body mass index (BMI) subcategories. Receiver operating characteristic (ROC) curves were generated using the variables BMI and revision surgery, as well as their respective subcategories (hematoma, infection, implant dislocation, and dural tear).

Results: Univariate analysis demonstrated that obesity (25.3% BMI ≥ 30 vs. 10.9% BMI < 30, p = 0.005), ASA-grade (12.4% ASA grade 1 and 2 vs. 24.4% ASA grade ≥ 3, p = 0.019), and increased intraoperative blood loss (474.1 ml ± 275.3 ml vs. 587.2 ml ± 310.5 ml, p = 0.026) were statistically significant factors associated with increased revision rates. However, logistic binary regression analysis revealed that increasing BMI was the only significant independent variable (OR 1.10; 95% CI 1.02-1.19; p = 0.01). The total revision rate was 17.2% and increased significantly from 5.7% in patients with normal weight to 31.0% in extremely obese patients (BMI ≥ 35 kg/m) (OR 0.13; 95% CI 0.035-0.51; p = 0.0017). This increase was observed with each additional BMI point. The results of the ROC analysis indicate that the test result variable BMI has an area under the curve of 0.70 (p = 0.00013) for the total revision rate. According to the Youden Index, a cut off value of 28.2 kg/m was identified, while the "closest top left" method yielded a value of 29.5 kg/m. The number of treated levels did not differ significantly between obese patients (2.00 ± 0.98) and non-obese patients (2.09 ± 1.00) (p = 0.50).

Conclusion: Obesity is associated with an increased likelihood of requiring early revision surgery following posterior thoracolumbar spinal fusion procedures. The risk increases with each BMI point with the cutoff being around 29 kg/m. Patients with extreme obesity exhibit an exceedingly elevated rate of revision surgery. These results can help surgeons better assess the risk of revisions and counsel their patients accordingly.