Associated Factors for Increased Fat Infiltration in the Erector Spinae in Patients Undergoing Lumbar Surgery for Degenerative Conditions

Background. Spinal disability often involves fat infiltration (FI) in paraspinal muscles (PM), indicating decreased muscle strength and potentially causing segmental instability. While the multifidus (MF) is well-studied and prone to atrophy, the erector spinae (ES) is less understood. This study investigates associated factors for ES fat infiltration in patients undergoing elective lumbar surgery. Methods. This single-center, secondary analysis of a prospective study analyzed patients undergoing lumbar surgery from 2014 to 2023. FI in the MF and ES was measured using T2-weighted MRI. Patients were divided into groups with ES fat infiltration >40% or <40%. Statistical analyses, including t-tests, Wilcoxon tests, and Fisher’s exact tests, were used to examine potential risk factors. Significant variables were further analyzed using multivariable logistic regression. Results. 381 patients (47% female, median age of 63[55-71] years) were included. Patients with increased FI in the ES were primarily female (51%), older ( P <0.001), and had a higher BMI ( P =0.003). They also showed significantly more cases of degenerative scoliosis ( P <0.001), higher combined Pfirrmann scores ( P <0.001), and higher vacuum severity scores ( P <0.001). Significantly higher rates of foraminal stenosis ( P =0.001), facet degeneration ( P =0.002), diabetes mellitus ( P =0.049), hypertension ( P <0.001), chronic heart failure ( P =0.028), and abdominal aortic calcification ( P <0.001) were detected as well. Multivariate logistic regression analysis revealed that a higher combined Pfirrmann score (OR1.2, 95% CI 1.04-1.26, P =0.004), a higher combined vacuum severity score (OR1.3, 95% CI 1.07-1.28, P <0.001), and lumbar scoliosis (OR1.9, 95% CI 0.71-1.90, P =0.038) were significantly associated with ES FI >40%. Conclusion. The study revealed high Pfirrmann- and vacuum severity scores, and degenerative scoliosis as significant factors for increased fat infiltration in the erector spinae. This highlights the importance of comprehensive spinal and muscular health assessments in patients with degenerative spine conditions to potentially improve outcomes.