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Objectives and questions: Patients with spinal disability often have increased fat infiltration (FI) in the paraspinal muscles (PM), which indicates decreased muscle strength. This atrophy can lead to segmental instability and uneven load distribution. The multifidus (MF) is particularly vulnerable to atrophy due to its role as a segmental stabilizer and proximity to degenerative spinal changes. Although the erector spinae (ES) is an important static and dynamic stabilizer of the spine and possibly key in the maintenance of global alignment, ES degeneration is less studied and generally less prone to atrophy than MF. This study investigates risk factors for increased FI specifically in the ES in patients undergoing elective lumbar surgery.

Materialand methods: This is a secondary analysis of a prospective study. T-tests, Wilcoxon tests, and Fisher’s exact tests were utilized, contingent on the distribution of the data, to examine potential risk factors for increased FI (>40%). A multivariate logistic regression analysis was conducted to investigate the relationship between increased ES FI and the significant variables identified in the t-tests and Fisher’s test, while adjusting for covariates.

Results: 381 patients (47% female, median age of 63 [55–71]) were included in this study. 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 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), and chronic heart failure (p=0.028) were detected as well. MF FI was significantly higher in patients with ES FI >40% (p<0.001). Multivariate logistic regression analysis revealed that a higher combined Pfirrmann score (OR 1.2, 95% CI 1.04–1.26, p=0.004) and a higher combined vacuum severity score (OR 1.3, 95% CI 1.07-1.28, p<0.001) were significantly associated with ES FI >40%, along with degenerative lumbar scoliosis (OR 1.9, 95% CI 0.71–1.90, p=0.038) increasing the risk after adjusting for covariates.

Discussion und conclusion: Advanced disc degeneration, as indicated by elevated Pfirrmann and vacuum severity scores are significant risk factors for increased ES FI. These findings highlight the necessity for comprehensive evaluations of both spinal and muscular health in patients with degenerative spine conditions and the importance of separately assessing PMs, including the ES in addition to the MF. Addressing these factors could enhance patient outcomes and advance clinical practices in the management of spinal disorders.