Introduction: Spinal fusion effectively improves pain and function for degenerative disease of the lumbar spine. However, some patients necessitate revision decompression or fusion procedures in their further course for complications such as adjacent segment disease (ASD), or same segment disease (SSD; i.e. recurring stenosis, pseudarthrosis, hardware loosening). While certain patient factors and alignment parameters are known to correlate with revision surgery and unfavorable outcomes, biomarkers on advanced imaging remain underexplored. This study aimed to investigate preoperative disc degeneration and paraspinal muscle morphology and their association with revision surgery after primary lumbar fusion.
Methods: This is a single center prospective cohort study on patients undergoing lumbar fusion. Patients were enrolled between 2014 and 2021, and were followed-up for a minimum of 2-years. Prior lumbar fusions and laminectomies were excluded. Demographics, surgical levels, spinopelvic alignment and the following preoperative MRI and CT parameters were assessed: functional cross-sectional area (fCSA) and percentage fatty infiltration (FI) of multifidus (MF), erector spinae (ES) and psoas (PS) muscles at upper level of L4; disc degeneration by Pfirrmann (grade 1-5); Modic changes (0-3); vacuum phenomenon (0-3). Means ± standard deviations and medians and interquartile ranges [IQR] for normally and non-normally distributed data were calculated, respectively. T-test and Mann-Whitney-U were used for statistical analysis, with significance set at p<0.05.
Results: 157 patients (51% female, age 62 [54-72] years) were enrolled, undergoing 1.6 ±0.8 level lumbar fusion with postoperative follow-up of 54 [44-84] months. Revision surgery for ASD (n=13) and SSD (n=3) was performed in 10% of cases (n=16) after 29 [19-41] months. Age, sex, BMI, fusion levels, follow-up time and spinopelvic alignment did not correlate with revision surgery. Disc degeneration in the operated, lower lumbar levels was significantly higher in patients necessitating further revision surgery with Pfirrmann grades of 4 [4-5] vs. 4 [3-4] at L4/5 (p=0.035), and 5 [4-5] vs. 4 [3-5] at L5/S1 (p=0.017). Similarly, vacuum phenomenon was not different at the adjacent discs, but was significantly higher at L5/S1 in the revision group, with grades of 1.5 [0.75-3] vs. 0 [0-2] (p=0.031). Modic changes and adjacent disc degeneration did not correlate with revision. fCSA was also not associated with revision surgery in any muscles, nor was FI in PS and ES muscles. In contrast, FI was significantly higher in MF in patients that required revision surgery 58±8% vs. patients that did not 51±15% (p=0.003).
Discussion: In this study, preoperative grade of degeneration in the operative levels and fatty infiltration in the multifidus positively correlated with revision surgery following primary lumbar fusion. These findings underline the importance of not only considering the health of operative and adjacent discs but also evaluating the surrounding muscular envelope for a successful outcome after lumbar fusion surgery. The functional status of the multifidus, acting as a segmental stabilizer, emerges as a crucial factor in maintaining a physiologic biomechanical environment and preventing accelerated degeneration of adjacent segments and failures within instrumented levels. Consequently, both disc degeneration and multifidus status should be integral considerations in patient counseling and decision-making before lumbar fusion.