The Degeneration of Paraspinal Muscles and Its Correlation with the Postoperative Clinical Outcomes Following Minimally Invasive Transforaminal Lumbar Interbody Fusion (MIS-TLIF).

Objective: This study aims to analyze the degeneration of paraspinal muscles after minimally invasive transforaminal lumbar interbody fusion (MIS-TLIF) surgery and its correlation with clinical outcome.

Methods: Retrospective analysis was conducted on data from patients who underwent single-segment MIS-TLIF surgery in our hospital. MRI examinations were performed before the operation, at 6 months, and at 12 months after the operation to evaluate changes in volume and steatosis of the psoas major muscle and lumbar posterior muscles. VAS scores and ODI were filled out at 12 months after the operation, and correlations between psoas volume, posterior muscle volume, steatosis rate, and clinical outcome were analyzed.

Results: After surgery, both the psoas major muscle and dorsal muscles of fused segments showed atrophy. The steatosis in the fusion segment improved significantly at 12 months compared to 6 months after surgery (29.7±8.2 vs 20.6±6.1, P<0.05), while there was no improvement in adjacent segment muscle steatosis during the follow-up period. VAS score was strongly negatively correlated with lumbar posterior muscle of fused segments (r=-0.819, P < 0.001), strongly positively correlated with steatosis of fused segments (r=0.868, P < 0.001), and moderately negatively correlated with psoas major muscle of fused segments (r=-0.435). ODI index was moderately negatively correlated with lumbar posterior muscles (r=-0.-512, P=0-004) as well as psoas major muscles (r=-0402, P<005). ODI index also had a moderate negative correlation with adjacent dorsal muscles (r=-0478, P=002).

Conclusion: Continuous atrophy was observed in both psoas major muscle and lumbar posterior muscles of fused segments as well as adjacent segments. However, by the end of the 12-month period after the operation, an improvement in fatty degeneration was noted specifically in the lumbar posterior muscles of the fused segment. The volume and steatosis rate of lumbar posterior muscles were found to have a significant correlation with clinical outcome.