Can fat infiltration in the multifidus muscle be a predictor of postoperative symptoms and complications in patients undergoing lumbar fusion for degenerative lumbar spinal stenosis? A case–control study

PURPOSE: This study aimed to explore whether 25% as the cutoff value of fat infiltration (FI) in multifidus (MF) could be a predictor of clinical outcomes of lumbar spinal stenosis (LSS) patients. METHODS: A total of 461 patients undergoing posterior lumbar interbody fusion for LSS with 1-year follow-up were identified. After sex- and age-match, 160 pairs of patients were divided into a FI < 25% group and a FI ≥ 25% group according to FI of MF at L4 on preoperative magnetic resonance imaging. Patient-reported outcomes including the visual analog scale scores (VAS) for back pain and leg pain and the Oswestry disability index (ODI) scores were evaluated. Bone nonunion and screw loosening were evaluated by dynamic X-ray. RESULTS: After matching, there was no significant difference in age, sex, body mass index, fusion to S1, number of fusion levels, osteoporosis, spondylolisthesis, smoking and diabetes. FI ≥ 25% group had significantly higher VAS for back pain, VAS for leg pain and ODI than FI < 25% group at 1-year follow-up. However, there was no significant difference in the change of them from baseline to 1-year follow-up between the two groups. In light of complications, FI ≥ 25% group had a significantly higher rate of bone nonunion than FI < 25% group, whereas there was no significant difference of screw loosening rates between the two groups. CONCLUSION: MF FI might be a pragmatic cutoff value to predict bone nonunion in LSS patients, but it has little predictive value on screw loosening and postoperative improvement of symptoms. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s13018-022-03186-2.