Relationship between fatty infiltration of paraspinal muscles and clinical outcome after lumbar discectomy

INTRODUCTION: Cross sectional area (CSA) and fat infiltration (FI) are important parameters to assess paravertebral muscle atrophy. However, the relationship of muscular fat infiltration in patients with symptomatic lumbar disc herniation undergoing surgery remains unclear. RESEARCH QUESTION: Does lumbar paravertebral muscle atrophy have prognostic value regarding the clinical outcome for patients with symptomatic lumbar disc herniation undergoing surgery? METHODS: Patients over 18 years of age with lumbar disc herniation and radicular pain who underwent single-level discectomy were included. Multifidus, erector spinae and psoas cross-sectional area (CSA) and fatty infiltration (FI) were measured by ImageJ software at the levels of L3-L4, L4-L5 and L5-S1 from T2-weighted Magnetic Resonance axial images. Clinical status was assessed preoperatively and one-year after surgery with patient reported outcome measurements (PROMS), that included Numeric Rating Score for back and leg pain, Core Outcome Measurement Index (COMI), Oswestry Disability Index and EuroQoL-5D. Univariate and multiple linear regressions were performed. RESULTS: Erector spinae FI was the only muscle-related factor that correlated to postoperative PROMS. Postoperative COMI was higher in patients with FI>30% (median: 4.4, IQR: 3.2) and lower when FI<15% (median: 1.2, IQR: 1.6) (Kruskal-Wallis, p ​< ​0.001). Male gender was associated with better outcome as well as erector spinae FI<15%, while FI >30% was related to worse postoperative status. CONCLUSIONS: In the current study, increased fat infiltration of erector spinae muscles correlated to less favorable clinical outcomes following lumbar discectomies.