Do Markers of Inflammation and/or Muscle Regeneration in Lumbar Multifidus Muscle and Fat Differ between Individuals with Good or Poor Outcome Following Microdiscectomy for Lumbar Disc Herniation?

STUDY DESIGN Observational study. OBJECTIVE To evaluate whether inflammatory and/or muscle regeneration markers in paraspinal tissues (multifidus muscle/fat) during microdiscectomy surgery in patients with lumbar disc herniation (LDH) with radiculopathy, differ between individuals with good or poor outcome. SUMMARY OF BACKGROUND DATA Structural back muscle changes, including fat infiltration, muscle atrophy and fiber changes, are ubiquitous with LBP and are thought to be regulated by inflammatory and regeneration processes. Muscle changes might be relevant for recovery after microdiscectomy, but a link between expression of inflammatory and muscle regeneration genes in paraspinal tissues and clinical outcome has not been tested. METHODS Paraspinal tissues from deep multifidus muscles and fat (intramuscular, sub-cutaneous, epidural) were harvested from twenty-one patients with LDH undergoing microdiscectomy surgery. Quantitative polymerase chain reaction (qPCR) measured expression of 10 genes. Outcome was defined as good (VAS LBP+) or poor (VAS LBP-) by an improvement of >33% or ≤33% on the pain visual analogue scale (VAS), respectively. Good functional improvement was defined as 25% improvement on the physical functioning scale (PFS). RESULTS Brain-derived neurotrophic factor expression in deep multifidus was 91% lower (P = 0.014) in the VAS LBP- than VAS LBP+ group. Expression of interleukin-1β in sub-cutaneous fat was 48% higher (P = 0.026) in the VAS LBP- than VAS LBP+ group. No markers differed based on PFS. CONCLUSION Results show a relationship between impaired muscle regeneration profile in multifidus muscle and poor outcome following microdiscectomy for LDH. Inflammatory dysregulation in sub-cutaneous fat overlying the back region might predict poor surgical outcome. LEVEL OF EVIDENCE 4.