This 32 year-old man sustained crush injury and resultant in paraplegia. Lumbar MRI was taken and revealed fracture and dislocation between L2 and L3 vertebrae bodies. On the day of the injury, he underwent a surgical intervention of posterolateral fixation and bone graft from L1 to L4 vertebrae. He was transferred to Rehabilitation Medicine Department of Asan Medical Center where patient was subsequently found to have an unexpected neurologic finding of decreased sensation below T5 dermatome on right and below T6 on left. Accordingly we took a thoracic MRI which showed features consistent with arachnoiditis at thoracic and lumbar cord segment. A dermatomal somatosensory evoked potential study was performed with finding of abnormal somatosensory pathway below mid thoracic dermatome. We reported an unusual case of thoracic arachnoiditis occurred after the surgical fixation of the lumbar vertebral fracture and dislocation.