Multiple randomized controlled trials and systematic review have been done to assess the efficacy of manual therapy. In a meta-analysis by Assendelft et al, spinal manipulation was found to be more effective than placebo for acute and chronic LBP.Santilli et al also found that active manipulation had more effect than simulated manipulation on pain relief of acute back pain and sciatica with disc protrusion. However, in a recent review article, the authors concluded that definitive values on safety and effectiveness of spinal manipulation cannot be made, but they admit that many patients with LDH did undergo manipulative treatment, and spinal manipulation may be effective in the treatment of symptomatic LDH.