Gravar-mail: Answer to the Letter to the Editor of Feng Li et al. entitled “Minimally invasive versus open transforaminal lumbar interbody fusion: a meta-analysis based on the current evidence” by Nai-Feng Tian, Yao-Sen Wu, Xiao-Lei Zhang, Hua-Zi Xu, Yong-Long Chi, Fang-Min Mao (2013). Eur Spine J, doi:10.1007/s00586-013-2747-z