Prospective randomized double-blinded diagnostic accuracy study about radiological grading of fusion after minimally invasive lumbar interbody fusion procedures (MI-LIFP).To determinate the intra and the inter-observer correlation between different radiological lumbar interbody fusion grading scales (RLIFGS) in patients undergoing MI-LIFP and their correlation to clinical outcome.Besides technological improvements in medical diagnosis and the many existing RLIFGS, surgical exploration continues to be the gold-standard to assess fusion in patients with radiological pseudarthrosis, with little if any research on the relationship between RLIFGS and clinical outcome.We collected data from patients undergoing MI-LIFP procedures operated by a single surgeon from 2009 to 2017, which had follow-up and CT-scan control greater than 12 months, whose clinical registers specified lumbar and radicular visual analogue scale (L and R-VAS) and Oswestry Disability Index (ODI) score preoperatively and at the end of follow-up. Interbody fusion levels were coded for blinded evaluation by three different minimally invasive spine (MIS) surgeons, using Lenke, Bridwell, BSF (Brantigan, Steffe, Fraser), and CT-HU RLIFGS. We established fusion criteria, as described in their original papers. Another independent spine surgeon blindly evaluated successful clinical outcome (SCO), defined as a significant improvement in 2 of 3 of the following issues: L-VAS, R-VAS, or ODI score at follow-up; otherwise, rated as clinical pseudarthrosis. Radiological and clinical data was coded and statistically analyzed using Student T-Test, Pearson P-Test, and ANOVA with statistical package for the social sciences 21 by another blinded researcher, positive and negative predictive values were also calculated for each RLFGS.We found a significant clinical improvement with a moderate intra-observer correlation between scales and no inter-observer or clinical correlation, with no sub-group statistically significant differences.This paper represents the first study about the diagnostic accuracy of RLFGS, we concluded that their diagnostic accuracy is pretty low to determine fusion or pseudoarthrosis based on its low correlation to clinical outcome, we recommend surgeons rely on clinical findings to decide whether a patient has clinical fusion or pseudoarthrosis based on successful clinical outcome.