“…In our quality assessment for spine surgery the 44% [ 15 , 23 , 27 , 29 , 32 – 38 , 40 – 42 , 46 – 49 , 51 , 55 , 56 , 61 , 67 , 68 , 70 ] of the studies were rated strong, 25% [ 17 , 18 , 21 , 22 , 25 , 28 , 31 , 39 , 43 , 44 , 60 , 62 , 63 , 65 ] were rated moderate, and 32% [ 16 , 19 , 20 , 24 , 26 , 30 , 45 , 50 , 52 – 54 , 57 – 59 , 64 , 66 , 69 , 71 ] were rated weak. Methodological weaknesses that led to moderate or weak quality scores often included the lack of a sample size justification, power description, or variance and effect estimates, the lack of subjects selected or recruited from the same population, the lack of results evaluation more than once over in time, the lack of blinded assessor and the lack of measurement of potential confounding variables.…”