Question: how many mm is grade 1 spondylolisthesis?
Answer: Spondylolisthesis was diagnosed in 120 patients. The mean range of the slip in the midline sagittal image was 9 mm, with a range of 3–17 mm of slip (Meyerding Grade I–IV). The distribution of the patients according to the Meyerding classification is shown in Table 1.