Since the vertebral body in a retrolisthesis moves in a posterior direction, the grading used for spondylolistheses is of little use. It is however useful to divide the anterior to posterior dimension of the intervertebral foramina (IVF) (4) into four equal units. A posterior displacement of up to ¼ of the IVF is graded as Grade 1, ¼ to ½ as Grade 2, ½ to ¾ as Grade 3, ¾ to total occlusion of the IVF as Grade 4. Alternatively, a measurement of the amount of displacement can also made by measuring the bone displacement in millimetres.