Variations in morphology of the lumbosacral junction on sagittal MRI: correlation with plain radiography

Objective. To identify on sagittal magnetic resonance imaging (MRI) scans of the lumbar spine the features that indicate the presence of a lumbosacral transitional vertebra (LSTV). Design. One hundred consecutive sagittal T1- and T2-weighted MRI scans of the lumbar spine were reviewed and separated into four types depending upon the absence or presence of disc material between what was considered to be the uppermost sacral segment and the remainder of the sacrum, as follows: type 1: no disc material present; type 2: a small residual disc, not extending for the whole anteroposterior (AP) diameter of the sacrum; type 3: a well-formed disc extending for the whole AP diameter of the sacrum; type 4: a well-formed disc extending for the whole AP diameter of the sacrum with, in addition, an abnormal upper sagittal sacral outline. The corresponding plain radiographs of each patient were then reviewed and assessed for the presence of an LSTV. These were classified according to the method of Castellvi et al. Patients. All patients had been referred for MRI of the lumbar spine, usually because of back pain with or without radiculopathy. There were 51 male and 49 female patients with a mean age of 42 years and an age range of 18–85 years. Results and conclusions. With regard to sacral morphology on MRI, 30 patients had type 1, 42 patients type 2, 16 patients type 3 and 12 patients type 4 morphology. Fifteen patients had an LSTV. There was a good correlation between the presence of a fused LSTV and a type 4 MRI appearance, indicating that this type of LSTV can be identified on sagittal MRI scans.