Sagittal shortening of the spondylolytic vertebra is common and may mimic spondylolisthesis. In order to define and measure spondylolisthesis the shortening of the spondylolytic vertebra has to be taken into account.

All 3 described forms of instability are common in spondylolysis or isthmic spondylolisthesis and associated with radicular pain. This finding stresses the value of positional MRI in the evaluation of patients with spondylolysis and isthmic spondylolisthesis, especially if radicular symptoms are present.

The position dependent changes in cerebral venous outflow can be imaged using positional MRI. The vertebral venous plexuses may mimic pathologies and physicians reading positional MRI images of the cervical spine should be aware of the physiological changes occurring in the erect position.

The detection rate of JFC improves with increasing lordosis of the spine and under weight-bearing conditions, particularly when standing. Unstable slipping or increased angular movement affects the size of JFC.