(7a) T1- and (7b) T2- weighted sagittal images of the lumbar spine in a 35 year-old male who presented with 4-5 months of bilateral lower extremity pain are provided. A defect of the pars interarticularis is seen (arrows) with cortical interruption and a resultant grade I spondylolisthesis. Reactive marrow changes are also present adjacent to the pars defect with increased signal within the marrow (arrowheads) on both the T1 and T2 weighted images.
To evaluate the sagittal diameter of the spinal canal, a ratio of the AP diameter at the L5 level to the AP diameter at the L1 level is used. The canal is measured from the posterior cortex of the vertebral body to the anterior aspect of the lamina on a mid-sagittal image. A ratio of 1.25 is normal. This ratio is increased in patients with spondylolysis due to posterior subluxation of the posterior elements, even in cases where no spondylolisthesis is present. Usually, the posterior subluxation of the posterior elements is evident on the mid-sagittal image with a resultant increase in the canal size at the level of the pars defect and actual calculation of a ratio is unnecessary (6a).
3 Fredrickson BE, Baker D, McHolick WJ, Yuan HA, Lubicky JP. The natural history of spondylolysis and spondylolisthesis. J Bone Joint Surg Am. 66:699, 1984.
Spondylolysis is an osseous defect found in both symptomatic and asymptomatic individuals. It predisposes to pathologic intervertebral subluxation or spondylolisthesis, most commonly occurring at the L5-S1 level. The pars defects are thought to represent chronic stress related injuries. Although these often occur during the first decade of life, accompanying vertebral problems develop somewhat later in life. It is important for the interpreter of MR to recognize both the primary and ancillary findings of spondylolysis, and in patients with spondylolisthesis, characteristic MR findings allow differentiation of degenerative versus isthmic causes. MR’s ability to grade disease severity and directly visualize nerve root involvement assists in treatment decisions.
6 Ulmer JL, Mathews VP, Elster AD, King JC. Lumbar spondylolysis without spondylolisthesis: recognition of isolated posterior element subluxation on sagital MR. Am J Neuroradiology. 7:1393, 1995.
An ache in the low back and buttock areas is the most common complaint in patients with spondylolisthesis. Pain is usually worse when bending backward and may be eased by bending the spine forward.
Degenerative changes in the spine (those from wear and tear) can also lead to spondylolisthesis. The spine ages and wears over time, much like hair turns gray. These changes affect the structures that normally support healthy spine alignment. Degeneration in the disc and facet joints of a spinal segment causes the vertebrae to move more than they should. The segment becomes loose, and the added movement takes a additional toll on the structures of the spine. The disc weakens, pressing the facet joints together. Eventually, the support from the facet joints becomes ineffective, and the top vertebra slides forward. Spondylolisthesis from degeneration usually affects people over 40 years old. It mainly involves slippage of L4 over L5.
A spondylolisthesis also is graded according to the amount that one vertebral body has slipped forward on another. A grade I slip means that the upper vertebra has slipped forward less than 25 percent of the total width of the vertebral body, a grade II slip is between 25 and 50 percent, a grade III slip between 50 and 75 percent, a grade IV slip is more than 75 percent, and in the case of a grade V slip, the upper vertebral body has slid all the way forward off the front of the lower vertebral body, a condition called spondyloptosis.
If a patient does not respond to conservative treatment, such as rest from physical activity or sports, bracing may be prescribed. Physical therapy will help the patient safely strengthen the back muscles, and periodic X-rays can help determine if slippage of the vertebra is occurring. Patients with spondylolysis typically do not need surgery unless the condition worsens, but if the bone continues to shift out of place, as in spondylolisthesis, or if nerves are damaged, spinal fusion surgery may be necessary.
Spondylolysis (spon-dee-low-lye-sis) and spondylolisthesis (spon-dee-low-lis-thee-sis) are separate, yet related conditions. Spondylolysis usually comes first, though not always. The term comes from "spondylo," which means "spine," and "lysis," which means to divide. Spondylolysis is a breakdown or fracture of the narrow bridge between the upper and lower facets, called the pars interarticularis. It can occur on one side (unilateral) or both sides (bilateral) and at any level of the spine, but most often at the fourth or fifth lumbar vertebra (Fig. 2). If spondylolysis is present, then you have the potential to develop spondylolisthesis.
A condition called can also cause the slippage that happens with spondylolisthesis. Spondylolysis is a defect in the bony ring of the spinal column. It affects the pars interarticularis, mentioned above. This defect is most commonly thought to be a "stress fracture" that happens from repeated strains on the bony ring. Participants in gymnastics and football commonly suffer these strains. Spondylolysis can lead to the spine slippage of spondylolisthesis when a fracture occurs on both sides of the bony ring. The back section of the bony ring separates from the main vertebral body, so the injured vertebra is no longer connected by bone to the one below it. In this situation, the facet joints can't provide their normal support. The vertebra on top is then free to slip forward over the one below.
Spondylolisthesis is the actual slipping forward of the vertebral body (the term "listhesis" means "to slip forward") (Fig. 3). It occurs when the pars interarticularis separates and allows the vertebral body to move forward out of position causing pinched nerves and pain. Spondylolisthesis usually occurs between the fourth and fifth lumber vertebra or at the last lumbar vertebra and the sacrum. This is where your spine curves into its most pronounced "S" shape and where the stress is heaviest.