Lumbar vertebral bodies are usually well aligned relative to one another.  On imaging studies of the normal spine, the front, back and side borders of vertebral bodies more or less “line up.  Alignment of the vertebrae may become impaired because of degenerative changes of the spine, which result in “looseness” of ligaments and the small vertebral joints.

spondylolisthesis L5-S1 XRay

L5-S1 spondylolithesis

The condition, where vertebral bodies are no longer aligned is called “spondylolisthesis”.  Wikipedia states: The term “spondylolisthesis” was coined in 1854, from the Greek σπονδυλος = “vertebra” and “ὁλισθος” = “slipperiness”, “a slip”.

The degree of  vertebral “slip” is usually classified in grades: grade I (<25% slip), grade II (25-50% slip), grade III (50-75% slip), grade IV (75-100% slip).  The most common grades are grades I and II.  Spondylolisthesis is often seen in the lumbar spine at L5-S1.

Spondylolisthesis is sometimes related to a congenital deformity of the upper sacrum or the vertebral arch and facet joints of  the fifth lumbar vertebra (L5).  Sometimes, there is incomplete formation of the laminar arch(es) of the lower lumbar or the upper laminar arch(es) of the sacral vertebrae (spina bifida occulta).  These deformities of the lumbosacral junction can result in spondylolisthesis.

In some cases, there is developmental or genetic failure of the pars intervertebralis of one of the lumbar vertebae, typically of L5, to turn into bone (ossify).  A  ribbon of cartilage remains in either one or both, otherwise bony, pars intervertebralis, which may later lead to separation (spondylolysis), with or without vertebral slip (spondylolisthesis), of the pars intervertebralis along the weaker zone of cartilage.

Trauma may play a role in the progression of spondylolyis.  It may be difficult to tell if there was a particular event, i.e. a particular trauma, which caused the spondylolysis of a particular individual to become symptomatic or if the development of spondylolysis was a gradual process, which took years or even decades to develop.  People with spondylolysis often have excessive degenerative tissue at the location of the pars defect, including new bone formation (osteophyte, bone callus) and overgrown (hypertrophic) ligament.   Such excessive degenerative tissue may be visible on diagnostic imaging studies and may impinge neural elements (nerve roots and/or spinal cord) in its vicinity.  Depending on the extent of the nervous tissue compression, people with spondylolisthesis may have varying neurological complaints.

Spondylolisthesis L5-S1 with pinched L5 root

Neurogenic claudication (inability to walk for longer distances without having pain or heaviness in the legs) and lower extremity radiculopathy (pain in the back, sometimes radiating to the buttock and leg). Treatment options in milder cases include treatment with medications, including non-steroidal medications, weight loss, exercise, optionally including a course of physical therapy, smoking cessation andd a trial of lumbar bracing. Treatment in more severe cases may include epidural or transforaminal steroid injections, nerve root decompression via laminectomy or laminotomy, with removal of the”Gill fragment” and degenerative tissue around the area of the pars defect in the case of a spondylolysis.

L5-S1 instrumented fusion with intervertebral spacer

Since spinal stability is frequently either not present before surgery or can be expected to be markedly  impaired after a successful surgical decompression, an instrumented fusion via pedicle screws and rods is often used in addition to decompression to stabilize the spine after the decompression.  Bone is harvested from the iliac bone of the hip and the bony tissue of the removed lamina and facet joints.  Harvested bone can be laid onto the side of the spine or can be packed in the disk space to achieve spinal fusion.


Often, artificial spacers, made of plastic (PEEK), titanium, ceramic or bone are inserted in the disk space to restore the previous height of the disk space and the neural foramina, in order to help decompress nerve roots.

Please note:  Images used in this post are, to the author’s knowledge, in the public domain or were used after obtaining written permission from the patient.  Enlarge any image by clicking on it.  Use the the browser’s return arrow to get back to the post.