Definition: This refers to the anterior subluxation of one vertebral body on another. It most often occurs between the 5th lumbar vertebra and the sacrum (L5S1) or between the 4th and 5th lumbar vertebrae (L4-5).
Grading: There are four grades of spondylolisthesis according to the Meyerding grading system. Each grade is determined by the amount of shift between the two vertebrae. The vertebrae are divided into 4 quarters and graded as follows;
- grade 1 0 – 25 %
- grade 2 25 – 50 %
- grade 3 50 – 75 %
- grade 4 75 – 100 %
over 100 % is referred to as spondyloptosis, where one vertebrae is completely off of the adjacent vertebrae.
Signs and symptoms: Many people with spondylolisthesis do not have any symptoms. It is found on 5 to 20% of all lumbar spine x-rays. In some people it can cause back pain. If the shift between the vertebrae results in compression of a nerve root it causes pain in one or both legs (sciatica).
Cause: There are five different types of spondylolisthesis according to the Wiltse classification system. These are dysplastic, isthmic, degenerative, traumatic and pathologic. Dysplastic is an abnormality of development and is present at birth. It is due to malformation of the lumbosacral junction (L5S1) with small incompetent facet joints. This is very rare. Isthmic spondylolisthesis is the most common form with an incidence of 5 – 7 % in the american population. It is due to a defect in the pars interarticularis.
It is believed that the defect develops from stress fractures that fail to heal and form a chronic non-union. It often appears in childhood between the age of 6 and 16. The slip between the vertebrae often occurs shortly after the injury and in most instances does not progress. It is more common in athletes that participate in sports with repeated hyperextension such as gymnastics, ballet and american football. It is felt that most of these do not become symptomatic (ie. do not cause back pain). Many people do not know that they have the spondylolisthesis. 90 % are grade 1 or 2 meaning less than 50 % shift between adjacent vertebrae. 10 % are grade 3 or 4 (greater than 50 % shift).
Occasionally an isthmic spondylolisthesis can become symptomatic as a result of trauma in adulthood.
Degenerative spondylolisthesis occurs in adults and results from osteoarthritis involving the lumbar facet joints. Remodeling of the facet joints allows a mild degree of slip to occur. This is very common being reported in 30 – 60% of women over 65 years of age. Most are asymptomatic but can be associated with symptomatic spinal stenosis. Patients with spinal stenosis and a spondylolisthesis should be considered for a fusion in addition to a decompression if they undergo surgery to relieve their symptoms.
Traumatic spondylolisthesis is very rare and is due to an acute fracture of the inferior facet or pars interarticularis as a result of trauma such as a fall or motor vehicle accident. They may be associated with neurological deficits due to nerve root injuries and are probably unstable and require surgical fusion.
Pathologic spondylolisthesis is also very rare and is due to damage to the posterior arch of bone, including the facet joints as a result of diseases such as metastatic tumors, tuberculosis and Paget’s disease. Treatment is focused on the underlying disease. Surgery may be necessary to relieve pain from nerve compression.
In syptomatic cases of spondylolisthesis the major symptom is back pain. The presence of a spondylolishesis can result in a change in a persons posture and gait, and lead to tight hamstring muscles. People can also develop pain radiating down the leg which occurs intermittently or can become persistent. The back and leg pain are often activity related and can persist for a few days after a day of increased physical activity. In most cases the slip is stable and does not change between flexion and extension. The exact cause of back pain in patients with no motion is uncertain but may be due to stress on the disc annulus or on other soft tissue elements such as muscles and ligaments. However, most people with isthmic spondylolisthesis do not have pain but should have the same amount of stress on these soft tissue structures as the people who have pain. If there is abnormal movement at the level of the spondylolisthesis then this instability is felt to be responsible for the pain. If people have foraminal stenosis which is narrowing of the small openings where the nerves leave the spine, it can result in nerve compression and radicular leg pain (sciatica).
Treatment: Like other causes of back pain the initial treatment consists of medication, activity modification and physiotherapy. Massage therapy, chiropractic care, accupuncture and other non-operative forms of treatment should be tried initially. Like people who do not have a spondylolisthesis, the back pain will usually resolve within 6 weeks. Many of these people have chronically tight hamstrings and should be given education on hamstring stretching exercises. Epidural steroid injections can improve radicular leg pain and facet joint injections can be effective for the back pain associated with isthmic or degenerative spondylolisthesis. The use of a lumbosacral brace for a short period of time may be beneficial. However long-term use can lead to atrophy of the paraspinal muscles.
Surgical treatment is reserved for people with disabling back and / or leg pain who have failed all other forms of treatment. Surgery is usually not considered for at least 3 months after the onset of symptoms as many people improve without surgery. If surgery is considered the most common procedure is a posterolateral fusion which involves putting bone graft material between the transverse processes to encourage a fusion. Decompression is usually performed in patients with radicular leg pain. Fusions are usually augmented with rods and screws to provide stability while the bony fusion becomes solid. The hardware is usually not removed unless complications such as breakage occur. Fusions can also be performed from an anterior approach with removal of the disc and insertion of a cage of some sort augmented with bone or some form of fusion material. Some infusions involve both an anterior and a posterior approach. New minimally invasive surgery (MIS) procedures often involve removal of the disc, insertion of a graft to restore the spinal alignment and insertion of rods and screws to produce stability. These MIS procedures are performed through a series of small incisions with minimal blood loss and very short hospital stays. Success of surgery depends on proper patient selection. Not everyone with a spondylolisthesis improves with surgery. Some can even be made worse.
Complications of surgery: Like other spinal operations the most common complications are infection, spinal fluid lead and nerve root injury. The last has a higher incidence in cases of spinal fusion where screws can be misplaced and injury a nerve. Other complications include bleeding requiring a transfusion, vascular injury, sexual dysfunction (with anterior approaches), non-union with persistent pain, rod and screw breakage which may cause recurrent pain.
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