What is Isthmic Spondylolisthesis?
Isthmic spondylolisthesis is a spinal condition which occurs when there is a fracture in the bone, known as pars interarticularis, which connects the two vertebral joints on the posterior side of the spine resulting in forward slipping of vertebral body on the one below it. Pars interarticularis is a small piece of bone and fracture in this occurs due to any type of stress to the bone. The fracture often tends to occur in young age when the patient is about 5 to 7 years old; however, the symptoms commonly do not develop until the patient is well into adulthood. When the patient is in adolescence, then he/she can feel a spike of lower back pain from the Isthmic spondylolisthesis.
According to statistics, about 5 to 7% of the entire population suffers from either a fracture of the pars interarticularis or slipped vertebral body (spondylolisthesis); however, symptoms will be absent in most of the cases. Majority of the patients suffering from Isthmic spondylolisthesis will not have symptoms. Even if there are symptoms present, then only some of them, like about 20% will need surgical correction.
Causes of Isthmic Spondylolisthesis
- Pars interarticularis is a latin word meaning “bridge between two joints,” and it helps in connecting the above facet joint to the one present below. Pars interarticularis is a thin piece of bone which has a poor blood supply thus making it more susceptible to stress fractures. Fracture can also occur alone in the pars interarticularis without any vertebral slip.
- Spondylolysis is a term used to describe the fracture itself, whereas pars interarticularis is also known as the isthmus. When there is fracture of this pars interarticularis or isthmus, then patient commonly does not experience pain or any other symptoms. Common cause for fracture is prolonged stress.
- Trauma is an uncommon cause for fracture of isthmus. Cumulative stress is the main cause of the fracture.
- Isthmic spondylolisthesis commonly occurs in the spinal level of L5-S1, which is the lowest level of the lumbar spine. If it occurs above this level, i.e. at L3-L4 or L4-L5, which is very rare, then trauma will be the cause, which is most common for this fracture, rather than prolonged stress.
- Till now, this fracture has not been found ever in a newborn, so that rules out it being a congenital problem. The forward slipping of the vertebral bodies, which occurs from the fracture tends to develop in adolescent or juvenile individuals. Advancement of this slippage occurring in adulthood is quite rare.
- At L5-S1 level of the spine, patient will not feel a lot of instability as there is a large ligament known as the sacral ala, which connects the L5 vertebral body to the sacrum, thus preventing the exacerbation of the slippage of L5 on to the sacrum.
- Individuals who do repeated heavy lifting, twisting or stooping are more prone to small fractures in the vertebral structure, which leads to the slippage of one vertebra over another. Sports people like football players, weightlifters and gymnasts are more prone to suffer from this disorder due to the great amount of repeated stress on their spines.
Symptoms of Isthmic Spondylolisthesis
- Patient suffering from Isthmic spondylolisthesis experiences symptoms of pain in the lower back, thighs, legs. Pain is also felt after any physical activity or exercise, which radiates into the buttocks.
- Patient also has muscle spasms.
- There is weakness in the legs along with pain.
- Patient has tight hamstring muscles.
- Patient has an irregular gait.
- In severe cases, patient suffering from Isthmic spondylolisthesis may experience swayback, shortened torso, protruding abdomen and a waddling gait.
Grading of Isthmic Spondylolisthesis
A side-view x-ray is taken to assess the severity of the slippage and grading is done from 1 to 4. The slippage is graded according to the amount the upper vertebral body has slipped forward onto the lower vertebral body.
- Grade 1 Isthmic spondylolisthesis: In this grading, 25% or lesser than that of the vertebral body has slipped forward.
- Grade 2 Isthmic spondylolisthesis: In this grading, there is about 26 to 50% forward slipping of the vertebral body.
- Grade 3 Isthmic spondylolisthesis: In this grading, there is about 51 to 75% of forward slipping of the vertebral body.
- Grade 4 Isthmic spondylolisthesis: In this grading, there is about 76 to 100% of forward slipping of the vertebral body.
- Grade V: This grading is also known as spondyloptosis which can occur very rarely where the L5 vertebral body slips off from the sacrum and into the pelvis.
Investigations to Diagnose Isthmic Spondylolisthesis
- Medical history is taken where the patient is questioned regarding his/her symptoms, their severity etc.
- Physical examination is done where the patient is examined for any limitations of movements, pain and any balance problems. Signs of neurological damage, such as loss of reflexes in the extremities, loss of sensation and muscle weakness are also looked for.
Treatment for Isthmic Spondylolisthesis
- Diagnostic tests, such as x-rays, to rule out infections and tumors are done. CT scan or MRI can also be done to confirm the diagnosis. In some cases, myelogram is done to assess the degree of nerve compression and slippage between the affected vertebrae.
Treatment is done according to the grading of the Isthmic spondylolisthesis. It is fortunate that most of the time the slips which occur are about grade 1 or grade 2. If the patient develops symptoms, then treatment for Isthmic spondylolisthesis can be done with medicines. In severe cases, surgery is required. Other factors which are taken into account before treatment is started include intractable pain and neurological symptoms. For majority of the cases of isthmic spondylolisthesis which are in the Grades I and II category, conservative treatment is sufficient which comprises of:
- Bed rest.
- Limited activities, which produce the symptoms
- Medicines, such as pain killers and NSAIDs are prescribed.
- Steroid or anesthetic, epidural injections are also beneficial.
- Spinal bracing also helps with the symptoms.
- Physical therapy is done
Surgery for Isthmic Spondylolisthesis
Surgical intervention is required for the more severe slips, i.e. which come under the Grade III and above category. Surgery is also needed in the following cases:
- Surgery is rarely required except in severe cases of Grade III isthmic spondylolisthesis and above.
- If there is any neurological damage due to isthmic spondylolisthesis, then also surgery may be needed.
- If the pain, which the patient has, is disabling and affects his/her quality of life and other conservative or non-operative treatment methods have failed.
- The commonest surgical procedure for treating Isthmic spondylolisthesis is laminectomy and fusion. The procedure consists of widening the spinal canal by trimming or removing or laminae, which is the roof of the vertebrae so that more space is created for the nerves thus relieving pressure on the spinal cord.
- The surgeon may also perform discectomy where the whole or a part of the vertebral disc is removed and the vertebrae are fused together. Different devices such as screws or interbody cages are implanted in case a fusion is done. This helps in enhancing the fusion and supporting the unstable spine.