Spondylolisthesis is the Latin term for a slipped vertebral body, and Isthmic refers to the fact that the slip is due to a stress fracture through a piece of bone in the back (the pars interarticularis). Approximately 5% of the population experiences a stress fracture in the lowest lumbar vertebral segment (L5), usually between the ages of five and seven. That segment then slides forward, encroaching on the first sacral vertebral body (S1). This is almost never due to an injury. The L5-S1 segment is the most likely to slip but it can also occur at L4-L5 or L3-L4.
This condition is the leading cause of back pain in adolescents, though most adolescents that have the condition will not experience any back pain because of it. It is not a very dangerous condition as there are almost never any neurological problems associated with it.
Probably 80% of people who have this condition never have any symptoms, and therefore never even realize they have it. For those who do develop low back pain, the cause may be from the vertebrae sliding forward and compressing a nerve or from resulting disc degeneration. With the bony segments of the spine not working properly the disc has to work harder. The disc is designed to work very well under normal compression, but the forward force applied to the disc in the case of spondylolisthesis can cause the disc to break down.
In addition to the low back pain, some patients also experience leg and foot pain due to the nerve being pinched (almost always the L5 nerve). This leg pain will generally be worse when the patient stands or walks. Pain can also come from the fracture, and the tissue in that area may become irritated and painful. Within the pars interarticularis the nerve endings (nociceptors) can become sensitized and create pain. Most of the pain will be activity related. Pain with rest is not typical.
If, upon physical exam, symptoms indicate a possible isthmic spondylolisthesis, an imaging study will be needed to confirm the diagnosis. Isthmic spondylolisthesis can be seen on a regular X-ray, and on a Magnetic Resonance Imaging (MRI) scan. As noted, the spondylolisthesis will almost always occur at the juncture of the L5 and S1 vertebral segments, so that is where the most attention will be focused on the images. The imaging study can also detect if there is degenerative disc disease leading to a nerve root being pinched.
Treatment need only be considered if the pain limits the patient’s pain to any great extent. It is not a dangerous situation, and the pain is generally not progressive.
If a patient who has isthmic spondylolisthesis is being limited in activity to an unacceptable point, some form of treatment may be reasonable. Usually a non-surgical course of treatment will be recommended, and only if that is unsuccessful will the more aggressive surgical treatment be considered.
Conservative (non-surgical) treatments
Conservative treatment methods are designed to reduce the level of pain being experienced. Although it may not make the patient pain free, if it helps manage the pain and allows the patient to be more functional it should be considered successful. Attempts at controlling the pain may include the following:
- Rest. This would probably be limited to no more than a few days, to see if it helped alleviate the symptoms.
- Anti-inflammatory medications. Nonsteroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen (e.g. Advil, Motrin, or Nuprin) and naproxen (e.g. Aleve or Naprosyn) can be used to reduce swelling and inflammation that may be causing pain in the affected area. Stronger therapies, such as oral steroids or epidurals, may be prescribed to treat severe flare-ups if needed.
- Pain reducing medications. Acetaminophen (e.g. Tylenol) can be used to reduce the pain. Because it acts in a different way than the anti-inflammatory drugs, the two types may be used together, and are often very effective when used that way. If the pain is severe, the doctor might prescribe a stronger medication such as codeine for short-term use.
- Physical therapy and exercise. With proper exercise and therapy the muscles around the affected area can be strengthened, which can reduce the amount of movement which causes pain.
- Injections. Depending on which structures is thought to be producing the pain, a pars interacticularis, selective nerve root, or epidural injection may considered to reduce the pain and allow the patient to progress further with their rehabilitation.
In some cases, conservative treatments are not enough to relieve the pain to a degree where the patient can maintain an acceptable level of activity. In those instances a surgical remedy might need to be considered.
The pain in isthmic spondylolisthesis is caused from the vertebrae sliding forward and a nerve being compressed. To successfully relieve this pain, the surgery needs to remove the pressure on the nerve and then fusing. If the motion is eliminated in a painful motion segment the pain should subside.
Spinal fusion involves using a bone graft and attaching it to the spine, often using instrumentation such an anterior cage and/or screws or rods. The bone graft can be taken from the patient’s hip (autograft bone) during the fusion surgery, or taken from cadaver bone (allograft bone). Bone graft substitutes may also be used. Over the course of about three months the bone will grow together and functionally spot weld the two vertebral bodies together. During that period of time the patient’s activity level should be limited to allow the bone to grow. Once it has grown together, activity will actually help the bone remodel. Bone is a live tissue, and when stressed it will become stronger.
The L5-S1 level does not move that much, so fusing it together does not change the biomechanics in the back all that much. Generally, after the fusion has taken, no activity restrictions are necessary, and the patient may do their activities as tolerated. They should also not notice any decrease in the range of motion of their back.
It should be noted that with any spine fusion surgery, one of the risks of the procedure is that despite a successful fusion the patient’s pain does not go away. However, a fusion procedure for an Isthmic Spondylolisthesis tends to be a very reliable procedure, and 90-95% of patients will be able to function better with less pain after they have healed.
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