New information from this study suggests that spondylolysis occurs more often than was once thought. Past estimates of its incidence relied on X-rays, which may not always show the defect. Updated rates of prevalence using CT scans suggest almost double the number of cases in the general population compared to what was previously reported.
Spondylolysis happens when a crack or bone fracture forms in the bony ring on the back of the spinal column. Most commonly, this occurs in the low back. In this condition, the bone that protects the spinal cord fractures as a result of excessive or repeated strain. The area affected is called the pars interarticularis, so doctors sometimes refer to this condition as a pars defect.
Older children and teens whose bones are still growing are at greatest risk for this condition. Low back pain in athletes with spondylolysis may be more common in football players, gymnasts, wrestlers, weightlifters, and volleyball players.
But older adults can also develop a degenerative form of spondylolysis. Most of the time (in adults and children), the defect is present on both sides. In anyone with spondylolysis, the condition can progress to something else called spondylolisthesis.
With spondylolisthesis, the bone separates at the fracture site. The affected vertebra slips forward over the one below it. The result can be a narrowing of the spinal canal (opening where the spinal cord travels down the spine). As the spinal canal gets smaller, any pressure or pulling on the spinal cord or nerve roots can cause neurologic problems.
Recognizing spondylolysis early is helpful as it may be possible to prevent further worsening into spondylolisthesis. And now, with the information from this study, we know that the risk of degenerative spondylolisthesis increases with age. Men are more likely to be affected after age 40. Women have three times the chance of developing degenerative spondylolisthesis (compared to men) after age 50.
On the other hand, the incidence of spondylolysis in the younger years is greater among men by a 3:1 ratio (men to women). Spondylolisthesis in younger adults (less than 40 years old) occurs in men twice as often as women (2:1 ratio of men to women).
How did they come up with this new understanding of spondylolysis and spondylolisthesis? They used information gathered from a large group studied as part of the Framingham Heart Study. Adults from the town of Framingham, Massachusetts have been part of an ongoing study for generations now. The study started in 1948 and has continued through three generations.
Since data of all kinds are collected on these individuals, other researchers can use the information to investigate problems of interest outside of heart disease. And because CT scans were taken of the abdomen and chest to detect heart disease, the authors could use those same imaging studies to look for changes in the spine.
At the same time, information was collected on a variety of health-related topics. For example, patients were asked to report on any recent (last 12 months) episodes low back pain. Using this information, it was possible to check and see if patients with low back pain also showed evidence of spondylolysis and spondylolisthesis.
They could also compare how many people with these spinal defects complained of low back pain. The authors wanted to know if the two factors could be related or linked somehow. However, the results showed no significant association between spondylolysis, spondylolisthesis, and low back pain.
Other observations made in this study included the higher rate of spondylolysis in certain ethnic groups (e.g., Native Americans, Eskimos). Spondylolysis occurs in as many as 53 per cent of those groups. The reason for this was not known or explained.
The authors conclude that spondylolysis and spondylolisthesis are more common than we thought. These conditions do not seem to be linked with low back pain. This is an important finding as surgery is one possible treatment option for spondylolisthesis. But if spondylolisthesis is not the true cause of the back pain, then surgery may not be needed. Conservative (nonoperative) care may be all that's needed.
When making the diagnosis, CT imaging is a better diagnostic tool (more accurate, more reliable) than X-rays. With these conditions, the fracture can be missed on X-rays depending on the patient's position (standing up or lying down. The effects of gravity and postural muscles can really make a difference on X-ray results.
Physicians are encouraged to assess low back pain patients who have spondylolysis and spondylolisthesis carefully. Knowing that the pain may not be related to the spinal defect means that care must be taken not to automatically assume one goes with the other. The plan of care may depend on the physician's understanding of this information.
Leonid Kalichman, PT, PhD, et al. Spondylolysis and Spondylolisthesis. In Spine. January 2009. Vol. 34. No. 2. Pp. 199-205.