To understand Schmorl’s nodes, picture two vertebral (spinal) bones with a disc between them. Now imagine a circular layer of cartilage between the disc and each vertebra. That bit of cartilage is called the end plate. Schmorl’s nodes occur when the disc pushes through the endplate and into the next vertebra. On imaging studies these look like small hollowed areas.
Schmorl’s nodes can be seen on X-rays and are often present in patients diagnosed with disc herniation. Like you, patients wonder: is this a coincidence or does it have some particular meaning? Do Schmorl’s nodes occur without disc degeneration? If a person does have Schmorl’s nodes, does that mean the disc is going to degenerate?
There are some theories about why Schmorl’s nodes develop and what they mean. In many cases, we just don’t know why they show up. They seem to develop without cause. That’s referred to as idiopathic. Sometimes, there is a clear cause such as a tumor, decreased bone mineral density, or trauma.
In order to understand the etiology (cause) of Schmorl’s nodes better, a study was done in Southern China where the researchers examined the lumbar spine of 2,449 (adult) volunteers using MRIs.
The participants in the study were everyday people from the general population. Some had low back pain but the majority had no history of back pain or problems. Anyone with a history of back surgery, spinal tumors or infection, or any diseases of the spine was not allowed to join the study.
After all the MRIs were read and interpreted, participants were divided into two groups: 1) those who had no evidence of Schmorl’s nodes and 2) anyone with clear evidence of one or more Schmorl’s nodes. As with most research, the patients’ ages, activity level and sports participation, height and weight (also known as body mass index or BMI), and use of tobacco was recorded.
They found that in the general population, slightly more than 80 per cent did not have any Schmorl’s nodes. For the nearly 20 per cent who did have evidence of this anatomic feature, more than half had multiple levels affected.
The upper lumbar spine (especially L23) was the most common site for Schmorl’s nodes to be seen. Age wasn’t a significant factor except that older adults were more likely to develop disc degeneration. And it was those participants with disc degeneration who had the most Schmorl’s nodes. In fact, the more severe the degeneration, the more likely they were to have Schmorl’s nodes.
Body mass index was also much higher in the group with Schmorl’s nodes. This seems to suggest that being overweight or obese puts older adults at increased risk for Schmorl’s nodes as a complication of disc degeneration. The most severe cases of disc degeneration also had the greatest disc narrowing.
So, is there a link between disc degeneration and Schmorl’s nodes? It looks like it. Why does it happen? It’s likely that there are multiple factors involved and not just one reason why Schmorl’s nodes develop. Genetics, nutrition, body mass index, and severity of disc degeneration may all work together to result in end-plate changes leading to Schmorl’s nodes.