Back pain, especially lower back pain, is a huge problem! In fact, back pain is the most common reason why I see patients in my office. According to the CDC’s National Ambulatory Medical Care Survey, over 13 million doctor’s visits occur each year for “back symptoms,” and most commonly this is in the lumbar spine region. Many patients tell me that they leave their primary doctor’s office with just a diagnosis of “low back pain.” That diagnosis tells us nothing about what’s actually causing the pain! For each case of low back pain, I work to identify the underlying cause so that we can treat it directly.
This is Part One in a series of posts on the problem of Back Pain, focusing on an overview of causes of back pain symptoms. Future posts will discuss treatment options, and focus more on each of these causes in depth.
Although the subject of back pain is very complicated, it becomes easier to understand by thinking of different parts of the body that can be the source of the pain. Based on a careful discussion of your specific symptoms, physical examination, and medical imaging when needed, we can pinpoint your pain generator and select the most effective treatment for that specific type of low back pain.
Discs in the spine act as shock absorbers between the bones of the spine (vertebrae). Discs are filled with a gel-like substance, held in place by a fibrous outer ring.
Discs cause pain in 2 ways:
Discogenic Back Pain from the Disc Itself
The fibrous outer ring, called the annulus, can develop tears called annular tears. These tears can be very painful because the outer ring of the disc contains many sensitive nerve endings. Some cases are related to the normal aging process, but trauma or even day-to-day wear and tear can cause similar tears in younger people. Many of my patients with disc pain are in their 20′s or 30′s! This process is also commonly called Degenerative Disc Disease.
Herniated Discs Compress and Irritate Nerves
The second way that degenerative disc disease can cause back pain is by compression or irritation of nerves in the low back. A herniated disc is a disc that, due to an annular tear, has allowed the inside gel-like substance to bulge out beyond the normal border of the ring, pressing on nerves. The substance also contains irritants which can directly inflame nerves. If this happens to the side, it can affect nerve roots as they exit the spine, causing a radiating “pinched nerve” sensation called sciatica pain. If it happens in the middle, it can cause spinal stenosis, a narrowing of the middle of the spine. Spinal stenosis often causes leg pain as well as back pain, and some patients report leg pain that is provoked by standing or walking.
Facet Joint Pain
Discs are not the only structures that connect the bones of the spine to each other. Each vertebrae has two zygapophyseal joints, better known as facet joints, that connect the levels at the back part of the spine. These are true joints, like minature versions of your knee or shoulder. Like bigger joints, facet joints can develop painful inflammation or arthritis, called facet joint arthropathy, either due to aging, trauma, or other wear and tear. This pain can be felt on one side, or across the low back like a band. It can even radiate to the buttock or thigh and mimic sciatica, but rarely goes below the knee.
The facet joints are located near the nerve roots, so when facet joints become inflamed, in some cases they can also cause mechanical stress on the nerve root itself.
Sacroiliac Joint Pain
So far we’ve covered discs, joints, and nerves. The bones themselves of the spine can cause low back pain too. Examples of back pain coming from the bone include compression fractures. More rarely, infections (vertebral osteomyelitis), cancers, or unusual diseases like Paget’s Disease can involve the spine — very serious diseases that we want to make sure to rule out if back pain does not get better with time.
Ligament Pain (Baastrup’s Disease)
One rare cause of low back pain is degeneration of the interspinous ligament, a ligament that connects the spinous processes at the back of each vertebrae. I mention it as an example of a rare but treatable cause of pain that usually is first diagnosed by a pain specialist.
Sometimes back pain has nothing to do with the spine, or the musculoskeletal system at all. As a physician I also consider organ disease, such as in the kidneys, pancreas, or pelvic organs, all of which can present as referred pain that feels like back pain.
Whew! As you can see, there are a lot of things that I think about whenever I see someone with chronic back pain. If you have any questions about causes of back pain, or chronic pain in general, feel free to comment below!
Sacroiliac joint image by BruceBlaus [CC-BY-3.0], via Wikimedia Commons