Most of us will experience low back pain at some point in our lives. When it is severe, we often seek a medical specialist to help us restore quality in our lives.
When we see a doctor, their first step will be identifying the sources of that low back pain. These sources involve structures in our body that are called pain generators.
We spoke to Dr. Roy Lerman, a Physician Medicine and Rehabilitation physician at Main Line Spine, to learn firsthand about the diagnostic approaches used as the first step in treatment. What follows is a summary of a short video he made for us. (To watch the full video of Dr. Lerman’s discussion, click HERE).
Setting a Starting Frame of Reference
Before we can effectively discuss what may be causing low back pain, we need to establish a common frame of reference. We’ll start by reviewing the core structures of the lower spine, known as the “lumbar spine” (see Figure 1, below).
The main bone structure in the spine is the vertebra, and there are five in your lower back (see Figure 1, above). These lumbar vertebrae are the largest in the entire spine.
Sitting between the vertebrae are discs (see Figure 1, above), and inside each disc is a soft center with gel-like material called a nucleus (nucleus pulposus) (see Figure 2, below).
Surrounding each disc is the annulus (annulus fibrosis), a denser protective shell containing the soft nucleus (see Figure 2, above).
Diseases and Disorders of the Lower Spine
Many problems can occur in the lower spine. They can cause pain, limit function or mobility, and lead to weakness, tingling, or numbness in your back, hips, thighs, or legs.
A spinal disc can deflate like a tire running low on air (thinning disc) (see Figure 3, below).
Discs can also bulge with a protrusion or bulging disc (see Figure 4, below).
When the soft, gel-like center of the disc pushes through the annulus protective outer layer, it’s known as a disc herniation. Continuing our tire analogy, it’s like a bubble in a tire that bursts (see Figure 5, below).
As the gel pushes out, it can press on and impact nearby nerves behind the vertebral body (see Figure 5, above).
The Epidural Space
The spinal canal is at the center of the spinal column, running through each vertebra and disc. At the center is the epidural space (See Figure 6, below).
Spinal nerve roots run through the epidural space, and some emerge at each level of the lower spine (See Figure 6, above). These nerves serve different parts of your legs, hips, thighs, and lower back.
Five Lower Back Vertebrae, the Facet Joint, and Sacrum
The five lower back vertebrae are numbered 1 through 5. When we refer to lumbar spine levels, we reference each vertebra by number and level (See Figure 7, below).
Behind the epidural space and the nerve canal is the facet joint. The facet joint is a small, knuckle-sized joint between the vertebrae (See Figure 7, above). When we bend, that joint moves.
Below the lumbar spine is the sacral spine, also known as the sacrum. The sacrum is made up of five vertebrae that are fused together (See Figure 8, below).
Finally, the sacroiliac, or SI joint is a weight-bearing joint where the sacrum meets the pelvis on both sides (See Figure 8, above).
Potential Structures That May Cause Pain in the Spine
As we consider potential structures that may cause pain in the spine, we’ll start with the vertebral body itself. We look for specific findings on an MRI scan to determine if the vertebrae or vertebral endplates may be a pain source (see Figure 9, below).
A disc can also be a source of pain (See Figure 10, below). A disc can bulge out of place or herniate, putting pressure on surrounding nerves. Both of these conditions can cause pain that radiates down the leg. Individual nerves emerging from different levels of the lower spine serve different parts of the leg.
For example, the L5 nerve serves the outside of your leg. If pain originates from the L5 nerve distribution, it will radiate down the outside of your leg and into the side of your calf (See, Figure 11, below).
Similarly, the S1 nerve, the first sacral nerve, runs down the back of your leg.
By identifying where leg pain symptoms are felt, we can identify the spinal level where they may originate.
Pain may also arise at the facet joint. It may become arthritic and cause symptoms when using that joint – like any arthritic joint in the body.
Similarly, the SI joint can become arthritic and a source of pain.
Determining Where Pain May Be Originating
A key factor in helping us determine where pain may be originating is based on a patient’s history. There are certain elements that we look for.
For example, sitting puts more pressure on a spinal disc. So, if someone says they are having trouble sitting for any period, that may suggest a disc or vertebral body may be the source.
Or, when we stand, we have a slight curvature of the arch in our back – and we place a load on the spinal joints. If a patient experiences more pain issues when standing, it may suggest that it’s a facet joint problem.
If the pain is radiating down the leg, we then suspect that there is an issue along the path of the nerve. Nerves can be impacted by disc issues or bone spurs that develop as a result of degenerative changes in the body. The growth of bone spurs is the body’s way of stabilizing the impact of deterioration and degeneration.
As previously noted, the facet joint is like a knuckle joint. You’ve probably seen people with knuckles that become enlarged due to arthritis. When facet joints become arthritic, they, too, may become enlarged. This often leads to a narrowing of the spinal canal – a condition called spinal stenosis – which can cause the pinching of nerves, particularly when we stand up.
Confirming Diagnoses
We may ultimately use targeting injections to confirm a diagnosis. If we suspect it is nerve-related, we may administer medication around the nerve in a procedure known as a nerve block. If this temporary action provides relief, we know we are on the correct path to proceed with longer-lasting solutions.
