What Is Centralization?
Most people have experienced neck or back pain at some point in their lives. Often this discomfort falls in the “normal aches and pains” category, and symptoms get better within a few days. Some people may experience symptoms that persist in their back for longer. Then there are those folks who experience neck or back pain, but also notice signs and symptoms in their arms or legs.
What if the symptoms you are feeling in your elbow are caused by a problem at your neck, or perhaps your hip pain is coming directly from your lower back? How do we determine if an issue in the spine is the source of your pain?
Centralization is the movement of pain from an area away from your spine to an area closer to your spine. Centralization of pain that occurs as you exercise is a good sign. I'll say it again: centralization of pain that occurs as you exercise is a good sign. If your PT has you perform a specific movement for your low back and the pain in your leg moves up towards your spine, this is considered a good sign and tells you (and your PT) that the exercise you are performing is the right one for you.
But why does centralization happen, and why is it so important?
Anatomy of Your Spine
Your spine is a collection of small bones stacked upon one another. Along the length of your spine, between each vertebral bone, there is a disc shaped piece of cartilage that acts to both absorb forces through your spine and to allow the bones to move. The disc consists of an outer ring of fibrous cartilage that is relatively firm called the annulus fibrosus, and an inner portion of softer, more gelatinous cartilage (enclosed by the annulus) called the nucleus pulposus.
A good way to think about the intervertebral disc is to picture a jelly donut. The outside (dough part) is like the annulus, and the nucleus in the middle is similar to the consistency of the jelly.
This represents the normal anatomy of a disc. Thinking about this jelly donut, if you were to squeeze one side of it, logically, the jelly would push toward the opposite side. The disc works in much the same way. Applying pressure to one side of the disc will cause compression on that side, therefore squeezing the central disc material to the other side. As the nucleus is pushed one way or another, this may cause disruption to the fibers of the annulus (the outer portion). A disruption in the normal alignment of the disc may be classified as a disc derangement. Essentially this indicates that the disc material is somehow displaced from its typical position in the spine.
The further the disc material is pushed out of the center, the more trouble it may cause. Unfortunately, this shift in position may cause a disruption in the normal movements associated with the spine. In addition to that, these areas outside the central column of the spine are the same spaces occupied by nerves exiting the spine that travel to your limbs. If there is pressure on the nerves from the disc being out of place, this can cause pain, tingling, numbness and weakness in your back, but could also cause these same symptoms in your arms and legs. The more displacement, the more compression on the nerve, and the more likely you are to have pain and symptoms that travel away from your spine and down the course of the nerve to your extremities. This process of your symptoms travelling further away from the spine or becoming more widespread is referred to as peripheralization. (Peripheralization is the opposite of centralization.)
If this pressure can be removed from the nerves the symptoms should reduce, travel back up the limb closer to the spine, or become more localized and less widespread. This alleviation of symptoms is caused by applying the appropriate forces to the disc, in order to displace the disc material OFF of the nerve. If your symptoms improve, this correlates with a reduction of the displaced or “deranged” disc material back toward the ideal alignment in the middle of the spine.
This concept that symptoms recede up the extremity and become more localized near the spine is referred to as centralization. Even if your symptoms exist only in your back, if they move closer to the center of the spine, this is also centralization. (Remember that centralization of symptoms that occur as you exercise is a good sign.)
If you are a “centralizer” there will be a number of expected symptom responses that you and your physical therapist will look for while and after having you perform spinal movements. These may include:
There will likely be a specific motion that improves your mobility and decreases symptoms associated with a disc derangement. This is called your directional preference. The opposite motion will likely cause an increase in symptoms and a decrease in mobility.
You will likely experience an improvement in motion in your spine near the source of the derangement, as the disc material physically moves out of the way.
Symptoms may feel more intense near the derangement, and less intense distally, and while this seems unhelpful it signifies improvement.
If your symptoms centralize you will often remain better as a result.
So, your PT can use centralization to help form a prognosis for you. People who centralize tend to get much better relief of sciatica than those who do not centralize.
If your symptoms centralize, your overall prognosis for recovery improves. The best way to determine if your pain is caused by a disc derangement and can be centralized is to have an evaluation with one of our McKenzie-trained physical therapists. Your PT will assess your movement, establish a working diagnosis and help determine your plan of care to address your symptoms and the source of the problem. Even if your symptoms do not follow the exact process of centralization, you will work with your therapist to find strategies that will help you move and feel better.