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Spinal Secret #2: The Back Has Poor 2 Point Discrimination

Do you remember that old commercial for auto service where people brought their cars in, imitated the sounds they made, and a mechanic guessed at the problem?

If only things were that straight forward with the physical body! (And I am sure they are not for mechanics either).

We have explored sensory systems within the body over the past few months.

Part of that sensory exploration, is understanding that the sensations that we feel, though important, cannot be used in a diagnostic manner.

Medical diagnosis is usually comprised of a physical examination, of which subjective experience or felt experience is a part, but it needs to include objective findings in order for a medical doctor to arrive at a diagnosis.

Objective information is obtained through a physical exam, and usually imaging (MRI if soft tissue is being considered, or radiographs/ bone scans (“x-rays”) if bone is being assessed.

All this just to say, your sensations are important, but are in no way diagnostic on their own.

Recall, that your sense receptors are like stethoscopes- listening all over the body for different information. They might be specially adapted to sense pressure within your carotid artery, or they might notice the lightest touch when a feather tickles your forearm.

Something important to know, is that though there are many, millions of sensors throughout your body, there are areas where the stethoscopes or sense receptors are a lot more abundant, and areas that are more like sense receptor deserts.

Our hands and face for instance, are areas that are jam packed with sense receptors. In these areas, we are able to distinguish with pretty good accuracy, when one part of the hand is being touched vs another. We describe these areas with intense sensory information as having good 2 point discrimination- when 2 distinct points are touched with a fine object (like the end of a pen), we can tell with fair accuracy (and without using other senses like vision) the difference between these two points.

Now, take a sense receptor desert- the back. When two points are touched on the back, our sensory system can get a bit confused. Because there is not a high degree of sensory “listening” in that area, we might feel like only one point is getting touched.

In this area, we would describe having poor 2 point discrimination.

It is important to know that the quality of 2 point discrimination within a body area is usually referring to superficial (skin) sensations that the body can pick up.

But even so, 2 point discrimination gives us a foundation for understanding, that the sensory system may not be as refined as we hoped. Where did we get the idea that we can sense the difference between a muscular contraction of the deep spinal muscles vs. an over stretched ligament?

Now this is really important in relation to the spine. Because when we have a history of pain in the spine, given that we have a bunch of structures all layered up on top of one another (the intervertebral discs, the joint capsule ligaments, the more superficial ligaments, the deep fascial structures) how do we know what the source of spinal pain is when we feel it?

I would argue, that unless we also have more objective work up done outside of ourselves (a physical exam relative to that day and new images), we can get confused about our sensation really easily and cannot infer diagnostic information based on our felt sense.

Back in 2006, I was in school at an orthopedic practice that used posterior pelvic tilting (flattening the lumbar lordosis) for many patient interventions. Lumbar stenosis? Posterior pelvic tilt. Spinal instability? Posterior pelvic tilt. Fractured wrist? Posterior pelvic tilt.

Not really, but you get the gist.

When I completed my rotation, I was studying for my boards with one of my fellow classmates. She looked over at me hunched over my books and started laughing. She asked if I could get out of my flattened lordosis posture. Firstly, I had no idea I was resting in complete spinal flexion. And secondly- I wasn’t sure. My friend helped me gauge where my neutral was. I was astounded! My neutral spine hurt! I had become so accustomed to the posterior pelvic tilt, my tissues were sensitive to muscle contraction and spinal compression (both healthy and nourishing elements).

I have also noted in many clients through the years, who assume a similar posture, that moving out of familiar postures is an uncomfortable event- even if it precludes a transition toward more spinal health.

Sensations are important. We don’t want to push into sensations that feel like pain. And, just as importantly, we need to be mindful of our narration around these experiences. We can learn to limit our reactivity to sensation. Is what we are feeling stiffness? Weakness? Can we allow it to just be without attempting to assign biologic meaning from it?

If our sensations are important, but cannot help us infer what is going on, where do we go?

We get help. Ask a trusted physical therapist to help you (or go to PT school and make some generous if ill-humored friends like I did!). Your PT will let you know if you need to see an MD for a medical diagnosis and/or imaging.

I hope this has been a helpful refresher for how to work with sensory information, and why it is so crucial when working with the spine.

Please join us next week to explore the bioplasticity of the spine- so that you can know that materials heal and change.

Until next time, happy moving!


These redwood branches are reminiscent of axonal dendrites reaching out to communicate with their neighbor!

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