Spinal manipulation is an intervention we commonly employ as Physical Therapists. We have several names for it (because of inter-professional turf wars) and loads of RCTs (supposedly) supporting its use. In addition, there are loads of continuing education courses and certifications, each claiming to teach you (more) effective ways to manipulate the spine. For gosh sakes, I get a new pamphlet every other day. But in all of this hype, what do we truly know about the effects of spinal manipulation? Can we truly design one more RCT to measure its effectiveness if we barely know the potential physiological mechanisms behind its effectiveness(ok I stole this idea from Jim Meadows at the AAOMPT conference this year, but it is just so good)? Should we simply employ a rule, when we don’t understand the process? I am not sure…but lets dig a bit deeper. Let’s attempt to understand the complexity of spinal manipulation.
Basic Anatomy/Physiology/and other good stuff:
I would like to discuss all of the potential anatomy and physiology which could be affected with a spinal manipulation. For this, I am going to use a description of spinal manipulation as described by Flynn et al in the derivation of a lumbar CPR.1 I don’t want to pick on them, this is simply a widely read study amongst PTs, and the description is of a very basic spinal manipulation many of us employ. In the study, they state:
At the first session, the therapist performed a spinalmanipulation technique with the patient supine. The therapist stood opposite the side to be manipulated. The patient was passively side-bent away from the therapist. The therapist passively rotated the patient and then delivered a quick posterior and inferior thrust through the anterior superior iliac spine.
Now Let’s Think: The human body has layers upon layers of tissue. For whatever reason, when many of us learn “spinal” manipulation, there is a HUGE emphasis on what happens at the level of the spine. But in the case above, what other organs may be affected? For example, where’s the love for the skin? The skin is our largest organ, comprised of layers of ectodermal tissue. It gets “twisted” and “stretched” during a “spinal” manipulation. So could we change the name to “skin manipulation”?
The skin is comprised of the epidermis, dermis, papillary region, reticular region and subcutaneous layers. The epidermis is the outer layer, which protects the body. It is our bodies armor. Some of us decorate it.
Random thought about the epidermis: I remember my anatomy professor once discussing the ridiculousness of body creams which claim to “penetrate” deep into the body, when they likely don’t even make it past this barrier.
Anyways, this layer is actually subdivided into a bunch more “stratum” layers which have individual roles.
Once you get past all of the epidermal layers, you reach the dermis. This part of the skin makes it “elastic” and “strong”. It is also comprised of a ton of little nerve endings which help us sense stimuli.
These nerve endings, also known as mechanoreceptors, do several things:
Pacinian corpuscles: sense vibration and pressure
Meissners corpuscles: sense light touch (they have the lowest threshold in sensing stimuli)
Merkel’s discs: provide touch and pressure information to the brain
Ruffini Corpuscles: kinesthetic sense
So regressing back to the description given for a spinal manipulation, the authors stated, “The patient was passively side-bent away from the therapist. The therapist passively rotated the patient and then delivered a quick posterior and inferior thrust through the anterior superior iliac spine.” This darn well sounds like the skin was “stretched”. It also sounds like the skin was touched. It sounds like the above nerve fibers were stimulated. Could they be the reason why spinal manipulation appears to work (note: while it does appear spinal manipulation is effective, it is likely just as effective as non-thrusting techniques.2 Maybe this is why…)?
Anyways, let’s say the variable of the skin is non-existent in spinal manipulation (far-fetched but let’s say it happens). The next layer of tissue are subcutaneous (ie. beneath the skin). Unlike skin, which is “ectodermal” in origin, this layer of tissue originates from “mesoderm”. Its main use: fat storage. It keeps you warm. But within this layer (which the fascia crew loves) are more nerves and free-nerve endings. But let’s say these aren’t stimulated either…
Once we get past all of this good stuff, we have layers of muscular tissue that receives and transmits afferent and efferent information from the nervous system. The “afferent leg” takes sensory information from the level of the muscle, all the way up to the command center (ie. the brain). This information is generally from proprioceptors and muscle spindles, conveying the degree of stretch/length of the muscle, as well as where it is in space. So when considering spinal manipulation, do you think position sense is potentially altered during a “spinal” manipulation? How about muscle length?
So if we can also ignore the effects of muscle, we arrive to the bones, which many have fought long and hard to defend as holding the key to answering the mechanism questions. Many argue alignment and/or faulty mechanics, while some talk about disc integrity and fluid… but wait a minute… what about all of the other “stuff” I just described above? Do the bones/disc move in isolation?
Now that we have overwhelmed ourselves with all of the internal variables to consider, we must also be cognoscente and account for the potential of external influences over effects. We must consider all of the noise. We must consider the clinical environment, therapeutic alliance and prosody of our speech. We must consider everything.
I hate to say this , but spinal manipulation doesn’t impress me any more than our other manual techniques. This is coming from someone who has completed a manual certification and an AAOMPT fellowship. I know how to manipulate. But I am very doubtful it is more effective than lower grade mobilizations (unless the patient is convinced it will be—which then acts likely as a placebo).
As we begin to critically examine what is happening within the things we do, we will begin to understand the complexity of the human experience and likely find that all these inputs, simply work the same way.
What are your thoughts?
1. Flynn T, Fritz J, et al. A clinical prediction rule for classifying patients with low back pain who demonstrate short-term improvement with spinal manipulation. Spine 2002; 27: 2835-2843.
2.Cook CE, et al., Can a within/between-session change in pain during reassessment predict outcome using a manual therapy intervention in patients with mechanical low back pain?, Manual Therapy (2012), doi:10.1016/j.math.2012.02.020