Why Does MDT Work? A Non-Mechanical Explanation
In debating with others who use a pain science approach to treating their patients, I have often stated there has to be a mechanical explanation for MDT. That is the directional preference, or DP. The DP is the direction of movement the patient repeats, often to end range that centralizes their complaints, and results in a lasting improvement of their symptoms. This does not mean I do not think there is also a neurophysiologic response as well.
NDT? Not THAT NDT
There are obviously neurophysiologic mechanisms at work here, especially in the derangement syndrome, where the response is rapid for better or for worse. More than 80% of the time the DP is toward the pain. This was confirmed recently by speaking with a DipMDT and McKenzie Institute faculty member. Whether it is backward bending for the lumbar spine, sidegliding toward for unilateral lumbar pain, trunk rotation toward for thoracic/rib pain, or cervical SB toward the painful side for unilateral complaints.
To be effective at MDT, you need to be a very assertive and educational practitioner. The patients who respond best have to understand what they need to do, and what they need to avoid. They need to be pushed to end range. Those who have failed at the MDT approach often do not get the patient to move to end range or have forgotten other planes of motion. I have seen it time and again, especially at MDT Clinical Skills Update courses; current patients of well trained CertMDTs who were not responding get pushed further into the pain by the instructor. They quickly respond and improve. The key most of the time was getting to the patient's real end range, and increased frequency of HEP dosage.
End range is the key, and what happens here? Similar to thrust manipulation, or repeated grade III-IV mobilizations, the joint mechanoreceptors are fired, perhaps better at end range, bombarding the CNS with proprioceptive information and possibly increasing a movement tolerance into the previously painful range. Joint closing works better than opening, or what most patients are already trying to do before they see the practitioner. Perhaps, closing fires the mechanoreceptors better than opening because it is easier to get to end range. The increased pain free range then decreases the perceived threat, and CNS sensitivity decreases. The patient is then instructed to repeat these repeated motions that continue to decrease their complaints, and not just 3x10, but often hourly or more. That is very powerful when you are increasing pain free movement!
There is also the active listening component to the entire treatment experience, as a MDT trained PT carefully listens to what makes them better and worse. They ask how each movement and position affects the patient's Sx. By the end of a successful MDT exam and treatment, the patient is empowered with not only an understanding of why they have these symptoms, but also a classification of their Sx. This experience also decreases hyperalgesia to movement and positions.
Those of you familiar with the MDT repeated motion exam will eventually be able to choose the positions and directions to assess repeatedly which will improve the complaints. Any active listener will be able to see if sitting, bending, squatting, etc makes Sx worse, are you really going to test repeated flexion? I just go immediately with repeated extension. When Sx are unilateral, I start with repeated sidegliding in standing to the side of pain (shoulders toward, not hips). I do not use cervical repeated motion testing, but instruct it for HEP. For unilateral cervical pain not responding to repeated retraction, I often progress after 1 week to repeated retraction and SB with patient overpressure to the same side.
My experience with acute flareups also shows that patients coming in with a 9/10, when they were previously a 2-3/10, often respond immediately to the lumbar hips offset "roadkill" position, or the cervical retraction with SB overpressure to the same side of pain. They can either leave with their previous baseline, or call 1-2 days later, often feeling even better than before.
So in summary, while I certain these neurophysiologic events are happening, many patients do not need this explanation and I stick with a more simplistic mechanical one, because it is easier for them to understand. However, I know it's more than just reducing a "disc" derangement.