Reversing Disc Protrusions, McKenzie Mostly Correct in Theory

Disc prolapse: evidence of reversal with repeated extension. Scannell JP, McGill SM. Spine (Phila Pa 1976). 2009 Feb 15;34(4):344-50.

A basic science study that used a porcine cervical spine model to produce disc prolapse subsequently exposed to an extension protocol.
This study investigated whether extension or combined extension and side flexion could move the displaced portion of nucleus from the annulus towards the nucleus.
Previous research has established that repeated flexion can create disc prolapse, the question here is whether repeated extension can reverse the process.
The C3/4 segments of 18 porcine cervical spines were dissected and potted in cups. Specimens were preloaded, then axially compressed (1472 N), and repeatedly rotated in either pure flexion or combined flexion and side flexion at a rate of 0.5 degrees /s. Specimens that prolapsed were axially compressed and repeatedly and rotated into extension.
Based on a blinded radiologist’s review of the radiograph images, all 18 specimens contained healthy discs before testing, but after testing 2 of the 18 specimens had endplate fractures, whereas 11 of the 18 specimens had prolapsed. Prolapsed nucleus was reduced in 5 of the 11 prolapsed specimens after the reversal testing, whereas the remaining 6 did not change. Subclassification analysis revealed that the prolapsed discs that centralized had significantly less disc height loss (P < 0.01). Neither the classification of the herniation (circumferential or radial) nor the angle of lordosis of the specimens was linked to the behavior of the specimens.
This study showed that with repeated flexion, in porcine cervical spines, disc prolapse was initiated and that the displaced portion of nucleus can be directed back towards the center of the disc in response to particular active and passive movements/positions.

My comments:
This study is interesting as it backs up a central tenant of Robin McKenzie’s popular treatment for low back pain. The study reinforced that repeated spine flexion (forward bending) causes the nucleus of a spine disc to work rearward causing disc protrusions (bulges), and as discussed in my last blog, eventually extrusions (ruptured or herniated disc) where the gel-like nucleus of the disc squirts from the disc, generally resulting in severe pain and often numbness and tingling in the legs.

In this study they (in agreement with McKenzie’s theory) found that repeated extension (backward bending) could sometimes reverse the process, helping to move the disc back to the center. I’ve met one of the primary researchers in this paper (Stuart McGill) and asked him if he started recommending repeated back extension to his exercise program in light of this study. He said he still didn’t, because the repeated extension would eventually result in arthritis in the facet joints of the spine. Rather, he thought laying prone (on one’s stomach) with the head raised either on two fists or up on elbows (at most) and staying in that position for as long as 15 minutes would likely have the same positive effect without stressing the facet joints of the spine. Since then, I have added this exercise/stretch to my physical therapy treatment programs of a number of my patients with low back pain. If it provides relief of symptoms I keep it, if it causes any irritation I discard it.

McGill also cautioned that extension in this study only worked in 45% of the spines with prolapsed discs while 55% did not. Also, it seemed to work in spines with only moderate disc height loss, and not in those with severe disc height loss secondary to disc prolapse. The cut off was about 60%, in which those discs that had at least 60% disc height maintained benefited from extension, while those with disc height of less than 60% (average of ~45%) did not.

What’s interesting is that while Robin McKenzie’s basic hypothesis has been largely justified by research, his diagnostic methods and treatment programs have not. In addition to other factors I discuss in my prior blogs, this is likely because repeated extension still works less than 50% of the time in those with disc protrusion as found in this paper. Like McGill cautioned, the extension forces in McKenzie’s more aggressive extension stretches may still be too great, potentially leading to additional spine problems. I still think McKenzie’s books are worth reading for physical therapists, as I think my own treatment programs benefited a lot after I started reading books about treatment methods I didn’t necessarily agree with. McKenzie was clearly ahead of his time, coming up with his hypotheses and programs well before the majority of this research existed.

Thanks for reading my blog. If you have any questions or comments (even hostile ones) please don’t hesitate to ask/share. If you’re reading one of my older blogs, perhaps unrelated to neck or back pain, and it helps you, please remember SpineFit Yoga for you or someone you know in the future.

Chad Reilly is a Physical Therapist, obtaining his Master’s in Physical Therapy from Northern Arizona University. He graduated Summa Cum Laude with a B.S. Exercise Science also from NAU. He is a Certified Strength and Conditioning Specialist, and holds a USA Weightlifting Club Coach Certification as well as a NASM Personal Training Certificate. Chad completed his Yoga Teacher Training at Sampoorna Yoga in Goa, India.


6 responses to “Reversing Disc Protrusions, McKenzie Mostly Correct in Theory”

  1. Meha Shah

    Hi Chad

    This is Meha here and I am working as MSK physiotherapist. I am keen to know what protocol do you use for patients with cervical protrusionspecially when you are looking to reverse it. I find the Static neck neck does help but somehow I am not able to prevent rotation of cervical vertebrae for longer duration of time, Unless the patient have sedentary lifestyle or not in to sports or less of physical activities. For patients who are kind of gym person or does lots of high impact sports what i notice is vertebrae tend to rotate on and off leading into misalignment of spine, How can i prevent that. ?
    Your help is much appreciated.

    Many thanks.

    1. Chad Reilly

      Hi Meha,

      Sorry for getting back to you late. I was in India studying yoga for a month and both my time and internet access were really limited. I don’t really try and reverse disc protrusions. I might promote some mild (sustained 10-15 min rather than repeated) cervical extension if it relieves symptoms. I’m skeptical that we can feel vertebral rotations. I think it more likely that the transverse processes are bent (a lot are) than the discs rotated, such that when one tries to push them back into what feels straight, we are actually rotating them “out of” alignment. I think 90% of neck pain is simply that people look down too much or have a forward head posture. So I train them to fix that, and if they don’t want to correct it and work at it until the spine stays way more neutral (all day) then to expect to have continued pain that’s only going to worsen. I think exercise helps to strengthen the neck muscles, but most of the neck strengthening studies globally strengthened the whole upper body, which I think is important, so that holding the neck in neutral is easier to do. But probably most of it is just awareness training, or else the person will just be strong and look good while their discs continue to deteriorate.


    Thanks for such an informative website. I practice Somatic movement, Feldenkrais and Yoga. I have always valued spine extension and viewed it as a necessary healing protocol, though this has been from personal experience rather than reading any research or being aware of the McKenzie method. Seemingly there is 6000n of compression during extension?! As a Yoga practitioner yourself I wonder how you counter the information from McGill on spine extension within your practice. Any advice or reference to articles would be massively appreciated!

    1. Chad Reilly

      Hi Steven, good question, it inspired me to read McGill’s newest book before I answered.

      First I don’t try and counter Stuart McGill’s research, because I think it’s all true. More so I try and learn from his findings and incorporate it into my rehab and fitness programs, first with resistance training and now with mat based yoga exercise.

      I don’t think extension itself is generally healing, or at least not as is often done in yoga. People tend to want to take good things too far, so they’ll see a dog or cat stretch for half a second, conclude stretching is natural and good (which is probably not a bad assumption) but then ruin it by trying to stretch beyond what’s normal, or hold the stretch longer and longer, neither of which a cat or dog ever does. In modern society repeated and prolonged flexion stretches are so prominent in how we move, lift, look and even sit, that any extension probably feels like a welcome relief, and in moderation probably is allowing for some healing. However, extension taken too far can cause it’s own problems, which I describe in the extension section of why your spine hurts.

      If you read McGill’s papers and his book Low Back Disorders he derides the active extension in the Superman or Locust pose not so much because of the 6000 N of compression force, but more that force is combined with the spine being in end range extension, thus putting inordinate stress on the posterior structures of the spine, most notably the facet joints. One of McGill’s earliest research papers was measuring the forces of powerlifters, and he found compressive forces during the deadlift reaching over 18,000 N without injury. The reason I wanted to read his newest book, The Gift of Injury, was because he coauthored it with one of the strongest powerlifters of all time, who lifted considerably more than anyone in his earlier research paper, probably reaching compressive forces well above 20,000 N. And he was able to after having herniating two discs and fracturing his sacrum. So I don’t think it’s compression that’s the problem. In the case of powerlifter Brian Carroll, it was more so compression combined with flexion when lifting, an impact from a fall on his sacrum, plus frequent and sustained compression during daily activities and sitting with bad postures. Compression with a neutral spine is well tolerate by the spine and without it, we would all end up with osteoporosis.

      If your spine is healthy, locust pose probably isn’t that bad so long as you don’t try and come up all the way and crunch your facet joints. If you have back pain already, then what’s otherwise a well tolerated compressive force might irritate what are already compromised discs until they heal. It’s worth noting that if the discs have prior herniations (usually from too much flexion, sitting without lumbar support, forward folds, etc.) they will be physically shorter, and because so the facet joints will be closer together then they ought to be, and collide sooner when the spine is extended, limiting range, causing pain, and eventually facet joint arthritis.

      For SpineFit Yoga I work around this by keeping the entire flow, if not neutral, as near neutral as possible. I have people warm up with Sunbird or Bird dog’s as McGill calls them, which gives equal muscle contraction as with Locust pose, but with half the vertebral compressive force per McGill’s research, which is usually well tolerated even if the spine is injured. I don’t think Sun Birds build that much strength however, so for difficulty and long term fitness I came up with what I’m calling a “single leg, long bridge, straight leg raise,” which unfortunately you have to be a member to see. But because my bridge is kept as low as possible, extension range of motion is limited, but the extensor muscles are still worked hard enough to build real strength. Levels 2 & 1 are the same exercise are proportionally easier. Thanks for your question, I hope that helps!

      1. Hi Chad,
        I was never notified that you had answered me!
        Please accept my sincere apologies and thank you so much for taking the time to address my question with such a wonderful and erudite response which helps a lot.
        We are definitely on the same page and your practice as described mirrors mine which I have intuitively found.
        Thank you so much.

        1. Chad Reilly

          Steve, you’re very welcome and that’s very nice of you to say! Thank you.

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