An overdue review of the venerable McKenzie Method (Member Post)

MDT is an “empire,” for better and worse

MDT is one of the great 20^th Century “modality empires”: proprietary methods (modes) of therapy, usually championed by a single charismatic entrepreneur (the emperor), selling books, workshops, and certifications. The emperor in this case was New Zealand physical therapist Robin McKenzie (1931–2013), who started MDT in the 1950s. It continues to be widely practiced around the world, although I suspect that its popularity has been declining. But a great many healthcare professionals — mostly physical therapists but not exclusively — have taken and appreciated MDT courses.

Unfortunately, there is a great deal of overlap between modality empires and quackery, mostly because it’s almost impossible to promote therapy methods for profit without corruption (and that’s assuming they were any good to begin with, which they often aren’t). As an example, trigger point therapy — which I have given plenty of attention and affection to in this book — is another one of the great modality empires, and it is a complex mixture of good, evil, and (mostly) just confused.

MDT is even more mainstream than trigger point therapy, and it has been so influential that much of what we think of as physical therapy today is extremely MDT-ish, so it cannot be judged simply (or even separately from PT). Like an empire, and like physical therapy in general, it is sprawling and complex, and certainly not all bad … or all good, so it defies easy summary. MDT has had several entire books devoted to it.

The heart of MDT: centralization and directional preference

Most modality empires grow out of some seed of truth, but MDT has a particularly robust one. It can attribute much of its success and popularity to the genuine prognostic power of centralization and directional preference (CDP from here on).

Before talking about CDP in any more detail, we should do a quick review:

• Centralization — The muting of spinal pain with repeated movement or sustained postures, and more specifically the tendency of pain to retreat from the periphery to the centre — hence the name. I prefer to think of it as pain “shrinkage.”
• Directional preference — The specific direction of movement or positioning that produces that centralization: usually extension, sometimes sidebending, and infrequently flexion.

Centralization (pain shrinkage) is strongly linked to happier endings to back pain stories.1 And so directional preference seems like a fine inspiration for the kind of exercise that is appropriate for back pain patients.

Back pain is a fiendishly slippery and difficult problem, obviously. In that sea of clinical uncertainty, there aren’t many life rafts. The phenomena of CDP might be one of the few: a strong prognostic sign found in many patients, and a possible justification and guide for exercise therapy.

Despite the self-help possibilities, ideally patients would explore CDP with an MDT professional. Many people can climb this mountain solo… but most will have a better time with an experienced guide. (Which is why I’m also reviewing MDT more generally here.)

Yoga’s “cobra” pose is an excellent example of a simple back extension exercise — which might be your (directional) preference. Extension is the direction most back pain patients prefer, if they have any preference.

The case for putting centralization front and centre in therapy

C & DP are no more — or less — than “it feels a bit better for a while when I lean this-a-way.” And yet much has been made of the fact that it is a genuine good-news prognostic factor, and it is also widely used as the basis for exercise prescriptions, mostly back extensions, because that’s the most common directional preference … hence the common dismissive oversimplification of critics: “McKenzie/MDT is just extension exercises.”2

Dr. Stephen May (who worked closely with McKenzie and wrote some books with him), in an interview for PT Pro Talk (episode 95):

“If you have something as highly prevalent as this, even in the chronic population, that has the potential for such a good prognosis and can guide your … management strategies, you would be foolish to ignore it.”

Or more emphatically stated later on:

“I don’t think there’s anything like it in terms of its high prevalence rate, its potential to indicate a good prognosis, and its potential to indicate a management strategy. And if a clinician doesn’t take such a gift into account they would seem to be shooting themselves in the foot in a very daft way.”

I’m a little uncomfortable with the implication that you’re a bit of a ninny if you don’t take this seriously. A more gracious interpretation is just that centralization is actually a useful thing to understand, worth considering. It probably is a legit phenomenon, something a bit peculiar to the nature of back pain: not all conditions ease with specific positions/movements, that’s for sure.

But are we really foot-shootin’ fools if we don’t take CDP seriously? That seems a bit much. There are reasonable reasons to question its importance…

Three reasons to doubt that centralization is all it’s cracked up to be

1. It’s possible, maybe even likely, that centralization just doesn’t actually mean much. It might just be a sign of a milder case. That is, it may only be a “good sign” because it’s just what you see with tamer and more tractable cases of back pain: Kilpikoski et al showed that it seems to occur mainly in milder cases, while non-centralizers have more pain/disability on average. The difference wasn’t huge, but it’s consistent with the rather obvious idea that it’s easier to find relieving movements and positions in less severe cases.3 So CDP can also just be seen as fancy framing of something super simple: “do whatever makes it feel better, if anything does” … and that mostly happens in cases that were destined for a good prognosis anyway.
2. The only way in which the CDP seed-of-truth has been validated is as a positive prognostic sign. There’s basically zero evidence that exercise guided by directional preference is an efficacious treatment. In the self-help section I mentioned one twenty-year-old promising trial.4 But an unreplicated trial in this business is the sound of one-hand clapping. In the quote above, May says that centralization has the “potential to indicate a management strategy,” but his 2018 paper clearly states — in the abstract and again in the main text — that there is “no evidence that these [CDP] might be important treatment effect modifiers.”5 And that’s after how many years? When May himself admits there’s no evidence that directional preference can guide effective treatment, it’s a little hard to square that with his opinion that we’re shooting ourselves in the foot if we ignore it. It actually seems like there’s a pretty decent argument for ignoring it (or at least not taking it super seriously).

3. It’s important historical context that MDT started in a way that is all-too familiar from the pre-scientific era of medicine: with an origin story of treatment success, with an inspiring clinical anecdote. Robin McKenzie tells the story in his book, Treat Your Own Back. “It all began when I noticed…” is how a lot of snakes oils get their start. This doesn’t mean McKenzie was wrong, but it is a big ol’ red flag.

   It’s dangerously easy for medical pet theories to get out of hand. You start with an observation, you cook up a pretty hypothesis, and before you know it you are deeply invested in it and very much inclined to “twist facts to suit theories, instead of theories to suit facts.” McKenzie worked on this idea for decades before anyone even tried to study it more rigorously. And although it certainly seems like the prognostic power of centralization has finally been rigorously validated in more recent history, it’s not like it’s a lot of data or all that rigorous, and it’s definitely possible for researchers to get the answers they want out of their studies. So I’m not saying centralization isn’t actually prognostic and a good inspiration for exercise therapy, but I am saying it’s possible, and things that start like this in medicine rarely end well.

CDP is by far the most distinctive major feature of MDT, so if MDT isn’t effective as a whole, then it’s biggest active ingredient probably ain’t so active. So what else does it offer? And does the whole enchilada help back pain patients?

MDT as a system

MDT is a complex approach to physical therapy that generally favours a “mechanical” perspective — it’s right in the name! And I am allergic to that. In many ways, MDT seems like the Death Star to this book’s Rebellion. Despite that, I am not actually a huge critic of MDT. Why not? It seems like a ripe target!

I cut MDT some slack because it isn’t particularly dogmatic or formulaic. It’s reputation for being “just extension exercises” is undeserved. It’s more a school of thought about how to do physical therapy that defies easy summary. The pitch for MDT is almost just “Like traditional physical therapy... but better! With more specific knowledge about back pain!” It certainly leans towards biomechanical thinking, but it doesn't seem to be limited by it — despite the name.

Unfortunately, MDT also just doesn’t work very well. The evidence is underwhelming.

A 2018 scientific review wasn’t entirely negative, but it was deep in “damned with faint praise” territory.6

In 2019, Halliday et al noted that the effects of MDT are somewhat larger “when the core principles are followed”7 — but they still weren’t exactly big effects. And how often do professionals in the real world successfully follow the core principles anyway?

In early 2023, MDT marketing hype had a particularly nasty collision with science. A big scientific review, Almeida et al, concluded:8

Based on low- to very low-certainty evidence, the treatment effects for pain and disability found in our review were not clinically important. Thus, we can conclude that the McKenzie method is not an effective treatment for (sub)acute NSLBP.

Although Almeida et al is very “garbage in, garbage out,” it did establish that there is in fact not any significant body of evidence… and what little there is shows little or no benefit. Despite a very likely pro-MDT bias in the trials that do exist, they still couldn’t p-hack their way to a happy ending.

The evidence of MDT efficacy as a whole is exactly as mediocre as all other smorgasbord therapies. Bummer.

•

For many professionals, any guru-driven therapeutic method is a deal-breaker, even if that guru is a legit smartypants that we can all learn from. Like all modalities, MDT can be a bit cultish and over-sold — because no brand succeeds without some marketing hype, and attracting devotees who will spread and amplify that hype. And marketing and buzz rely heavily oversimplification and bullshit. For instance, the McKenzie system website proudly declares that “The McKenzie Method® of Mechanical Diagnosis and Therapy® (MDT) is an internationally researched and acclaimed system” … which is obvious marketing noise. The reality is that it is barely researched.

The MDT hype isn’t inherently evil. It overlaps with sincere marketing. I am not naive: I understand that you have to put butts in seats to pay the bills, and hardly anything can happen in this world without the engine of commerce. I’m not saying MDT can’t be useful in the right hands, or that no one ever learns anything useful from it. But it also does not have any clear advantage over the competition. It is just another perspective, another way to help — and one that is generally too structuralist for my tastes. Not really my cup of tea.

Notes

1. May S, Runge N, Aina A. Centralization and directional preference: An updated systematic review with synthesis of previous evidence. Musculoskelet Sci Pract. 2018 Dec;38:53–62. PubMed 30273918 ❐

2. Wikipedia puts this right in the intro to their McKenzie method page: "McKenzie exercises involve spinal extension exercises…."

   It’s not just that, obviously, and I don’t think anyone’s actually confused about this (and if they are it’s because they aren’t paying attention or giving credit where due). The more nuanced version is this: “McKenzie Method and MDT have a strong focus on screening for centralization and identifying directional preference where it exists and that usually turns out to be extension when a DP is clear, and so that is then used a reasonable justification for prescribing extension exercises… but “often” isn’t always! Some people don’t have any directional preference, or they have a different one, and extension exercise can make some people worse. So obviously there’s a lot more to MDT than just “treat back pain with extension exercises.”

3. Kilpikoski S, Suominen EN, Repo JP, et al. Comparison of magnetic resonance imaging findings among sciatica patients classified as centralizers or non-centralizers. J Man Manip Ther. 2023 Feb:1–10. PubMed 36756675 ❐
4. Long A, Donelson R, Fung T. Does it matter which exercise? A randomized control trial of exercise for low back pain. Spine (Phila Pa 1976). 2004 Dec;29(23):2593–602. PubMed 15564907 ❐

5. May, Runge, and Aina (op. cit.): “Because of the nature of all study designs it was not possible to determine if either symptom response was a useful treatment effect modifier; no trial had determined their presence at baseline, and then randomized patients to management based on those concepts versus another management strategy.”

6. Lam OT, Strenger DM, Chan-Fee M, et al. Effectiveness of the McKenzie Method of Mechanical Diagnosis and Therapy for Treating Low Back Pain: Literature Review With Meta-analysis. J Orthop Sports Phys Ther. 2018 Jun;48(6):476–490. PubMed 29602304 ❐
7. Halliday MH, Garcia AN, Amorim AB, et al. Treatment Effect Sizes of Mechanical Diagnosis and Therapy for Pain and Disability in Patients With Low Back Pain: A Systematic Review. J Orthop Sports Phys Ther. 2019 Apr;49(4):219–229. PubMed 30759358 ❐
8. Almeida MO, Narciso Garcia A, Menezes Costa LC, et al. The McKenzie method for (sub)acute non-specific low back pain. Cochrane Database Syst Rev. 2023 Apr;4(4):CD009711. PubMed 37017272 ❐ PainSci Bibliography 51299 ❐