McKenzie: You’re all I ever needed /
So tell me what to do now?

What do you think about the McKenzie method? Also known as Mechanical Diagnosis and Therapy, the McKenzie method is popular and influential.

But is it any good?

This issue of Physio Weekly addresses some recent research findings on spinal pain, with some interesting implications for physios.

Let Me Show You a Few Things

If MDT is new to you, then here is a quick and dirty rundown. MDT is a classification system that divides patients into four groups.
 

  1. Posture syndrome is caused by “mechanical deformation of soft tissues or vascular insufficiency” which comes from prolonged positional stresses. The way to alleviate pain for this syndrome, as MDT suggests, is to correct the posture.
     
  2. Dysfunction syndrome is caused again by “mechanical deformation” of structurally impaired soft tissues, though this time pain only presents at end range movement. Movement is therefore impaired in one or more directions, though pain should subside when the patient is not at the end range movement in question. Treatment for this syndrome involves the goal of remodeling tissue.
     
  3. Derangement syndrome is allegedly the most common of the syndromes, and is associated with a mechanical obstruction of the affected joint. For derangement syndrome, one goal is to find the directional preference, which may or may not centralize symptoms. There may be irreducible or reducible derangements; irreducible derangements occur when no loading strategies decrease, abolish, or centralize symptoms, whereas reducible derangements find loading strategies that decrease, abolish, or centralize symptoms. Anterior derangements have a directional preference for flexion, and posterior derangements prefer extension.
     
  4. Other. The other category includes pathologies like cancer, cauda equina syndrome, spinal fracture, infection. This category also includes “chronic pain syndrome,” post-surgical pain, ankylosing spondylitis, spinal stenosis, and pelvic girdle pain, among others.

As Long As I’ve Got My Suit & Tie

One of the most important scientific questions to ask about a classification system is whether the system is reliable. In other words, will two clinicians be able to agree on how to classify the same patient? If not, then the system isn’t of much use in my opinion.
 

Garcia et al. (2018) put this question to the test in a JOSPT systematic review. The authors evaluated 12 studies of spinal pain. The authors found acceptable inter-rater reliability with respect to classifying pain into syndromes and sub-syndromes in low back pain, but only when performed by clinicians who were either credentialed in MDT or had the MDT diploma. There is conflicting evidence of inter-rater reliability with respect to identifying the centralization phenomenon or directional preference in low back pain, and there is mixed evidence for inter-rater reliability for any aspect of evaluation of neck pain or thoracic pain.

I’m not sure what to make of these findings, because on one hand it’s a decent advertisement for taking more courses in MDT in order to get credentialed, but on the other hand, reliability is only one aspect. Does it actually lead to better outcomes?

Another recent JOSPT paper, this time a meta-analysis by Lam and colleagues, tested this questions for low back pain. The authors extracted data from 11 studies of acute and chronic back and neck pain. In acute low back pain, there was no difference in pain resolution or disability between MDT and other physical therapy interventions overall. In chronic low back pain, the authors concluded that MDT offers an advantage over “exercise” alone with respect to disability (not pain), and was not more effective than a combination of manual therapy and exercise.

Baby bye, bye, bye?

I believe that it is vital to address some interesting aspects of the studies included in this meta-analysis.

First, some of the studies included only patients that fit within the derangement subgroup, and others included only patients that fit within the 3 mechanical syndromes (not the “other” category).

Second, some of the control groups were poorly defined, or poorly dosed, such that it may be unfair to say that MDT outperformed “exercise.”

Third, the control groups were not tailored to patients, whereas other paradigms such as treatment-based classification, movement system impairments, the STarT Back approach, or cognitive functional therapy all offer tailored treatment.


One of my primary concerns about systems like MDT is — well — how mechanical it is. Low back pain has a strong psychosocial component, and a recent study by Lam and colleagues identified some interesting information about patients with chronic neck pain.

The study found that patients could be sorted into derangement, dysfunction, posture, and other subgroups at a rate of 74.4, 2.4, 1.2, and 20.7 percent respectively. I’m blown away by how rare the dysfunction and posture subgroups are.

The study also examined the prevalence of central sensitization and psychological distress, with findings that a whopping 62% had central sensitization (defined as >= 40 on the Central Sensitization Inventory). Importantly, 64.7% of the derangement group also had central sensitization, and 38% of the sample had a combination of derangement, central sensitization, and kinesiophobia. The authors conclude that merely classifying patients into their respective MDT subgroups may miss crucial characteristics of patients.
 

What’s your conclusion? If you have experience with MDT or other classification systems, then we would love to hear from you on the Facebook group, or on Twitter — just use the hashtag #physioweekly.

What’s Next?

If you liked this post, then I would love to hear from you! Leave a comment or tweet me @zachrstearns — just use the hashtag #physioweekly.

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