In 1981, Robin McKenzie proposed a diagnostic classification system – MDT, or Mechanical Diagnosis And Therapy - in which patients would be classified according to the mechanical and symptomatic responses to mechanical loading strategies. Diagnostic classification would then establish the appropriate criteria for treatment.

McKenzie proposed three mechanical syndromes: postural, dysfunction, and derangement. Postural syndrome is characterized by end-range stress of normal structures, thereby producing pain with sustained end-range loading. Dysfunction is characterized by end-range stress of shortened structures (secondary to scarring, fibrosis, and/or nerve root adherence), thereby producing pain with repeated movements to end-range. These two syndromes fit neatly into a traditional pathoanatomical, tissue-based model.

It is the third syndrome – the derangement syndrome – which is perhaps the most intriguing and which garners the greatest debate amongst clinicians. The derangement syndrome is characterized by “anatomical disruption or displacement within the motion segment”. But does the derangement syndrome fit into a traditional pathoanatomical model? And if not, does it matter anyways?

McKenzie noted in 1981:

“With this book I present a new concept of diagnosis for the whole musculoskeletal system. The procedures I developed for the lumbar spine to arrive at appropriate conclusions regarding diagnosis and treatment, may also be applied successfully to the thoracic and cervical spine, and indeed to all peripheral joints and their surrounding soft tissues.”  

Mechanical and symptomatic responses to mechanical loading strategies consistent with the operational definitions of the derangement syndrome are common in patients with lumbar spine pain. From a pathoanatomic perspective, it is easy to conceptualize an “anatomical disruption or displacement within the motion segment” – the lumbar intervertebral disc. In the lumbar spine, it all makes perfect sense - the lumbar intervertebral disc “deranges”, thus producing both mechanical and symptomatic responses which are alleviated with the appropriate repeated movements and/or sustained positions.

But the naysayers will then tell us that that is all fine and good, but what about the cervical spine? The cervical intervertebral disc has some significant anatomical variations and is not just a “smaller lumbar disc” like it was once thought. What about the elbow? What is “deranging” in the elbow? Or how about the shoulder – what is “deranging” there?

If I put on my pathoanatomic glasses – rose-colored ones, I might add – then I see where the issues lie. But the problem isn’t in the existence or presence of derangements – we see those mechanical and symptomatic behaviors regularly. Mechanical and symptomatic responses to mechanical loading strategies consistent with the operational definitions of the derangement syndrome are common in patients with pain of spinal and peripheral origin.

The problem lies in the color of glasses you wear to understand the musculo-skeletal system itself. Do the answers lie under the microscope? Or in the behaviors of the system itself?

The use of mechanical loading strategies – including repeated movements and sustained postures - is applicable to both spinal and extremity conditions and has great utility in providing the basis for an effective approach to patient self-care. But what is the physiological “glue” that provides consistency and context to McKenzie’s derangement syndrome throughout the musculo-skeletal system? How does this explain the mechanical and symptomatic responses we witness clinically with the derangement syndrome?

My thoughts and proposal for an answer to this challenging issue will appear next week.

Photo credits: Monica’s Dad