Posted on 10 April, 2014 by Joe Brence

Recently, many in the manual therapy community have been questioning the mechanisms of how spinal manipulation works.  While some hold onto the belief that spinal manipulation has more of a biomechanical and structural influence, others believe the effects to be neurophysiological.    In a 2011 study published in the journal Spine, Fritz et al concluded that the mechanisms are likely multi-factorial.  These researchers reported measuring a decrease in global and terminal stiffness and improved recruitment of the lumbar multifidus following a lumbar manipulation.¹  A more recent randomized controlled trial published in Physical Therapyassessed and compared the immediate effects of regional and non-regional spinal manipulation in patients with chronic low back pain.²   This study was necessary to determine if we need to segmentally target vertebrae to get the positive effects, that others have found.   Let’s take a closer look at what they did and what they discovered:

The Methods:

This study included 148 individuals who had at least a 12-week history of low back pain.  They were divided into one of two groups to receive either a:  lumbar manipulation (to the painful segments) or upper thoracic manipulation (non-regional).   Pain, pain pressure thresholds and level of perceived disability (via Roland-Morris Disability Questionnaire) were measured by a blinded researcher at baseline and following the intervention.

The Findings:

The researchers found that there were “immediate” effects in pain and pain pressure thresholds following both manipulations.  Furthermore, they found that the degree of reduction did not differ between the two groups.  Each appeared to have an immediate 30% reduction in pain intensity.

What this means:

This study refutes the concept that a biomechanical approach needs to be taken when manipulation is performed to those with chronic low back pain (it further supports the notion that manipulation likely elicits a neurophysiologic response).  It also makes one speculate the idea that the dramatization of manipulation may elicit non-specific effects (expectations and psychosocial factors) and that environment or interaction may have some effect on outcomes.

The cohort tested in this study had chronic symptoms.   From our understanding of pain neurophysiology (as I have written about in the past), when a tissue is damaged, an output of pain will likely occur to protect it (this leads to an adaptation within the pain pathways). The longer (more chronic)  the nervous system reacts to protect the tissue, the more efficient it becomes. This creates a nervous system that is more “sensitive” and eventually, the simple suspicion that a tissue is in danger will cause it to react.  A prolonged output of pain can result in a process called central sensitization which is due to an augmentation of responsiveness of central neurons to input from unimodel and polymodal nociceptors.. This results in a central process of an increased responsiveness to peripheral stimuli, even if they are non-threatening.

This study demonstrated that manipulation (even outside of the region of suspected damage), can alter this sensitivity.  It appears to make the brain less reactive, demonstrated by the “reduced pain”.

Limitations:

• The researchers used “Mitchell’s Test” to verify vertebral position and mobility for the regional manipulation.  In a search of the literature, I was unable to find any literature which has validated or found this method reliable.
• The researchers only assessed “immediate” effects and did not track long-term outcomes.  Between-session changes were not even accounted for.
• This study only involved one therapist who applied the interventions.  The interactions with this one individual may limit clinical variability and applicability of results.
• This study did not assess a combination of manipulation and therapeutic exercise, which is more likely to occur in clinical practice.

Conclusion:

We must be cautious when interpreting the results from this study.  With the manual techniques being performed in isolation, and only immediate effects measured, the applicability to clinical practice is limited.  This study does have importance for our understanding of “how manipulation works” but I would be interested to see if its reproducible.  We shall wait and see.

1. Fritz JM, Koppenhaver SL, Kawchuk GN, et al. Preliminary investigations of the mechanisms underlying the effects of manipulation: exploration of a multivariate model including spinal stiffness, multifidus recruitment, and clinical findings. Spine 2011; 36: 1772-1781.
2. de Oliveira RF, Liebano RE, Costa LCM, et al. Immediate effects of region-specific and non-region specific spinal manipulative therapy in patients with chronic low back pain: a randomized controlled trial. Physical Therapy 2013 Published online February 21, 2013 doi: 10.2522/ptj.20120256.

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