Mechanisms of Manual Therapy

What does Manual Therapy (MT) do?

By MT I mean what do our passive joint mobilisation techniques do?

The following summarises some interesting research regarding the Mechanisms of Manual Therapy.

Schmid et al (2008)

• Conducted a systematic review of the literature in relation to the effects of MT. They concluded that:
  • MT may help with muscle activation by reducing pain and hence the effects of pain inhibition.
  • Reducing pain may also:
    • assist with restoration of movement.
    • assist in promoting normal physiological/biological function in the area.
    • complement education etc. to address CNS aspects of pain (e.g. central sensitization).
  • MT can assist the regulation of the top/down, bottom/up pain regulatory pathways by facilitating the inhibitory pain modulating pathways.
  • We must be wary to not increase pain significantly with MT as it can lead to promotion of inhibition of inhibitory pain modulating pathways via the above-mentioned mechanisms.

Bialosky et al (2009)

• Concluded the following:
  • Mechanical Stimulus
    • Whilst the literature suggests a biomechanical effect from MT, lasting structural changes have not been identified.
    • In addition the choice of technique does not seem to effect outcome and the sign and symptom response is also shown to occur in areas separate from the region of application.
    • Given the above it is likely that the mechanical force from the MT causes predominantly a neurophysiological effect/mechanism that results in the observed outcomes.
  • Neurophysiological Mechanism
    • Evidence of hypoalgesia and sympathetic responses following MT. This suggests neurophysiological effects of MT that are likely to be originating from peripheral mechanisms, spinal cord mechanisms, and/or supraspinal mechanisms.
    • Peripheral Mechanisms
      • Evidence of reduction in cytokine and substance P levels in patients receiving MT (compared to sham MT or control groups).
    • Spinal Mechanisms
      • MT has a likely spinal cord mediated effect given that has been associated with:
        • Hypoalgesia
        • Afferent discharge
        • Motoneuron pool effect
        • Changes in muscle activity
    • Supraspinal Mechanisms
      • MT is proposed to have an effect on supraspinal structures such as the anterior cingulate cortex (ACC), amygdala, periaqueductal gray (PAG) and rostral ventral medulla (RVM).
      • Support for the supraspinal effects is shown given research findings of MT causing:
        • a trend towards decreased activation in supraspinal regions responsible for central pain processing.
  • The clinical use of MT is frequently dependent upon a purported biomechanical mechanism e.g. a mal-aligned joint or a hypomobile joint/soft tissue. A MT technique may then be used to impart a specific movement to the observed dysfunction. Clinical outcomes are then attributed to alleviation of the biomechanical fault. Such practice is common and has lead to many continuing education dollars and valuable clinical time spent in search of biomechanical dysfunction of questionable validity and treatments of questionable specificity.
  • The limitation to the current literature is the failure to account for non-specific mechanisms, such as placebo, associated with MT in the treatment of musculoskeletal pain. Given that a number of neurophysiological effects associated with MT are also associated with non-specific effects such as placebo, future studies on MT should consider determining the influence of these non-specific effects.

Yeo and Wright (2011)

• Assessed the response of subjects with sub-acute ankle sprains to an accessory ankle joint mobilisation.
• Dorsiflexion ROM, Pressure pain thresholds (PPT), Visual Analogue Scale (VAS) of pain and Ankle Functional Scores were assessed before and after the mobilisation.
• A manual contact control group and no contact control group were also included in the study.
• Results:
  • The mobilisation group demonstrated significant improvements in PPT and Ankle ROM when compared to the control groups.
  • There was no significant improvement in VAS or Functional Scores in any of the 3 treatment groups.

Zusman (2011)

• A discussion paper that surmised the following key points regarding effects of MT/mobilisation:
  • MT was initially thought to be addressing pain secondary to correction of biomechanical joint/muscle faults.
    • This belief still makes an important non-specific (? placebo) contribution to the patients recovery.
  • Research implies a negligible structural-anatomical-biomechanical basis for MT.
  • Major clinical value of MT seems to lie with stimulus-induced (temporary) inhibition of pain.
  • In addition to inhibiting pain, MT has been shown to influence autonomic nervous system function (sudomotor, heart rate, blood pressure and plasma hormones) and the motor system (muscle power).
  • Whilst effect sizes of MT may not always be large, they are convincingly significant.
  • Little doubt that MT activates descending brainstem pain inhibitory pathways. This is a mechanism of significant clinical importance when it comes to manual mobilisation of soft tissue and is in fact the only mechanism known so far.
  • The endorphin system does not seem to be involved.
  • The demonstration of extra-segmental effects (clinical benefit from mechanical stimuli applied some distance from the identified problem) suggests that MT does not appear to be structurally specific.
  • The mechanism of MT appears to be one of peripheral mechanical stimulus-induced long-term depression (LTD) of central synaptic function.
  • The parameters associated with inducing LTD are:
    • Low stimulus frequency 1-2Hz (1-2 per second).
    • Should be delivered for some minutes.
    • There appears to be an additive effect i.e. the depression/inhibition is likely to deepen with successive bouts (3 or 4 repetitions).
    • Interestingly these parameters appear to fit the typical “Maitland” treatment parameters!

Zusman (2013)

• “I for one completely endorse ‘hands-on’ with its currently well recognised (stimulus-induced pain inhibition) and hopefully other yet to be revealed mechanisms”.

My brief conclusion on all the above being:

MT would seem to primarily have a neurophysiological effect, rather than a biomechanical effect (reducing/correcting a biomechanical fault such as a “stuck” joint or “tight” muscle). Nevertheless reduction in pain from correctly and appropriately applied MT is no doubt a powerful clinical tool for us to utilise. Perhaps some of us just need to rethink what our MT techniques are most likely doing.

Thoughts? Comments?

References:

Bialosky JE, Bishop MD, Price DD, Robinson ME, George SZ. The mechanisms of manual therapy in the treatment of musculoskeletal pain: a comprehensive model. Man Ther. 2009 Oct;14(5):531-8. 

Schmid A, Brunner F, Wright A, Bachmann LM. Paradigm shift in manual therapy? Evidence for a central nervous system component in the response to passive cervical joint mobilisation. Man Ther. 2008 Oct;13(5):387-96. 

Yeo HK, Wright A. Hypoalgesic effect of a passive accessory mobilisation technique in patients with lateral ankle pain. Man Ther. 2011 Aug;16(4):373-7.