The mechanisms of manual therapy in the treatment of musculoskeletal pain: Critically Appraised Paper by Stefan Schiller

Synopsis:
Summary of Bialosky, J.E. et al., 2009. The Mechanisms of Manual Therapy in the Treatment of Musculoskeletal Pain: A Comprehensive Model. Manual therapy, 14(5), pp.531–538.

Question
What are the underlying mechanisms of manual therapy (MT) in the treatment of musculoskeletal pain?
Background
MT is a specialized form of treatment directed at joints (manipulation, mobilization), soft tissue (different forms of massage) or nerve tissue (neural mobilization). Evidence exists that MT can be an effective form of treatment for various musculoskeletal disorders. However, the underlying mechanisms for its effectiveness are not understood. A better understanding thereof would help to (1) identify individuals likely to benefit from MT and (2) increase the acceptance of MT in the medical society.
Design
Narrative review of the existing literature and presentation of a comprehensive model
Need for a comprehensive model
A limitation of the current literature is the failure to acknowledge the potential for a combined effect of both biomechanical and neurophysiological mechanisms. Prior studies have often examined only one biomechanical or neurophysiological mechanism without consideration of competing explanations. A comprehensive model is needed to direct future research.
Proposed model
The proposed model suggests a mechanical stimulus that initiates a number of neurophysiological effects.
Mechanical stimulus
Even though suggested by some literature, it is questionable how much biomechanical mechanisms elicit the effect of MT because (1) lasting structural changes have not been identified, (2) clinicians are unable to reliably identify areas requiring MT via palpation tests, (3) the forces associated with MT are not specific to a given location or structure, (4) choice of technique does not seem to affect outcomes and (5) sign and symptom responses occur in areas separate from the region of application. The inconsistencies associated with a biomechanical explanation suggest that additional mechanisms may be more important. However, a mechanical force is necessary to initiate this chain of neurophysiological responses.
Neurophysiological mechanisms
Human pain experience is caused by complex interactions of the peripheral and central nervous system that cannot be directly and entirely observed by current studies. Therefore conclusions must be drawn from associated responses that indicate specific mechanisms. The model categorizes these implied neurophysiological mechanisms into (1) peripheral, (2) spinal cord and (3) supraspinal mechanisms.
Peripheral mechanisms: MT may directly affect inflammatory mediators and peripheral nociceptors that interact in the healing process and pain experience. Numerous RCTs have shown blood and serum level changes of various cytokines and neuropeptides following MT interventions. This is recognized as a potential mechanism of MT.
Spinal mechanisms: Counter irritation by MT to modulate pain in the spinal cord is another proposed mechanism recognized by the proposed model. Decreased activation of the dorsal horn was noted by functional MRI following MT. Hypoalgesia, afferent discharge, motoneuron pool activity and changes in muscle activity following MT may all indirectly implicate a spinal cord mediated effect.
Supraspinal mechanisms: Using functional MRI, one study provided direct support for these mechanisms by detecting decreased activation of supraspinal regions responsible for pain processing following a MT intervention. Several studies measured associated autonomic and opioid responses to indirectly imply supraspinal mechanisms. Expectation and psychosocial factors may also play a role in the efficacy of MT as indicated by at least one study.
Implementation of comprehensive model
The proposed comprehensive model should help researchers to identify inadequately considered mechanisms that may be influencing the effects of their examined MT intervention apart from the mechanism of the focus of their study.
Additionally, the model encourages clinicians to visualize all potential effects of MT. Manual therapists commonly depend on purported biomechanical mechanisms in the examination and treatment of their patients. Clinical outcomes are then attributed to alleviation of the biomechanical fault. This paradigm causes many of them spending much continuing education money and treatment time in search of biomechanical dysfunction of questionable validity and treatments of questionable specificity. While acknowledging a biomechanical effect, the proposed model allows clinicians to consider all potential mechanisms of MT.
Limitations of proposed model and future directions
Although the model is applicable to all forms of MT, it is intended to explain the mechanisms of MT on musculoskeletal pain. Mechanisms in the treatment of other body system are beyond the scope of this model.
It is intended to guide research regarding the mechanisms of MT. The current body of literature has not adequately accounted for non-specific effects such as placebo as a possible factor determining outcomes of MT treatments. Future mechanistic study designs should try to incorporate all mechanisms suggested by this model, ideally through interdisciplinary collaboration. They should also use technology to directly observe regions of interest and not draw their conclusions based on associated responses.
Conclusion
Since the mechanisms behind the clinical effectiveness of MT are not established, a comprehensive model is proposed to consolidate current research and guide future study designs to consider all possible mechanisms of MT and especially account for non-specific effects.

Commentary:

Bialosky et al. (2009) highlight the multitude of mechanisms that are potentially responsible for the clinically proven benefits of MT. The authors urge researchers to always consider every possible mechanism when drawing conclusions from their data. The key message to clinicians is, that the reasoning to use MT should not be based on biomechanical but rather on neurophysiological reasons.

On a critical note, it should be mentioned that the article of Bialosky et al. (2009) should be considered as evidence-based expert opinion. Even though the arguments of the authors are backed up by citations, no systematic search within the current literature was performed for the development of the proposed model. Studies that contradict the opinion of Bialosky et al. (2009) might exist that the authors are not aware of or even intentionally avoided to mention in their paper. However, other experts share the opinion of Bialosky et al. (Wright 1995) and a systematic review examining a similar research question reached a conclusion in agreement with this appraised article (Schmid et al. 2008).

Even though many clinicians with a more traditional, biomedical view will have difficulties in accepting it, the model proposed by Bialosky et al. (2009) is very valuable in the justification of MT as an intervention for patients with musculoskeletal pain. Considering that modern research has not been very successful in linking many musculoskeletal pain syndromes that are treated by manual therapists to clear biomechanical or structural sources (Bogduk 2003; Waddell 2004; Lederman 2010), the proposed model can be considered good news for the use of manual therapy in the treatment of such conditions. If dealing with non-specific pain syndromes, it is more legitimate to use a non-specific treatment technique than to reason how a specific treatment technique will influence the non-specific condition. In the end, what matters is that the intervention is safe and effective, for which there is plenty of evidence in favor of MT in the current literature (Bronfort et al. 2004; Tsertsvadze et al. 2014; Vincent et al. 2013; Pillastrini et al. 2012).
The model proposed by Bialosky et al. (2009) is also in line with the “Brickwall” model of thinking introduced by Maitland (1968). This model divides the clinical reasoning process in a theoretical side and a clinical side. In complex reasoning situations, the therapist should always consider multiple mechanisms on the theoretical side but ultimately focus with his treatment decisions on the clinical side. Within the Maitland-Concept (Hengeveld et al. 2014), the “Brickwall” model also emphasizes that theoretical explanations for clinically observed improvements will always remain hypothetical and should never be considered as facts. This way of thinking is in concordance with the appeal of Bialosky et al. (2009) for manual therapists to always consider all possible mechanisms as the underlying reason for the efficacy of their intervention.
Furthermore, accepting that the main mechanisms of MT are neurophysiological rather than biomechanical, makes MT interventions much more suitable for the treatment of chronic pain conditions from a biopsychosocial perspective. Modern guidelines on the management of chronic non-specific pain conditions usually recommend shifting the focus of the intervention away from a structural-focused approach to a cognitive-behavioral approach (Royal Dutch Society for Physical Therapy 2013; Gatchel et al. 2007). Using the model of Bialosky et al. (2009) in their explanations about treatment efficacy to the patients allows the therapists to implement the benefits of MT in the overall patient management without necessarily shifting the focus back on a tissue-based source (O’Sullivan 2011; Nijs et al. 2013; Lluch Girbés et al. 2015).
Bialosky et al. (2009) rightly mention the poor validity and reliability of palpation test in the examination procedure to decide on which MT intervention to use. However, by basing the choice of treatment technique on pain provocation tests the therapist can significantly improve the reliability of the examination procedure (Seffinger et al. 2004; Potter & Rothstein 1985). Even though a manual therapy intervention might not be structure specific, a symptom specific intervention is likely more beneficial than a randomly picked intervention. Conflicting evidence exists in the literature regarding this last statement (Aquino et al. 2009; Chiradejnant et al. 2002; Chiradejnant et al. 2003), but methodological errors as well as not a strict adherence to a symptom-guided approach might explain why some studies fail to show a difference between therapist-chosen and randomly picked treatment levels (Aquino et al. 2009; Chiradejnant et al. 2003).
I also disagree with the authors of the appraised study (Bialosky et al. 2009) that spending time for a thorough examination procedure is a waste of time. By taking much care to find the most symptomatic location or movement direction, to then decide on the ideal technique at the best location with the correct intensity, the therapist will most likely deliver a more beneficial input to the nervous system to produce the desired results then by choosing a random technique with a random intensity. Probably more importantly though, through this demonstration of precision and care, and by deliberately including the patient in the examination procedure, the therapist will greatly increase the positive expectation within the patient and thereby enhance the efficacy of the intervention. Since patient-therapist communication is usually minimized in clinical trials, the reduction of this expectation might explain why this benefit is not represented in the results of some studies (Aquino et al. 2009; Chiradejnant et al. 2003). As Bialosky et al. (2009) request themselves, future studies should choose study designs that allow conclusions about the effects of these expectation-based non-specific mechanisms.

With a focus on symptoms rather than structures, and by implementing the proposed model of Bialosky et al. (2009) in the information given to the patient, the manual therapist can effectively implement hands-on therapy without compromising a multifactorial approach within a biopsychosocial framework.

References

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