Author Names
Sparks, C., Cleland, J., Elliott, J., Zagardo, M., Liu, W.C.
Reviewer Name
Sara Yuen, student physical therapist
Reviewer Affiliations
Duke University School of Medicine, Doctor of Physical Therapy Division
Paper Abstract
Study Design: Case series. Objectives: To use blood oxygenation level-dependent functional magnetic resonance imaging (fMRI) to determine if supraspinal activation in response to noxious mechanical stimuli varies pre-and post-thrust manipulation to the thoracic spine. Background: Recent studies have demonstrated the effectiveness of thoracic thrust manipulation in reducing pain and improving function in some individuals with neck and shoulder pain. However, the mechanisms by which manipulation exerts such effects remain largely unexplained. The use of fMRI in the animal model has revealed a decrease in cortical activity in response to noxious stimuli following manual joint mobilization. Supraspinal mediation contributing to hypoalgesia in humans may be triggered following spinal manipulation. Methods: Ten healthy volunteers (5 women, 5 men) between the ages of 23 and 48 years (mean, 31.2 years) were recruited. Subjects underwent fMRI scanning while receiving noxious stimuli applied to the cuticle of the index finger at a rate of 1 Hz for periods of 15 seconds, alternating with periods of 15 seconds without stimuli, for a total duration of 5 minutes. Subjects then received a supine thrust manipulation directed to the mid-thoracic spine and were immediately returned to the scanner for reimaging with a second delivery of noxious stimuli. An 11-point numeric pain rating scale was administered immediately after the application of noxious stimuli, premanipulation and postmanipulation. Blood oxygenation level-dependent fMRI recorded the cerebral hemodynamic response to the painful stimuli premanipulation and postmanipulation. Results: The data indicated a significant reduction in subjects’ perception of pain (P<.01), as well as a reduction in cerebral blood flow as measured by the blood oxygenation level-dependent response following manipulation to areas associated with the pain matrix (P<.05). There was a significant relationship between reduced activation in the insular cortex and decreased subjective pain ratings on the numeric pain rating scale (r = 0.59, P<.05). Conclusion: This study provides preliminary evidence that suggests that supraspinal mechanisms may be associated with thoracic thrust manipulation and hypoalgesia. However, because the study lacked a control group, the results do not allow for the discernment of the causative effects of manipulation, which may also be related to changes in levels of subjects’ fear, anxiety, or expectation of successful outcomes with manipulation. Future investigations should strive to elicit more conclusive findings in the form of randomized clinical trials.
NIH Risk of Bias Tool
Was the study question or objective clearly stated?
- Yes
Was the study population clearly and fully described, including a case definition?
- Yes
Were the cases consecutive?
- Yes
Were the subjects comparable?
- Yes
Was the intervention clearly described?
- Yes
Were the outcome measures clearly defined, valid, reliable, and implemented consistently across all study participants?
- Yes
Was the length of follow-up adequate?
- Cannot Determine, Not Recorded, Not Applicable
Were the statistical methods well-described?
- Yes
Were the results well-described?
- Yes
Key Finding #1
The study explores the potential of fMRI to help identify supraspinal structures associated with pain reduction following spinal manipulation.
Key Finding #2
The insular cortex was the only area analyzed that showed a significant relationship with the reduction in subjective pain reports using the verbal 11- point numeric pain rating scale.
Key Finding #3
This study offers insight into mechanisms that might underlie manual therapy’s contribution to pain management via the insular cortex. The insular cortex is part of the limbic system and is theorized to be involved in modulating how much attention the patient should allot to the nociceptive stimulus based on memory and the selective transmission of sensory information based on context. It is possible that high velocity end-range thrust manipulations to the spine affect that neural process.
Please provide your summary of the paper
It is a classic question: By what mechanism(s) does spinal manipulation affect a patient’s pain reduction? This study uses hemodynamic displacement as a theorized correlate of neural activity to measure levels of activation to noxious stimuli pre and post thrust manipulation. Although the real-world processing of pain is complicated by other psychosocial and physiological stimuli, the authors of this paper state that previous literature notes the “somatosensory cortices, insula, anterior cingulate cortex, the premotor and supplementary motor areas, and subcortical structures, including the thalami and amygdala” are the cortical and subcortical structures that are most commonly activated in correlation with nociception. A comparison of pre and post manipulation imaging revealed a significant decrease in activation in those brain structures following thrust manipulation to the thoracic spine.
This thoracic thrust manipulation technique was described as “a high velocity, end-range, anterior/ posterior force applied through the elbows and directed to the midthoracic spine on the lower thoracic spine in cervical thoracic flexion…. performed with the patient positioned in supine….[T]he therapist used her manipulative hand to stabilize the inferior vertebra of the targeted motion segment and used her body to push down through the patient’s arms, performing a high velocity, low amplitude thrust.”
The authors single out the insular cortex as the only area analyzed that showed a significant relationship with the reduction in subjective pain reports using the verbal 11- point numeric pain rating scale. The authors also discuss that belief in the effectiveness of thrust manipulation and habituation may also modulate participant’s expectations and the excitability or inhibition of their dorsal horn structures to fire and report sensory information up the chain. The authors suggest pain reduction following high velocity, end-range manipulation to the thoracic spine may be influenced by cortical and subcortical interactions within the human brain.
A limitation of fMRI studies is their ecological validity–a real patient’s pain experienced during activity out in the community is not likely well simulated by monofilaments applied to the finger, and no one lives in an fMRI. Another limitation is that the participants were recruited from a “physical therapist education program.” They may have had prior beliefs about manual therapy. The sample size of the study is small and performed on healthy, pain-free adults– different from the patient population to which the treatment technique would be applied. This study also lacked a control group and does not follow the participants’ change over time. The authors write that this was purposeful, as their objective was to create a testing protocol to apply noxious stimuli and fMRI pre and post manipulation to a human population.
Please provide your clinical interpretation of this paper. Include how this study may impact clinical practice and how the results can be implemented.
Clinicians should keep in mind that while fMRI studies can be useful, an fMRI measures changes in levels of deoxygenated hemoglobin; it measures a correlate of neural activity, not neural activity itself. As these authors put it, images allow, “inferences to be made regarding neural activity within the brain.” For these reasons, clinicians should not throw out fMRI studies altogether, but approach them with a healthy perspective. It is helpful to remember that firing a specific neuron does not repeatedly lead to the same physiological action or experience, it is not a one-to-one relationship that can be applied across all patients. The nervous system is a network of firings continuously adapting its wirings based on an individual’s experiences.
