Thoracic Spinal Manipulative Therapy
Chapter 5: Conclusion of Dissertation
The purpose of this dissertation research was to examine the affects of thoracic spinal manipulative therapy (SMT) on thoracic spine and scapular kinematics, thoracic excursion, and pressure pain sensitivity in patients with subacromial pain syndrome. Several single-arm clinical trials have reported clinical improvements with the use of thoracic SMT in treating patients with shoulder pain.14, 61, 79 Additionally, evidence exists in randomized clinical trials showing that thoracic SMT as part of a multi-modal manual therapy treatment approach leads to greater clinical improvements in patients receiving manual therapy compared to treatment groups receiving rehabilitative exercise and primary care treatments for shoulder pain.3, 6, 91 One previous single-arm trial has assessed the affects of thoracic SMT on scapular kinematics and trunk range of motion measurements and found only a small, and clinically insignificant, increase in scapular upward rotation following treatment.63 That study also reported improvements in patient rated outcomes of pain and Penn scores.63 These single-arm trials lacked a control group from which to draw direct comparisons.
Manual therapy has been shown to reduce the symptoms of shoulder pain.3, 4, 6, 10, 74, 75, 91 Clinically, manual therapy may be directed at the shoulder or the axial skeleton based on patient presentation and clinical exam findings. There are a multitude of possible mechanisms by which manual therapy intervention may help to improve the symptoms of musculoskeletal pain.
Researchers have suggested that the effects of manual therapy may involve biomechanical and/or neurophysiologic mechanisms, and both types of variables should be included in studies of
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manual therapy.9, 63 Therefore, this research assessed biomechanical factors at the thoracic spine and shoulder in response to thoracic manipulation, as well as pressure pain sensitivity over the deltoid and the lower trapezius muscles. This allowed for comparisons at the affected region of the shoulder and the region of application of treatment, in close proximity to the thoracic spine.
Chapter 2 provided a systematic review of randomized controlled trials (RCT) that used manual techniques at the shoulder and the thoracic spine in treating shoulder pain symptoms.
Improvements in patient-rated outcomes were seen more often in the studies that incorporated thoracic SMT as part of the manual therapy intervention.3, 6, 91 The RCTs that applied treatment only at the shoulder girdle provided mixed results with respect to patient-rated outcomes.2, 4, 10, 19, 20, 38, 62, 74, 75, 92 To date, there has not been a published randomized clinical trial examining thoracic SMT alone as a treatment for shoulder pain.
The only previous study to assess immediate scapular kinematic changes in response to thoracic SMT lacked a comparator.63 Similarly, two clinical trials assessing the immediate effects of thoracic SMT on shoulder pain also lacked comparator groups.14, 79 Therefore, the research for this dissertation compared kinematic changes at the thoracic spine and shoulder, as well patient-rated outcomes from the treatment of subacromial pain syndrome with thoracic SMT versus a sham SMT. Chapter 3 of this dissertation reported the findings of the thoracic spine and shoulder kinematics during arm elevation, as well as thoracic excursion following thoracic SMT.
There were no differences noted between thoracic SMT or the sham thoracic SMT treatment groups in any of the thoracic or scapular variable, but both treatment groups showed greater scapular external rotation during the arm elevation task following treatment. This study assessed thoracic kinematics during an arm elevation task, as well as a measure of overall excursion from maximum flexion to maximum extension. Unlike the measure of thoracic displacement in
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relation to a global reference that was measured by Muth et al.,63 this dissertation research used a static measure of excursion of the thoracic spine motion based on angular measurement of this region of the spine rather than their measure of diplacement of the thoracic relative to the global coordinate system. We also measured active thoracic kinematics during an arm elevation activity. Similarly to the results reported by Muth et al., we found no differences in thoracic motion with thoracic excursion or thoracic kinematics during the arm elevation task.
A study in patients with neck pain measuring pressure pain thresholds (PPT) at the neck, elbow, and leg following treatment with either cervical or thoracic SMT found improvements in both groups but no differences between the treatment groups.52 The use of cervical SMT in isolation has also shown decreases in pressure pain sensitivity at the cervical region and regions innervated by cervical spinal levels in people with musculoskeletal pain.27, 31, 51, 52, 88 However, this region specific effect was not seen at the lumbar region following lumbar manipulation.23, 28 Chapter 4 of this dissertation focused on examining changes in PPT taken at the shoulder (over the deltoid) and at the thoracic region (over the lower trapezius) in comparison to patient-rated outcomes. Despite improvements noted in patient-rated pain, Penn shoulder scale, and global rating of changes that occurred in both the thoracic and sham SMT groups, no change in PPT was found to accompany these improvements. It is possible that the level specific results seen with respect to cervical manipulation may not be seen with treatment of the thoracic spine. It is also possible that the mechanism of reduction of shoulder pain may involve neurophysiologic mechanisms that may be better assessed by methods of experimental pain measurement other than the mechanical stimulus from pressure algometry.
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Clinical Implications
The results of this research have implications for clinicians using thoracic SMT to treat patients with shoulder pain. The patients who participated within this research showed decreases in pain, improvements in shoulder function, and positive ratings of change following treatment with a single dose of thoracic SMT or a sham thoracic SMT. However, there were no significant differences between the two treatment groups in the mechanistic measures of scapular or thoracic kinematics, thoracic excursion, or pressure pain sensitivity at the thoracic region or the shoulder.
Based on the lack of difference in mechanistic measures between the treatment groups, the improvements noted in patient-rated outcomes may be due in part to placebo effect, positive contributions from manual contact, interatction with a healthcare provider, or the natural course of disease. It is also possible that a single dose of thoracic SMT may lead to changes that are perceivable by the patient but not yet measurable within the design of this study. Clinically, manual therapy interventions are typically provided in multiple doses over time, as well as combined with other therapeutic modalities. Therefore, the positive changes in patient-rated outcomes observed in this study could have been further enhanced with multiple treatments over time or in combination with other therapeutic modalities.
The lack of significant changes in scapular and thoracic kinematics and thoracic excursion leads to question whether a biomechanical model is the most appropriate method of assessing patients for treatment with thoracic SMT. It is possible that particular medical history or examination findings may be predictors for patients who respond to manual therapy for musculoskeletal disorders. Studies examining the effects of SMT techniques at the thoracic spine for shoulder pain and the lumbar spine for low back pain have reported a cluster of
symptoms from patient history and clinical exam findings that predict success with SMT.33, 61 It
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is also possible that predictive variables may identify individuals with a natural history that leads to quicker symptom resolution with treatment rather than a positive response to SMT.
Researches have noted that SMT and manual therapy in general may have several mechanistic affects that lead to positive patient outcomes.7, 9, 37 Therefore, improvements in patient-rated outcomes in the absence of significant changes in kinematics or pressure pain sensitivity may mean that thoracic SMT has benefits for patients with shoulder pain through mechanisms other than those measured in this study.
Future Research
Further research is needed to assess the mechanisms of thoracic SMT in patients with shoulder pain. Clinical trials noting positive improvements in shoulder pain from thoracic SMT have used multiple treatment doses.3, 6, 61, 91 Therefore, future research examining changes in kinematics following SMT should examine changes over time following multiple treatments rather than just immediate effects from a single dose of treatment. Comparisons of treatments such as exercise with and without augmentation with thoracic SMT may also help to discern additional mechanistic effects that could be provided by thoracic SMT. It is possible that factors associated with patient history and clinical exam findings may influence or predict success with treatment of shoulder pain using thoracic SMT.61 Future research should examine changes in kinematics or neurophysiologic variables in groups of patients with shoulder pain who respond to thoracic SMT compared to those who do not. In light of the findings within this research project that thoracic SMT and sham SMT led to similar improvements in patient-rated outcomes, use of a control group receiving another treatment intervention or a natural history group (no treatment) should also be considered in developing future studies.
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