Repeated Applications of Thoracic Spine Thrust Manipulation do not Lead to Tolerance in Patients Presenting with Acute Mechanical Neck Pain: A Secondary Analysis

It has been demonstrated that patients receiving mobilization techniques do not exhibit tolerance to repeated applications. However, this phenomenon has not been investigated for thoracic manipulation. Our aim was to determine if patients receiving thoracic thrust manipulation exhibit tolerance to repeated applications in acute mechanical neck pain. Forty-five patients were randomly assigned to two groups. The control group received electro- and thermotherapy for 5 sessions, and the experimental group received the same program and also received a thoracic thrust manipulation once a week for 3 consecutive weeks. Outcome measures included neck pain and cervical mobility. Within-session change scores for pain and mobility during treatment sessions #1, 3, and 5 were examined with a one-way repeated measured ANOVA. A 2-way ANOVA with session as within-subject variable and group as between-subject variable was used to compare change scores for each visit between groups to ascertain if there were significant between-group differences in within-session changes for the experimental versus the control group. The ANOVA showed that for either group the 3 within-session change scores were not significantly different (P > 0.1). The 2-way ANOVA revealed significant differences between groups for both pain and neck mobility in within-session change scores (all, P < 0.001). Change scores in each session were superior in the experimental group as compared to those in the control group. The results suggest that patients receiving thoracic manipulation do not exhibit tolerance to repeated applications with regard to pain and mobility measures in acute mechanical neck pain. Further studies should investigate the dose-response relationship of thoracic thrust manipulation in this population.KEYWORDS: Neck Pain, Thoracic Thrust Manipulation, ToleranceNeck pain is a significant problem in society. The incidence rate for self-reported neck pain in the general population has been reported to be between 146 and 213 per 1,000 patient years¹. The reported point prevalence of neck pain varies between 9.5–35%^2,3. The 12-month prevalence for neck pain ranges from 30–50%, and the 12-month prevalence of activity-limiting pain is reported to be between 1.7% and 11.5%¹. Nearly half of patients with neck pain will go on to develop chronic symptoms⁴, and many will continue to exhibit moderate disability at long-term follow-up⁵. In the United States, neck pain accounts for almost 1% of all visits to primary care physicians⁶. After lumbar spine-related diagnoses at 19%, cervical spine diagnoses were the second most common reason for referral at 16% in a US study on outpatient physical therapy⁷. Similarly, the economic burden associated with the management of neck pain patients is second only to low back pain in annual workers'' compensation costs in the United States⁸.In the majority of patients with neck pain, no patho-anatomic diagnosis can be provided resulting in a diagnostic label of non-specific or mechanical neck pain for many patients. Childs et al⁹ have proposed a treatment-based classification system to further differentiate among this likely heterogeneous group of patients. In this classification, manual therapy to the cervical and thoracic spine, particularly thrust and non-thrust manipulation, is the main treatment intervention proposed for management of the mobility subgroup. There is growing evidence supporting the use of thoracic thrust manipulation in the management of this subgroup of patients with mechanical neck pain with multiple studies showing noted improvements in pain, range of motion, and function^10–13.However, the design of previous studies^10–13 has varied in that the researchers have used different numbers of manipulations. This makes it difficult for clinicians to determine how many applications of thrust manipulation are likely to maximize patient outcomes. In this context, one issue we need to consider is whether repeated application of thoracic manipulation leads to tolerance. Tolerance is defined here as a decrease in the effect size or magnitude of the intervention over time, as measured within sessions. Tolerance should affect the number of interventions provided. In the context of thoracic manipulation for patients with mechanical neck pain, tolerance to thoracic manipulation would logically decrease the number of manipulations that are applied and that are required for the demonstrated positive study outcomes.Paungmali et al¹⁴ studied tolerance to repeated applications of a manual non-thrust technique directed at the elbow region. They showed that the technique had a hypoalgesic effect measured as an increase in pressure pain threshold levels at each session that was of similar magnitude to the first time the technique was administered, suggesting that non-thrust techniques do not cause tolerance to repeated applications. It should be noted that this study did not include a control group so the possibility of consistent improvements in their cohort could have potentially been related to a placebo effect. Irrespective, this phenomenon of cumulative tolerance has yet to be investigated with regards to thrust techniques. Studying thrust in addition to non-thrust techniques is relevant, since non-thrust and thrust interventions stimulate different axial sensory beds¹⁵. Also, thoracic spine manipulation was shown to result in significantly greater short-term reductions in pain and disability than thoracic non-thrust manipulation in neck pain patients¹⁶. From a clinical perspective, one could argue that it is necessary to investigate the tolerance aspect not only with regard to neurophysiological measures, such as pressure pain thresholds, but also with regard to clinically relevant outcomes, such as pain and mobility.We recently conducted a randomized clinical controlled trial comparing the effectiveness of an electro- and thermotherapy program alone or in combination with thoracic spine thrust manipulation in patients with acute neck pain¹⁷. This paper presents a secondary analysis of data related to the tolerance aspect of the thoracic spine thrust manipulation. The purpose of this paper is to analyze whether repeated application of thoracic manipulation causes tolerance with regard to pain and mobility outcomes in patients with acute neck pain. We hypothesized that repeated application of thoracic spine manipulation would not lead to tolerance to repeated applications both with regard to pain and neck mobility outcomes.