A randomized controlled trial comparing different sites of high-velocity low amplitude thrust on sensorimotor integration parameters

Participants

• Number: 83 people (49 female and 37 male)

• Criteria of inclusion: age 18 to 50 years; a history of recurrent and persistent neck pain without having sought treatment; absence of pain at the time of the study.
• Criteria of exclusion: lack of spinal dysfunction during chiropractic evaluation; presence of metal implants in the skull; history of severe neck pain (pain greater than 6 out of 10); presence of severe spinal pathology (eg, cancer, fracture, infection, hematoma, cervical arterial dissection); having received thrust for anything other than neck pain in the 7 days prior to the study.

• Groups of study: 2 groups obtained by randomization
  • Group 1: thrust on dysfunctional vertebrae, 43 people (23 female and 20 male, mean age 24.41 years).
  • Gruppo 2: thrust on healthy vertebrae, 43 people (26 female and 17 male, mean age 24.83 years).

Interventions and evaluations

• Evaluation of the cervical vertebral region looking for dysfunctional or subluxated vertebrae.
• Evaluation of the amplitude of the N30 component of SEPs before and immediately after surgery.
  • SEPs were evoked by stimulating the median nerve of the dominant hand using an electrical stimulator.
• 1 treatment session (thrust was applied once per person).
• Thrust on cervical vertebrae:
  • High-velocity low-amplitude technique directed to a dysfunctional cervical spine segment (restricted motion, pain inducible by movement or palpation, hypertonic musculature or joint disruption);
  • in case of multiple dysfunctional vertebrae, the most superior or cranial one was chosen;
  • thrust administration using a handheld tool to standardize maneuver application parameters.
• Thrust on healthy cervical vertebrae:
  • High-velocity low-amplitude technique directed to a dysfunction-free spinal segment;
  • the healthy vertebra was chosen as the one farthest from the dysfunctional vertebrae;
  • thrust administration using a handheld tool to standardize maneuver application parameters.
• The evaluation and thrusts were performed by a chiropractor with more than 10 years of experience.

Results

• Primary outcomes: the application of thrust to dysfunctional vertebrae induced a statistically significant reduction in N30 amplitude, whereas the application of thrust to a healthy vertebra showed a nonsignificant increase in N30 amplitude.
• Secondary outcomes: in group 1, in which dysfunctional vertebrae were treated, 25 thrusts were performed on C1, 14 on C2 and 4 on C3. In group 2, in which healthy vertebrae were treated, 17 thrusts were performed on C3, 16 on C2, 8 on C1, 1 on C5 and 1 on C6, and the maximum distance between healthy and dysfunctional vertebrae was of two vertebrae.

Discussion

A thrust applied to a dysfunctional cervical spinal segment is able to reduce N30 SEP complex amplitude, unlike a thrust applied to a healthy segment. This is a relevant result because the decrease in N30 suggests changes in sensorimotor activity at the level of the prefrontal cortex.

This study is in line with previous animal studies, in which thrusts have been shown to maximize proprioceptive afferent inputs and neuromuscular spindle responses. Consequently, to promote the recovery of a particular sensorimotor function, it becomes central to carefully assess cervical spinal segments so as to apply thrust to an actually dysfunctional segment.

Although past studies, including a systematic review, have not shown a difference between thrusts applied to dysfunctional segments and thrusts applied to healthy segments with regard to clinical outcome measures (eg, pain, pain threshold, or grip strength), it should be noted that in those studies the concept of “dysfunctional segment” was not well defined and, therefore, both experimental groups may have received thrusts on dysfunctional segments. Moreover, in some studies, thrusts were applied according to a preconceived decision of the investigators and not as a result of clinical evaluation. Another limitation can also be found in the parameters measured: pain intensity or perceived disability are indeed subjective and can be influenced by the patient’s expectations. Not to mention that they may require multiple therapy sessions, not just one thrust. To assess whether thrusts induce actual and immediate changes, more objective measures such as imaging techniques are needed. However, X-rays are not suitable since they emit ionising radiation, and some MRIs are particularly expensive.

Nevertheless, these negative results are part of the literature and prevent proper guidance on thrust application in case of pain.

Since the N30 SEP complex is derived from somatosensory processing at the prefrontal level, but also from the activity of other areas, such as the primary sensory cortex, basal ganglia, thalamus, premotor areas, and primary motor cortex, thrusts on dysfunctional vertebrae could involve activation of paravertebral proprioceptive sensory circuits. In case of dysfunction, in fact, muscle fibers in deep paravertebral muscles may atrophy, undergo fatty infiltration and fibrotic processes, as well as alterations in neuromuscular spindles, thus negatively modifying the processing and organization of the primary sensorimotor cortex. This alteration would promote the onset and chronicization of pain since it is now known that, in the state of pain, there is often a complex reorganization of the brain’s sensorimotor maps (homunculi). By modifying the activity of these cortices, thrusts seem to have the potential to “revive” these circuits. Further studies are therefore needed to fully assess the clinical relevance of the findings of this study.

Of course, this study is limited by having applied only one thrust per person, which does not reflect a real clinical treatment plan. In addition, N30 amplitude was measured only immediately after the thrust: without follow-up, therefore, it is not possible to know how this effect evolves. Furthermore, given the anatomical and functional neuromuscular differences, the results of this study cannot be generalized to other spinal segments. Similarly, having used a tool to apply thrusts, the results cannot be extended to other methods of application, although the reduction in N30 amplitude that emerged in this study is quite comparable to that found in studies where thrusts were applied manually. Another limitation is that no clinical outcomes (eg, decrease in pain or improvement in range of motion) were measured and, therefore, it is unclear whether the change in N30 amplitude has any actual consequences. Furthermore, the study was carried out on young adults: therefore, it is important to understand whether any age-related degenerative changes might interfere with thrust-induced mechanoception. It is also to be considered that the results are not applicable to people with special conditions such as cervical radiculopathy or herniated discs. Finally, the chiropractor knew whether he was performing a thrust on a dysfunctional or healthy vertebra, which may have introduced bias into the results.