Last week I wrote about the neurophysiological mechanisms involved in manual therapy so that we could explore what processes happen in the body when mechanical stimulation is applied. It's an interesting topic to me because it relates to a much broader conversation "What evidence is there to support the use of manual therapy in the treatment of musculoskeletal conditions, compared to placebo, exercise therapy, medication, cognitive behavioural therapy and other therapies?" If you asked me this question a few weeks ago I might have answered that the evidence for some conditions is stronger, others mild and many weak, and that exercise gets a good wrap in the literature. But we still use manual therapy everyday right? Because, anecdotally, we know it works.

After looking at the neurophysiological mechanisms involved in manual therapy I have become aware that the way we objectively measure and quantify the effects of manual therapy is really challenging. How do we measure the effect on the peripheral and central nervous system in clinical practice? Pain, palpation findings, range of movement and function is our bread and butter for reassessment tools.

Do these objective tests truly measure what we know now to be happening?

Is the reason our research is limited not due to the effect of manual therapy, but how we measure it?

For this blog I'd like to explore the findings of five research papers exploring the effects of mobilisation on the spine. In later blogs I hope to compare this knowledge to the research surrounding manipulation and then finish by identifying the systematic reviews which support the use of manual therapy in the management of musculoskeletal pain conditions.

To use a different style of writing though, this blog is in the format of an annotated bibliography. An annotated bibliography is a summary of a research paper. It provides a critical review of the paper, identifies how it is applicable to current knowledge base, provides a description of the paper's purpose, study design and other important elements and gives an opinion on why it is valuable to know about. I've also written each one is a slightly different manner to provide variety.

Annotated bibliographies are a great way to keep a running list of what you've read and easily compare papers side by side. It's challenging at first to write them but definitely helps consolidate what you learnt from the paper. If you can't summarise what the main argument was about, then you need to read it again. The aim of writing this blog with a series of annotated bibliographies is that I want to provide my readers with a summary so that they can make their own informed choices about what the information means.

Krouwel, O., Hebron, C., & Willett, E. (2010). An investigation into the potential hypoalgesic effects of different amplitudes of PA mobilisations on the lumbar spine as measured by pressure pain thresholds (PPT). Manual therapy, 15(1), 7-12.

These authors conducted another study exploring the hypoalgesic effects of mobilisation and established that there is an immediate hypoalgesic effect following mobilisation which is not impacted by the rate of mobilisation. In this study, they explored the effect of amplitude on the hypoalgesic effect as many other studies use a standardised Gr III mobilisation technique. This study investigated the different effects of large amplitude, small amplitude and sustained mobilisation on 30 asymptomatic volunteers. The volunteers received 3 x 1 minute mobilisation on three separate occasions with at least 48 hours between sessions. The results of this study showed that if the same pressure is applied during mobilisation of 200N, that the amplitude of the mobilisation doesn't produce a significant difference in pain pressure threshold (PPT). All groups were better post treatment, which begs the question "Is amplitude an important aspect of treatment dosage?".

Pentelka, L., Hebron, C., Shapleski, R., & Goldshtein, I. (2012). The effect of increasing sets (within one treatment session) and different set durations (between treatment sessions) of lumbar spine posteroanterior mobilisations on pressure pain thresholds. Manual therapy, 17(6), 526-530.

Published two years after the two articles by Krouwel, Hebron & Willett, Pentelka et al (2012) investigated the effect of sets of mobilisations (as opposed to rate or amplitude) which contributes well to the studies discussed within this blog as it explores the effect of sets and duration on hypoalgesic effects. 19 asymptomatic volunteers were recruited for single-blinded, randomised, repeat measures cross-over design study. Each patient received 5 sets of large amplitude central PA on L4 for either 30 or 60 seconds, with pain pressure threshold being measured between each set. The results of this study showed that when mobilised for 60 seconds there was a 56% improvement in PPT and in the 30 second group, a 35% change. These changes were noticed locally and widespread which is a consistent pattern of local and systemic hypoalgesic effects noticed by many other authors. The authors also noted that the greatest hypoalgesic effect was achieved after the forth set and therefore concluded with their recommendation for mobilisation dosage of 60 seconds in length and at least four sets.

Perry, J., & Green, A. (2008). An investigation into the effects of a unilaterally applied lumbar mobilisation technique on peripheral sympathetic nervous system activity in the lower limbs. Manual therapy, 13(6), 492-499.

In 2008, Perry & Green conducted a research trial through Coventry University, UK, to explore the hypothesis "that a specific mechanical mid-to-end range mobilisation technique, applied to the left Lumbar 4/5 ZP joint at a rate of 2 Hz, would result in a significant change from baseline in peripheral SNS activity (as measured by skin conductance—SC) that would be greatest in the ipsilateral leg during the intervention period compared to the contralateral limb, the placebo and the control conditions" (p. 493). A similar hypothesis had been previously well studied in the cervical spine but not the lumbar spine. Although the neurophysiological effects of manual therapy are still unclear, it is speculated that there are local physiological effects, neurophysiological effects at the spinal and supraspinal levels, and endocrine/hormonal and placebo effects. With 58.9% of UK therapists and 83.7% of North American Therapists using spinal manipulative therapy as a preferred treatment modality for low back pain, it is important to clarify what effects manual therapy is having. Perry & Green (2008) conducted a double-blinded, placebo controlled, randomised control trial using Gr III unilaterally PA, sustained gentle pressure and no touch to evaluate the skin conduction changes at the 2nd and 3rd toe on both sides. The results showed a significant increase of 13.5% in skin conduction on the ipsilateral side during mobilisation, a non significant change of 4.11% in the contralateral leg, and no change in the control and placebo groups. In clinical practice it is good to know that mobilisation will have an excitatory effect on the sympathetic nervous system. However, we don't measure skin conduction in the clinical setting or incorporate measures of sympathetic function into objective examination. Aside from supporting the current model of the neurophysiological changes associated with mobilisation, does this study change our current practice?

Sterling, M., Jull, G., & Wright, A. (2001). Cervical mobilisation: concurrent effects on pain, sympathetic nervous system activity and motor activity. Manual therapy, 6(2), 72-81.

Sterling, Jull & Wright (2001) conducted a condition randomised, placebo controlled, double blinded trial to investigate if spinal manipulative therapy has an effect on superficial neck flexor muscle activity in 30 people with a history of neck pain. Their aim was to further support the role of descending spinal inhibition from the dorsal periaquaductal gray (dPAG). In animal research the dPAG has shown to impact muscle function and these authors wished to explore it's role in human subjects. To measure muscle activity they used the cranio-cervical flexion test, which was both well described and justified in this paper. EMG activity of the superficial neck flexor muscles (sternocleidomastoid and anterior scalenes) were evaluated, as well as pain pressure threshold, thermal pain threshold, visual analogue scale (analgesic effect), skin conductance and skin temperature (sympathetic nervous system activity). These measures, along with the inclusion/exclusion criteria were consistent with other study designs, allowing for generalisability of results and strengthening the external validity of the study. Following spinal mobilisation of a Gr III unilateral PA on C5/6 there was a .3 reduction in VAS rating at rest, no change in VAS at end range cervical rotation and a 22% increase in pain pressure threshold. There was evidence of sympathoexcitation with reduced skin temperature and increased skin conductance. This can occur through stimulation of local sympathetic fibres adjacent to the corresponding spinal level, however as there is no change in temperature pain threshold, it can be speculated that the sympathetic excitation is more a result of stimulation of the dorsal periaquaductal grey. This studied confirmed a reduction in muscle activity in the superficial neck flexor muscles at lower levels of the cranio-cervical flexion test. This paper is a landmark study referenced by many other papers, for its strong methodological design and evidence supporting the neurophysiological mechanisms involved in spinal mobilisation.

Willett, E., Hebron, C., & Krouwel, O. (2010). The initial effects of different rates of lumbar mobilisations on pressure pain thresholds in asymptomatic subjects.Manual Therapy, 15(2), 173-178.

Willett, Hebron & Krouwel (2010) conducted a single blinded, randomised, within group, repeated measures design on 30 asymptomatic volunteers to evaluate the changes in pain pressure threshold which occur locally (L5) and widespread ( L2 and L5 dermatome and 1st dorsal interossei) following mobilisation. Their aim was to explore if different rates of mobilisation 0, 1Hz and 2 Hz (1 oscillation or 2 oscillations per second) would change the PPT. A highly experienced Physiotherapist was used to provide the Gr III central PA at the level of L5 for 3 x 1 minute intervals. Similar to other studies, pain pressure threshold was measures with an algometer. The results of the study demonstrated a 19% change in PPT locally and 12-14% change widespread. It should be remembered that the subjects were asymptomatic and therefore these results may be different in people with chronic low back pain. None the less, it was shown that the rate of mobilisation does not provide a clinically or statistically different change in the improvement in pain pressure thresholds. When deciding which rate of mobilisation is best suited for the patient, this study can be drawn on to support that the rate of a GR III lumbar mobilisation doesn't impact the immediate hypoalgesic effect and therefore the most comfortable mobilisation can be chosen.

What conclusion can be draw from this annotated bibliography?

After looking at those five studies, which I felt were very well conducted from a methodological perspective, and all contribute a new piece of information about mobilisation, this is what I would conclude...

Spinal manual therapy:

Produces a local hypoalgesic affect which is specific to mechanical nociception. This is reflected in increased pain pressure thresholds and reduced ratings on the visual analogue scale (VAS).
Results in excitation of the sympathetic nervous system, mainly on the ipsilateral side to where the mobilisation is performed, which is reflected in reduced skin temperature and increase skin conductance (Perry & Green., 2008; Sterling, Jull & Wright., 2001).
Activates descending inhibitory mechanisms from projections from the dorsal periaquaductal gray (dPAG), which results in reduced muscle tone in the superficial neck flexor muscles in the cervical spine (Sterling, Jull & Wright., 2001).

Following mobilisation there is widespread improvement in pain pressure threshold which can be attributed to the central pathways activated during the mobilisation i.e dPAG which has bilateral progressions. The rate of mobilisation does not change the hypoalgesic effect that mobilisation has on improving pain pressure threshold, i.e. if you mobilise at a rate of 1 oscillation or 2 oscillations per second, the hypoalgesic response is the same (Willett, Hebron, & Krouwel., 2010). Amplitude is another aspect of mobilisation and it has been shown that the amplitude of a mobilisation doesn't alter the hypoalgesic effect, i.e a pressure of 200N whether sustained, small amplitude or large amplitude, all produce the same outcome (Krouwel, Hebron, & Willett., 2010). This definitely gives Physiotherapist's confidence that changing the amplitude and rate of mobilisation to suit patient comfort and expectations is not going to result in altered neurophysiological effects. When determining mobilisation dosage, one important variable is duration and the studies above note that a duration of 60 seconds with at least four sets is the minimum desired dosage for optimum hypoalgesic effects (Pentelka, et al., 2012).

Hopefully this blog has highlighted the way an annotated bibliography is completed and demonstrated how conclusions can be drawn after reading each paper, while also sharing a special message about the neurophysiological effects of mobilisation in the cervical and lumbar spine. The take home message is that both local and systemic effects occur during and after mobilisation, that the duration and number of sets impact the amount of pain relief obtained, and that you can choose between a fast or slow mobilisation or a sustained, small amplitude and large amplitude mobilisation applied for 200N (into resistance) when using mobilisation for treatment.

Sian

References

Krouwel, O., Hebron, C., & Willett, E. (2010). An investigation into the potential hypoalgesic effects of different amplitudes of PA mobilisations on the lumbar spine as measured by pressure pain thresholds (PPT). Manual therapy, 15(1), 7-12.

Pentelka, L., Hebron, C., Shapleski, R., & Goldshtein, I. (2012). The effect of increasing sets (within one treatment session) and different set durations (between treatment sessions) of lumbar spine posteroanterior mobilisations on pressure pain thresholds. Manual therapy, 17(6), 526-530.

Perry, J., & Green, A. (2008). An investigation into the effects of a unilaterally applied lumbar mobilisation technique on peripheral sympathetic nervous system activity in the lower limbs. Manual therapy, 13(6), 492-499.

Sterling, M., Jull, G., & Wright, A. (2001). Cervical mobilisation: concurrent effects on pain, sympathetic nervous system activity and motor activity. Manual therapy, 6(2), 72-81.

Willett, E., Hebron, C., & Krouwel, O. (2010). The initial effects of different rates of lumbar mobilisations on pressure pain thresholds in asymptomatic subjects.Manual Therapy, 15(2), 173-178.