Introduction

Spinal manipulation is a treatment option that is frequently used by manual therapists in patients with low back pain. In clinical practice guidelines, the use of manipulations is often recommended as a second-line intervention, besides exercise and education. In general, a pragmatic choice is made to determine the site to be treated with spinal manipulation: the most painful or stiff segment. Previous studies have already studied the outcomes following spinal manipulation but effects were small and tended to be short-lasting in nature. The rationale for this study was that normalization of both segmental biomechanics and pain sensitivity could explain pain relief following a manipulation. However, it was uncertain whether the effects of spinal manipulation can be improved if they are used to target stiffness or pain. Therefore this randomized trial compared whether manipulation to stiff or painful segments is more effective in reducing low back pain intensity.

Methods

Patients between 18-60 years with chronic low back pain that lasted for more than 3 months were enrolled in this study. Possible candidates were excluded in case an indication for surgical evaluation of low back pain was necessary, they had spinal manipulation in the 4 weeks prior to the start of this study, took opioids exceeding 40mg of morphine or equivalent, or had comorbid conditions like a BMI exceeding 35.

The intensity of the low back pain was measured with the validated Low Back Pain Rating Scale, which consists of 3 11-point numerical rating scales to measure the average, worst, and current low back pain intensity. Spinal segments were marked using ultrasonography with the patient prone. Spinal stiffness was measured using a device called VerteTrack, which measures the vertical displacement in spinal tissues by a potentiometer. For the pain pressure threshold, a pressure algometer was used.

The treatment was a manipulation of stiff or painful segments. Here 2 subsequent groups were created. For each participant, the most stiff or the most painful segment was determined at baseline. The participants were then categorized into group A where the most stiff segment was treated or into group B where manipulations were directed to the most painful segment. The primary outcome of interest was patient-reported low back pain intensity following treatment.

The manipulation to stiff or painful segments was standardized with the patient in side-lying and the direction of the low amplitude high-velocity thrust was from posterior to anterior. Maximal 3 attempts of manipulation to stiff or painful segments were allowed and it was up to the therapist to determine whether or not the manipulation had been successful. A cavitation sound was not required to conclude a successful manipulation.

Results

A total of 132 participants with chronic low back pain were included and 123 of them completed the study. At baseline, the mean low back pain intensity was 6/10. The participants were randomly assigned to group A or B where the most stiff versus most painful segment was treated respectively. The analysis showed no significant between-group difference in the primary outcome following the manipulation to stiff or painful segments. Within each group, small significant differences were observed, but they are small and likely not clinically relevant.

Questions and thoughts

Patients were recruited from a specialized spine center and had been referred to it by other healthcare practitioners. Therefore we can assume that the patients included in the present study may have been more largely affected by their low back pain than you would expect in patients presenting in regular physiotherapy practice. This may partially explain why no clinically relevant difference was observed. Chronic pain patients often have multiple factors influencing their symptoms and may be non-responders to treatment that is assumed to primarily correct biomechanical abnormalities without addressing additional psychosocial comorbidities.

Adverse events were registered and it was noted that “Of the participants who completed the intervention, 69% reported minor side effects.” These minor side effects included an increase in local muscle pain and stiffness. But adverse events like headache, worsening of leg pain, and nausea which were reported as well raise the question of whether these effects can be considered as minor side effects. The fact that they appear at a remote location (in the leg), or at a site different from the targeted area (headache) makes us raise an eyebrow at least.

The use of standardized procedures and tools was very informative in this study. However, the measurement equipment used here is not regularly available in physiotherapy practice.

Talk nerdy to me

Good aspects we note in the methodological part of the study include the protocol registration and the presentation of an overview of the protocol in the article. A statistician was enrolled in the analyses, and errors in stiffness data were removed from the analyses but were minimal. There was no sham intervention which implies that it cannot be stated that the observed outcomes were truly attributable to the spinal manipulation to stiff or painful segments alone, but this was not the purpose of the present study. The sample size was determined beforehand based on an expected small, 10% group difference in low back pain intensity between the stiff and pain group. Secondary outcomes were described but not overemphasized which is good as the sample size calculation is based on the primary outcome alone.

Considering the pain pressure threshold measurements, a remote location was tested first to familiarize the patient with the testing procedure and segments were tested in a random order. The use of such pain pressure threshold measurements is an excellent measure as it was previously shown that it demonstrates excellent intra-rater reliability in low back pain populations. Only 1 assessor was responsible for conducting the tests. The treating physician was blinded to the meaning of the A and B groups, the assessor was blinded to the randomization allocation, and the patient was blinded to both.

Take home messages

So, should we target a spinal manipulation to stiff or painful segments? Not per se. This study showed no differences in low back pain intensity between groups receiving either a manipulation at the most painful or stiff segment. Therefore the application of spinal manipulative therapy should not be limited to pain provocation or stiffness assessment alone. Rather, as we saw small decreases in low back pain intensity in both groups, the possibility to use manual therapy as an adjunct treatment can be considered.

Reference

Nim, C. G., Kawchuk, G. N., Schiøttz-Christensen, B., & O’Neill, S. (2020). The effect on clinical outcomes when targeting spinal manipulation at stiffness or pain sensitivity: a randomized trial. Scientific Reports, 10(1), 14615.