Are Nerve Sliders and Tensioners Effective for Sciatica? (part 1)
As an MSK physiotherapist aligned to a spinal pathway I treat a lot of people with sciatica. It is a condition I find frustrating to treat and have inconsistent results with. I was recently asked to clinically reason my use of nerve sliders and tensioners and realised how little I knew of their supporting evidence. This blog aims to establish whether the research advocates their clinical use with sciatica and identify factors which may improve patient outcomes.
Sliders and tensioners are types of neurodynamic mobilisation interventions commonly used to treat sciatica. Butler (2000) and Shacklock (2005) suggest they can be used to aid assessment of neural health and movement properties. Impairment to movement properties during everyday movements may, over time, impair nerve health causing pain and axonal dysfunction (Nee and Butler, 2006). Whilst neurodynamic testing may help the clinician determine if the pain generating tissue is neural or non-neural (Nee et al., 2012b) the diagnostic accuracy of neurodynamic tests is poor (Van der Windt et al., 2010) and can only accurately indicate the presence of heightened neural mechanosensitivity (Schmid, Hailey and Tampin, 2018).
Clinically I have naively explained sliders and tensioners to patients as a process of ‘freeing up nerves’ along their path, but now realise the physiological effects are far more complex and they produce quite different biomechanical effects. During nerve tensioners strain is systematically applied throughout the nervous system by sequential joint movements which elongate the nerve bed. During a nerve slider this strain is offset by synchronized movements of other joints (Shacklock, 2005). Nerve sliders have been shown in cadaveric (Coppieters and Butler, 2008) and in vivo studies (Coppieters, Hough and Dilley, 2009; Coppieters et al., 2015a) to produce greater neural excursion than tensioning techniques (relative to surrounding structures) with less strain. These movement properties are well established, what is less established is the therapeutic efficacy of their use, although as we will see there are reasons to be optimistic.
Small studies, global application: 6 of one, half-a-dozen of the other
Sliders and tensioners have been utilised in several studies with positive effects generally, such as immediate global hypoalgesic effects on asymptomatic individuals (Beltran-Alacreu et al., 2015). Studies on carpal tunnel syndrome have reported reduction of temporal summation (Bialosky et al., 2009), reduction in reported pain, as well as improved function and nerve conduction (Wolny et al., 2017; Wolny and Linek, 2018(a); Wolny and Linek, 2018(b)). Nerve sliders (as part of neural tissue management) are reported to improve neck pain, arm pain, disability, and function in people with nerve-related neck and arm pain when compared with advice to remain active (Nee et al., 2012a). This outcome had a large confidence interval (meaning we cannot be sure this result would be found in a greater population) however, the results are supported by further research (Savva et al.,2016). These single studies seem positive, contrastingly though some relatively small systematic reviews (Ellis & Hing, 2008; Su and Lim, 2016) investigating the therapeutic effects of neural mobilisations report inconclusive evidence to support combinations of sliding and tensioning, or slump stretching for ‘neurodynamic dysfunction’, and that neural mobilisations were of benefit for pain relief and disability only when compared with ‘minimal intervention’. So, when considering sliders and tensioners generally the reviews are mixed. Frustratingly, larger studies yield similar results.
Big Systematic Review: limited by the quality of available research
The most comprehensive systematic review and meta-analysis into the effects of neural mobilisations on MSK conditions was conducted by Basson et al. (2017) and included 40 studies (1759 participants). The main conditions identified were chronic nerve-related low back pain, nerve-related neck & arm pain, and carpal tunnel syndrome. The study’s aim is clear, authors ensured an extensive search for all relevant literature from main databases with appropriate inclusion/exclusion criteria and a large, justified inclusion date (1980-2016), so we can be confident all relevant studies within this timeframe are included. The methodological quality is high and repeatable – improving rigour; independent reviewers assessed the selected studies using the MAStARI tool which is universally recognised. Disputes between reviewers were resolved by discussion with a third party, and agreement between reviewers was evaluated using Cohen’s Kappa (Cohen’s Kappa measures interrater reliability and evaluates extent of chance of the agreement). Authors assessed risk of bias independently of appraisal using the GRADE guidelines which considers a host of criteria. One of the study’s strengths is the number of studies included, which allowed for extensive data inclusion and subsequent meta-analysis. Unfortunately, this meant disproportionally low-quality studies and high levels of clinical heterogeneity, which inevitably detract from the overall rigour of the study, and clinical application of results. The high risk of bias in 8/11 included studies for chronic nerve-related low back pain demonstrates this well. Due to the diversity of interventions and outcomes measured it is impossible to succinctly summarise results of the relevant studies so I will group them as best I can below.
Slump (sliders and tensioners)
3 short-term studies investigated sliders and tensioners in slump position, one as a slider in combination with stabilization exercises and electrotherapy on chronic radicular low back pain (ali et al., 2015), one as a tensioner in comparison with straight leg raise tensioner on lumbar disc herniation (Rezk-allah et al., 2011), and one in comparison with Mulligan’s bent leg raise on low back pain with positive neurodynamic test (Patel, 2014). All studies reported improvement in pain, disability (ali et al., 2015), and neurophysiology (H-reflex response) (Rezk-allah et al., 2011). These results should be used with caution as all studies reported no blinding of participants or assessors, and no concealment of treatment group (meaning they have a high risk of performance and ascertainment bias which may have severely affected results). They also claim they are investigating radicular pain, but only use neurodynamic testing for inclusion which is not accurate (Schmid, Hailey and Tampin, 2018), so consequently we cannot be confident in a cause-and-effect finding.
Straight Leg Raise (sliders and tensioners)
Two short-term studies (Ahmed et al., 2013; Kaur and Sharma, 2011) combined sliders and tensioners in straight leg raise with TENS plus exercise, and advice plus exercise, respectively. They reported significant improvement in pain and function (Ahmed et al., 2013), and pain and disability (Kaur and Sharma, 2011). It is unclear whether sliding or tensioning techniques were used though, so the transference to practice is challenging. Again, these studies reported no blinding and are high risk for performance and ascertainment bias. High Bias can be mitigated in improved study design but remains prevalent in this body of research, frustratingly it is not the only methodological limitation frequently found.
Inclusion issues present a significant issue within the literature; Ahmed et al. (2013) reportedly investigated effects of neural mobilisation on ‘sciatica’ but do not offer any clinical criteria or definition. In similar fashion, studies claiming to investigate neural mobilisation and radiculopathy either reported no testing to confirm radiculopathy within their sample (Sharma and Sheth 2017), or actively excluded it (Plazo-Menzano et al., 2019)! Such discrepancies highlight the importance of universally agreed criteria to ensure parity in research.
Imprecision in reporting and low methodological quality limits the value of further work (Dwornik et al., 2009; Machado and Bigolin, 2010; Colakovic and Advic, 2013) detailed in another relevant systematic review by Neto et al. (2017). As the exact application of neural mobilisation is not reported in any of these short-term studies investigating chronic nerve-related low back pain (with leg pain). Results do support positive findings from Basson et al. (2017) however, and both nerve sliders (Colakovic and Advic, 2013) and tensioners (Machado and Bigolin, 2010) were calculated to have medium and small effect size on pain respectively when compared to range of movement and stabilisation exercises alone over 4 weeks (Colakovic and Advic, 2013), and a stretching regime over 10 weeks (Machado and Bigolin, 2010). The other study included (Dwornik et al., 2009) was calculated as having medium effect size on pain versus standard physiotherapy treatment over 2 weeks, but reported their intervention only as ‘neuromobilisation based physiotherapy’. The three studies mentioned here were considered to be of poor to fair quality based on the PEDro score for internal validity & statistical analysis, or in other words, we can say with a poor to fair degree of confidence that the effect obtained was caused by the intervention.
To conclude the research review we move to Schafer et al. (2011), who investigated participant heterogeneity in their blinded prospective cohort study. They explored whether subgroups of patients with chronic unilateral low back pain and leg pain below buttocks respond differently to neural mobilisations. They measured pain, disability, and global perceived change scale (GPC).
Their sample of 74 was divided into 4 categories based on clinical presentation: musculoskeletal (n=19), peripheral nerve sensitization (PNS) (n=9), denervation (n=27) & neuropathic sensitization (NS) (n=19) (see figure 1).
Participants received 2 weekly sessions for 7 sessions consisting of lumbar lateral flexion mobilisations (5x 60sec), and passive hip & knee sliding technique (5 x 30sec) which they were asked to perform at home.
Results indicate significant between-group difference and greatest minimum clinically important change (MCIC) in favour PNS group for pain intensity, disability, and GPC. NS was the least responsive group. This is a small, dated trial without a control group and the results are of limited value. However, the objective was to determine if the concept warranted further investigation and I feel it does, as it raises some important questions about each group’s proposed underlying pathobiology and why NS responded more favourably.
The literature reviewed here suggests consistent, modest improvement across frequently used outcome measures. However, there is no indication of superiority for either intervention. This may not be surprising, but I did expect some indication of a recommended application and/or treatment dose, and am left unsure of which modality, frequency and application may offer my patients the greatest relief. We have learnt that most studies are limited by high clinical diversity, low methodological quality and only offer insight into short-term, high frequency, multimodal interventions on chronic presentations, comparing treatment to a myriad of controls. These shortcomings are compounded by confused terminology and a lack of universally applied diagnostic criteria, making firm conclusion on coupling effective interventions with appropriate presentations impossible. The concept of a classification-based approach alludes to a greater understanding of the pathophysiology of sciatica and appreciating that effects of neural mobilisations may extend beyond biomechanics alone. I will explore this further in part 2.
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