Effectiveness of focal muscle vibration on hemiplegic upper extremity spasticity in individuals with stroke: A systematic review

1Introduction

Stroke is a leading cause of morbidity and mortality worldwide and is frequently linked with upper extremities persistent involvement (Broeks et al., 1999). According to recent research, the incidence of stroke worldwide ranged from 76 to 119 per 100,000 (Thrift et al., 2016). About 80% of stroke patients require upper extremity treatment (Friedman et al., 2014) with 40% of patients experience moderate to severe impairments in the upper extremity (Paquin et al., 2016.

More than 40% of stroke survivors experience this deficit chronically and more than 80% acutely (Cramer et al., 1997). Stroke individuals with mild to moderate upper extremity paresis have a good prognosis for functional recovery in the acute stage; only 71% of these patients perform at least some skills at 6 months following stroke (Nijland et al., 2010). Severely affected stroke patients have a poor prognosis with about 60% failing to achieve some activities of daily livings at 6 months post-stroke (Kwakkel et al., 2003, van Kuijk et al., 2008). Stroke is characterized by positive features include spasticity (O’Dwyer et al., 1996). About 39 % of patients with first-ever stroke are spastic after 12 months (Watkins et al., 2002). Spasticity is defined as a velocity-dependent motor disorder characterized by an increase in tonic stretch reflexes (Lance, 1980).

The available treatment options for managing spasticity post stroke include numerous physical methods such as electrostimulation, splinting and muscle lengthening, use of spasmolytic drugs, surgeries such as muscle-tendon lengthening, neurectomy, and tenotomy, as well as various invasive procedures for neuromuscular blockade (Caldwell et al., 1969, Caldwell et al., 1974, Katz,1980, Glenn & Elovic,1997, Keenan,1988, Skeil & Barnes, 1994). Researches have shown that in order for rehabilitation intervention to be effective, treatment needs to be highly repetitive, raise afferent input and be functional, as well as engage the individual and encourage frequent practice (Pollock et al., 2014).

Focal muscle vibration (FMV) defined as a technique that applies a vibratory stimulus to a specific muscle or its tendon using a mechanical device. FMV generates the Ia inputs as a consequence of the activation primary ending of the muscle spindle (Roll et al., 1989), leading to alteration of corticospinal pathways (Styvers et al., 2003). Many studies reported an increase excitability in the primary motor cortex following low amplitude FMV when applied to the intrinsic hand muscles and flexor carpi radialis muscle in healthy subjects (Rosenkranz et al., 2003). Concerning individuals with stroke, several studies were published recently. One of these studies demonstrated a reduction in elbow joint spasticity after exposed to FMV (Annino et al., 2019). While another study by Celletti et al., (2017) did not show that reduction.

There is a significant increase in researches that investigated the influences of FMV on spasticity among people with stroke in the past decade. Besides, no systematic review has yet been published that provides clear assent about the effects of focal muscle vibration on upper extremity post-stroke. Thus, the aims of this systematic review were to investigate the effects of FMV on spasticity of the upper extremity in individuals with stroke, and if possible, to identify the effective treatment protocol.

2Methods

2.1Search strategy

A systematic literature search of multiple databases; SCOPUS, PEDro, PUBMED, REHABDATA, and Web of Science, was conducted for articles randomized clinical trials (RCTs) and pseudo-RCTs published in English. The keywords used for the electronic search were (focal muscle vibration OR local muscle vibration OR segmental muscle vibration OR localized muscle vibration OR vibration OR muscle vibration) AND (stroke OR cerebrovascular accident OR cerebral hemorrhage OR cerebral ischemia) AND (upper limb OR upper extremity OR arm) AND (Spasticity OR hypertonia OR tone OR spastic). MeSH terms were used in relevant databases: (STROKE [MeSH] OR stroke^* OR cerebrovascular^* OR cerebral^*) AND (Vibration [MeSH]) AND (Upper Extremity [MeSH] OR upper limb OR arm) AND (Muscle Spasticity [MeSH]). No restriction in time was applied to the search strategy that was conducted in February 2019. A summary of the literature search strategy is presented in Fig. 1.

Fig.1

Summary of literature review process.

3Results

4Discussion

To our knowledge, this is the first systematic review aimed to examine the impacts of FMV in the treatment of upper extremities spasticity post stroke and to detect the effective training protocol. The initial findings showed that the FMV interventions may produce a reduction in hemiplegic upper extremity spasticity in patients with stroke. In agreement with our findings, Rosenkranz & Rothwell, (2006) demonstrated to increase the primary motor cortex excitability following vibrated intrinsic hand muscles focally. FMV generates the Ia inputs as a consequence of the activation primary ending of muscle spindle (Roll et al., 1989). Alteration of the excitability of the corticospinal pathway result of activation of Ia inputs by FMV (Steyvers et al., 2003) by facilitating inputs and modulating of intracortical inhibiting to the primary motor cortex in the brain (Rosenkranz et al., 2003, Rosenkranz et al., 2006). The vibration of a specific muscle can increase the motor evoked potential (MEP) recorded from the muscle at rest (Mileva et al., 2009), suggesting the progress of corticospinal excitability changes during vibration (Rosenkranz et al., 2006, Smith & Brouwer, 2005). Increased duration of cortical silent period (CSP) in flexor muscles of the forearm during vibration of the antagonist forearm extensors has been exhibited (Binder et al., 2009) and evidence strongly proposes that a period of pure sensory stimulation can affect motor cortical excitability (Ford et al., 1995).

Selected studies were superior in the research pyramid being randomized control trials or pseudo-randomized control trials. Most studies had poor results in the blinding of participants and therapists (Annino et al., 2019, Caliandro et al., 2012, Tavernese et al., 2013, Paoloni et al., 2014, Noma et al., 2012, Costantino et al., 2016, Casale et al., 2014) leading to potential bias. While it is difficult to blind participants or therapists to vibration intervention, it is possible to blind the examiner to the vibration intervention. This is important to reduce the bias correlated with measurement based on outcomes (Higgins & Green, 2008). Five studies have poor results in incomplete outcome data (Annino et al., 2019, Tavernese et al., 2013, Paoloni et al., 2014, Noma et al., 2012, Casale et al., 2014), and four studies have poor results in allocation concealment (Annino et al., 2019, Tavernese et al., 2013, Paoloni et al., 2014, Casale et al., 2014).

Six out of eight studies reported a positive effect of FMV in inhibiting hemiplegic upper extremity spasticity in patients with stroke (Annino et al., 2019, Tavernese et al., 2013, Paoloni et al., 2014, Noma et al., 2012, Costantino et al., 2016, Casale et al., 2014). Three of these studies demonstrated a reduction in the spasticity of the upper extremity in the experimental group (30 min FMV + 60 min CPT×5/wk×2 wk) compared to the control group (Tavernese et al., 2013, Paoloni et al., 2014, Casale et al., 2014). These studies were of moderate methodological quality and the sample sizes were large so the clinical conclusion can be confirmed. Moreover, Costantino et al., (2017) demonstrated a reduction in the spasticity of the upper extremity in the experimental group (30 min FMV×3/wk×6 wk) compared to the control group. This study was of high methodological quality and the sample size was large, the effect sizes were small to moderate for wrist and elbow (0.10–0.34), and small to medium for shoulder joint (0.11–0.52), so the clinical significance of reported effects can be established. Furthermore, in a study by Annino et al., (2019), the participants demonstrated a reduction in upper extremity spasticity following (5 min FMV + 30 min CPT×3/wk×8 wk) compared to the control group. This study was of moderate methodological quality and the sample size was large, the effect sizes were small to moderate (0.12–0.25) so the clinical meaning of reported effects can be confirmed. As well, a study by Noma et al., (2012), he reported improvement after a single session of FMV, despite it was of high quality and involved large sample size, however, one study using a single session is not enough to generalize their results.

On the other hand, two studies reported a reduction in upper extremity spasticity in both experimental and control groups (Celletti et al., 2017, Caliandro et al., 2012). Although one of these studies was of high methodological quality, it involved small sample size, and the time since stroke <6 months (months) (Celletti et al., 2017), so we propose that the reduction in upper extremity spasticity of both groups was due to spontaneous recovery. As the sample size was also small, we cannot generalize the results. Regarding another study by Caliandro et al., (2012), we propose that three sessions per week for one week are not enough to produce a significant reduction in upper extremity spasticity.

This review was limited by articles published in English. This can lead to bias as studies with significant results have more chance to get published than studies that fail to report significant results (Egger & Smith, 1998). Effect size not reported for some outcome measures because of insufficient data (Tavernese et al., 2013, Paoloni et al., 2014). We did not conduct meta-analysis because of the heterogeneity treatment protocols and dosages as well as the inability to contact the authors of many articles.

Due to the heterogeneity of studies, the effects of FMV on stroke patients were not fully understood. Besides, the effective treatment protocol and dosage remain unclear. Furthermore, the selected studies did not report details about the vibration apparatuses, which makes it difficult to homogenize the outcomes. Reporting characteristics of the vibration device in future studies would allow specifying the outcomes. Further high quality studies with large sample sizes are definitely warranted.

5Conclusion

In conclusion, the FMV may reduce the spasticity of the upper extremity in individuals with stroke if it is applied to the antagonist muscle. In fact, it seems that vibrated antagonist muscle may reduce the spasticity of the agonist muscle. We propose that adding the FMV into conventional physiotherapy intervention may produce superior effects than FMV intervention alone. No confirmed conclusion can be established regarding efficient treatment protocols and dosages due to the heterogeneity of the treatment interventions. Keeping in mind that there was a reduction in spasticity with various frequency ranges, it seems that the vibration frequency is not a discriminative factor in FMV intervention. We suppose that the treatment protocol and dosage could depend on the affected muscles and degree of spasticity more than other factors considered in the analysed studies. In this context, further high quality methodological trials with large sample size are strongly warranted to understand effects of FMV on upper extremity spasticity in stroke patients.

Conflict of interest

None to report.

Funding

None to report.