Mirror Therapy with Neuromuscular Electrical Stimulation for improving motor function of stroke survivors: A pilot randomized clinical study

Maximum tolerable daily dose of mirror movement therapy ankle exercises after stroke: an early phase dose screening study

BACKGROUND

Mirror movement therapy may reduce lower limb motor impairment after stroke. The dose is unknown.

OBJECTIVE

identify the maximum tolerable dose a day (MTD) of lower limb mirror movement therapy DESIGN: 3 + 3 cohort rule-based, dose escalation/de-escalation study. After undertaking baseline measures participants performed mirror movement therapy for 14 consecutive days. Participants then undertook outcome measures. Cohort One trained for 15 minutes daily. Subsequent cohorts exercised at a dose set according to pre-set rules and the modified Fibonacci sequence. The study stopped when the difference between set doses for consecutive cohorts was 10% or less.

SETTING

Participants' homes (intervention) and a movement analysis laboratory (measures).

PARTICIPANTS

Adults discharged from statutory stroke rehabilitation services.

INTERVENTION

Mirror movement therapy ankle exercises.

OUTCOME MEASURES

Motricity Index (primary) and bilateral time symmetry from movement onset to peak activation of Tibialis Anterior muscles during standardised sit-to-stand (secondary).

RESULTS

Five cohorts of three participants were included (n = 15). Mean (SD) age and time after stroke were 61 (9) years and 35 (42) months respectively. Set daily doses for the five cohorts were: 15, 30, 50, 40 then 35 minutes. The set dose for a subsequent cohort (six) would have been 38 minutes thus the difference from cohort five would have been three minutes i.e., 9% different. Therefore, the study stopped CONCLUSION: The identified MTD of lower limb mirror therapy was 35 minutes daily when frequency was set at seven days a week and duration as two weeks.

CLINICAL TRIAL REGISTRATION NUMBER

NCT04339803 (ClinicalTrials.gov) CONTRIBUTION OF THE PAPER: This early phase study found that the maximum tolerable dose per day (MTD) of mirror movement therapy ankle exercises was 35 minutes when frequency was set at seven days a week and duration as two weeks. The optimal therapeutic dose will therefore be somewhere in the range of 15 (starting dose) to 35 minutes per day. Further dose articulation studies are required to identify the optimal therapeutic dose before use of findings in clinical practice. This study is the first step in that research process.

Mirror therapy combined with neuromuscular electrical stimulation for poststroke lower extremity motor function recovery: a systematic review and meta-analysis

The combination of mirror therapy (MT) and neuromuscular electrical stimulation (NMES) has been devised as an intervention method in stroke rehabilitation; however, few studies have investigated its efficacy in lower extremity motor function recovery. In this systematic review and meta-analysis, we examined the effectiveness of combined MT and NMES therapy in improving poststroke walking speed, spasticity, balance and other gait parameters. Randomized controlled trials (RCTs) were selected from PubMed, Cochrane Library, EMBASE, and Scopus databases. In total, six RCTs which involving 181 participants were included. Our findings indicate that MT combined with NMES elicits greater improvement relative to control group in walking speed (SMD = 0.67, 95% confidence interval [CI] 0.26-1.07, P = 0.001), Berg Balance Scale (SMD = 0.72; 95% CI 0.31-1.13; P = 0.0007), cadence (SMD = 0.59, 95% CI 0.02-1.16, P = 0.04), step length (SMD = 0.94, 95% CI 0.35-1.53, P = 0.002), and stride length (SMD = 0.95, 95% CI 0.36-1.54, P = 0.002) but not in modified Ashworth scale (SMD =  - 0.40, 95% CI - 1.05 to 0.26, P = 0.23). Our findings suggest that MT combined with NMES may be a suitable supplemental intervention to conventional therapy in stroke survivors.

Synergic effect of the combination of mirror therapy and electrical stimulation for lower extremity motor function recovery in stroke survivors: a meta-analysis of randomized controlled trials

OBJECTIVES

To explore the synergic effect of the combination of mirror therapy and electrical stimulation on lower limb motor function recovery in stroke survivors.

MATERIALS AND METHODS

PubMed, Web of Science, Embase, Cochrane Library, CINAHL, CNKI, Wan Fang, CBM were searched from inception to December 2020. Randomized controlled trials that compared the combined therapy with another single therapy were included. A pre-determined data collection form was used to extract data. Two authors independently extracted data and used the Cochrane Handbook criteria to assess the quality of included studies.

RESULTS

Six studies, with a total of 437 patients were included. There was an overall positive effect on lower limb motor function recovery, according to Fugl-Meyer Assessment for the Lower Extremity [all: WMD in fixed effects model: 5.63, 95% CI 4.86, 6.39] and Brunnstrom stage [all: WMD in fixed effects model: 0.49, 95% CI 0.32, 0.66].

CONCLUSIONS

The results indicate that the combination of mirror therapy and electrical stimulation for lower extremity motor function recovery in stroke survivors may have a positive effect.

Using Mirror Therapy to Optimize the Efficacy of Balance Programs for Older Adults With Poststroke Balance Impairment

PURPOSE

Poststroke rehabilitation is an inevitable element of the treatment for stroke survivors. This study aimed to investigate the effect of balance training with mirror therapy in older adults with poststroke balance impairment.

DESIGN/METHODS

The study adopted a two-arm randomized clinical trial and included 38 older adults with poststroke balance impairment. The intervention group received balance exercises with mirror therapy, whereas the control group received the same balance exercises without mirror therapy (a nonreflective plate was used instead). The patient outcome, the balance score, was measured using the Berg Balance Scale. Analysis of covariance was used for statistical analysis.

RESULTS

Results showed that balance exercises combined with mirror therapy were significantly more effective than balance exercises without mirror therapy in improving balance in the stroke survivors (p < .001).

CONCLUSION

Mirror therapy combined with regular balance exercises is an effective and practical method for enhancing balance in older adults suffering from balance impairment.

CLINICAL RELEVANCE

Balance training combined with containing mirror therapy may be included in the rehabilitation programs of older adults with poststroke balance impairment.

A lower limb rehabilitation platform with mirror therapy, electrical stimulation and virtual reality for people with limited dorsiflexion movement

This paper presents a low-cost portable system for applying a rehabilitation therapy, based on virtual reality, functional electrical stimulation and a training device. This open-hardware system, intended to support a home-made therapy process in people with reduced dorsiflexion ability, contains three main building blocks: an electromechanical platform, an immersive virtual reality interface and the firmware. The electromechanical training platform is the core of the system, which acts as a gateway interface of sensors-actuators for a closed loop system, through an immersive virtual reality application, the patient closes the loop by acting as the controller by means of a "virtual dummy" preforming in mirror configuration. The platform measures and process the dorsiflexion angle described by both ankles, real-time transmitting the information to the mobile phone virtual application to be presented as a mirror. The onboard microprocessor drives the operation of the electric stimulation interface, which is sent through two channels to both, healthy and affected lower limbs. The platform communicates continuously through a USB bidirectional interface with a personal computer, in which the physician enters the rehabilitation protocol and follows the patient performance. A first case study by using this device has been reported in [1].

Effects of Mirror Therapy Combined with EMG-Triggered Functional Electrical Stimulation to Improve on Standing Balance and Gait Ability in Patient with Chronic Stroke

This study was performed to evaluate the effects of EMG-triggered functional electrical stimulation on balance and gait ability on patient with Chronic Stroke. A total of 60 chronic stroke patients were divided into mirror treatment and functional electrical (MT-EF) Group, MT group, CON group. Each group performed 60 min a day five times a week for eight weeks. MT-FE group was performed 30 min five times a week for eight weeks in mirror therapy process with EMG-FES. MT group performed 30 min five times a week for eight weeks in mirror therapy process. CON group was performed 30 min five times a week for eight weeks in conservative treatment. To measure the balance ability, Biorescue (COP, LOS), Berg balance scale (BBS) and FRT, and the gait ability test was performed by 10 m walk test. MT-FE group revealed significant differences in COP, LOS, BBS, FRT and 10 m walk test as compared to the MT and CON groups (p < 0.05). Our results showed that MT-FE was more effective on COP, LOS, BBS, FRT and 10 m walk test in patients with chronic stroke. Our results also showed that MT-EF group was more effective on balance and gait ability in patients with chronic stroke. We suggest that this study can be used for intervention data for recovering balance and gait ability in chronic stroke patients.

Motor imagery for gait rehabilitation after stroke

BACKGROUND

Motor imagery (MI) is defined as a mentally rehearsed task in which movement is imagined but is not performed. The approach includes repetitive imagined body movements or rehearsing imagined acts to improve motor performance.

OBJECTIVES

To assess the treatment effects of MI for enhancing ability to walk among people following stroke.

SEARCH METHODS

We searched the Cochrane Stroke Group registry, CENTRAL, MEDLINE, Embase and seven other databases. We also searched trial registries and reference lists. The last searches were conducted on 24 February 2020.

SELECTION CRITERIA

Randomized controlled trials (RCTs) using MI alone or associated with action observation or physical practice to improve gait in individuals after stroke. The critical outcome was the ability to walk, assessed using either a continuous variable (walking speed) or a dichotomous variable (dependence on personal assistance). Important outcomes included walking endurance, motor function, functional mobility, and adverse events.

DATA COLLECTION AND ANALYSIS

Two review authors independently selected the trials according to pre-defined inclusion criteria, extracted the data, assessed the risk of bias, and applied the GRADE approach to evaluate the certainty of the evidence. The review authors contacted the study authors for clarification and missing data.

MAIN RESULTS

We included 21 studies, involving a total of 762 participants. Participants were in the acute, subacute, or chronic stages of stroke, and had a mean age ranging from 50 to 78 years. All participants presented at least some gait deficit. All studies compared MI training versus other therapies. Most of the included studies used MI associated with physical practice in the experimental groups. The treatment time for the experimental groups ranged from two to eight weeks. There was a high risk of bias for at least one assessed domain in 20 of the 21 included studies. Regarding our critical outcome, there was very low-certainty evidence that MI was more beneficial for improving gait (walking speed) compared to other therapies at the end of the treatment (pooled standardized mean difference (SMD) 0.44; 95% confidence interval (CI) 0.06 to 0.81; P = 0.02; six studies; 191 participants; I² = 38%). We did not include the outcome of dependence on personal assistance in the meta-analysis, because only one study provided information regarding the number of participants that became dependent or independent after interventions. For our important outcomes, there was very low-certainty evidence that MI was no more beneficial than other interventions for improving motor function (pooled mean difference (MD) 2.24, 95% CI -1.20 to 5.69; P = 0.20; three studies; 130 participants; I² = 87%) and functional mobility at the end of the treatment (pooled SMD 0.55, 95% CI -0.45 to 1.56; P = 0.09; four studies; 116 participants; I² = 64.2%). No adverse events were observed in those studies that reported this outcome (seven studies). We were unable to pool data regarding walking endurance and all other outcomes at follow-up.

AUTHORS' CONCLUSIONS

We found very low-certainty evidence regarding the short-term benefits of MI on walking speed in individuals who have had a stroke, compared to other therapies. Evidence was insufficient to estimate the effect of MI on the dependence on personal assistance and walking endurance. Compared with other therapies, the evidence indicates that MI does not improve motor function and functional mobility after stroke (very low-certainty evidence). Evidence was also insufficient to estimate the effect of MI on gait, motor function, and functional mobility after stroke compared to placebo or no intervention. Motor Imagery and other therapies used for gait rehabilitation after stroke do not appear to cause significant adverse events.

Effect of afferent electrical stimulation with mirror therapy on motor function, balance, and gait in chronic stroke survivors: a randomized controlled trial

BACKGROUND

When solely mirror therapy is applied for a long period of time, spatial perception and attention to the damaged side may decrease, and the effect of mirror therapy may be limited. To overcome this limitation, it has recently been suggested that the combination of mirror therapy with mirror treatment is effective.

AIM

The aim of this study was to investigate the effects of afferent electrical stimulation with mirror therapy on motor function, balance, and gait in chronic stroke survivors.

DESIGN

A randomized controlled trial.

SETTING

Rehabilitation center.

POPULATION

Thirty stroke survivors were randomly assigned to two groups: the experimental group (N.=15) and the control group (N.=15).

METHODS

Participants of the experimental group received afferent electrical stimulation with mirror therapy, and participants of the control group received sham afferent electrical stimulation with sham mirror therapy for 60 minutes per day, 5 days per week, for 4 weeks. Motor function was measured using a handheld dynamometer and the Modified Ashworth Scale, balance was measured using the Berg Balance Scale, and gait was assessed using the GAITRite® (GAITRite, CIR System Inc., Franklin, NJ, USA) pressure-sensitive walkway at baseline and after 4 weeks.

RESULTS

The experimental group showed significant differences in muscle strength, Modified Ashworth Scale, and Berg Balance Scale results, and velocity, cadence, step length, stride length, and double support time of their gait (P<0.05) in the pre-post intervention comparison. Significant differences between the two groups in muscle strength, Berg Balance Scale, gait velocity, step length, and stride length (P<0.05) were found.

CONLCUSIONS

Mirror therapy with afferent electrical stimulation may effectively improve muscle strength and gait and balance abilities in hemiplegic stroke survivors.

CLINICAL REHABILITATION IMPACT

Afferent electrical stimulation combined with mirror therapy can be used as an effective intervention to improve lower limb motor function, balance, and gait in chronic stroke survivors in clinical settings.

Exploring Hemodynamic Responses Using Mirror Visual Feedback With Electromyogram-Triggered Stimulation and Functional Near-Infrared Spectroscopy

In recent years, mirror visual feedback (MVF) therapy combined with electrical stimulation (ES) have been proposed for patients with hemiparesis. However, the neurophysiological effect remains unknown. We investigated the effects of MVF by itself and along with electromyogram-triggered ES (ETES) on hemodynamic responses using functional near-infrared spectroscopy (NIRS). Eighteen healthy subjects participated in this study. We measured changes in brain oxygenation using 48 NIRS channels. We investigated the effects of three main factors of visual feedback (observation of a mark, right hand, and hand movements via mirror) with or without ES on bilateral precentral gyrus (PrG), postcentral gyrus (PoG), supplementary motor area (SMA), supramarginal gyrus area (SMG), and angular gyrus (AG) to determine the contribution of each factor. The results showed that the left PoG was significantly more activated when performing mirrored tasks (MT) than when performing circle or Right-hand Tasks (RTs). In addition, the right PoG and right SMA in MT were significantly more activated than in MT + ES cases. Our findings suggested that observation of movements through the mirror caused activation of the postcentral gyrus rather than the PrG, and MVF along with ETES decreased cortical activation.

Effect of Mirror Therapy on Recovery of Stroke Survivors: A Systematic Review and Network Meta-analysis

Mirror therapy (MT) as a relatively new rehabilitation technique has been widely applied in stroke patients. A number of randomized controlled trials (RCTs) have investigated the effects of MT for stroke survivors. The main purpose of this network meta-analysis was to investigate the effects of MT on motor function, activities of daily living (ADL), and pain perception in stroke survivors. Several databases were searched to identify RCTs evaluating the effects of MT in stroke patients to perform this network meta-analysis. Thirty-seven RCTs (42 analyses, 1685 subjects) were eligible for inclusion in the meta-analysis. Standard meta-analysis showed that MT significantly improved of motor function according to the increased Fugl-Meyer Assessment (FMA), Functional Independence Measure (FIM), and decreased Modified Ashworth Scale (MAS) score. In addition, ADL was promoted by MT as the elevated Modified Barthel Index (MBI) and Motor Activity Log (MAL) score. Moreover, MT effectively relieved the pain of stroke patients as the Visual Analog Scale (VAS) score was reduced. Subgroup analyses and meta-regressions identified that the sources of heterogeneity might be different intervention arms and duration of interventions. Network meta-analysis showed that MT combined with electrical stimulation (ES) for less than 4 weeks along with conventional rehabilitation therapy (CT), and MT accompanied with CT for less than 4 weeks might be the most suitable interventions for improvement of motor function and ADL, respectively. Overall, MT could effectively improve motor function and ADL, as well as relieve pain for stroke survivors. The study was registered at PROSPERO (CRD42017081742).

The Efficacy of Lower Extremity Mirror Therapy for Improving Balance, Gait, and Motor Function Poststroke: A Systematic Review and Meta-Analysis

BACKGROUND

Mirror therapy is less commonly used to target the lower extremity after stroke to improve outcomes but is simple to perform. This review and meta-analysis aimed to evaluate the efficacy of lower extremity mirror therapy in improving balance, gait, and motor function for individuals with stroke.

METHODS

PubMed, Cochrane Central Register of Controlled Trials, MEDLINE, Embase, Cumulative Index to Nursing and Allied Health Literature, Physiotherapy Evidence Database, and PsychINFO were searched from inception to May 2018 for randomized controlled trials (RCTs) comparing lower extremity mirror therapy to a control intervention for people with stroke. Pooled effects were determined by separate meta-analyses of gait speed, mobility, balance, and motor recovery.

RESULTS

Seventeen RCTs involving 633 participants were included. Thirteen studies reported a significant between-group difference favoring mirror therapy in at least one lower extremity outcome. In a meta-analysis of 6 trials that reported change in gait speed, a large beneficial effect was observed following mirror therapy training (standardized mean differences [SMD] = 1.04 [95% confidence interval [CI] = .43, 1.66], I² = 73%, and P < .001). Lower extremity mirror therapy also had a positive effect on mobility (5 studies, SMD = .46 [95% CI = .01, .90], I² = 43%, and P = .05) and motor recovery (7 studies, SMD = .47 [95% CI = .21, .74], I² = 0%, and P < .001). A significant pooled effect was not found for balance capacity.

CONCLUSIONS

Mirror therapy for the lower extremity has a large effect for gait speed improvement. This review also found a small positive effect of mirror therapy for mobility and lower extremity motor recovery after stroke.

Interventions involving repetitive practice improve strength after stroke: a systematic review

QUESTIONS

Do interventions involving repetitive practice improve strength after stroke? Are any improvements in strength accompanied by improvements in activity?

DESIGN

Systematic review of randomised trials with meta-analysis.

PARTICIPANTS

Adults who have had a stroke.

INTERVENTION

Any intervention involving repetitive practice compared with no intervention or a sham intervention.

OUTCOME MEASURES

The primary outcome was voluntary strength in muscles trained as part of the intervention. The secondary outcomes were measures of lower limb and upper limb activity.

RESULTS

Fifty-two studies were included. The overall SMD of repetitive practice on strength was examined by pooling post-intervention scores from 46 studies involving 1928 participants. The SMD of repetitive practice on strength when the upper and lower limb studies were combined was 0.25 (95% CI 0.16 to 0.34, I²=44%) in favour of repetitive practice. Twenty-four studies with a total of 912 participants investigated the effects of repetitive practice on upper limb activity after stroke. The SMD was 0.15 (95% CI 0.02 to 0.29, I²=50%) in favour of repetitive practice on upper limb activity. Twenty studies with a total of 952 participants investigated the effects of repetitive practice on lower limb activity after stroke. The SMD was 0.25 (95% CI 0.12 to 0.38, I²=36%) in favour of repetitive practice on lower limb activity.

CONCLUSION

Interventions involving repetitive practice improve strength after stroke, and these improvements are accompanied by improvements in activity.

REVIEW REGISTRATION

PROSPERO CRD42017068658. [de Sousa DG, Harvey LA, Dorsch S, Glinsky JV (2018) Interventions involving repetitive practice improve strength after stroke: a systematic review. Journal of Physiotherapy 64: 210-221].

Mirror therapy for improving motor function after stroke

BACKGROUND

Mirror therapy is used to improve motor function after stroke. During mirror therapy, a mirror is placed in the person's midsagittal plane, thus reflecting movements of the non-paretic side as if it were the affected side.

OBJECTIVES

To summarise the effectiveness of mirror therapy compared with no treatment, placebo or sham therapy, or other treatments for improving motor function and motor impairment after stroke. We also aimed to assess the effects of mirror therapy on activities of daily living, pain, and visuospatial neglect.

SEARCH METHODS

We searched the Cochrane Stroke Group's Trials Register, the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, Embase, CINAHL, AMED, PsycINFO and PEDro (last searched 16 August 2017). We also handsearched relevant conference proceedings, trials and research registers, checked reference lists, and contacted trialists, researchers and experts in our field of study.

SELECTION CRITERIA

We included randomised controlled trials (RCTs) and randomised cross-over trials comparing mirror therapy with any control intervention for people after stroke.

DATA COLLECTION AND ANALYSIS

Two review authors independently selected trials based on the inclusion criteria, documented the methodological quality, assessed risks of bias in the included studies, and extracted data. We assessed the quality of the evidence using the GRADE approach. We analysed the results as standardised mean differences (SMDs) or mean differences (MDs) for continuous variables, and as odds ratios (ORs) for dichotomous variables.

MAIN RESULTS

We included 62 studies with a total of 1982 participants that compared mirror therapy with other interventions. Of these, 57 were randomised controlled trials and five randomised cross-over trials. Participants had a mean age of 59 years (30 to 73 years). Mirror therapy was provided three to seven times a week, between 15 and 60 minutes for each session for two to eight weeks (on average five times a week, 30 minutes a session for four weeks).When compared with all other interventions, we found moderate-quality evidence that mirror therapy has a significant positive effect on motor function (SMD 0.47, 95% CI 0.27 to 0.67; 1173 participants; 36 studies) and motor impairment (SMD 0.49, 95% CI 0.32 to 0.66; 1292 participants; 39 studies). However, effects on motor function are influenced by the type of control intervention. Additionally, based on moderate-quality evidence, mirror therapy may improve activities of daily living (SMD 0.48, 95% CI 0.30 to 0.65; 622 participants; 19 studies). We found low-quality evidence for a significant positive effect on pain (SMD -0.89, 95% CI -1.67 to -0.11; 248 participants; 6 studies) and no clear effect for improving visuospatial neglect (SMD 1.06, 95% CI -0.10 to 2.23; 175 participants; 5 studies). No adverse effects were reported.

AUTHORS' CONCLUSIONS

The results indicate evidence for the effectiveness of mirror therapy for improving upper extremity motor function, motor impairment, activities of daily living, and pain, at least as an adjunct to conventional rehabilitation for people after stroke. Major limitations are small sample sizes and lack of reporting of methodological details, resulting in uncertain evidence quality.

Effects of mirror therapy combined with neuromuscular electrical stimulation on motor recovery of lower limbs and walking ability of patients with stroke: a randomized controlled study

OBJECTIVE

To investigate the effectiveness of mirror therapy combined with neuromuscular electrical stimulation in promoting motor recovery of the lower limbs and walking ability in patients suffering from foot drop after stroke.

DESIGN

Randomized controlled study.

SETTING

Inpatient rehabilitation center of a teaching hospital.

SUBJECTS

Sixty-nine patients with foot drop.

INTERVENTION

Patients were randomly divided into three groups: control, mirror therapy, and mirror therapy + neuromuscular electrical stimulation. All groups received interventions for 0.5 hours/day and five days/week for four weeks.

MAIN MEASURES

10-Meter walk test, Brunnstrom stage of motor recovery of the lower limbs, Modified Ashworth Scale score of plantar flexor spasticity, and passive ankle joint dorsiflexion range of motion were assessed before and after the four-week period.

RESULTS

After four weeks of intervention, Brunnstrom stage ( P = 0.04), 10-meter walk test ( P < 0.05), and passive range of motion ( P < 0.05) showed obvious improvements between patients in the mirror therapy and control groups. Patients in the mirror therapy + neuromuscular electrical stimulation group showed better results than those in the mirror therapy group in the 10-meter walk test ( P < 0.05). There was no significant difference in spasticity between patients in the two intervention groups. However, compared with patients in the control group, patients in the mirror therapy + neuromuscular electrical stimulation group showed a significant decrease in spasticity ( P < 0.001).

CONCLUSION

Therapy combining mirror therapy and neuromuscular electrical stimulation may help improve walking ability and reduce spasticity in stroke patients with foot drop.

Systematic review of mirror therapy compared with conventional rehabilitation in upper extremity function in stroke survivors

BACKGROUND/AIM

Stroke is a leading cause of disability in developed countries. One of the most widespread techniques in clinical practice is mirror therapy (MT). To determine the effectiveness of MT over other methods of intervention in the recovery of upper limb function in people who have had a stroke.

METHODS

A systematic review was conducted. The search string was established based on the last systematic review about MT that dated from 2009: "upper extremity" OR "upper limb "AND "mirror therapy" AND stroke. For this search Pubmed, Scopus and SciELO databases were used.

RESULTS

Fifteen studies were included in the systematic review. Recovery of the upper limb, upper limb function and gross manual dexterity were frequently measured in these studies.

CONCLUSIONS

In the primary variables in promoting recovery, MT alone showed better results in acute and chronic stroke patients in upper limb functioning than either conventional rehabilitation (CR) or CR plus MT. PROSPERO registration number: CRD42015026869.