Transcutaneous Electrical Nerve Stimulation
Transcutaneous electrical nerve stimulation (TENS) is a non-invasive treatment, traditionally used for pain management (Teoli et al. 2019). Electrical current is applied through surface electrodes on the skin, which facilitates activation of nerves (Teoli et al. 2019). The electrical current administered is highly adjustable with low frequencies (<10Hz) applied to produce muscle contractions and high frequencies (>50Hz) applied to produce paresthesia without muscle contractions (Teoli et al. 2019). More recently, TENS was found to have a potential role in the rehabilitation of motor function as the application of electrical stimulation at the sensory level may enhance neuroplasticity of the motor cortex (Veldman et al. 2015). Given the affordability of the TENS unit, its compact design and ease of clinical use, it is a promising rehabilitative therapy for SCI. However, very little research to date has focused on investigating TENS as a rehabilitative therapy for SCI. The methodological details and results of one crossover RCT are presented in Table 13.
| Author Year
Country Research Design Score Total Sample Size |
Methods | Outcome | ||||
| Gomes-Osman & Field-Fote 2015
USA Crossover RCT N=24 |
Population: Mean Age: 43.7 yr; Gender: males=21, females=3; Injury etiology: Motor Vehicle Accident=17, Diving=2, Non-traumatic=1, Unspecified=4; Severity of Injury: AIS C=9, AIS D=11, Unspecified=4; Level of Injury: C4=1, C5=4, C6=10, C7=5. Intervention: Patients received three types of stimulation in a randomized order; transcranial direct current stimulation (tDCS), transcutaneous electrical nerve stimulation (TENS), and vibration therapy. Both TNS and vibration therapy was performed on the volar aspect of the wrist. tDCS was performed on the primary left/right motor area and on the contralateral supraorbital area. During each condition, the patients engaged in functional task practice. The intervention was provided once for each condition with a 1 wk break between each. Assessments were conducted at baseline, post-treatment and at 30 min post treatment. Outcome Measures: Nine-hole Peg Test (9HPT), pinch strength, Corticomotor excitability/motor-evoked potentials, Visuomotor tracking task. |
1. Results on the 9HPT improved significantly from baseline to post treatment after patients received TENS (p=0.003) and tDCS (p=0.05) with improvements maintained from baseline to 30 min post treatment (p<0.001 and p=0.003 respectively). 2. Vibration therapy did not significantly change from baseline to post treatment or 30 min post treatment. 3. Pinch strength significantly improved from baseline to post treatment after vibration therapy only (p=0.03). At 30 min post treatment, patients demonstrated improved pinch strength after both vibration therapy (p=0.03) and tDCS (p=0.005) compared to baseline. 4. Visuomotor tracking did not improve from baseline to post treatment for any of the conditions. Only tDCS improved from baseline to 30 min post treatment (p=0.05). 5. Corticomotor excitability improved significantly from baseline to post treatment after TENS (p=0.003) only but at 30 min post treatment, only vibration therapy demonstrated a significant improvement compared to baseline (p=0.006). |
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| Effect Sizes: Forest plot of standardized mean differences (SMD±95%C.I.) as calculated from pre- and post-intervention data.
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Hoffman & Field-Fote 2013 USA RCT PEDro=4 N=24 |
Population: Experimental Group (n=11): Mean Age: N/R; Gender: males=7, females=4; Level of Injury: C3=2, C4=3, C5=1, C6=3, C7=2; Severity of Injury: AIS B=1, AIS C=4, AIS D=6. Control Group (n=13): Mean Age: N/R; Gender: males=10, females=3; Level of Injury: C4=2, C5=2, C6=5, C7=4; Severity of Injury: AIS A=2, AIS B=3, AIS C=5, AIS D=3. Intervention: Patients were randomly assigned to either an experimental group or a control group then further divided into four conditions, Unimanual Somatosensory Stimulation (Uni-SS), Bimanual SS (Bi-SS), Unimanual Functional Electrical Stimulation (Uni-FES) and Bimanual FES (Bi-FES). For patients who received SS, electrodes were placed over median nerve in the wrist. FES electrodes were also placed on the median nerve in the wrist but FES was only triggered when muscle activation exceeded the threshold value. During each session, patients completed a set of activities (either unimanually or bimanually) including grasping, grasping and rotation, pinching, pinch with rotation, and finger isolation. Control patients received the interventions after an initial delayed control period. The interventions were provided 2hr/day, 5day/wk for a total of 3 wk. Assessments were conducted at baseline and at post treatment. Outcome Measures: Jebsen Taylor Hand Function Test (JTHF), Corticomotor activity, Chedoke Arm and Hand Activity Inventory (CAHAI). |
1. A significant Time x Group interaction was reported for JTHF scores with the experimental group improving significantly from baseline to post treatment on the JTHF compared to the control group (p=0.03). 2. A significant improvement in JTHF scores were found after the control group received the interventions (p=0.01) when comparing baseline to post treatment. However, the correlation between initial scores and the amount of change was not significant (p=0.19) indicating the improvement may have been due to chance. 3. After analysing all four conditions, only a significant effect of Time was found (p=0.0006) indicating that regardless of intervention, patients all demonstrated improvement on JTHF scores from baseline to post treatment. 4. No significant difference in JTHF scores were found between FES and SS from baseline to post treatment (p=0.46). 5. No significant difference in JTHF scores were found between bimanual and unimanual activities from baseline to post treatment (p=0.57). 6. A significant Time x Group interaction was reported for Corticomotor activity with the experimental group demonstrating an increase in Corticomotor map area whilst the control group did not demonstrate any changes (p=0.03). 7. A significantly greater amount of change from baseline to post treatment was found for patients in both bimanual conditions on the CAHAI compared to patients in the unimanual conditions (p=0.03). |
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| Effect Sizes: Forest plot of standardized mean differences (SMD±95%C.I.) as calculated from pre and post-intervention data.
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Beekhuizen & Field-Fote 2008 USA RCT PEDro=5 NInitial=24; NFinal=18 |
Population: Mean age: 38 yr; Gender: males=22, females=2; Level of injury: tetraplegia; Severity of injury: AIS C=11, D=13; Mean time since injury: 67 mo; Chronicity=chronic. Intervention: One of four conditions two hr per day, 5 days/wk: 1) Massed practice training (MP); 2) Somatosensory peripheral nerve stimulation (SS); 3) MP +SS combined; 4) No intervention (control). Outcome Measures: Jebson-Taylor Hand Function Test, Wolf Motor Function Test, Key pinch force, Monofilament testing, Motor evoked potential thresholds. |
1. Intervention groups differed significantly in hand function (p<0.001). All intervention groups had a significant improvement in their hand function (MP, p<0.01; SS, p<0.05; MP+SS, p<0.001), as compared to the control group. The MP+SS group improved more than the MP and SS group alone (p<0.01). 2. MP+SS and SS groups significantly improved motor function scores when compared to the control group (p<0.001, p<0.05, respectively). MP+SS improved more than MP and SS alone (p<0.01). 3. MP+SS and SS groups also significantly improved pinch grip forces (p<0.01). 4. MP+SS was the only group to have a significant sensory function improvement (p=0.01). |
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| Beekhuizen & Field-Fote 2005
USA RCT PEDro=8 N=10 |
Population: Age: 22-63 yr; Gender: males=9, females=1; Level of injury: C5-C7; Severity of injury: AIS C=4, D=6; Time since injury: 12-154 mo. Intervention: Subjects participated in two hours of massed practice (MP) therapy five times per week for three weeks or MP+median nerve somatosensory stimulation (SS). Massed practice (MP) training focused on continuous repetitions of the following: gross upper extremity movement, grip, and grip with rotation, pinch and pinch with rotation. Tasks in each block were performed for 25 min before moving to the next category. Outcome Measures: Maximal pinch grip force, Wolf motor function test timed task scores, Jebson hand function test scores, Stimulus intensity required to elicit motor threshold response in muscles, Motor evoked potentials amplitude. |
1. Pinch grip scores: differences were noted in the MP+SS group (Z=-2.023, p<0.05) only. 2. The MP+SS group also showed greater increase in pinch grip strength than the MP group (U=2.0, p<0.05). 3. Upper extremity Functional tests: the Pre/post Wolf Motor Function Test timed scores in the MP+SS group showed a difference (Z=-2.023, p<0.05). No statistical differences were noted for the MP group. 4. Timed test scores between the two groups were also found to be statistically different (U=1.0, p<0.05). 5. Jebsen test scores: pre-and post-test scores were different for the MP+SS group (Z=-2.023, p<0.05). The MP+SS group showed greater improvement than the MP group (U=3.0, p<0.05). 6. Cortical Excitability: No significant differences were noted between the two groups. |
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| Gomes-Osman et al., 2017
USA RCT PEDro=6 N=37 |
Population: FTP + PNSS (n=14): Mean age=42.4±13.5 yr; Gender: males=12, females=2; Time since injury: 13.7±12.9 yr; Level of injury: C4 – C8; Severity of injury: AISA A=0, B=3, C=11, D=0. PNSS (n=13): Mean age=34.2±16.4 yr; Gender: males=12, females=1; Time since injury: 6.5±9 yr; Level of injury: C4 – C8; Severity of injury: AISA A=1, B=2, C=9, D=1. CET (n=10): Mean age=36.6±13.2 yr; Gender: males=6, females=4; Time since injury: 4±3.8 yr; Level of injury: C4 – C8; Severity of injury: AISA A=0, B=0, C=9, D=1. Intervention: Participants were randomized to one of two corticomotor priming approaches: functional task practice (FTP) plus peripheral nerve somatosensory stimulation (PNSS) (n=14), or PNSS alone (n=13), or to conventional exercise training (CET) (n=10). Participants were training two h daily, five d/wk for four wk. Outcome Measures: Grip force (precision and power); Tactile sensation. |
1. Following intervention, significant improvements in precision grip force were observed in the stronger and weaker hand in the FTP + PNSS group (p=0.04). 2. Significant improvements were observed in weak hand precision grip force with both PNSS (p=0.03) and CET (p=0.02). 3. No significant changes were observed in power grip force or somatosensory scores in any group (p>0.05). |
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| Gad et al., 2018
USA Pre-Post N=6 |
Population: Mean age=40.2 yr; Gender: males=5, females=1; Time since injury: 10 yr; Level of injury: C4 – C8; Severity of injury: AISA A=0, B=2, C=4, D=0. Intervention: Participants completed eight, one – two hr sessions of non-invasive transcutaneous stimulation, combined with voluntary hand grip training tasks over four wk. Outcome measures were assessed at baseline and at the end of the four wk training program. Outcome Measures: Voluntary hand function (handgrip force). |
1. Maximum voluntary handgrip forces increased significantly by 325% in the presence of stimulation and 225% when grip strength was tested without simultaneous stimulation (p<0.05).
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| Nasser et al., 2014
Eqypt Pre-Post N=25 |
Population: Group 1 (n=10): Mean Age: 33.2±6.1 yr; Gender: males=8, females=2; Handedness: Rt=9, Lt=1; Level of injury: C5=5, C6=4, C7=1; Severity of Injury: AIS C=4, AIS D=6; Mean time since injury: 21.8±19.1 yr. Group 2 (n=10): Mean Age: 38.7±12.1 yr; Gender: males=8, females=2; Handedness: Rt=8, Lt=2; Level of injury: C5=5, C6=4, C7=1; Severity of Injury: AIS C=3, AIS D=7; Mean time since injury: 24.1±22.1 yr. Group 3 (n=5): Mean Age: 33.4±7.1 yr; Gender: males=3, females=2; Handedness: Rt=4, Lt=1; Level of injury: C5=2, C6=2, C7=1; Severity of Injury: AIS C=2, AIS D=3; Mean time since injury: 18.0±12.2 yr. Intervention: Group I: 10 patients received massed practice (MP) training. Group II: 10 patients received somatosensory (SS) with massed practice. Group III: 5 patients received traditional rehabilitation program. Outcome Measures: Maximal grip force, Wolf Motor Function Test (WMFT) timed score, Jebsen–Taylor hand function test score (JTHFT). |
1. There was no statistically significant difference between the 3 groups in age, sex, duration of illness, ASIA scale, handedness and level of injury (p>0.05). 2. There was a highly significant increase in post-treatment ASIA motor score in group I and group II (p<0.001) but not group III (p>0.05). 3. Comparison between pre- and post-treatment scores in light touch and pinprick values showed a significant increase in both post -treatment in group II (p<0.05); but not in group I and III (p>0.05). 4. Pinch grip force showed a significant increase after treatment in group II (p<0.001) and group I (p<0.05) but not in Group III (p>0.05). 5. Comparison between pre and post-treatment WMFT timed scores showed significant decrease in group I and group II (p<0.05) but not in group III (p>0.05). 6. There was no significant difference between groups on JTHFT timed scores (p>0.05). 7. There was a significant decrease in group I and group II in JTHFT score post-treatment compared to pre-treatment value (p<0.05). |
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Discussion
There is considerable evidence that adding TENS to functional task practice significantly improves hand motor function and performance. All of the studies reported improvements in functional measurements such as the nine-hole peg test and pinch grip. However, it is important to note that outcome measures related to quality of life or activities of daily living were not reported. When evaluating TENS as a therapy by itself, the evidence is much more conflicting, with the majority of studies suggesting that TENS is not effective alone. Given the availability and low cost of TENS therapy, it may be a good adjunct to functional task practice for the improvement of arm and hand function; however, more clinical research is necessary to determine the long-term rehabilitative effects and impact on quality of life. Future research is also necessary to determine the efficacy of TENS therapy alone.
Conclusion
There is level 1a evidence (from one crossover RCT: Gomes-Osman & Field-Fote 2015) that TENS and tDCS, when combined with functional task practice improves aspects of hand-related function.
There is level 1a evidence (from three randomized controlled trials: Bekkhuizen & Field-Fote 2005, 2008; Hoffman & Field-Fote 2013) that showed that massed practice (repetitive activity) and somatosensory stimulation (median nerve stimulation) demonstrated significant improvement in upper extremity function, grip and pinch strength required for functional activity use.
There is level 1b evidence (from one randomized controlled trial: Gomes-Osman et al. 2017) that peripheral sensory stimulation combined with functional task practice improves grip force in individuals with SCI.
There is level 4 evidence (from one pre-post test: Gad et al. 2018) that transcutaneous spinal cord stimulation combined with hand grip training significantly improves hand function.
There is level 4 evidence (from one pre-post study: Nasser et al. 2014) that showed massed practice and somatosensory stimulation significantly improved motor function and pinch grip strength compared to traditional rehabilitation programs over time.
