Can transcutaneous electrical nerve stimulation improve achilles tendon healing in rats?

Transcutaneous Electric Nerve Stimulation in Animal Model Studies: From Neural Mechanisms to Biological Effects for Analgesia

OBJECTIVE

This systematic and meta-analysis review evaluated the transcutaneous electrical nerve stimulation (TENS)-induced action mechanisms for animal analgesia.

MATERIALS AND METHODS

Two independent investigators identified relevant articles published until February 2021 through a literature review, and a random-effects meta-analysis was performed to synthesize the results.

RESULTS

Of the 6984 studies found in the data base search, 53 full-text articles were selected and used in the systematic review. Most studies used Sprague Dawley rats (66.03%). High-frequency TENS was applied to at least one group in 47 studies, and most applications were performed for 20 minutes (64.15%). Mechanical hyperalgesia was analyzed as the primary outcome in 52.83% of the studies and thermal hyperalgesia in 23.07% of studies using a heated surface. More than 50% of the studies showed a low risk of bias on allocation concealment, random housing, selective outcome reporting, and acclimatization before the behavioral tests. Blinding was not performed in only one study and random outcome assessment in another study; acclimatization before the behavioral tests was not performed in just one study. Many studies had an uncertain risk of bias. Meta-analyses indicated no difference between low-frequency and high-frequency TENS with variations among the pain models.

CONCLUSIONS

This systematic review and meta-analysis suggests that TENS has presented a substantial scientific foundation for its hypoalgesic effect in preclinical studies for analgesia.

Histological evaluation of the effect of low-frequency electric stimulation on healing Achilles tendons in rats

PURPOSE

Histologically evaluate the effects of low frequency electrical stimulation in the treatment of Achilles tendon injuries in rats.

METHODS

Thirty-four rats underwent Achilles tendon tenotomy and tenorrhaphy. They were randomly allocated in two groups. Half of the sample constituted the experiment group, whose lesions were stimulated with 2 Hz, nonpolarized current and 1 mA, for 14 days. The other animals formed the control group. They were evaluated at 2, 4 and 6 weeks. The histological study was carried out, the collagen density and the wound maturity index were measured.

RESULTS

The healing score was higher in the group stimulated at the 6th week (p = 0.018). The density collagen 1 was higher in the group treated at the three times (p = 0.004) and that collagen 3 was higher in the group treated at 6 weeks (p = 0.004). Together, collagen 1 and 3 were higher in the group stimulated at 4 and 6 weeks (p = 0.009, p = 0.004). The maturity index was higher in this group at the three moments (p = 0.017 p = 0.004 and p = 0.009).

CONCLUSION

Low frequency electric stimulation improved healing and increased the quantity of collagen.

Tensiometric evaluation of the effect of lowfrequency electric stimulation on healing Achilles tendons in rats

PURPOSE

To evaluate the effects of low-frequency electric stimulation on biomechanics following surgical treatment of the Achilles tendon in rats.

METHODS

Forty-two rats were divided into two groups. One was given electric stimulation and the other was not. All were submitted to Achilles tenotomy and tenorrhaphy performed with a modified Kessler stitch. The experiment group underwent electric stimulation with 2 Hz, a nonpolarized current of 1 mA intensity for 14 days. The animals were euthanized at 2, 4 and 6 weeks for the biomechanical study.

RESULTS

The work performed, that is, the tendon's capacity to absorb energy until rupture, was greater in the electrically stimulated group in the 2nd (p = 0.032) and in the 6th week (p = 0.010). The maximum tension, which is the capacity to support a load, was higher in the treated group in the 2nd (p = 0.030) and the 6th week (p = 024). These results indicate greater resistance of the electrically stimulated tendons. An analysis of the elastic module showed no differences.

CONCLUSION

Low-frequency electric stimulation increased the resistance of the tendons at 2 and 6 weeks of evolution in rats.

Does electrode placement influence tens-induced antihyperalgesia in experimental inflammatory pain model?

•

This study challenges the notion that TENS can only be applied at the site of pain.

•

The study supports the use of TENS in patients with significant skin injuries.

•

This helps to understand the action of TENS in edema.

Background

Transcutaneous electrical nerve stimulation (TENS) is a treatment commonly used for managing pain; however, the ideal placement of the electrodes is not fully understood.

Objective

To investigate the best way to apply TENS electrodes in an experimental inflammatory pain model.

Method

Knee joint inflammation was induced in rats, followed by administration of low-frequency TENS (4 Hz) under anesthesia for five days. Animals were randomly allocated to five groups according to electrode placement (n = 6, each): dermatome, contralateral, paraspinal, acupoint, and control. Interventions: Low-frequency TENS at sensory intensity and 100 μs pulse duration. Withdrawal thresholds to mechanical (von Frey) and thermal stimuli and joint edema were assessed before induction of inflammation and immediately before and after application of TENS.

Results

Reduced paw withdrawal threshold and thermal latency that occur 24 h after the induction of inflammation were significantly reversed by the administration of TENS in all groups when compared with sham treatment or with the condition before TENS treatment. No difference was observed in the edema measurement.

Conclusion

These results offer more options for practitioners to choose the area of the body most commodious for electrode placement, depending on the clinical condition of the patient, because the effect was similar at all sites. In addition, there was a loss of the effectiveness of TENS in reversing mechanical and thermal hyperalgesia on the fifth day, suggesting the development of the tolerance phenomenon.

High voltage pulsed current in collagen realignment, synthesis, and angiogenesis after Achilles tendon partial rupture

Objective

To verify the efficacy of high voltage pulsed current in collagen realignment and synthesis and in angiogenesis after the partial rupturing of the Achilles tendon in rats.

Method

Forty male Wistar rats were randomized into four groups of 10 animals each: sham, cathodic stimulation, anodic stimulation, and alternating stimulation. Their Achilles tendons were submitted to direct trauma by a free-falling metal bar. Then, the treatment was administered for six consecutive days after the injury. In the simulation group, the electrodes were positioned on the animal, but the device remained off for 30 minutes. The other groups used a frequency of 120 pps, sensory threshold, and the corresponding polarity. On the seventh day, the tendons were removed and sent for histological slide preparation for birefringence and Picrosirius Red analysis and for blood vessel quantification.

Results

No significant difference was observed among the groups regarding collagen realignment (types I or III collagen) or quantity of blood vessels.

Conclusion

High voltage pulsed current for six consecutive days was not effective in collagen realignment, synthesis, or angiogenesis after the partial rupturing of the Achilles tendon in rats.