Efficiency of tissue penetration by currents induced by 3 electrotherapeutic techniques: A comparative study using a novel deep-tissue measuring technique

Background. Electrotherapy provides a wide range of treatment alternatives for musculoskeletal pathologies. However, for the electrical stimulation to exert a significant therapeutic effect, the induced current must often penetrate deep inside the target tissue. Objective. The objective was to systematically compare the penetration efficiency of 3 electrotherapeutic stimulation modalities: transcutaneous electrical nerve stimulation (TENS), interferential (IF) stimulation, and combined therapy with pulsed ultrasound and IF current (CTPI). Design. This was a comparative, experimental laboratory study. Methods. The penetration efficiency was evaluated as a voltage difference between 2 of an 8-contact spinal cord stimulation array. Each of 20 participants with a preimplanted spinal cord stimulation array was stimulated with TENS (3 different electrode configurations), IF current (3 configurations), and CTPI (1 configuration). Results. Significant differences in penetration efficiency were found between the various stimulation conditions and electrode configurations. CTPI showed the highest penetration efficiency, followed by IF, and finally TENS. Penetration efficiency was inversely and significantly correlated with skinfold thickness in all conditions, but this correlation was lowest for the CTPI stimulation. Limitations. Our study design did not include a condition of combined therapy with pulsed ultrasound and TENS, and it did not directly control for current or voltage density under the stimulating electrodes. In addition, further research is required to determine whether a higher stimulation intensity of the target tissue is advantageous clinically. Conclusions. Pending further testing, CTPI stimulation could prove more effective than IF and TENS in reaching deeper tissues, especially considering the variability in adipose tissue thickness in the population, for example, in cases of patients with obesity.