Aim
Our objective was to analyze the thermal behavior and transmission of electric current in the Achilles tendon and the musculotendinous junction of the gastrocnemius muscle with different CRet protocols, using non-living specimens and invasive temperature measurements.
Study design
This was a cross-sectional study designed to assess the effect of resistive energy/electrical capacitive transfer with the T-Plus Wintecare device on the temperature in the Achilles tendon, musculotendinous junction and superficial region of the calf in cadaveric specimens. The body donor program of the Faculty of Medicine and Health Science of Universitat Internacional de Catalunya provided all specimens. The study was conducted in July 2019. The Ethics Committee “Comitè d’Ètica de Recerca (CER) from the Universitat Internacional de Catalunya” approved the study with CBAS201907 reference number.
Cadaveric specimens
The study material included 5 fresh frozen cadavers: 4 male and 1 female (10 legs). The age range at the time of death was 60–80 years (mean 69.80 ± 6.04). The bodies were stored at 3 °C and brought to room temperature a day before the test to make it stable. The basal superficial, Achilles tendon and musculotendinous junction temperatures were measured prior to any intervention to ensure the same starting values. None of the cadaveric specimens used for this study had evidence of traumatic injuries or surgical scars on the lower limbs.
Intervention
To better understand the temperature behavior and passage of current in conditions similar to rehabilitative treatments, we applied a power limit similar to that typically applied with a T-Plus device during real-life treatments. This was based on the power level, which is easily identifiable and controllable by the therapist during therapy, and the watts (absorbed power) shown by the device during the therapy.
The power range of a very large T-Plus device ranges from 1 to 300 watts in resistive and from 1 to 450 Volt-Ampere (VA) in capacitive mode.
Two thresholds were identified: high power and low power, based on the real powers that the therapist typically applies when she/he wants to generate a thermal or non-thermal reaction. On this basis, high-power thresholds were set at 90VA in capacitive mode (HPC) and 60 watts in resistive mode (HPR), while low-power thresholds were set at 20VA in capacitive mode (LPC) and 10 watts in resistive mode (LPR). In real-life use, on average, thresholds of 10 watts and 20 VA respect the limit of 0.3 A, while applications at 60 watts and 90 VA are widely-used for a thermal effect.
The 4 interventions (capacitive and resistive mode; low- and high-power) were performed for 5 min each, by a physiotherapist with experience in the use of T-Plus. Dynamic movements similar to those used with real patients were performed with constant pressure to the posterior region of the heel (Fig. 1).
Experimental procedures
Cadavers were placed in the prone position. Hips were placed in neutral rotation, with the knee in 30° of flexion, and a thermoplastic splint maintained the ankle joint position. The skin was cleaned with chlorhexidine-isopropyl alcohol [23].
The order of the 4 treatment protocols and the specimen (leg side) were both randomized generating a pre-listing through Random.org. by one of the researchers not involved in the recruitment. The temperature generated in the specimen was allowed to return to normal before the next application.
All instrumentation received a calibration certificate prior to the study. Thermocouples “Hart Scientific PT25 5628-15” were used to measure the musculotendinous junction and Achilles tendon temperature, and a digital thermometer “Thermocomed” was used to measure the superficial temperature of the calf (Fig. 2a). Thermocouples were placed under ultrasound guidance “US Aloka Prosound C3 15.4”, with a high-frequency linear transducer (USTTL01, 12 L5), by a researcher expert in the use of the instrument (Fig. 2b). One thermocouple was placed in the middle of the Achilles tendon and the other in the musculotendinous junction (Fig. 2c).
The return electrode of the T-Plus was placed on the abdomen of the specimen and the treatment was carried out with the movable electrode of the T-Plus on the heel for 5 min. The initial superficial, Achilles tendon and musculotendinous junction temperatures were measured. These measurements were recorded at 1-min intervals for 5 min and at 5 min after the end of each treatment. Prior to treatment, impedance was always measured (Multimeter Fluke 8846A) to ensure that the values marked by the T-Plus Wintecare device were correct. In addition, the current flow of each application was calculated. Using the average voltage divided by the initial impedance.
Statistical analysis
Analyses were performed using SPSS Statistics version 22.0. Normality of distribution was analyzed using the Shapiro-Wilk test (p > 0.05). Mean and standard deviation were calculated for the superficial, Achilles tendon and musculotendinous junction temperatures. The percentages of temperature change respect to baseline temperature were calculated.
For intra-protocol differences, the Friedman test and Wilcoxon signed-rank test were used. Inter-protocol comparisons were performed using the Kruskal-Wallis test and Mann-Whitney U test. A p value < 0.05 was considered statistically significant.