The main objective of this study was to verify whether changing the position of the electrodes modified current flow and temperature in superficial and deep shoulder tissues by measuring these factors invasively during the application of capacitive and resistive CRet protocols in cadaveric specimens
A cross-sectional study was designed to establish the effect of transferring electrical capacitive/resistive energy from the Wintecare T-Plus device on the temperature and current flow in the shoulder area (superficial, supraspinatus tendon and glenohumeral capsule) in cadaveric specimens. The body donation programme at the Faculty of Medicine and Health Sciences of the Universitat Internacional de Catalunya (Spain) provided all the samples. The study was approved by the “Comitè d´Ètica de Recerca” (CER) research ethics committee at the Universitat Internacional de Catalunya (Reference number CB12020).
The sample was composed of 5 complete, fresh, cryopreserved cadavers (3 men and 2 women; 10 limbs). The cadavers were stored at 3ºC; they were kept at room temperature for 24 hours the day before the study. Mean cadaver age was 80.6 ± 14.6 years. None of the cadaveric samples used in this study had evidence of trauma or surgical scars on the limbs.
For better understanding of the temperature changes and electric current flow in conditions similar to rehabilitation treatments, we used a power threshold similar to that normally used during treatments on real patients with the T-Plus model. This is based on the power level that the therapist can easily identify and control during the therapy, and the watts (absorbed power) that the device samples during application. The power range of a T-Plus device varies from 1 to 300 watts in resistive mode and from 1 to 450 volt-ampere (VA) in capacitive mode (19).
Two thresholds for high and low power were identified, based on the empirical evidence that the therapist applies clinically when inducing a thermal or non-thermal reaction, respectively, is desired. The power depends on the protocol used, which is a function of the area to be treated. In the shoulder area, high power-capacitive (HPC) application is defined as applying 130 VA in capacitive mode, and high power-resistive (HPR), as applying 100 watts in resistive mode; for the low power applications, LPC is defined as applying 40 VA in capacitive mode and LPR, 20 watts in resistive mode. In comparison with treatments typically used in real patients, these low power thresholds respect the limit of 0.3 amperes, while the high power thresholds are above 0.3 amperes, so thermal effects are expected (19).
Four interventions (HPC, HPR, LPC and LPR) of 5 minutes each were performed, with the return electrode on the lower back of the cadaveric specimen and the movable electrode on the antero-lateral shoulder area. The same 4 interventions were applied changing the movable electrode position to the postero-superior part of the shoulder area, near the acromioclavicular joint. Dynamic movements similar to those used with real patients were made using constant pressure. The treatments were given by a physiotherapist skilled in the use of the T-Plus (Figure 1).
Each cadaver was placed in a supine position with the forearm in a neutral pronation-supination position, the elbow extended and the shoulder in neutral flexion-extension.
The order of the 8 treatment protocols and the arm of each cadaver were randomly assigned before the study. An external researcher randomised these 2 factors using the computer programme “random.org”. Before applying each treatment, it was ensured that the basal temperature of each cadaver had returned to the initial values.
Before beginning the CRet application, all instruments used were verified to have a calibration certificate. Hart Scientific PT25 5628-15 temperature devices were used to measure the tendinous and capsular temperature (ºC) of the shoulder. A "Thermocomed" digital thermometer was used to measure the superficial skin temperature in the shoulder area. Thermocouples were placed under ultrasound guidance (US Aloka ProSound C3 15.4") with a high-frequency linear transductor (USTTL01, 12L5) in the middle of the supraspinatus tendon and in the glenohumeral joint capsule by a researcher expert in the use of the instrument. The return electrode of the T-Plus was placed on the lower back of the cadavers. Each treatment was performed with the T-Plus movable electrode on the previously-explained treatment areas for 5 minutes. The initial superficial temperatures and those registered by the invasive temperature monitors were measured. These measurements were registered at intervals of 1 minute during the 5-minute treatment period and then at 5 minutes after the end of each treatment. Prior to treatment, the impedance was always recorded (Fluke 8846A Digital Multimeter) to guarantee that the values marked by the Wintecare T-Plus device were correct. The current flow existing at that time was also calculated for each application, using the mean voltage divided by the initial impedance.
Statistical analysis was performed with the SPSS Statistics version 22.0 programme. Normal distribution was calculated using the Shapiro-Wilk test (P>0.05). The mean, standard deviation and difference between applications were calculated, as well as the percent of temperature increase.
Two-way repeated measures analysis of variance (ANOVA) was used for the comparative analysis. Statistical significance was set to p<0.05.