Heating produced by therapeutic ultrasound in the presence of a metal plate in the femur of canine cadavers

Abstract

Heating produced by therapeutic ultrasound in the presence of a metal plate in the femur of canine cadavers ABSTRACTThe present study aimed to assess the heat generated by a therapeutic ultrasound (TUS) in a metal bone plate and adjacent structures after fixation to the femur of canine cadavers. Ten pairs of hind limbs were used, and they were equally distributed between groups that were subjected to 1-and 3-MHz frequencies, with each frequency testing 1-and 2-W/cm² intensities. The right hind limb was defined as the control group (absence of the metal plate), and the left hind limb was the test group (presence of the metal plate). Therefore, the control groups (CG) were denominated CGI, using TUS with 1-MHz frequency and 1-W/cm² intensity; CGII, using 1-MHz frequency and 2-W/cm² intensity; CGIII, using 3-MHz frequency and 1-W/cm² intensity; and CGIV, using 3-MHz frequency and 2-W/cm² intensity. For each control group, its respective test group (TG) was denominated TGI, TGII, TGIII and TGIV. The TUS was applied to the lateral aspect of the thigh using the continuous mode and a 3.5-cm² transducer in a 6.25-cm² area for 2 minutes. Sensors were coupled to digital thermometers that measured the temperature in different sites before (t 0 ) and after (t 1 ) of the TUS application. The temperatures in t 1 were higher in all tested groups. The intramuscular temperature was significantly higher (P < 0.05) in the groups used to test the 3-MHz frequency in the presence of the metal plate. The therapeutic ultrasound in the continuous mode using frequencies of 1 and 3 MHz and intensities of 1 and 2 W/cm 2 for 2 minutes caused heating of the metal plate and adjacent structures after fixation to the femur of canine cadavers.

Simplified Theoretical Model for Temperature Evaluation in Tissue–Implant–Bone Systems during Ultrasound Diathermy

“…The biophysical effects of therapeutic ultrasound on tissues 2 of 16 result from two mechanisms: (1) thermal effects due to continuous acoustic wave, and (2) non-thermal effects due to pulse acoustic wave [8]. However, there are few studies [9][10][11][12][13] that take into account the presence of implants during ultrasound diathermy and discuss the influence of implants on the temperature field in the tissues near the implant.…”

“…However, the standing wave pattern in front of the implants was not observed in the transparent hydrogel phantom. In addition, some in vitro experiments showed that the intramuscular temperature was significantly higher (p < 0.05) in groups with a presence of a metal plate [13]. From the literature review, some uncertainties remain about the effect of implants on ultrasound thermal therapies.…”