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To determine the rate and magnitude of temperature change in response to ultrasound in human patellar tendon for two treatment sizes.
A thermistor was inserted into the medial aspect of each subject's right patellar tendon, and the baseline temperature was recorded. Using stratified random sampling and using a transducer head with an effective radiating area (ERA) of 4.5 cm2, we had eight subjects each undergo either the 2-or 4-ERA ultrasound treatment first. Each subject received a 3-MHz continuous ultrasound treatment at 1 W/cm2 for both the 2-and 4-ERA treatment sizes.
Sixteen subjects (8 males, 21.3 ± 1.9 years, and 8 females, 21.0 ± 2.8 years) participated.
We moved the sound head at a speed of 2 to 3 cm/sec while recording the tendon temperature every 30 seconds during, and for 20 minutes after, the 4-minute treatment. Twenty minutes after the treatment, we applied the second treatment to the other ERA treatment size.
At the end of the treatment, the mean temperature increase was significantly different (P = .006) between treatment sizes (8.3°C ± 1.7°C (2 × ERA) and 5.0°C ± 1.0°C (4 × ERA)). The rate of increase was also significantly different (P < .001). The heating rate per minute for the 2-ERA treatment was 2.1°C ± 0.4°C and 1.3°C ± 0.3°C for the 4-ERA treatment. There was a significant difference in the cooling between treatment sizes (P = .001). The rate of temperature decrease between treatment sizes was significantly different only during the first 5-minute interval post-treatment.
Three-megahertz ultrasound at an intensity of 1 W/cm2 significantly increased patellar tendon temperature at both 2 and 4 × ERA, but our results confirm that the 2-ERA treatment size provided higher and longer heating than the 4-ERA treatment size.