Temperature changes in human patellar tendon in response to therapeutic ultrasound

Abstract

Objective: To determine the rate and magnitude of temperature change in response to ultrasound in human patellar tendon for two treatment sizes.

Design and setting: 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 cm(2), 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/cm(2) for both the 2-and 4-ERA treatment sizes.

Subjects: Sixteen subjects (8 males, 21.3 +/- 1.9 years, and 8 females, 21.0 +/- 2.8 years) participated.

Measurements: 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.

Results: At the end of the treatment, the mean temperature increase was significantly different (P = .006) between treatment sizes (8.3 degrees C +/- 1.7 degrees C (2 x ERA) and 5.0 degrees C +/- 1.0 degrees C (4 x ERA)). The rate of increase was also significantly different (P < .001). The heating rate per minute for the 2-ERA treatment was 2.1 degrees C +/- 0.4 degrees C and 1.3 degrees C +/- 0.3 degrees 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.

Conclusion: Three-megahertz ultrasound at an intensity of 1 W/cm(2) significantly increased patellar tendon temperature at both 2 and 4 x ERA, but our results confirm that the 2-ERA treatment size provided higher and longer heating than the 4-ERA treatment size.