Study Design: Counterbalanced, within-subjects experimental design. Objective: To determine the effect of continuous 1-MHz ultrasound, given at 1.5 W/cm² and 2.0 W/cm² for 10 minutes, on tissue temperature in the region of the L4-L5 zygapophyseal joint. Background: Ultrasound is a modality commonly used for the treatment of lower back pain syndromes. Randomized controlled trials supporting the clinical effectiveness for ultrasound in the treatment of any type of lower back condition are lacking. While one purported purpose of ultrasound is the deep-heating effect, it has not been demonstrated that ultrasound can heat tissues in the area of the lumbar zygapophyseal joints, and the specific parameters needed for a heating effect have not been investigated. To aid in the design of the ultrasound intervention for future randomized controlled trials, it would be beneficial to have insight into the thermal effects of ultrasound on tissues of the lumbar spine and the parameters needed to produce a thermal effect. The present study examined the heating effect of ultrasound on periarticular tissue in the lumbar spine. Methods and Measures: Continuous, 1-MHz ultrasound at intensities of 1.5 W/cm² and 2.0 W/cm² was applied for 10 minutes to the lower back of 6 healthy individuals without lower back pain, while temperature measurements were taken with a hypodermic thermocouple implanted next to the L4-L5 zygapophyseal joint. ANOVA models were used for statistical analysis. Results: Statistical analysis confirmed that the 2.0-W/cm² ultrasound application produced (a)a more rapid increase in temperature over time, (b) a greater overall level of heating, and (c) significantly greater heating 6 minutes after the beginning of ultrasound administration. The mean terminal temperatures (at 10 minutes) obtained during the 1.5-W/cm² and 2.0-W/cm² ultrasound applications were 38.1°C and 39.3°C, respectively. Conclusion: Continuous 1-MHz ultrasound given at either 1.5-W/cm² or 2.0-W/cm² intensity has the capability of heating lumbar periarticular tissue. The higher-intensity ultrasound resulted in greater and faster temperature increase.

J Orthop Sports Phys Ther. 2004;34(12):754-760. doi:10.2519/jospt.2004.1349

Key Words: heat, low back, lumbar spine, physical agents