Detection of changes of scar thickness under mechanical loading using ultrasonic measurement

The intervention of pressure therapy on management of hypertrophic scar (HS) after burn is based on the theoretical assumption that the mechanical force added onto the scar tissue will reduce the growth of myofibroblasts which create the collagen clusters and the interstitial space, and to realign fibrous tissues, thus reducing the thickness of HS. In this experimental study, a high frequency ultrasound imaging system (12 MHz) was applied to measure the real time changes of thickness of the post burn HS under a mechanical loading system with similar pressure generated to the scar tissue. The validity of the ultrasound system in measurement of the changes of scar thickness underneath the tissue was tested on the porcine skin in vitro followed by measurement of human skin in vivo. Results showed that the ultrasound measurement of thickness had both good validity (r(2)=0.98, p<0.0001) and good intra-rater reliability (ICC=0.89). Then, the system was used to test the thickness of 14 human HS samples in vivo among 7 subjects. External loading force with similar pressure range (10-45 mmHg) was then applied to these scar samples via ultrasound probe with rectangular contacting area at 4 cm(2) and each loading force was maintained unchange for 2 min over the scar tissue. The real time scar thickness was documented. Results showed that the mean scar thickness was found to be significantly decreased when the loading force applied was increased from 5 to 35 mmHg (with 10 mmHg interval) (p<0.001). A significant negative correlation between the pressure level and scar thickness was observed (r(2)=0.96, p=0.005). The decline of thickness was found more significant between 0 mmHg and 15 mmHg. The findings were in line with the postulate that pressure therapy is effective in reducing the thickness of HS. A long term followup study should be administered to determine the prolonged effect of pressure intervention.