In vivo low-intensity pulsed ultrasound (LIPUS) following tendon injury promotes repair during granulation but suppresses decorin and biglycan expression during remodeling

Abstract

Study design: Bench research, cross-sectional.

Objective: To determine if the effects of low-intensity pulsed ultrasound (LIPUS) on matrix synthesis change at different stages of tendon healing.

Background: LIPUS is effective in promoting tendon healing by stimulation of matrix synthesis. The timing of initiation and duration of LIPUS treatment have been shown to affect its effectiveness to promote tendon healing, suggesting a change of tissue responses to LIPUS stimulation. Understanding how the cellular responses to LIPUS stimulation change during tendon healing is thus important.

Methods: In a rat model of patellar tendon donor site injury, a single sonication of LIPUS or mock sonication was delivered to the injured knee of the rats on the fourth, 14th or 28th day postinjury. Tendon samples were harvested at 4 hours and 24 hours after sonication and the mRNA expression of COL1A1, COL3A1, decorin, biglycan, and TGF-beta 1 was analyzed.

Results: The results showed that a single sonication of LIPUS increased COL1A1 and COL3A1 mRNA in healing patellar tendons when administered on the fourth or 14th day postinjury, but not when administered on the 28th day postinjury. Both decorin and biglycan mRNA were decreased by treatment with LIPUS on the 28th day postinjury. Our results showed that LIPUS enhanced collagen synthesis in vivo only during the granulation phase. Matrix remodeling may be affected by LIPUS with the suppressed expression of decorin and biglycan.

Conclusion: Our findings suggest that LIPUS should be applied during the granulation phase but not during the remodeling phase, to promote tendon healing.