In vitro evaluation of low-intensity pulsed ultrasound in herniated disc resorption

Herniated disc (HD) is often resolved spontaneously without surgical intervention. HD resorption (HDR) is associated with abundant vascularization and infiltration of macrophages (Mphi) into the intervertebral disc (ID), as well as with high levels of matrix metalloproteinases (MMPs). Low-intensity pulsed ultrasound (LIPUS) accelerates bone fracture healing in clinical studies, and angiogenic factors are involved in the mechanism of action. In the present study, we examined the effects of LIPUS on HDR in a rat in vitro HD model. HDR was enhanced by LIPUS as measured by the change in the wet weight of the cultured ID. The secretion of tumor necrosis factor-alpha (TNF-alpha) and macrophage chemoattractant protein-1 (MCP-1) from Mphi into the culture medium was stimulated by LIPUS. LIPUS also enhanced matrix metalloproteinase-3 (MMP-3) maturation. Moreover, many apoptotic cell death were observed in the HDR groups with LIPUS exposure. These results suggest that LIPUS enhanced the HDR via MMP-3 activation through TNF-alpha and MCP-1 pathways. Although animal studies and clinical trial are needed to understand the LIPUS effects on HDR, LIPUS treatment might be an effective treatment for accelerating HDR.