Therapeutic applications for pulsed laser and ultrasound

Abstract

Arthrofibrosis is a condition that causes a painful reduction in joint range of motion, which is caused by a buildup of scar tissue in and around joint. The overall goal of this research project was to develop new non-invasive treatments for the buildup of scar tissue that can occur in joints after major injury or surgeries. Pulsed high intensity laser (PHIL) and pulsed high intensity focused ultrasound (PHIFU) are two methods that have been identified as having the potential to provide a non-invasive method of breaking down scar tissue. These methods can also be combined into a treatment called photo-mediated ultrasound therapy (PUT). These new treatment methods create a stress wave inside the scar tissue without breaking the skin. The strong stress waves physically pull the dense fibers in the scar tissue apart, releasing the stiffness in the joint. These noninvasive treatments can be repeated to slowly break down the scar tissue over the course of several weeks, allowing the body to heal without new scarring. To test the effectiveness of PHIL, PHIFU, and PUT an appropriate animal model must be developed. This animal model used rabbits and involved a single surgery to create scar tissue in posterior capsule of one of the hind limbs. The range of motion (ROM) of the operated leg was compared to the ROM of the non-operated leg to demonstrate significant loss in joint function. Once the animal model had been established PHIL, PHIFU, and PUT were performed twice weekly on the operated leg. ROM was measured as the primary metric for success. All three treatments were successful and resulted in the same ROM in both the operated and non-operated knees. In vitro experiments were performed on tissue phantoms to explore the underlying mechanisms behind these treatments. Numerical simulations of PUT were performed to explore potential optimizations in treatment parameters. The results of this research is compiled in this dissertation along with ideas on the future direction of the research.