Augmentation of tendon-bone interface healing with low-intensity pulsed ultrasound

The capacity of low-intensity pulsed ultrasound to accelerate the integration of grafted tendon-within-bone tunnel was evaluated. The extensor digitorum longus tendons of 20 New Zealand white rabbits were transplanted into bone tunnels in both proximal tibias. One side was chosen randomly to receive low-intensity pulsed ultrasound. The other side served as control. Six rabbits each were sacrificed at 2 and 3 weeks postoperatively for biomechanical testing, and 2 rabbits each were sacrificed at 1, 3, 6, and 12 weeks postoperatively for histological study. At 2 weeks postoperatively, the mean maximal tensile strength in the ultrasound-treated group (30.676 N) was significantly stronger (P<.05) than the control group (17.924 N). There was no significant difference of the maximal tensile strength (33.674 vs 33.340 N; P=.753) between the ultrasound-treated and control groups at 3 weeks postoperatively. In the ultrasound-treated group, the histological study revealed the interface filled with denser granulation tissue and diffuse perpendicular anchored fibers in the 1- and 3-week specimens, and interface new bone formation in the 6- and 12-week specimens. The biomechanical and histological studies demonstrated that the low-intensity pulsed ultrasound enhanced the healing of grafted tendon-to-bone tunnel in the early stages. Our findings indicate that low-intensity pulsed ultrasound is a potentially promising mechanical tool to accelerate early tendon healing to bone tunnel.