Multi-evaluation of the healing at bone-tendon junction with the treatment of mechanical stimulation

Many trauma and reconstructive surgeries involve the re-establishment of bone-tendon junction (BTJ) tissues. A direct BTJ repair requires a long period of immobilization which may be associated with a postoperative weak knee. To enhance the tissue healing, researchers use postoperative mechanical stimulation, such as low intensity pulsed ultrasound (LIPUS), to accelerate the BTJ repair and the restoration of fibrocartilage zone. LIPUS has been proven to accelerate fracture healing and as demonstrated in this study, has beneficial effects on acceleration of BTJ repair. In our experiment, standard partial patellectomy was conducted on one knee of twenty four rabbits which were randomly divided into an ultrasound group and control group. The bony changes of BTJ complexes around the BTJ healing interface were measured by anteroposterior x-ray radiographs; then the volumetric bone-mineral density (BMD) of the new bone was assessed using a peripheral computed tomography scanner. After radiographic measurement, we utilized a novel ultrasound water jet indentation system to noninvasively measure the stiffness values of the patellar cartilage, fibrocartilage and the tendon, which have been usually difficult to evaluate in situ. Not only significantly more newly formed bone at the BTJ healing interface but also increased stiffness of the junction tissues were found in the ultrasound group compared with the controls at week 18. In addition, the ultrasound group also showed significantly 44% higher BMD at week 6 than controls.