Low-intensity pulsed ultrasound accelerates bone-tendon junction healing: A partial patellectomy model in rabbits

Background: Low-intensity pulsed ultrasound has been demonstrated to be beneficial for accelerating fracture healing, delayed union, nonunion, and soft tissue repair. Hypothesis: Low-intensity pulsed ultrasound accelerates healing of bone-to-tendon junction repair by promoting osteogenesis and tissue remodeling at the healing junction. Study Design: Controlled laboratory study. Methods: Standard partial patellectomy was conducted in forty-eight 18-week-old rabbits divided into an ultrasound treatment and control group. Daily ultrasound was delivered 3 days after surgery onto the patellar tendon-patella healing junction and continuously up to weeks 2, 4, 8, and 16 postoperatively, when the patella-patellar tendon complexes were harvested for radiographic, histologic, and biomechanical evaluations. Results: Radiographic measurements showed significantly more newly formed bone at the patellar tendon-patella healing junction in the ultrasound group compared with the controls at week 8 (4.91 ± 2.74 mm2vs 2.50 ± 1.83 mm2, P < .05) and week 16 (7.22 ± 2.34 mm2vs 4.61 ± 2.22 mm2, P < .05) after partial patellectomy. Histologically, the ultrasound group at weeks 8 and 16 showed improved tissue integration, characterized by trabecular bone expansion from the remaining patella and regeneration of fibrocartilage layer at the patellar tendon-patella healing junction. Fluorescence microscopy revealed earlier bone formation in the ultrasound group when compared with the controls at week 8 (1.78 ± 0.32 vs 1.23 ± 0.43, P < .01) and week 16 (2.10 ± 0.67 vs 1.29 ± 0.35, P < .01). Mechanical testing showed significantly higher failure load and ultimate strength in the ultrasound group (300.2 ± 61.7 N and 7.10 ± 1.29 MPa, respectively) as compared with controls (222.3 ± 65.1 N and 5.26 ± 1.36 MPa, respectively) at week 16 (P < .05 for both). Conclusion: Low-intensity pulsed ultrasound was able to accelerate bone-to-tendon junction repair. Clinical Relevance: These results may help establish treatment efficacy for accelerating bone-to-tendon junction repair and facilitating earlier rehabilitation.