Low-Intensity Pulsed Ultrasound Accelerates Bone-Tendon Junction Healing

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 mm 2 vs 2.50 ± 1.83 mm 2 , P < .05) and week 16 (7.22 ± 2.34 mm 2 vs 4.61 ± 2.22 mm 2 , 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.