Low-Intensity Pulsed Ultrasound on Tendon Healing

Background Low-intensity pulsed ultrasound has been reported to be effective in promoting tendon healing. However, its optimal time and duration has not yet been determined. Hypothesis Tendons at different stages of healing may respond differently to low-intensity pulsed ultrasound. In the present study, the timing effects of low-intensity pulsed ultrasound on tendon healing were investigated in a rat model with a patellar tendon graft harvest lesion. Study Design Controlled laboratory study. Methods Sixty Sprague-Dawley rats underwent central third patellar tendon donor site harvest. Low-intensity pulsed ultrasound sonication was then delivered to the injured knees at day 1, 14, or 28 after harvest for 2, 4, or 6 weeks. Tendon samples were harvested at day 14, 28, and 42 after lesion for histological examination and mechanical testing. Results A 2-week session of low-intensity pulsed ultrasound applied from day 1 postlesion (D1-2W) significantly improved the ultimate mechanical strength of the healing tendons from 23.1 ± 8.5 MPa to 36.6 ± 9.0 MPa. Low-intensity pulsed ultrasound did not improve healing when it was given at later stages in D15-2W and D29-2W. When low-intensity pulsed ultrasound treatment was extended from 2 weeks (D1-2W) to 4 weeks (D1-4W) or 6 weeks (D1-6W), the beneficial effects on tendon healing became insignificant. Histological examination showed that low-intensity pulsed ultrasound sonication at late healing stages may disturb remodeling with a poor collagen fiber alignment. Conclusion Low-intensity pulsed ultrasound promoted restoration of mechanical strength and collagen alignment in healing tendons only when applied at early healing stages. Clinical Relevance The present findings indicate that low-intensity pulsed ultrasound may be an effective treatment to reduce tendon donor site morbidity.