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First published on July 21, 2008, doi:10.1177/0363546508318193
This version was published on September 1, 2008
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The American Journal of Sports Medicine 36:1742-1749 (2008)

Low-Intensity Pulsed Ultrasound on Tendon Healing

A Study of the Effect of Treatment Duration and Treatment Initiation

Sai-Chuen Fu, MPhil, Wai-Ting Shum, MSc, Leung-Kim Hung, MD*, Margaret Wan-Nar Wong, MBBS, Ling Qin, PhD and Kai-Ming Chan, MD

From the Department of Orthopaedics & Traumatology, The Chinese University of Hong Kong, Prince of Wales Hospital, Hong Kong, and The Hong Kong Jockey Club Sports Medicine and Health Sciences Centre, Hong Kong SAR, China

* Address correspondence to Leung-Kim Hung, Department of Orthopaedics & Traumatology, The Chinese University of Hong Kong, Prince of Wales Hospital, Shatin, New Territories, Hong Kong (e-mail: leungkimhung{at}cuhk.edu.hk).

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.

Key Words: pulsed ultrasound • tendon healing • mechanical test • patellar tendon






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