Low-Intensity Pulsed Ultrasound on Tendon Healing

Abstract

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.