title: Low-intensity pulsed ultrasound on tendon healing: a study of the effect of treatment duration and treatment initiation.
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.
  
  
  OBJECTIVE
  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.
  
  
  METHODS
  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.
  
  
  CONCLUSIONS
  Low-intensity pulsed ultrasound promoted restoration of mechanical strength and collagen alignment in healing tendons only when applied at early healing stages.
  
  
  CONCLUSIONS
  The present findings indicate that low-intensity pulsed ultrasound may be an effective treatment to reduce tendon donor site morbidity.
authors.affiliation: Department of Orthopaedics & Traumatology, The Chinese University of Hong Kong, Prince of Wales Hospital, Shatin, New Territories, Hong Kong, China.
authors.forename: Sai-Chuen
authors.initials: SC
authors.lastname: Fu
authors.forename: Wai-Ting
authors.initials: WT
authors.lastname: Shum
authors.forename: Leung-Kim
authors.initials: LK
authors.lastname: Hung
authors.forename: Margaret Wan-Nar
authors.initials: MW
authors.lastname: Wong
authors.forename: Ling
authors.initials: L
authors.lastname: Qin
authors.forename: Kai-Ming
authors.initials: KM
authors.lastname: Chan
mesh_terms: D000818:Animals; D008297:Male; D017847:Patellar Ligament / Q000293:injuries / Q000473:pathology; D051381:Rats; D017207:Rats, Sprague-Dawley; D013708:Tendon Injuries / Q000473:pathology / Q000628:therapy*; D013718:Tensile Strength; D013997:Time Factors; D014464:Ultrasonic Therapy / Q000379:methods*; D014945:Wound Healing