EFFECT OF TRANSOSSEOUS APPLICATION OF LOW-INTENSITY ULTRASOUND AT THE TENDON GRAFT-BONE INTERFACE HEALING: GENE EXPRESSION AND HISTOLOGICAL ANALYSIS IN RABBITS

Abstract

The present study investigates the effect of transosseous low-intensity pulsed ultrasound (LiUS) on the healing at tendon graft-bone interface, in molecular and histological level. The anterior cruciate ligament (ACL) in both knees of 52 New Zealand White rabbits was excised and replaced with the long digital extensor. A custom-made ultrasound transducer was implanted onto the medial tibial condyle, adjacent to the surface of the bone tunnel at both knees of the rabbits. The LiUS-treated right knees received 200-mu s bursts of 1 MHz sine waves at a pulse repetition rate of 1 kHz and with 30 MW/cm(2) spatial-average temporal-average intensity for 20 min daily (study group), while the left knee received no LiUS (control group). Thirty-six rabbits were used to perform semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) analysis from both study and control groups for transforming growth factor-beta 1 (TGF-beta 1), biglycan and collagen I. RT-PCR products showed statistically significant upregulation of biglycan and collagen I gene expression in the study group, while TGF-beta 1 gene expression exhibited a bimodal profile. Histological examination performed in 16 rabbits from both groups supported the findings of the molecular analysis, indicating a faster healing rate and a more efficient ligamentization process after ultrasound treatment. These findings suggest that transosseous application of LiUS enhances the healing rate of the tendon graft-bone interface, possibly by affecting the expression levels of genes significant for the tendon to bone healing process. (E-mail: malizos@med.uth.gr) (c) 2009 World Federation for Ultrasound in Medicine & Biology.