Low-Intensity Pulsed Ultrasound Accelerates Repair Of Articular Cartilage Defect

Background and objectives: Repair of damaged articular cartilage is one of the most difficult problems in orthopaedics and no satisfactory treatment modality has been found in this field. Low-intensity pulsed ultrasound (LIPU) can accelerate bone healing via upregulation of cartilage formation and maturation phases of endochondral bone formation. In this study, we investigated if LIPU could accelerate repair of articular cartilage defect and found out the optimal parameter in frequency of LIPU to accelerate repair.Methods: (1) 33 healthy adult New Zealand White rabbits with 3.0 mm in diameter by 5.0 mm deep osteochondral defect in the intercondylar fossa of each femur were randomly assigned into 3 groups. Exterior LIPU exposure was made to the left femur intercondylar fossa with a intensity of 30 mW/cm 2 at a frequency of 1.5 MHz for 20 minutes daily. False exposure was made to the right as control. Groups of 11 animals each was sacrificed at 2, 4 and 8 weeks postoperatively for gross appearance grades, histological grades and toluidine blue staining to assess the effect of LIPU. All the data were analyzed by matched paired student test. (2) 30 healthy adult New Zealand White rabbits were divided into 2 groups randomly to investigate the effects of different frequencies. The first 30 knees with the same osteochondral defects, which wereto be treated by the ultrasound in the same way, were divided into 3 groups at random: 0.6MHz, 1.0MHz and 1.5MHz. The animals were sacrificed at 4 weeks postoperatively for gross appearance grades, histological grades and toluidine blue staining. The other 30 knees received the same disposal for SDS-PAGE, and then the ratios of collagen â…¡ in the samples were got. All the data were analyzed by one way analysis of variance.Results: (1) Ultrasound-treated defects had significantly improved gross appearance grades and histological grades at 2, 4 and 8 weeks postoperatively and significantly improved optical density of toluidine blue at 4 and 8 weeks postoperatively compared with nontreated controls (both p < 0.05). (2) 0.6MHz-treated defects had significantly improved histological grades and optical density of toluidine blue compared with 1.0MHz and 1.5MHz (p < 0.05), while no significant differences were got in gross appearance grades and the ratios of collagen â…¡ in the samples among different frequency groups.Conclusions: (1) LIPU can accelerate repair of articular cartilage defect with proteoglycan increased in the repaired tissues. LIPU is a noninvasive, safe, convenient and economical treat modality. (2) Different frequencies have different biological effects. LIPU with a frequency of 0.6MHz can increase more proteoglycan of repaired tissues, which is essential to the function of articular cartilage, than that of 1.0MHz and 1.5MHz...