| Background and objectives: It is well known that self-repair ability of articular cartilage is very limited. 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. Some studies have shown that low-intensity pulsed ultrasound (LIPU) can accelerate bone healing and full-thickness articular cartilage defect repair via upregulation of cartilage formation and maturation phases of endochondral bone formation and enhance proliferation,differentiation into chondrocyte of mensenchymal stem cell(MSC). The effects of LIPU on acute and chronic articular cartilage damages limited in the articular cartilage without source of MSC and synovial fluid penetrate into articular cartilage now are studied. Method: (1) 4 partial-thickness defects with 2.0 mm in length and 1.0mm in width and 0.1 mm in depth in the intercondylar fossa of each femur in 9 healthy adult New Zealand White rabbits which were randomly assigned into 3 groups. Exterior LIPU treatment was performed to the treat side femur intercondylar fossa with an intensity of 30 mW/cm 2 at a frequency of 0.6 MHz for 20 minutes daily, 5 days per week. Pseudo-treatment was performed to the other as control. Groups of 3 animals each were sacrificed at 2, 4 and 8 weeks postoperatively for histology-histochemistry assessment and the numbers of chondrocyte clusters around degenerative cartilage under the defect are counted. All the data were analyzed by matched paired student test.(2)Experimental osteoarthritis was made in 30 adult male New Zealand White rabbits bilateral hindlims by Hulth method. LIPU treatment with an intensity of 30 mW/cm 2 at a frequency of 1.5 MHz for 20 minutes daily, 5 days per week was performed to the treat side femur internal condyle 2 weeks after operation. Pseudo-treat was performed to the other as control. Groups of 10 animals each were sacrificed after 2, 4 and 8 weeks treatment for gross grades and histology-histochemistry grades to assess the effect of LIPU. All the data were analyzed by matched paired student test.(3)Intracavitary injection was made into 10 adult New Zealand White rabbits bilateral hindlimb articular cavity with 0.1% methylene blue 5ml each. One hindlimb was chosen randomly as LIPU treatment side accept 5 minutes LIPU treatment with an intensity of 30mW/cm2 at a frequency of 0.6MHz immediately after injection and the other side accept pseudo- treatment as control. All animals were sacrificed immediately after treatment. Articular cartilage specimens were obtained in 0.5 thickness and taken photos by anatomic microscope. The depths of penetration of dye into articular cartilage were measured on photos. All the data were analyzed by matched paired student test.Results:(1)There are no cells or neo-tissue filled in the partial-thickness cartilage defect in 2,4,8 weeks after operation. Deeper cartilage under the defect degenerate. Chondrocyte clusters form around the degenerative cartilage. The number of chondrocyte cluster of LIPU group is more than that of control group in 2 weeks after operation(P<0.05), and is fewer in 4weeks(P<0.05), then is similar in 8weeks(P>0.05).(2)Gross scores and histology-histochemistry scores of LIPU group and control group show that the articular cartilage damage of each group progresses followed with time. At the same observation duration, the damage degree of LIPU groups is less than those of control groups with statistics difference significance(P<0.05)。(3)LIPU treatment enhanced methylene blue penetrate into articular cartilage. In LIPU group, the width of methylene blue penetrate into articular cartilage deep than that of control group with statistics difference significance(P<0.05). Conclusions: (1) LIPU has no positive effect on partial-thickness cartilage defect repair. LIPU increase chondrocyte cluster formation around degenerative cartilage under the defect. (2) LIPU delay physio-progress of experimental osteoarthritis. (3) LIPU en...
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