This study quantified changes in the DNA content and extracellular matrix composition of\nboth the cartilaginous repair tissue and the adjacent cartilage in a large animal model of a chondral\ndefect treated by subchondral drilling. Content of DNA, proteoglycans, and Type II and Type\nI collagen, as well as their dierent ratios were assessed at 6 months in vivo after treatment of\nfull-thickness cartilage defects in the femoral trochlea of adult sheep with six subchondral drill holes,\neach of either 1.0 mm or 1.8 mm in diameter by biochemical analyses of the repair tissue and the\nadjacent cartilage and compared with the original cartilage. Only subchondral drilling which were\n1.0 mm in diameter significantly increased both DNA and proteoglycan content of the repair tissue\ncompared to the original cartilage. DNA content correlated with the proteoglycan and Type II collagen\ncontent within the repair tissue. Significantly higher amounts of Type I collagen within the repair\ntissue and significantly increased DNA, proteoglycan, and Type I collagen content in the adjacent\ncartilage were identified. These translational data support the use of small-diameter bone-cutting\ndevices for marrow stimulation. Signs of early degeneration were present within the cartilaginous\nrepair tissue and the adjacent cartilage.
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