Abstract
This study quantified changes in the DNA content and extracellular matrix composition of both the cartilaginous repair tissue and the adjacent cartilage in a large animal model of a chondral defect treated by subchondral drilling. Content of DNA, proteoglycans, and Type II and Type I collagen, as well as their different ratios were assessed at 6 months in vivo after treatment of full-thickness cartilage defects in the femoral trochlea of adult sheep with six subchondral drill holes, each of either 1.0 mm or 1.8 mm in diameter by biochemical analyses of the repair tissue and the adjacent cartilage and compared with the original cartilage. Only subchondral drilling which were 1.0 mm in diameter significantly increased both DNA and proteoglycan content of the repair tissue compared to the original cartilage. DNA content correlated with the proteoglycan and Type II collagen content within the repair tissue. Significantly higher amounts of Type I collagen within the repair tissue and significantly increased DNA, proteoglycan, and Type I collagen content in the adjacent cartilage were identified. These translational data support the use of small-diameter bone-cutting devices for marrow stimulation. Signs of early degeneration were present within the cartilaginous repair tissue and the adjacent cartilage.
Highlights
Marrow stimulation techniques, such as subchondral drilling [1], are established first-line treatment options for symptomatic small articular cartilage defects of less than 3 cm2 [2,3]
Biochemical evaluation of the articular cartilage repair tissue: Upon evaluation of the cartilaginous repair tissue retrieved at 6 months postoperatively, the DNA, proteoglycan, Type I and Type II collagen contents, as well as the proteoglycan/DNA, Type II collagen/DNA, Type I collagen/DNA, and Type I/Type II collagen ratios did not vary significantly between the two groups (Table 1)
DNA and proteoglycan content was 1.4- and 1.7-fold higher in 1.0 mm diameter defects compared with 1.8 mm diameter defects, without reaching statistical significance (Table 1; p = 0.344 and p = 0.162, respectively)
Summary
Marrow stimulation techniques, such as subchondral drilling [1], are established first-line treatment options for symptomatic small articular cartilage defects of less than 3 cm2 [2,3]. The effect of the subchondral drill hole diameter has only recently been investigated, suggesting a supremacy of small- (≤1.0 mm) versus large-diameter (≥1.5 mm) perforations for the histological aspect of the cartilaginous repair tissue and for micro-computed tomography (micro-CT) parameters of subchondral bone reconstitution [8,9]. Such a possible effect of drill hole size on the extracellular matrix (ECM) composition and molecular properties of the repair tissue remains unknown. The biochemical composition of articular cartilage is thought to be a surrogate for its mechanical properties [15,17]
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