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Cartilage regeneration methods have been examined in various animal models. The major limitation of those studies is the biological difference between human and animal cartilage. We propose an in vivo model for human chondrocytes in a human cartilage defect environment. Human full-thickness (2-4 mm) articular cartilage discs (diameter 10 mm) attached to 3-6 mm subchondral bone, were obtained from human femur heads. Chondral defects (diameter 4 mm) were set within the cartilage disc without violating the subchondral bone. Human chondrocytes were isolated, cultivated for three passages and then suspended at a concentration of 10(7) cells/ml. The defect was completely filled with the cell suspension (approximately 30 microl) and then covered with a thin sheet of human periosteum, fixed with fibrin sealant. Discs were implanted subcutaneously in the backs of nude mice for 5 and 8 weeks. Controls were uncovered discs filled with cell suspension and covered discs without cells. Histological evaluation revealed a gradient of differentiation from the cartilage lateral side to the centre of the defect. A proteoglycan-rich matrix was formed with some chondron-like structures at the border of native cartilage, whereas fibrous tissue was built in the centre of the defect. After 8 weeks the areas of differentiating cells enlarged compared to 5 weeks, indicating the progress of cartilage repair. The control discs without cells or cover showed no chondrogenesis. Interestingly, uncovered discs filled with cells showed comparable areas of differentiating cells at the defect surface but lack of fibrous tissue in the middle. The histological results were supported by MRI measurement.

Objective: Purpose of the paper is to present and validate a device for cartilage compression for assessment of MR parameters (T1, T2, ADC) in cartilage explants before, during and after compression operating with novel features. Design: This device fits into a BGA-12 micro-imaging gradient system capable of delivering 200mT/m. A 35 mm inner diameter resonator was used. The reproducibility and accuracy of cartilage compression possible with the device were evaluated. Sixteen human cartilage explants from knee joints were examined by delayed Gadolinium enhancement MRI of cartilage (dGEMRIC) for T1 mapping, T2 mapping and ADC measurements.Results: Cartilage compression studies demonstrated both low inter-observer (CV 4.7 %) and intra-observer (CV 11.9 %) variation. No undesired movements were observed. The compressive piston could be moved with high accuracy (error ~ 1.07 %). The waterproof chamber of the compression device allowed contrast enhanced T1 mapping without repositioning the cartilage samples. Preliminary results of MR parameters depending on compression are presented. Conclusions: In vitro MR cartilage compression studies are feasible with the custom-build device with high reproducibility and accuracy. Valuable information about biomechanical cartilage properties can be recorded using this device.

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