[Study on shape and structure of calcified cartilage zone in normal human knee joint]

To explore the shape and structure of calcified cartilage zone and its interface between the non-calcified articular cartilage and subchondral bone plate.

The normal human condyles of femur (n=20) were obtained from the tissue bank donated by the residents, 10 males and 10 females, aged 17-45 years. The longitudinal and transverse paraffin sections were prepared by the routine method. The shape and structure of calcified cartilage zone were observed with the Safranin O/fast green and von kossa stain method. The interface conjunction among zones of cartilage was researched by SEM and the 3D structural model was established by serial sections and modeling technique.

Articular bone-cartilage safranin O/fast green staining showed that cartilage was stained red and subchondral bone was stained blue. The calcified cartilage zone was located between the tidemark and cement line. Von kossa staining showed that calcified cartilage zone was stained black and sharpness of structure border. Upper interface gomphosised tightly with the non-calcified cartilage by the wave shaped tidemark and lower interface anchored tightly with the subchondral bone by the uneven comb shaped cement line. The non-calcified cartilage zone was interlocked tightly in the manner of "ravine-engomphosis" by the calcified cartilage zone as observed under SEM, and the subchondral bone was anchored tightly in the manner of"comb-anchor" by the in the calcified cartilage zone 3D reconstruction model.

The calcified cartilage zone is an important structure in the articular cartilage. The articular cartilage is fixed firmly into subchondral bone plate by the distinctive conjunct interfaces of calcified cartilage zone.