Histomorphometric analysis of adult articular calcified cartilage zone

The aim of this study was to carry out a histomorphometric analysis of calcified cartilage zone (CCZ) and its interfaces between hyaline cartilage and subchondral bone. The study used 40 donated normal human femoral condyles, from which paraffin-embedded sections were prepared after fixation and decalcification. The histomorphology of the CCZ were qualitatively and quantitatively observed by staining, scanning electron microscopy (SEM) and three-dimensional (3D) reconstruction. The hyaline cartilage and CCZ were stained red with Safranin-O, and the subchondral bone was stained blue with Fast green. CCZ was stained black after von Kossa staining. The hyaline cartilage was interlocked tightly in the manner of “ravine-engomphosis” by the CCZ. The surface roughnesses of tidemark and cement line were 1.14 ± 0.04 and 1.99 ± 0.38. The maximum, minimum and mean thicknesses of CCZ were 277.12 ± 8.6, 9.83 ± 6.72 and 104.162 ± 0.87 μm, respectively. The cell density of CCZ (51.25 ± 21.26 cells/mm2) was significantly lower than that of the hyaline cartilage (152.54 ± 35.77 cells/mm2) (P < 0.05). The subchondral bone was anchored tightly in the manner of a “comb-anchor” by the CCZ in our 3D reconstruction model. Thus, we discovered two junctional interfaces of CCZ using different histomorphometric methods. The upper interface of CCZ is a “ravine-engomphosis” shape, while its lower interface is a “comb-anchor” shape.