Cartilage and subchondral bone interaction in normal and osteoarthritic human knee joint: a histological and histomorphometrical study

The aim of this study was to determine the correlation between the morphological changes in articular cartilage and underlying subchondral bone in human knee joint. Tibial condyles were examined: 7 from autopsy specimen (average age 70, height 174 cm, weight 84 kg ; equal gender distribution ; articular cartilage macroscopicaly normal in appearance) and 8 from patients undergoing total endoprothesis surgery due to severe osteoarthritis (OA) (average age 66, height 170 cm, weight 75 kg, female).Articular cartilage and correspondent underlying subchondral bone specimens wete taken at 8 constant points from both medial and lateral condyle using bone trephine. Specimens were washed in saline solution, decalcified in EDTA, embedded in paraffin and cut in serial slices (5 micro m) using Leica RM 2155 microtome. Tissue slices were stained with Safranin O and Toluidine blue. Human articular cartilage was histologically graded by the method of Mankin et al. for degenerative changes as well as the thickness of cartilage. Subchondral bone was studied histomorphometrically by image analysis (Sform, VAMS, Zagreb). The following static parameters were measured: BV/TV, BS/TV, Tb.Th., Tb.Sp., Tb.N.. The results of histomorphometrical study were divided into 3 groups according to the Mankin score: Mankin 0-6 (minimal changes), 7-9 (moderate changes) and 10-14 (severe changes). Such correlated results show that the Mankin score corresponds with the higher values of BV/TV and BS/TV. At the same time Tb.Th. was increased while Tb.Sp. was decreased. The cartilage thickness did not correspond to degenerative changes graded by the method of Mankin or to the subchondral bone architecture. Analysis of subchondral bone of the normal tibial condyles revealed lower values of BV/TV, BS/TV, Tb.Th and higher values of Tb.Sp., and Tb.N when compared to the OA tibial condyles. Comparing resultsof morphometry of both normal condyles we determined that lateral condyle had greater bone volume of subchondral bone especially on the central part of the articular surface. In OA tibial condyles, the results were inversed ; medial condyle was changed more strongly.