COMPARATIVE HISTOMORPHOMETRICAL STUDIES OF THE SUBCHONDRAL BONE-DENSITY AND ARTICULAR-CARTILAGE THICKNESS OF THE TIBIAL HEAD IN EARLY HUMAN OSTEOARTHROSIS

The articular cartilage thickness and subchondral bone density of 50 human tibial heads were histomorphometrically measured by an image analysing system and topographically examined in relation to age, sex and grade of osteoarthrosis (OA). Altogether we evaluated 12000 items. Independent of OA the lateral tibial plateau shows a significant thicker cartilage layer than the medial. In central joint areas we find a thicker cartilage cover than in marginal. Corresponding to the literature cartilage fibrillation according to OA grade 1 and 2 (Otte 1969, Fassbender 1975) accumulates in the lateral and dorsal tibial head including the meniscus covered area. The cartilage thickness decreases with age independent of OA. Without major alterations of the topographical pattern the cartilage thickness however shows a significant increase in early OA (grade 1). For that reason measurements of the cartilage thickness and joint space narrowing are not appropriate for defining early OA. The subchondral bone density shows high values ventromedially and dorsolaterally independent of sex, age or OA. Beneath central joint areas higher values are found than marginally. Corresponding to the topical literature our results point at the model of the real loaded knee joint, which says that the mean loading forces do not act on the middle of the joint but on the medial plateau. The dorsolateral density centre could be an expression of the functional adaptation of the bended knee joint. In joint areas with cartilage fibrillation (OA grade 1) we find a significant higher subchondral bone density without major alterations of the topographical pattern. It is not possible to define cause and effect, we interpret both as result of higher joint loading.