Solute transport in the deep and calcified zones of articular cartilage

Abstract

Objectives:(1) To establish whether the tidemark and calcified cartilage are permeable to low molecular weight solutes, thereby providing a potential pathway for nutrition of cells in the deep cartilage. (2) To investigate transport from the subchondral microcirculation into calcified cartilage in an intact perfused joint and the effects on transport of static loading.Methods: The permeability of the tidemark and calcified cartilage was investigated in plugs of cartilage and subchondral bone which formed the membrane of a diffusion cell. Transport from the subchondral microcirculation and the effects of load were studied in an intact perfused joint. Both preparations used the metacarpophalangeal joints of mature horses and fluorescein and rhodamine (m.w. w 400 Da) were employed as tracers, assayed by quantitative fluorescence microscopy on histological sections.Results: Calcified cartilage was permeable to both solutes, both from the superficial and the subchondral sides. The effective diffusivity of both solutes was of the order of 9 Â 10 À9 cm 2 s À1 , fivefold less than in the uncalcified cartilage. The calcified zone was heterogeneous, with high uptake of both tracers in the vicinity of the tidemark. The distribution volume of rhodamine B was higher than for fluorescein, consistent with a significant anionic charge in the calcified matrix. Static loading of the intact joint did not affect the transport of rhodamine B but caused a significant decrease in concentration of fluorescein both in the surface and deep zones of the tissue.Conclusions: Calcified cartilage is permeable to small solutes and the subchondral circulation may make a significant contribution to the nutrition of deep cartilage in the mature horse. Static loading reduces the uptake of small anionic solutes in the intact joint.

The role of the cartilage matrix in osteoarthritis

“…85 Whether any altered mechanical quality of the bone will affect how the car tilage reacts to stimuli is not known. An interesting observation, which suggests that the mechanical properties of the structures below the articular cartilage may not be critical, can be derived from follow-up of patients treated for giant cell tumors.…”

Lipid Transport and Metabolism in Healthy and Osteoarthritic Cartilage

“…No nutrient diffusion from SB has been found in mature rabbits [13–15]; however, transport of molecules from SB has been shown in horses and mice [16,17]. In fact, mice present non-mineralized regions in calcified cartilage, forming pores to allow solute transport between cartilage and SB in mature joints [16].…”

Fabrication and in vitro evaluation of an articular cartilage extracellular matrix-hydroxyapatite bilayered scaffold with low permeability for interface tissue engineering

“…Calcified cartilage becomes established at the edges of a “permanent” epiphyseal bone layer (i.e., proximal reserve zone and articular cartilage hypertrophic zone), and the tidemark serves as a barrier to vascular invasion and the calcification of hyaline cartilage [9]. This structure is semi-permeable and permits the passage of small molecules (<500 Da) from the subchondral bone to the articular cartilage layer [10]. Moreover, this special barrier is essential for maintaining the integrity of repaired cartilage over time and preventing osseous upgrowth into full-thickness defects [11].…”