The chondron concept was first introduced in 1925 by Benninghoff who used polarized light microscopy to show that the chondrocyte in hyaline cartilages was surrounded by a specialized region of matrix. However, this concept was not widely accepted at the time, and it was until 1969 that Szirmai rekindled interest in the chondron concept. Using new histochemical interpretations coupled with microchemical analysis, Szirmai showed the "micro-world" of the chondron consisted of a fine collagenous "perilacunar rim" surrounding a proteoglycan rich "lacunar space". He also showed that chondrons could be extracted from horse nasal septum by high speed homogenization and concluded that the chondron was mechanically robust and represented the primary functional and metabolic unit of hyaline cartilages. Again the chondron concept was not widely embraced despite the rapid accumulation of data indicating common specializations in the vicinity of hyaline cartilage chondrocytes. In 1985, our own research on the structure and function of adult articular cartilage matrices led to the discovery of chondrons in the homogenate produced by slow speed homogenization of canine tibial cartilage. The isolation of intact chondrons conclusively established the chondron as a microanatomical unit of adult articular cartilage. Each chondron consisted of a chondrocyte intimately associated with a proteoglycan rich pericellular matrix which was surrounded by a densely compacted pericellular capsule composed of fine collagen species. We have now developed the isolated chondron as a model to study the natural interrelationship between the chondrocyte and its pericellular microenvironment. Using morphological, histochemical, ultrastructural, immunohistochemical, biochemical and metabolic techniques, we have successfully shown the isolated chondron is rich in chondroitin sulfate, keratan sulfate and hyaluronan glycosaminoglycans, collagen types II, VI, IX, and XI, and glycoproteins such as fibronectin and possibly laminin. Further studies of chondrons extracted from osteoarthritic cartilage suggest the chondron is remodeled during the degenerative process causing the pericellular microenvironment to expand and the chondrocyte to proliferate into the large clusters typical of osteoarthritic pathology. The data presented in this short review indicates that the chondron is a highly specialized microanatomical unit of adult articular cartilage and plays a fundamental role in the initiation and progression of degenerative arthritis. Future studies on the isolated chondron model will ensure a highly greater understanding of the role of the cellular microenvironment in articular cartilage biology and pathology.
Biomedical Reviews 1992; 1: 53-62.
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