Minute Anatomy of Articular Cartilage

Description

Microscopic articular (hyaline) cartilage is organized into a superficial (tangential) zone at the joint surface, a middle (transitional) zone, a deep (radial) zone, and a calcified cartilage zone anchored to the subchondral bony plate. Chondrocytes lie flattened and aligned parallel to the surface superficially, then become rounder in the middle zone, and arrange in vertical columns toward the tidemark. Collagen type II fibrils run chiefly parallel to the articular surface in the superficial zone, shift to a more oblique meshwork centrally, and orient perpendicular in the deep zone as they approach mineralized cartilage and the underlying bone. That zonal architecture matters because the superficial zone and its proteoglycan-poor, collagen-dense matrix governs shear resistance and lubrication, while the proteoglycan-rich deep zone bears compressive load by retaining water under hydrostatic pressure. Early osteoarthritis is often a superficial-zone problem first, with fibrillation, chondral softening (chondromalacia), and loss of the smooth lamina splendens before deeper delamination and full-thickness chondral defects occur. For surgeons planning microfracture, osteochondral autograft transfer, or autologous chondrocyte implantation, the tidemark and calcified cartilage layer set the boundary between repairable cartilage and the subchondral bone response. Use this illustration in histology and MSK anatomy teaching to connect cartilage microstructure with biomechanics and degenerative joint disease. It also fits orthopedic and rheumatology texts discussing chondral injury grading, osteoarthritis pathogenesis, and the interface between hyaline gristle and subchondral plate. Anatomical accuracy verified by SciePro's Medical Advisory Board.