Electron microscopy of articular cartilage in the young adult rabbit.

Few previous studies have been made of the appearance of articular cartilage under the electron microscope. Cameron and Robinson (1958) examined the matrix of both articular and epiphysial cartilages in femora of infants who had died in the neonatal period. No observations were made upon the cells as they were unable to assess the extent of post mortem change. They described the presence in the articular cartilage of bundles of fibres having the characteristic cross-striations seen in mature collagen; these bundles were arranged parallel with the surface in the superficial 25,u, but irregularly in the deeper parts of the cartilage. Zelander (1959) examined the appearances of femoral and patellar articular cartilage in adult guinea-pigs, mice, and rats, describing both cells and matrix. He noted the characteristics of one type of chondrocyte, but did not describe any variations in its appearance at different levels, except in the calcified zone, where he described the dying chondrocyte. Each healthy cell was always surrounded by a region almost devoid of fibres, which he termed the capsule. Around this was a zone 2 to 4,u thick in which were fibres of steadily increasing diameter, the innermost fibres being unstriated, but the outer ones showing the characteristic banding of mature collagen. Zelander equated this zone with the "territory" of Bargmann (1956). In the interterritorial regions he found fibres of constant diameter which were uniformly striated with a periodicity of 580 A. In the deeper parts of the matrix he described the appearances of early calcified foci. Martin (1954) studied the appearances of the collagen fibres in cartilage obtained from the developing tibia of the fowl, including the articular surfaces. Zbinden (1953) gave an account of some age changes in articular cartilage from guinea-pigs and rats. Little and Pimm (1957) and Little, Pimm, and Trueta (1958) described the changes which occur in the collagen fibres of human articular cartilages in the presence of osteo-arthritis. The remaining studies of the electron microscopic appearance of cartilage have been limited to the epiphysial region. Robinson and Cameron (1956) studied the distal epiphysial cartilage in the femora of newborn infants, and described the appearances in the process of ossification. Using material from the proximal humeral epiphysis of young kittens, Scott and Pease (1956) described the appearances seen during ossification, and in particular the degenerative changes seen in the chondrocytes.