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| The Surgical Technologist | OCTOBER 2017 448 A N A T O M Y A N D P H Y S I O L O G Y O F A R T I C U L A R C A R - T I L A G E I N T H E K N E E Articular cartilage consists of hyaline (derived from the Greek word “hyalos,” meaning glass 3 ) cartilage, one of the three types of cartilage that exist as connective tissues in the human body. 15 Articular hyaline cartilage covers the distal portions of the femur that communicate with the rest of the knee joint: the lateral and medial condyles, and the trochlea. It also covers the tibial plateau, and is found on the articulating side of the patella bone. 12 Articular cartilage has a smooth, lubricated surface with a low friction coefficient, which aids in joint articulation. It is also responsible for distributing weight load on the joint and exhibits superior durability and viscoelastic properties. 2 Articular cartilage thickness ranges approximately from 1-5 mm. 14 Unlike most other body tissues, articular cartilage does not pos- sess any blood vessels, lymphatics or nerves. Rather, in the adult individual it is populated by relatively few chondro- cytes (specialized cartilage cells) and a dense extra cellu- lar matrix (ECM). As much as 80% of the ECM wet weight consists of water, with collagen fibrils, proteoglycans and other molecules accounting for the remaining dry weight. Collagen is the structural protein found in greatest abun- dance in the ECM. Of the various collagen types, Type II collagen is significant in articular cartilage structure, as it accounts for 90% to 95% of the collagen in ECM. Type II collagen fibrils intertwine with proteoglycan aggregates to provide a strong matrix in the ECM. Nourishment of the cartilage tissue is provided by the joint synovial fluid through diffusion. 2 A R T I C U L A R C A R T I L A G E Z O N E S Articular cartilage is arranged into four zones, with each zone contributing in a specific way with the task of bearing body weight and balancing stress on the joint. • Superficial (tangential) zone: contributes 10%-20% of the thickness of the articular cartilage. It is responsi- ble for protecting deeper layers from the sheer stresses of articulation. Collagen fibrils are tightly packed together and are aligned parallel to the surface of articular cartilage. Chondrocytes in this layer are flat in shape. • Middle (transitional) zone: contributes 40% to 60% of the articular cartilage volume. Thicker collagen fibrils appear in this layer, and the proteoglycan content increases. Chondrocytes in this layer take on a spheri- cal shape, and the collagen fibrils are arranged in an oblique manner. This layer provides a bridge between the superficial and deep layers. • Deep zone: contributes 30% to 40% percent of articu- lar cartilage. This zone provides the most resistance to compressive forces resulting in the collagen fibrils as In this image, the femoral condyle lesion has been exposed. The femoral condyle lesion has been debrided in preparation for the graft.