1. Buckwalter JA, Mankin HJ: Articular cartilage: Part I. Tissue design and chondrocyte-matrix interactions. J Bone Joint Surg Am 1997;79:600-611.

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Aggrecans – An aggregating form of proteoglycan composed of many glycosaminoglycan chains bound to a protein core

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Osteoarthritis (OA), also referred to as degenerative joint disease, is characterized by a generally progressive loss of articular cartilage accompanied by attempted repair of articular cartilage, remodeling, and sclerosis of subchondral bone, and in many instances, the formation of subchondral bone cysts and osteophytes19-24 (Fig. 7).

Figure 7 A, Histologic section of osteoarthritic cartilage from a humeral head removed at surgery for total shoulder arthroplasty. Note the significant fibrillation, vertical cleft formation, the tidemark, and the subchondral bony end plate. B, Another viewof surface fibrillation showing vertical cleft formation and widespread large necrotic regions of the tissue devoid of cells. Clusters of cells, common in osteoarthritic tissues, are also seen. (Reproduced from Mankin HJ, Mow VC, Buckwalter JA: Articular cartilage repair and osteoarthritis, in Buckwalter JA, Einhorn TA, Simon SR (eds): Orthopaedic Basic Science: Biology and Biomechanics of the Musculoskeletal System, ed 2. Rosemont, IL, American Academy of Orthopaedic Surgeons, 2000, pp 471-488.)

 

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Injuries that disrupt articular cartilage and the underlying subchondral bone are referred to as osteochondral fractures.

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High-level force applied to articular surfaces can cause articular cartilage ruptures or tears that do not extend into the underlying bone (Fig. 6).

Figure 6 Arthroscopic image of a partial-thickness lesion of the articular cartilage of the patella. (Reproduced from Boden BP, Pearsall AW, GarrettWE Jr, Feagin JA: Patellofemoral instability: Evaluation and management. JAm Acad Orthop Surg 1997;5:47-57.)

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Although articular cartilage can withstand many decades of joint use, excessive force can disrupt the tissue.

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Unlike many other tissues, immature articular cartilage differs considerably from adult articular cartilage.

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Joint motion and loading are required to maintain the normal composition, structure, and mechanical properties of adult articular cartilage.1,13

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Because articular cartilage is an aneural tissue, the nerve impulses that regulate many body processes cannot provide information to chondrocytes.

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Despite the lack of a blood supply, articular cartilage chondrocytes have a high level of metabolic activity1 (Fig. 5).

Figure 5 Schematic diagram of the metabolic events controlling the proteoglycans in cartilage. The chondrocytes synthesize and secrete aggrecan, link protein and hyaluronate, and they become incorporated into functional aggregates. Enzymes released by the cells break down the proteoglycan aggregates. The fragments are released from the matrix into the synovial fluid, and from there the fragments are taken up by the lymphatics and moved into the circulating blood. (Reproduced from Mankin HJ, Mow VC, Buckwalter JA, Iannotti JP, Ratcliffe A: Articular cartilage structure, composition, and function, in Buckwalter JA, EinhornTA, Simon SR (eds): Orthopaedic Basic Science: Biology and Biomechanics of the Musculoskeletal System, ed 2. Rosemont, IL, American Academy of Orthopaedic Surgeons, 2000, pp 443-470.)

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