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Arthrocentesis – Aspiration of the joint

Capsule – Part of the synovial joint that, along with the lining, creates a pouch in which synovial fluid is secreted

Desmosomes – A small body that forms the site of attachment between cells

Hemarthrosis – The presence of blood in the joint

Monoarticular – Affecting a single joint

Pannus – A proliferation of synovium beginning at the periphery of the joint surface as seen in rheumatoid arthritis

Pigmented villonodular synovitis – A proliferative process of the synovial membrane of unknown etiology

Polyarticular – Affecting multiple joints

Primary synovial chondromatosis – A condition in which hyaline cartilage nodules grow within the synovial lining of a joint, bursa, or tendon sheath

Synovial fluid – The straw-colored fluid in the joint that is formed by filtration of capillary plasma

Synovial joints – Joints that have two opposing surfaces covered with articular cartilage and are attached at their periphery by the joint capsule

Synoviocytes – Cells that form the synovial membrane, remove debris, and secrete hyaluronic acid

Synovitis – A condition characterized by inflammation of the synovial lining

Synovium – A membrane-like lining of the synovial joints, tendon sheaths, and bursae

Type A synoviocytes – A type of synovial cell that plays a role in removing particulate debris from the joint

Type B synoviocytes – A type of synovial cell that secretes hyaluronic acid

Neoplasms of the synovium are uncommon and can involve the synovial lining of joints, bursae, and tendons.

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Inflammatory and noninflammatory synovitis alters both the synovium and the composition of synovial fluid. In the synovial fluid of inflammatory joint diseases, the lysosomal enzymes released break down the hyaluronic acid “sieve” barrier.

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Synovitis is a nonspecific term that simply means inflammation of the synovial lining. Numerous conditions cause or are associated with synovitis. The pathologic characteristics of the synovitis vary depending on the condition.

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In the embryo, joints develop from the primitive mesenchyme located between the moving components of the maturing skeleton.

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Normal joints contain only a small amount of clear, straw-colored synovial fluid.

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The number of cell layers that form the synovium varies but usually ranges between two and four cell layers thick (Fig. 1).

Figure 1
Normal synovium consisting of two cell layers of synoviocytes overlying fibrofatty supportive stroma. Note the presence of blood-filled capillaries (arrows) immediately beneath the synoviocytes. (Reproduced with permission from Carpenter CA, Rosenberg AE, Freiberg AA: Synovial conditions of the knee, in JJ Callahan, AG Rosenberg, HE Rubash, PT Simonian, TAWickiewicz (eds): The Adult Knee. Philadelphia, PA, Lippincott-Williams & Wilkins, in press.)

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Synovial cells are classically defined as type A or type B synoviocytes.

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Synovial joints have two opposing surfaces covered with articular cartilage that are attached at their periphery by the joint capsule.

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