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Structure of Joints

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Joints are specialized areas of the skeletal system situated between two bones, permitting postural movements: flexion, extension, rotation, etc. The ends of the bone in the joint cavity are covered with smooth hyaline cartilage (articular cartilage). The joint is held together by a joint capsule composed of collagen, which is strengthened by ligaments. The inside of the joint capsule is lined by a layer of flat synovial cells that secrete synovial fluid. The synovial fluid in the joint cavity serves as a lubricant.

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Clinical Manifestations of Joint Disease

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Joint Pain (Arthralgia)

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Most joint diseases cause pain. The term arthralgia is used when there is joint pain without evidence of acute inflammation. When pain is accompanied by other features of inflammation such as swelling, redness, and increased temperature, the term arthritis is used.

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Joint Swelling

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Joint swelling is the result of an increase in synovial fluid volume. It may result from fluid exudation in inflammatory conditions or from bleeding. Swelling due to bleeding is called hemarthrosis. Fluid imparts a fluctuant feel and produces a wave when tapped that can be felt on the side opposite to tapping (fluid thrill).

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Joint Mass Lesions

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An increase in size of a joint may result from the presence of solid tissue within the cavity. This occurs in rare neoplastic lesions of joints. The distinction between a mass lesion and fluid can be made by x-ray examination, needle aspiration, and careful clinical examination: A mass lesion produces a “boggy” feel compared with the fluctuant feel of fluid, and a fluid thrill is absent.

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Joint Crepitus

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The movement of one articular surface on another is normally smooth and silent. Crepitus is an abnormal sensation and sound of grating that accompanies joint movement. Because the articular cartilage represents the rubbing surface of a normal joint, crepitus occurs in diseases associated with loss of articular cartilage and exposure of subchondral bone.

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Abnormal Joint Mobility

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Most joint diseases result in restricted range of motion in the affected joints due to pain or stiffness. Rarely, the range of motion may be increased, as when structural components that hold the joint together are damaged. Tearing of cruciate ligaments in the knee and the general destruction associated with neuropathic joints are examples of disorders associated with an abnormal increase of joint mobility. Increased joint mobility may also be seen in congenital diseases characterized by abnormal collagen synthesis (eg, Ehlers-Danlos syndrome).

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Evaluation of Joint Disease

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Physical Examination

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Physical examination permits detection of acute inflammation, which is characterized by swelling, redness, increased temperature, tenderness, and restriction of motion. The presence of joint swelling is best assessed by measurement of its circumference and comparing it with ...

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