Definitions

joint

joint

[joint]
joint, in anatomy, juncture between two bones. Some joints are immovable, e.g., those that connect the bones of the skull, which are separated merely by short, tough fibers of cartilage. Movable joints are found for the most part in the limbs. Hinge joints provide a forward and backward motion, as at the elbow and knee. Pivot joints permit rotary movement, like the turning of the head from side to side. Ball-and-socket joints, like those at the hip and shoulder, allow the greatest range of movement, as the rounded end of one bone fits into the hollow or socket of another bone, separated by elastic cartilage. Joints can further be classified as fibrous, cartilaginous, and synovial. Collagen fibers connect fibrous joints. Synovial joints ease movement through the use of a lubricating liquid, supplied by the synovial membrane that lines movable joints. In synovial joints, a cushioning sac known as a bursa contains the fluid, which lubricates and nourishes the joint. Those joints which lack synovial fluid are nourished by blood. Holding the joints in place are strong ligaments fastened to the bones above and below the joint. Joints are subject to sprains and dislocations, as well as to infections and disorders caused by such diseases as arthritis. In recent years, the use of artificial joints has become increasingly common, particularly in hip and knee replacement. Many orthopedic surgeons now perform operations of this sort, using metal or plastic replacement joints in order to relieve pain, or to prevent or correct joint deformity.
joint, in geology, fracture in rocks along which no appreciable movement has occurred (see fault). Nearly vertical, or sheet, joints that result from shrinkage during cooling are commonly found in igneous rocks. Similar joints occur in thick beds of sandstone and gneiss, with the sheets resembling the structure of a sliced onion. The prismatic joints of the Palisades of New Jersey and Devil's Tower, Wyoming, are examples of joints caused by contraction during the cooling of fine-grained igneous rock masses. Deep-seated igneous rocks often have joints approximately parallel to the surface, suggesting that they formed by expansion of the rock mass as overlying rocks were eroded away. Some joints in sedimentary rocks may have formed as the result of contraction during compaction and drying of the sediment. In some cases, jointing of the rock may result from the action of the same forces that cause folds and faults. In relatively undisturbed sedimentary rocks, such joints are often in two vertical sets perpendicular to one another. Commonly, streams develop along zones of weakness caused by joints in rocks, and thus the regional pattern of joint orientation often exerts a strong control on the development of drainage patterns.
or osteoarthrosis or degenerative joint disease

Most common joint disorder, afflicting over 80percnt of those who reach age 70. It does not involve excessive inflammation and may have no symptoms, especially at first. Cartilage softens and wears away, and bone grows in its place, distorting the joint's surface and causing pain, stiffness, and limited movement, usually in weight-bearing joints (vertebrae, knees, hips). Treatment may include analgesics, rest, weight loss, corticosteroids, and/or physical medicine and rehabilitation or an exercise program. Hip or knee replacement or surgical removal of unhealthy tissue may be needed.

Learn more about osteoarthritis with a free trial on Britannica.com.

A joint is the location at which two or more bones make contact. They are constructed to allow movement and provide mechanical support, and are classified structurally and functionally.

Classification

Joints are mainly classified structurally and functionally. Structural classification is determined by how the bones connect to each other, while functional classification is determined by the degree of movement between the articulating bones. In practice, there is significant overlap between the seven types of classifications.

Terms ending in the suffix -sis are singular and refer to just one joint, while -ses is the suffix for pluralization.

Structural classification

Structural classification names and divides joints according to how the bones are connected to each other. There are three structural classifications of joints:

Functional classification

Joints can also be classified functionally, by the degree of mobility they allow:

Biomechanical classification

Joints can also be classified based on their anatomy or on their biomechanical properties. According to the anatomic classification, joints are subdivided into simple and compound, depending on the number of bones involved, and into complex and combination joints:

  1. Simple Joint: 2 articulation surfaces (eg. shoulder joint, hip joint)
  2. Compound Joint: 3 or more articulation surfaces (eg. radiocarpal joint)
  3. Complex Joint: 2 or more articulation surfaces and an articular disc or meniscus (eg. knee joint)

Anatomical

The joints may be classified anatomically into the following groups:

  1. Articulations of hand
  2. Elbow joints
  3. Wrist joints
  4. Axillary articulations
  5. Sternoclavicular joints
  6. Vertebral articulations
  7. Temporomandibular joints
  8. Sacroiliac joints
  9. Hip joints
  10. Knee joints
  11. Articulations of foot

Arthritis

Arthritis and direct physical trauma to a joint are the causes of joint damage. Arthritis is a group of conditions where there is damage caused to the joints of the body. Arthritis is the leading cause of disability in people over the age of 55.

There are many different forms of arthritis, each of which has a different cause. The most common form of arthritis, osteoarthritis (also known as degenerative joint disease) occurs following trauma to the joint, following an infection of the joint or simply as a result of aging. Furthermore, there is emerging evidence that abnormal anatomy may contribute to early development of osteoarthritis. Other forms of arthritis are rheumatoid arthritis and psoriatic arthritis, which are autoimmune diseases in which the body is attacking itself. Septic arthritis is caused by joint infection. Gouty arthritis is caused by deposition of uric acid crystals in the joint that results in subsequent inflammation. Additionally, there is a less common form of gout that is caused by the formation of rhomboidal shaped crystals of calcium pyrophosphate. This form of gout is known as pseudogout.

References

See also

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