joint

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joint

, in anatomy

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

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.

Joint (anatomy)

The structural component of an animal skeleton where two or more skeletal elements meet, including the supporting structures within and surrounding it. The relative range of motion between the skeletal elements of a joint depends on the type of material between these elements, the shapes of the contacting surfaces, and the configuration of the supporting structures.

In bony skeletal systems, there are three general classes of joints: synarthroses, amphiarthroses, and diarthroses. Synarthroses are joints where bony surfaces are directly connected with fibrous tissue, allowing very little if any motion. Synarthroses may be further classified as sutures, syndesmoses, and gomphoses. Sutures are joined with fibrous tissue, as in the coronal suture where the parietal and frontal bones of the human skull meet. Syndesmoses are connected with ligaments, as are the shafts of the tibia and fibula. The roots of a tooth that are anchored in the jaw bone with fibrous tissue form a gomphosis. Amphiarthroses are joints where bones are directly connected with fibrocartilage or hyaline cartilage and allow only limited motion. An amphiarthrosis joined with fibrocartilage, as found between the two pubic bones of the pelvis, is known as a symphysis; but when hyaline cartilage joins the bones, a synchondrosis is formed, an example being the first sternocostal joint. The greatest range of motion is found in diarthrodial joints, where the articulating surfaces slide and to varying degrees roll against each other. See Ligament

The contacting surfaces of the bones of a diarthrodial joint are covered with articular cartilage, an avascular, highly durable hydrated soft tissue that provides shock absorption and lubrication functions to the joint (see illustration). Articular cartilage is composed mainly of water, proteoglycans, and collagen. The joint is surrounded by a fibrous joint capsule lined with synovium, which produces lubricating synovial fluid and nutrients required by the tissues within the joint. Joint motion is provided by the muscles that are attached to the bone with tendons. Strong flexible ligaments connected across the bones stabilize the joint and may constrain its motion. Different ranges of motion result from several basic types of diarthrodial joints: pivot, gliding, hinge, saddle, condyloid, and ball-and-socket. See Collagen

Cross section of the human knee showing its major components

Joint

The space between the stones in masonry or between the bricks in brick work. In concrete work, joints control the shrinkage on large areas and isolate independent elements.

angle joint

Any joint formed by uniting two members at a corner which results in a change of direction.

bevel joint

Any joint in which the ends of the two abutting elements are cut at an angle, especially when not forming a right angle.

blind joint

A joint that is invisible.

bridle joint

A carpentry joint connecting a slotted end of one timber to the double-notched end of another timber; used to connect a rafter to a tie beam or two rafters at a ridge.

broken joint

A pattern where the elements are installed so that the adjacent butt joints between pieces are not aligned, such as in flooring and brickwork.

butt joint

A plain square joint between two members, when the contact surfaces are cut at right angles to the faces of the pieces; the two are filled squarely against each other rather than lapped.

cogged joint

A carpentry joint formed by two crossed structural members, each of which is notched at the place where they cross.

construction joint

A separation provided in a building that allows its component parts to move with respect to each other; a joint where two placements of concrete meet.

control joint

A joint that is premolded, tooled, or sawed, and installed to prevent shrinkage of large areas. It creates a deliberately weakened section to induce cracking at the chosen location rather than at random.

dovetail joint

A splayed tenon, shaped like a dove’s tail, broader at its end than at its base; the joint is formed by such a tenon fitting into the recess of a corresponding mortise.

end-lap joint

A joint formed between the ends of two pieces of timber, normally at right angles; each piece is notched equal to the width of the other piece, to form a flush surface in the assembled joint.

expansion joint

Designed to permit the expansion or contraction due to temperature changes. It generally extends through the entire structure from the footings to the roof.

finger joint

An end joint made up of several meshing fingers of wood made with a machine and glued together.

flush joint

Any joint finished even or level with the surrounding surfaces.

indented joints

A joint used in joining timbers end to end; a notched fishplate is attached to one side of the joint to fit into two corresponding notches in the joined timbers; the entire assembly is fastened with bolts.

interlocking joint

A form of joggle in which a protrusion on one member complements a slot or routed groove in another; a joint formed between sheet-metal parts by joining their preformed edges to provide a continuous locked piece.

isolation joint

A joint that separates one concrete section from another so that each one can move independently; found in floors, at columns, and at junctions between the floor and walls.

joggle joint

A notch or projection in one piece of material, which is fitted to a projection or notch in a second piece, to prevent one piece from slipping past the other.

lap joint

A joint in which one member overlaps the edge of another and is connected.

miter joint

A joint between two members at an angle to each other; each member is cut at an angle equal to half the angle of the junction, usually at right angles to each other.

mortise and tenon

A joint between two members, formed by fitting a tenon at the end of one member into a mortise cut into the other.

rigid joint

A joint that is capable of transmitting the full extent of force at the end of the member to the other members framing into the joint.

scarf joint

A wood joint formed by two members cut diagonally to overlap and interlock; pegs, glue, straps, or other devices are used to attach the members.

semirigid joint

A joint in either steel or concrete that is designed to permit some rotation; also called a partially fixed joint.

spline joint

A joint formed by inserting a spline of long strips of wood or metal in a slot cut into the two butting members.

standing-seam joint

In metal roofing, a type of joint between the adjacent sheets of material, made by turning up the edges of two adjacent sheets and then folding them over.

straight joint

A line created by the meeting of two or more separate elements or pieces, often continuing in a straight line from one end to another.

tongue-and-groove joint

A joint formed by the insertion of the tongue of one member into the corresponding groove of another.

tooled joint

Any mortar joint finished with a tool, other than a trowel, that compresses and shapes the mortar; common types include a beaded joint, concave joint, and raked joint.

The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Joint

a conventional term used by miners to designate cracks in a rock mass. Joints occur during geological dis-locations (tectonic shoves) or are formed as a result of detonating borehole charges (frequently parallel to the line of distribution of the charges). Joints contribute to rockslides (at times sudden) from the upper area of the mine face during the loading of a detonated body of rock.

Joint

a movable junction of bones that enables them to move in relation to one another. The main elements of a joint include the cartilage-covered surfaces of articulating bones, a cavity containing fluid, and a capsule enclosing the cavity. Some joints also have such auxiliary structures as ligaments, disks, menisci, and synovial bursae. The shape of joints has changed in the course of animal evolution and the development of locomotion. In man, the characteristics of joints result from the body’s upright position, which conditions the number of axes of rotation and of degrees of movement.

In simple joints, two bones articulate, whereas in composite joints, several bones articulate. The joint surfaces resemble geometric figures and may be spherical, ellipsoidal, saddle-shaped, or flat. Joints may be movable, for example, the spherical shoulder joint, or immovable, for example, the joint between a rib and the sternum. The range of joint movements is measured in the degrees of the angles formed by the articulating bones. Movements may occur around one, two, or three axes. Uniaxial movement is characteristic of cylindrical and hinged joints, biaxial movement, of ellipsoidal and saddle-shaped joints, and polyaxial movement, of spherical joints. Movements are normally restricted by bony prominences and by the tension of ligaments and of the joint capsule.

Joint injuries may be caused by traumas (dislocation), congenital defects (arthrogryposis), destructive metabolic changes (arthrosis), or inflammatory changes (arthritis). Limited mobility or total immobility of a joint may result from a variety of pathological processes. Joint diseases and methods of treating and preventing them are the concerns of traumatology, orthopedics, and a special branch of clinical medicine called arthrology.

REFERENCES

Sinel’nikov, R. D. Atlas anatomii cheloveka, vol. 1. Moscow, 1963.
Astapenko, M. G., and E. G. Pikhlak. Bolezni sustavov. Moscow, 1966.

V. IU. GOLIAKHOVSKII

joint

[jȯint]

(anatomy)

A contact surface between two individual bones. Also known as articulation.

(electricity)

A juncture of two wires or other conductive paths for current.

(engineering)

The surface at which two or more mechanical or structural components are united.

(geology)

A fracture that traverses a rock and does not show any discernible displacement of one side of the fracture relative to the other.

Joint (structures)

The surface at which two or more mechanical or structural components are united. Whenever parts of a machine or structure are brought together and fastened into position, a joint is formed. See Structural connections

Mechanical joints can be fabricated by a great variety of methods, but all can be classified into two general types, temporary (screw, snap, or clamp, for example), and permanent (brazed, welded, or riveted, for example).

joint

1. The space between adjacent surfaces (as between masonry units), or the place where two members or components are held together by nails, fasteners, cement, mortar, etc.

2. In steel construction, the area where two or more steel surfaces are attached; often characterized by the type of weld or fastener employed. Also see masonry joint and wood joint.

joint

1. Anatomy the junction between two or more bones, usually formed of connective tissue and cartilage

2. the point of connection between movable parts in invertebrates, esp insects and other arthropods

3. the part of a plant stem from which a branch or leaf grows

4. Geology a crack in a rock along which no displacement has occurred

5. out of joint

a. dislocated

b. out of order or disorganized

6. Law (of persons) combined in ownership or obligation; regarded as a single entity in law