Portal:Joints
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Introduction
A joint or articulation (or articular surface) is the connection made between bones in the body which link the skeletal system into a functional whole. They are constructed to allow for different degrees and types of movement. Some joints, such as the knee, elbow, and shoulder, are self-lubricating, almost frictionless, and are able to withstand compression and maintain heavy loads while still executing smooth and precise movements. Other joints such as sutures between the bones of the skull permit very little movement (only during birth) in order to protect the brain and the sense organs. The connection between a tooth and the jawbone is also called a joint, and is described as a fibrous joint known as a gomphosis. Joints are classified both structurally and functionally.
Selected general articles
In anatomy, a joint capsule or articular capsule is an envelope surrounding a synovial joint. Each joint capsule has two parts: an outer fibrous layer or membrane, and an inner synovial layer or membrane. Read more...
Cartilaginous joints are connected entirely by cartilage (fibrocartilage or hyaline). Cartilaginous joints allow more movement between bones than a fibrous joint but less than the highly mobile synovial joint. Cartilaginous joints also forms the growth regions of immature long bones and the intervertebral discs of the spinal column. Read more...
1: Ball and socket joint; 2: Condyloid joint (Ellipsoid); 3: Saddle joint; 4 Hinge joint; 5: Pivot joint;
A hinge joint (ginglymus) is a bone joint in which the articular surfaces are molded to each other in such a manner as to permit motion only in one plane. According to one classification system they are said to be uniaxial (having one degree of freedom).
The direction which the distal bone takes in this motion is seldom in the same plane as that of the axis of the proximal bone; there is usually a certain amount of deviation from the straight line during flexion.
The articular surfaces of the bones are connected by strong collateral ligaments. Read more...
Synovial fluid, also called synovia,[help 1] is a viscous, non-Newtonian fluid found in the cavities of synovial joints. With its egg white–like consistency, the principal role of synovial fluid is to reduce friction between the articular cartilage of synovial joints during movement. Synovial fluid is a small component of the transcellular fluid component of extracellular fluid. Read more...- Motion, the process of movement, is described using specific anatomical terms. Motion includes movement of organs, joints, limbs, and specific sections of the body. The terminology used describes this motion according to its direction relative to the anatomical position of the joints. Anatomists use a unified set of terms to describe most of the movements, although other, more specialized terms are necessary for describing the uniqueness of the movements such as those of the hands, feet, and eyes.
In general, motion is classified according to the anatomical plane it occurs in. Flexion and extension are examples of angular motions, in which two axes of a joint are brought closer together or moved further apart. Rotational motion may occur at other joints, for example the shoulder, and are described as internal or external. Other terms, such as elevation and depression, describe movement above or below the horizontal plane. Many anatomical terms derive from Latin terms with the same meaning. Read more...
The teeth, viewed from the right
A gomphosis, also known as a dentoalveolar syndesmosis, is a joint that binds the teeth to bony teeth sockets in the maxillary bone and mandible. The fibrous connection between a tooth and its socket is a periodontal ligament. Specifically, the connection is made between the maxilla or mandible to the cementum of the tooth.
The motion of a gomphosis is minimal, though considerable movement can be achieved over time—the basis of using braces to realign teeth. The joint can be considered a synarthrosis. Read more...
1: Ball and socket joint; 2: Condyloid joint (Ellipsoid); 3: Saddle joint; 4 Hinge joint; 5: Pivot joint;
In animal anatomy, a pivot joint (trochoid joint, rotary joint, lateral ginglymus) is a type of synovial joint. In pivot joints, the axis of a convex articular surface is parallel with the longitudinal axis of the bone.
According to one classification system, a pivot joint like the other synovial joint —the hinge joint has one degree of freedom. Note that the degrees of freedom of a joint is not the same as the same as joint's range of motion. Read more...
Rotation of body parts is referred to as internal or external, referring to rotation towards or away from the center of the body.
Internal rotation (or medial rotation) refers to rotation towards the axis of the body. Read more...
Flexion and extension describe movements that affect the angle between two parts of the body. These terms come from the Latin words with the same meaning.
Flexion describes a bending movement that decreases the angle between a segment and its proximal segment. For example, bending the elbow, or clenching a hand into a fist, are examples of flexion. When sitting down, the knees are flexed. When a joint can move forward and backward, such as the neck and trunk, flexion refers to movement in the anterior direction. Flexion of the shoulder or hip refers to movement of the arm or leg forward. Read more...- Inversion and eversion refer to movements that tilt the sole of the foot away from (eversion) or towards (inversion) the midline of the body.
Eversion is the movement of the sole of the foot away from the median plane.
Inversion is the movement of the sole towards the median plane. For example, inversion describes the motion when an ankle is twisted. Read more...
Fibrous joints are connected by dense connective tissue, consisting mainly of collagen. These are fixed joints where bones are united by a layer of white fibrous tissue of varying thickness. In the skull the joints between the bones are called sutures. Such immovable joints are also referred to as synarthroses. Read more...- A ligament is the fibrous connective tissue that connects bones to other bones. It is also known as articular ligament, articular larua, fibrous ligament, or true ligament. Other ligaments in the body include the:
- Peritoneal ligament: a fold of peritoneum or other membranes.
- Fetal remnant ligament: the remnants of a fetal tubular structure.
- Periodontal ligament: a group of fibers that attach the cementum of teeth to the surrounding alveolar bone.
Ligaments are similar to tendons and fasciae as they are all made of connective tissue. The differences in them are in the connections that they make: ligaments connect one bone to another bone, tendons connect muscle to bone, and fasciae connect muscles to other muscles. These are all found in the skeletal system of the human body. Ligaments cannot usually be regenerated naturally; however, there are periodontal ligament stem cells located near the periodontal ligament which are involved in the adult regeneration of periodontal ligament. Read more... - Dorsiflexion and plantar flexion refer to extension or flexion of the foot at the ankle. These terms refer to flexion between the foot and the body's dorsal surface, considered the front of the leg, and flexion between the foot and the body's plantar surface, considered the back of the leg. These terms are used to resolve confusion, as technically extension of the joint refers to dorsiflexion, which could be considered counter-intuitive as the motion reduces the angle between the foot and the leg.
Dorsiflexion where the toes are brought closer to the shin. This decreases the angle between the dorsum of the foot and the leg. For example, when walking on the heels the ankle is described as being in dorsiflexion. Read more...
An interosseous membrane is a broad and thin plane of fibrous tissue that separates many of the bones of the body. It is an important component of many joints.
Interosseous membranes in the human body: Read more...
In anatomy, a joint capsule or articular capsule is an envelope surrounding a synovial joint. Each joint capsule has two parts: an outer fibrous layer or membrane, and an inner synovial layer or membrane. Read more...
1: Ball and socket joint; 2: Condyloid joint (Ellipsoid); 3: Saddle joint; 4 Hinge joint; 5: Pivot joint;
A condyloid joint (also called condylar, ellipsoidal, or bicondylar) is an ovoid articular surface, or condyle that is received into an elliptical cavity. This permits movement in two planes, allowing flexion, extension, adduction, abduction, and circumduction. Read more...
A synovial joint, also known as diarthrosis, joins bones with a fibrous joint capsule that is continuous with the periosteum of the joined bones, constitutes the outer boundary of a synovial cavity, and surrounds the bones' articulating surfaces. The synovial cavity/joint is filled with synovial fluid. The joint capsule is made up of an outer layer, the articular capsule, which keeps the bones together structurally, and an inner layer, the synovial membrane, which seals in the synovial fluid.
They are the most common and most movable type of joint in the body of a mammal. As with most other joints, synovial joints achieve movement at the point of contact of the articulating bones. Read more...
A synovial joint, also known as diarthrosis, joins bones with a fibrous joint capsule that is continuous with the periosteum of the joined bones, constitutes the outer boundary of a synovial cavity, and surrounds the bones' articulating surfaces. The synovial cavity/joint is filled with synovial fluid. The joint capsule is made up of an outer layer, the articular capsule, which keeps the bones together structurally, and an inner layer, the synovial membrane, which seals in the synovial fluid.
They are the most common and most movable type of joint in the body of a mammal. As with most other joints, synovial joints achieve movement at the point of contact of the articulating bones. Read more...
The synovial membrane (also known as the synovial stratum, synovium or stratum synoviale) is a specialized connective tissue that lines the inner surface of capsules of synovial joints and tendon sheath. It makes direct contact with the fibrous membrane on the outside surface and with the synovial fluid lubricant on the inside surface. In contact with the synovial fluid at the tissue surface are many rounded macrophage-like synovial cells (type A) and also type B cells. Type A cells maintain the synovial fluid by removing wear-and-tear debris. As for type B cells, they produce hyaluronan, as well as other extracellular components in the synovial fluid. Read more...
A synovial bursa (plural bursae or bursas) is a small fluid-filled sac lined by synovial membrane with an inner capillary layer of viscous synovial fluid (similar in consistency to that of a raw egg white). It provides a cushion between bones and tendons and/or muscles around a joint. This helps to reduce friction between the bones and allows free movement. Bursae are found around most major joints of the body. Read more...
Synostosis (plural: synostoses) is fusion of two bones. It can be normal in puberty, fusion of the epiphysis, or abnormal. When synostosis is abnormal it is a type of dysostosis.
Examples of synostoses include:- craniosynostosis – an abnormal fusion of two or more cranial bones;
- radioulnar synostosis – the abnormal fusion of the radius and ulna bones of the forearm;
- tarsal coalition – a failure to separately form all seven bones of the tarsus (the hind part of the foot) resulting in an amalgamation of two bones; and
- syndactyly – the abnormal fusion of neighboring digits.
Synostosis within joints can cause ankylosis. Read more...
A suture is a type of fibrous joint that is only found in the skull. The bones are bound together by Sharpey's fibres. A tiny amount of movement is permitted at sutures, which contributes to the compliance and elasticity of the skull.
These joints are synarthroses. It is normal for many of the bones of the skull to remain unfused at birth. The fusion of the skull's bones at birth is known as craniosynostosis. The term "fontanelle" is used to describe the resulting "soft spots". The relative positions of the bones continue to change during the life of the adult (though less rapidly), which can provide useful information in forensics and archaeology. In old age, cranial sutures may ossify (turn to bone) completely.
The joints between the teeth (gomphoses) and the joint between the mandible and the cranium, the temporomandibular joint, form the only non-sutured joints in the skull. Read more...
1: Ball and socket joint; 2: Condyloid joint (Ellipsoid); 3: Saddle joint; 4 Hinge joint; 5: Pivot joint;
The ball and socket joint (or spheroid joint) is a type of synovial joint in which the ball-shaped surface of one rounded bone fits into the cup-like depression of another bone. The distal bone is capable of motion around an indefinite number of axes, which have one common center. It enables the bone to move in many places (nearly all directions).
An enarthrosis is a special kind of spheroidal joint in which the socket covers the sphere beyond its equator. Read more...- A syndesmosis is a slightly movable fibrous joint in which bones such as the tibia and fibula are joined together by connective tissue. Examples include the distal tibia fibular joint as well as the radioulnar joint. Injuries to the ankle syndesmosis are commonly known as a "high ankle sprain". Although the syndesmosis is a joint, in the literature the term syndesmotic injury is used to describe injury of the syndesmotic ligaments. It comes from the Greek σύν, syn (meaning "with") and δεσμός, desmos (meaning "a band"). Syndesmosis sprains have received increasing recognition during recent years because of a heightened awareness of the mechanism, symptoms, and signs of injury. Read more...
The enthesis (plural entheses) is the connective tissue between tendon or ligament and bone.
There are two types of entheses: Fibrous entheses and fibrocartilaginous entheses. Read more...
Abduction is the motion of a structure away from the midline while adduction refer to motion towards the center of the body. The centre of the body is defined as the midsagittal plane. These terms come from Latin words with similar meanings, ab- being the Latin prefix indicating "away," ad- indicating "toward," and ducere meaning "to draw or pull" (cf. English words "duct," "conduct," "induction").
Abduction refers to a motion that pulls a structure or part away from the midline of the body. In the case of fingers and toes, it refers to spreading the digits apart, away from the centerline of the hand or foot. Abduction of the wrist is also called radial deviation. For example, raising the arms up, such as when tightrope-walking, is an example of abduction at the shoulder. When the legs are splayed at the hip, such as when doing a star jump or doing a split, the legs are abducted at the hip. Read more...
Kinesiology is the scientific study of human or non-human body movement. Kinesiology addresses physiological, biomechanical, and psychological dynamic principles and mechanisms of movement. Applications of kinesiology to human health (i.e., human kinesiology) include biomechanics and orthopedics; strength and conditioning; sport psychology; methods of rehabilitation, such as physical and occupational therapy; and sport and exercise. Studies of human and animal motion include measures from motion tracking systems, electrophysiology of muscle and brain activity, various methods for monitoring physiological function, and other behavioral and cognitive research techniques.
The word comes from the Greek κίνησις kínēsis, "movement" (itself from κινεῖν kineîn, "to move"), and -λογία -logia, "study". Read more...
Where the connecting medium is hyaline cartilage, a cartilaginous joint is termed a synchondrosis. An example of a synchondrosis joint is the first sternocostal joint (where the first rib meets the manubrium). In this example, the rib articulates with the manubrium via the costal cartilage. (The rest of the sternocostal joints are synovial plane joints.)
Sometimes, this is a temporary form of joint called epiphyseal growth plate, where the cartilage is converted into bone before adult life. Read more...- Pronation (/proʊˈneɪʃən/) and supination (/suːpɪˈneɪʃən/) refer most generally to assuming prone or supine positions, but often they are used in a specific sense referring to rotation of the forearm or foot so that in the standard anatomical position the palm or sole is facing anteriorly (supination) or posteriorly (pronation).
Pronation at the forearm is a rotational movement where the hand and upper arm are turned inwards. Pronation of the foot refers to turning of the sole outwards, so that weight is borne on the medial part of the foot. Read more...
1: Ball and socket joint; 2: Condyloid joint (Ellipsoid); 3: Saddle joint; 4 Hinge joint; 5: Pivot joint;
In a saddle joint (sellar joint, articulation by reciprocal reception) the opposing surfaces are reciprocally concave-convex. Read more...
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