AC joint

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AC Joint

The joint between the acromium process of scapula and the distal end of the clavicle; it is the location of most shoulder separations, which are particularly common in collision sports—e.g.,  ice hockey, rugby, American football, and Australian rules football.

AC joint

Acromio-clavicular joint Orthopedics The point where the acromium process of scapula and the distal end of the clavicle meet, which is the location of most frequent shoulder separations.


(joynt) [Fr. jointe, fr L. junctio, a joining]
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The place where two or more bones meet. Some joints are fixed or immobile attachments of bones; other joints allow the bones to move along each other. A joint usually has a thin, smooth articular cartilage on each bony surface and is enclosed by a joint capsule of fibrous connective tissue. A joint is classified as immovable (synarthrodial), slightly movable (amphiarthrodial), or freely movable (diarthrodial). A synarthrodial joint is one in which the two bones are separated only by an intervening membrane, such as the cranial sutures. An amphiarthrodial joint is one having a fibrocartilaginous disk between the bony surfaces (symphysis), such as the symphysis pubis; or one with a ligament uniting the two bones (syndesmosis), such as the tibiofibular articulation. A diarthrodial joint is one in which the adjoining bone ends are covered with a thin cartilaginous sheet and joined by a joint capsule lined by a synovial membrane, which secretes synovial fluid. Synonym: arthrosis (1) See: illustration


Joints are also grouped according to their motion: ball and socket (enarthrodial); hinge (ginglymoid); condyloid; pivot (trochoid); gliding (arthrodial); and saddle joint.

Joints can move in four ways: gliding, in which one bony surface glides on another without angular or rotatory movement; angulation, occurring only between long bones, increasing or decreasing the angle between the bones; circumduction, occurring in joints composed of the head of a bone and an articular cavity, the long bone describing a series of circles, the whole forming a cone; and rotation, in which a bone moves about a central axis without moving from this axis. Angular movement, if it occurs forward or backward, is called flexion or extension, respectively; away from the body, abduction; and toward the median plane of the body, adduction.

Because of their location and constant use, joints are prone to stress, injury, and inflammation. The main diseases affecting the joints are rheumatic fever, rheumatoid arthritis, osteoarthritis, and gout. Injuries comprise contusions, sprains, dislocations, and penetrating wounds.

acromioclavicular joint

Abbreviation: AC joint
A gliding or plane joint between the acromion and the acromial end of the clavicle.

amphidiarthrodial joint

A joint that is both ginglymoid and arthrodial.

ankle joint


arthrodial joint

Diarthrosis permitting a gliding motion. Synonym: gliding joint

ball-and-socket joint

A joint in which the round end of one bone fits into the cavity of another bone. Synonym: enarthrodial joint; multiaxial joint; polyaxial joint

biaxial joint

A joint with two chief movement axes at right angles to each other.

bilocular joint

A joint separated into two sections by interarticular cartilage.

bleeders' joint

Hemorrhage into joint space in hemophiliacs. Synonym: hemophilic joint

Budin joint

See: Budin joint

cartilaginous joint

A joint with cartilage between the bones.

Charcot joint

See: Charcot, Jean M.

Chopart joint

See: Chopart, François

Clutton joint

See: Clutton joint

cochlear joint

A hinge joint permitting lateral motion. Synonym: spiral joint

compound joint

A joint made up of several bones.

condylar joint

Ellipsoid joint.

condyloid joint

A joint permitting all forms of angular movement except axial rotation.

cracking joint

The sound produced by forcible movement of a joint by contracting the muscles that contract or extend a joint, esp. the metacarpophalangeal joints. The cause is not known.
See: crepitation

craniomandibular joint

Either of the encapsulated, double synovial joints between the condylar processes of the mandible and the temporal bones of the cranium. The double synovial joints are separated by an articular disk and function as an upper gliding joint and a lower modified hinge or ginglymoid joint.
Synonym: temporomandibular joint See:

diarthrodial joint

A joint characterized by the presence of a cavity within the capsule separating the bones, permitting considerable freedom of movement.

dry joint

Arthritis of the chronic villous type.

elbow joint

The hinge joint between the humerus and the ulna.

ellipsoid joint

A joint with two axes of motion through the same bone.
Synonym: condylar joint

enarthrodial joint

Ball-and-socket joint.

facet joint

Any of the zygapophyseal joints of the vertebral column between the articulating facets of each pair of vertebrae.

false joint

A false joint formation after a fracture.

fibrous joint

Any of the joints connected by fibrous tissue.

flail joint

A joint that is extremely relaxed, the distal portion of the limb being almost beyond the control of the will.

ginglymoid joint

A synovial joint having only forward and backward motion, as a hinge. Synonym: ginglymus See: hinge joint

gliding joint

Arthrodial joint.

hemophilic joint

Bleeders' joint.

hinge joint

a synovial joint in which two bones flex and extend in only one plane, usually because side (collateral) ligaments limit the direction of motion, e.g., elbow joint.

hip joint

A synovial ball-and-socket joint in which the head of the femur fits into the acetabulum of the hip bone. More than seven separate ligaments hold the joint together and restrict its movements.

immovable joint


intercarpal joint

Any of the articulations formed by the carpal bones in relation to one another.

irritable joint

A recurrent joint inflammation of unknown cause.

knee joint

The joint formed by the femur, patella, and tibia.

midcarpal joint

A joint separating the navicular, lunate, and triangular bones from the distal row of carpal bones.

movable joint

A slightly movable or freely movable joint, amphiarthrodial and diarthrodial, respectively.

multiaxial joint

Ball-and-socket joint.

pivot joint

A joint that permits rotation of a bone, the joint being formed by a pivot-like process that turns within a ring, or by a ringlike structure that turns on a pivot. Synonym: rotary joint; trochoid joint

plane joint

A synovial joint between bone surfaces, in which only gliding movements are possible.

polyaxial joint

Ball-and-socket joint.

joint protection

A technique for minimizing stress on joints, including proper body mechanics and the avoidance of continuous weight-bearing or deforming postures.

receptive joint

Saddle joint.

rotary joint

Pivot joint.

sacroiliac joint

The articulation between the sacrum and the ilium of the hip bone. Joint movement is limited because of interlocking of the articular surfaces.

saddle joint

A joint in which the opposing surfaces are reciprocally concavoconvex. Synonym: receptive joint

shoulder joint

The ball-and-socket joint between the head of the humerus and the glenoid cavity of the scapula.

simple joint

A joint composed of two bones.

spheroid joint

A multiaxial joint with spheroid surfaces.

spiral joint

Cochlear joint.

sternoclavicular joint

The joint space between the sternum and the medial extremity of the clavicle.

stiff joint

A joint with reduced mobility.

subtalar joint

Any of the three articular surfaces on the inferior surface of the talus.

sutural joint

An articulation between two cranial or facial bones.

synarthrodial joint


synovial joint

A joint in which the articulating surfaces are separated by synovial fluid.
See: joint for illus

talocrural joint


tarsometatarsal joint

A joint composed of three arthrodial joints, the bones of which articulate with the bases of the metatarsal bones.

temporomandibular joint

Craniomandibular joint.

trochoid joint

Pivot joint.

ulnomeniscal-triquetral joint

The functional articulation of the distal ulna, articular disk, and triquetrum. The disk may subluxate following injury or with arthritis and block supination of the forearm.

uniaxial joint

A joint moving on a single axis.

unilocular joint

A joint with a single cavity.

acromioclavicular joint

Abbreviation: AC joint
A gliding or plane joint between the acromion and the acromial end of the clavicle.
See also: joint
References in periodicals archive ?
It is important that a structured, active rehabilitation program is promptly initiated to decrease the risk of pain and disability after a type III AC joint injury.
Finally, it has been suggested that a direct communication between the lesion and the AC joint is a distinguishing pathological feature.
An MRI of the left shoulder was performed that demonstrated an effusion in the AC joint, minimal effusion in the glenohumeral joint, and a partial supraspinatus tear (Fig.
In fact, in the operation they actually removed the AC joint completely, so I can't have any further problem with it - because there isn't one there any more
The patient was followed for one year postoperatively and continued to report pain directly over the site of the os acromiale, as well as over the AC joint.
Elsewhere, Brent Wilson takes the No 7 shirt in place of injured captain Phil Dowson, who dislocated his AC joint against Leeds.
And his backup, Clay Matthews, sprained the AC joint in his right shoulder last week against Washington State.
RUGBY UNION: Saracens' problems have mounted following the news that Australian utility back Mark Bartholomuesz will be out of action for up to six weeks after rupturing the AC joint in his shoulder during last Sunday's clash with Wasps.
Leinster skipper Heaslip is still nursing the shoulder injury he sustained on New Year's Day, a blow to the AC joint against Ulster.
There are three grades of damage with the AC joint - and unfortunately, Darren has suffered a grade-three injury where all the ligaments between the joints are ruptured.
To make matters worse, Cushing's replacement, Clay Matthews (Agoura High), sprained the AC joint in his right shoulder against Washington State and already has his left hand in a cast because of a broken thumb.
However, one player who almost certainly will not make it for Sunday is the powerful lock Andy Perry, who damaged the AC joint in his shoulder at Bristol.