6.12 Joints (+ IMAGE OCCLUSION)

joints

Joints, or articulations, are commonly named according to the bones or portions of bones that join together

fibrous, cartilaginous, synovial

Joints are classified structurally as fibrous, cartilaginous, or synovial, according to the major connective tissue type that binds the bones together and whether a fluid-filled joint capsule is present.

motion

Joints can also be classified in functional categories according to their degree ol motion

synarthroses

Nonmovable joints are classified as synarthroses

amphiarthroses

Slightly movable joints are classified as amphiarthroses

diarthroses

Freely moveable joints are classified as diarthroses

little or no

In general, fibrous and cartilaginous joints have little or no movement

considerable

In general, synovial joints have considerable movement

fibrous

Fibrous joints are the articulating surfaces of two bones united by fibrous connective tissue

sutures, syndesmoses, gomphoses

Fibrous joints are further subdivided on the basis of structure as (1) sutures, (2) syndesmoses, or (3) gomphoses

sutures

Sutures are fibrous joints between the bones of the skull

fontanels

In a newborn, some parts of the sutures are quite wide and are called fontanels

syndesmoses

Syndesmoses are fibrous joints in which the bones are separated by some distance and held together by ligaments.

gomphoses

Gomphoses consist of pegs fitted into sockets and held in place by ligaments.cartilaginous joints

synchondroses, symphyses

Cartilagenous joints are subdivided on the basis of the type of cartilage as (1) synchondroses, which contain hyaline cartilage, and (2) symphyses, which contain fibrocartilage.

synovial

Synovial joints contain synovial fluid and allow considerable movement between articulating bones

articular

The articular surfaces of bones within synovial joints are covered with a thin layer of hyaline cartilage called articular cartilage.

bones

The articular cartilage provides a smooth surface where the bones meet.

meniscus

In some synovial joints, a flat pad of fibrocartilage, called a meniscus is present

disk

A meniscus is a type of articular disk that only partially spans the synovial cavity such that there is an opening in the center.

connection

The meniscus helps adjust the connection between articulating bones, which improves joint stability and reduces wear on the articular cartilage.

joint cavity

The space around the articular surfaces of the bones in a synovial joint is called the joint cavity

joint capsule

The joint cavity is filled with synovial fluid and surrounded by a joint capsule.

movement

The joint capsule helps hold the bones together while still allowing for movement.

fibrous capsule, synovial membrane

The joint capsule consists of two layers: an outer fibrous capsule and an inner synovial membrane.

fibrous capsule

The fibrous capsule is the outer layer of the joint capsule

synovial membrane

The synovial membrane is the inner layer of the joint capsule

synovial fluid

The synovial membrane produces synovial fluid, a viscous lubricating film that covers the surfaces of a joint.

bursa

In certain synovial joints, such as the shoulder and knee, the synovial membrane extends as a pocket, or sac, called a bursa

cushion

Bursae contain synovial fluid and provide a cushion between structures that would otherwise rub against each other, such as tendons rubbing on bones or other tendons.

tendon sheaths

Other bursae extend along tendons for some distance, forming tendon sheaths.

bursitis

Bursitis, inflammation of a bursa, may cause considerable pain around the joint and restrict movement.

blood vessels

Articular cartilage receives nourishment from blood vessels that are at the peripheral margin of the cartilage but do not actually penetrate the cartilage or enter the joint cavity.

shape

Synovial joints are classified according to the shape of the adjoining articular surfaces.

plane, saddle, hinge, pivot, ball-and-socket, ellipsoid

The six types of synovial joints are (1) plane, (2) saddle, (3) hinge, (4) pivot, (5) ball-and-socket, and (6) ellipsoid

uniaxial, biaxial, multiaxial

Movements at synovial joints are described

as uniaxial, occurring around one axis; biaxial, occurring around two axes situated at right angles to each other; or multiaxial, occurring around several axes.

plane joint

A plane joint, or gliding joint, consists of two flat bone surfaces of about equal size between which a slight gliding motion can occur

saddle joint

A saddle joint consists of two saddle-shaped articulating surfaces oriented at right angles to each other so that their complementary surfaces articulate

hinge joint

A hinge joint is a uniaxial joint in which a convex cylinder in one bone is applied to a corresponding concavity in the other bone

pivot joint

A pivot joint is a uniaxial joint that restricts movement to rotation around a single axis

ball-and-socket joint

A ball-and-socket joint consists of a ball (head) at the end of one bone and a socket in an adjacent bone into which a portion of the ball fits

ellipsoid joint

An ellipsoid joint (condyloid joint) is a modified ball-and-socket joint with the articular surfaces are ellipsoid rather than spherical

flexion

Flexion is a bending movement that decreases the angle of the joint to bring the articulating bones closer together.

extension

Extension is a straightening movement that increases the angle of the joint to extend the articulating bones.

hyperextension

Hyperextension is usually defined as extension of a joint beyond 180 degrees and can result in injury

plantar flexion

Movement of the foot toward the plantar surface, as when standing on the toes, is commonly called plantar flexion

dorsiflexion

movement of the foot toward the shin, as when walking on the heels, is called dorsiflexion

abduction

Abduction is movement away from the median or midsagittal plane

adduction

adduction is movement toward the median plane

pronation

When the elbow is flexed, pronation is rotation of the forearm so that the palm is down

supination

supination is rotation of the forearm so that the palm faces up

eversion

eversion is turning the foot so that the plantar surface (bottom of the foot) faces laterally

inversion

inversion is turning the foot so that the plantar surface faces medially.

rotation

Rotation is the turning of a structure around its long axis, as in shaking the head "no."

circumduction

In circumduction, the arm moves so that it traces a cone where the shoulder joint is at the cone's apex

protraction

protraction is a movement in which a structure, such as the mandible, glides anteriorly.

retraction

In retraction, the structure glides posteriorly.

elevation

Elevation is movement of a structure in a superior direction.

depression

Depression is movement of a structure in an inferior direction.

excursion

excursion is movement of a structure to one side, as in moving the mandible from side to side.

opposition

opposition is a movement unique to the thumb and little finger. It occurs when the tips of the thumb and little finger are brought toward each other across the palm of the hand.

reposition

Reposition returns the digits to the anatomical position.

sprain

When the bones of a joint are forcefully pulled apart and the ligaments around the joint are pulled or torn, a sprain results.

separation

A separation exists when the bones remain apart after injury to a joint.

dislocation

A dislocation is when the end of one bone is pulled out of the socket in a ball-and-socket, ellipsoid, or pivot joint.