Joints

joint or articulation

any point where two bones meet, whether or not the bones are movable at that interface

synostosis

bony joint

an immobile joint formed when the gap between two bones ossifies

examples of synostosis

Left and right frontal and mandibular bones in infants

Ilium, ischium, pubis fuse to form hip bone in adult

Attachment of first rib and sternum with old age

Parietal bones along sagittal suture with old age

synarthrosis

fibrous joint

adjacent bones are bound by collagen fibers that emerge from one bone and penetrate into the other

sutures

immobile or slightly mobile fibrous joints in which short collagen fibers bind the bones of the skull to each other

serrate suture

interlocking wavy lines

ex: coronal, sagittal, and lambdoid sutures

lap (squamous) suture

overlapping beveled edges

ex: temporal and parietal bones

plane (butt) suture

straight, non-overlapping edges

ex: palatine processes of the maxillae

gomphosis

attachment of a tooth to its socket

held in place by fibrous periodontal ligament

syndesmosis

fibrous joint at which two bones are bound by long collagen fibers

amphiarthrosis

cartilaginous joint

two bones are linked by cartilage

synchondrosis

bones joined by hyaline cartilage

examples of synchondrosis

first rib attachment to sternum

epiphyseal plate cartilage

symphysis

two bones joined by fibrocartilage

examples of symphysis

pubic symphysis joined by interpubic disc

bodies of vertebrae joined by intervertebral discs

diarthrosis

synovial joint

joint in which two bones are separated by a joint cavity

articular cartilage

layer of hyaline cartilage, 2-3 mm thick

covering the facing surfaces of two bones

joint cavity

separates articular surfaces

synovial fluid

slippery lubricant in joint cavity

rich in albumin and hyaluronic acid

viscous, slippery texture

function of synovial fluid

nourishes articular cartilage and removes waste

makes movement of joints almost synovial free

joint capsule

connective tissue that encloses the cavity and retains the fluid

synovial membrane

composed mainly of fibroblast-like cells that secrete synovial fluid and marcophages that remove debris from the cavity

articular disc

pad crosses the entire joint capsule

examples of articular disc

jaw, joints of the clavicle, between the ulna and carpal bones

meniscus

crescent-moon pad does not cross joint entirely

found in knee

function of meniscus

absorb shock and pressure, stabilize joint

tendon

strip of collagenous tissue attaching muscle to bone

ligament

strip of collagenous tissue attaching one bone to another

bursa

fibrous sac filled with synovial fluid

function of bursa

cushions muscles, helps tendons slide more easily, modifies direction of tendon pull

tendon sheath

elongated cylindrical bursa wrapped around a tendon

found in hand and foot

range of motion

the degrees through which a joint can move

types of axis rotations

multiaxial, biaxial, monoaxial

multiaxial joints

joint has three degrees of freedom

biaxial joints

movement in two planes

ball-and-socket joints

smooth, hemispherical head fits within cup-like socket

ball-and-socket examples

shoulder joint and hip

condylar joints

oval convex surface of one bone fits into a complementary-shaped depression on the other

condylar examples

radiocarpal joint, metacarpophalangeal joints

saddle joints

both bones have an articular surface that is shaped like a saddle, concave and convex

saddle examples

trapeziometacarpal, sternoclavicular joint

plane joints

flat articular surfaces, bones slide over each other

plane examples

between

• carpal bones of wrist

• tarsal bones of ankle

• articular processes of vertebrae

hinge joints

one bone with convex surface fits into a concave depression of another bone

hinge examples

elbow, knee, finger joints, toes

pivot joints

a bone spins on its longitudinal axis

pivot examples

atlantoaxial joint (C1 nd C2), radioulnar joint at the elbow

flexion

movement that decreases joint angle

extension

movement that straightens a joint and returns a body part to the zero position

hyperextension

extension of a joint beyond the zero position

abduction

movement of a body part in the frontal plane away from the midline of the body

hyperabduction

raise arm over back or front of head

adduction

movement in the frontal plane back toward the midline

hyperadduction

crossing fingers, crossing ankles

elevation

movement that raises a body part vertically in the frontal plane

depression

movement that lowers a body part in the same plane

protraction

anterior movement of a body part in the transverse plane

retraction

posterior movement of a body part in the transverse plane

circumduction

one end of an appendage remains stationary while other end makes a circular motion

medial (internal) rotation

movement that turns the bone inward

lateral (external) rotation

movement that turns the bone outward

supination

forearm movement that turns palm to face anteriorly or upward

pronation

forearm movement that turns palm to face posteriorly or downward

osteoarthritis

wear-and-tear arthritis, resulting from years of joint wear

rheumatoid arthritis

autoimmune attacks against joint tissues

arthroplasty

replacement of diseased joint with artificial joint prosthesis