Articular system and joints

articular system

made up of joints, associated ligaments and accessory structures

articulation

point of contact between bones or cartilage

ligaments

connect bone to bone

how are joints classified

structurally based on

• presence or absence of synovial cavity

• type of cartilage

cartilage

resilient, semirigid connective tissue located in parts of skeleton where flexibility is required

• nourished via diffusion bc doesn’t have dedicaed blood vessels or nerves

types of cartilage

• hyaline

• elastic

• fibrocartilage

hyaline cartilage

most common - covers bony articular surfaces

• model for early fetus skeleton

• moderate amounts of collagen

elastic cartilage

flexible and forms discrete structures in external ear, auditory tube and parts of larynx

• contains bundles of elastic fibres

fibrocartilage

forms specialised in joints e.g. disc, meniscus and labrum

• mix of fibrous tissue and hyaline surfaces

• can withstand prolonged pressure

• substantial amount of collagen

types of joints

synovial, fibrous and cartilaginous

• fibrous and cartilaginous lack joint cavity

synovial joint

moveable - has synovial cavity containing fluid and offers extensive range of movement

• 6 different types based on shape of articular surfaces and their possible movements

fibrous joint

solid, minimal movement - bones united by fibrous tissue and degree of movement depends on length of fibres

3 types of fibrous joints

• sutures - only in skull

• gomphosis - only in mouth between tooth and bone by periodontal ligament

• syndesmosis - bones connected by interosseous membrane

cartilaginous joints

solid and minimal movement - bones united by hyaline or fibrocartilage

• for strength and shock absoprtion

• either primary or secondary

primary cartilaginous joint

aka synchondrosis - joint held together with hyaline

• between 2 ossification centers of developing bones e.g. epiphysis plate

secondary cartilaginous joint

aka symphysis joint united by fibrocartilage

• permits limited movement

• e.g interverebral discs and pubic symphysis

major features of synovial joints

• articular cartilage

• joint capsule

• accessory structures - vary based on which joint

joint capsule

space between bones allowing movement. includes

• inner synovial membrane - highly vascular and provides synovial fluid

• outer fibrous membrane - dense connective tissue = extra stability

types of synovial joints

from least to most mobile

1. plane

2. hinge

3. pivot

4. condylar

5. saddle

6. ball-and-socket

plane joint

flat articular surface = sliding and gliding e.g. intercarpal joints in wrist

• nonaxial

hinge joint

uniaxial - flexion and extension

• cylinder trough of 1 bone

• e.g. elbow joint

modified hinge joint

primarily allows flexion and extension with limited rotation e.g. knee

pivot joint

rotation around single longitudinal axis

• e.g. proximal radioulnar joints

condylar joint

oval articular surface into concave surface = biaxial

• flexion/extension along lateral/medial axis

• abduction/adduction along anterior/posterior

• e.g. metacarpophalangeal/knuckle

saddle joint

biaxial where concave surface sits on convex surface like a saddle

• flexion, extension, abduction, adduction

• e.g. 1st carpometacarpal joint of thumb

ball and socket joint

multiaxial - spherical head fits into cup-shaped surface

• flexion/extension, abduction/adduction, rotation, circumduction

• shoulder and hip joints

articular disc

fibrocartilage disc that completely divides joint cavity into 2 separate compartments

• joint congruence

• absorb shock

• e.g. temporomandibular joint

meniscus

fibrocartilage strucure partially divides joint cavity

• joint congruency

• medial and lateral menisci in knee

labrum

fibrocartilage lip that extends from joint socket = deepens socket = increases joint stability and congruence

• prominent in ball-and-socket joint

fat pads

space fillers around synovial joint = cushion joint and helps spread synovial fluid

bursa

small fluid-filled sac that reduce friction of moving tissue between ligament/tendon and bone

tendon sheath

flattened fibrous sacs filled with synovial fluid that wraps around tendons

range of movement

range measured in degrees of a circle (360) through which he bones of a joint can be moved

factors affecting how healthy joints move

• structure/shape of articulating bones and congruency

• strength and tension of joint ligaments

• arrangement and tension muscles

• contact of soft parts

• hormones

• use and disuse

simple, complex and compound synovial joint

• simple = only 2 bones in joint

• compound = 2+ bones

• complex = cavity partially or completely divided by intra-articular disc into more than 1 compartment

close packed position

articular surfaces are closely apposed and key ligaments are maximally taut = position with max stability

sprain

ligaments forcibly stretched beyond their resting length

• grade 1 - micro tearing = painful bu minimal disruption of collagen fibres

• grade 2 - ligament partially teared = instability of joints

• grade 3 - complete tear = total loss of function