Bones and Joints

Structural Classification of joints/articulations

Fibrous

Bones firmly joined by fibrous tissue- no joint cavity
i) sutures: interlocking, negligible movement- cranial bones only

ii) syndesmoses: longer fibrous tissue- distal tibiofibular joint

iii) gomphosis: ligament holding tooth in socket

Cartilaginous

Bones firmly joined by cartilage- no joint cavity

i) synchondroses: plate of hyaline cartilage
1st costochondral joint- ribcage
epiphyseal plate (temp)
ii) symphyses: bones joined by fibrocartilage pad

Intervertebral joint, pubic symphysis

Synovial Joints

Freely movable, most joints

Features

i) No blood (avascular) or nerve (aneural) supply
covers bone ends, cushions, and smooth motion

ii) Joint cavity
houses fluid, allows for movement
iii) joint/articular capsule: encloses bone ends; outer fibrous layer, inner synovial membrane (synovium)

iv) Synovial fluid: lubricates and nourishes joints

Very small volume
v) ligaments: reinforce joints
a) capsular lig.: thickening of joint capsule
b) extracapsular lig.: just outside capsule

c) intracapsular lig: within capsule
vi) nerves and vessels: supply joint capsules (sensory receptors)
vii) fat pad: between capsule and membrane, act as swab, spread synovial fluid
viii) articular (fibrocartilage) discs or meniscus: stability, cushioning, guides rotations.

ix) bursa: sacs of synovial fluid reduces friction cushion

Tendon sheath: elongated bursa around tendon: ankle, wrist, biceps, tendons.

Movement at synovial Joints
Flexion: decreases angle between bones/segments (except shoulder motion)

Extension: angle increases between segments- moves past 180-body angle it is referred to as hyperextension

Abduction: movement away from the midline
adduction: movement towards body midline

Rotation: turning along segment long axis (scapular can also rotate up/downwards)

Supination (up) of forearm: movement so palm faces up or forward
pronation of forearm: movement so palm faces downward or backward

Protraction: forward movement of body parts

Retraction: backward movement of body part

Elevation: body part lifted upwards

Depression: lowering of body parts
Inversion: sole of foot turned in (supination)
Eversion: sole of foot turned out (pronation)

Plantar flexion: ankle extension (toes point down)

Dorsiflexion: ankle flexion (toes point up)

Synovial joints classified by shape