Joints

Dr. Anderson GCIT

Joints

• Where two or more bones meet

• Function– Connection (ligaments)– Movement (muscles)– Protection (joint

capsule)

Joint ClassificationStructural FunctionalFibrous – synostoses (immovable), syndesmoses (variable movement), gomphoses (peg-in-socket)

Synarthroses – bones don’t move relative to each other

Cartilaginous – synchondroses, symphyses

Amphiarthroses – “slightly” moveable

Synovial – articulating bones are separated by a fluid-filled cavity (most joints)

Diarthroses – freely moveable

Sutures

• Fibrous joints, slightly mobile in youth, immobile as adult (e.g. cranial sutures)– Limited mobility

allows brain to grow during development

– Immovability as adult serves as a protective function

Top of Skull (newborn baby)

Syndesmoses

• Bones connected exclusively by ligaments

• Movement varies according to length of the ligaments forming the joint, e.g.:– Very limited movement

between tibia and fibula– Very pronounced

movement of ulna around radius

Gomphoses

• Peg-in-socket, fibrous joint

• Only example is the teeth in their alveolar cavities connected by the periodontal ligament

Cartilaginous Joints

• Articulating bones are united by cartilage– Synchondroses and symphyses

Synchondroses

• Cartilage that unites two bones (such as the epiphyses to the diaphyses in the long bones of children and young adults)

• E.g. Epiphyseal plates

Symphyses

• Where articulating bones are lined with cartilage, which is fused to a pad or plate of fibrocartilage

– E.g. – intervertebral discs, pubic symphysis

Synovial Joints• Features

1. Articular cartilage – covers opposing bone surface2. Synovial cavity – space that contains synovial fluid3. Articular Capsule – provides tensile strength and covers all surfaces not lines with cartilage4. Synovial fluid – provides joint lubrication, released from the cartilage itself during activity (weeping lubrication)5. Reinforcing ligaments6. Nerves and blood vessels -

Joint Structure

Articular Discs (Menisci)

• Fibrocartilage pads that partially or completely divide the synovial cavity – (Knee, jaw meniscus)

• Improve the fit of some articular surfaces in the joint

Bursae and Tendon Sheaths

• Fibrous connective tissue that serves as a pliable “ball bearing” for some joints (e.g. shoulder) and closely packed tendons (e.g. wrist)

• Bursa rolls in opposing direction of movement

What holds joints together?

• Articular Surfaces -Deeply fitting articulations more stable than shallow ones

• Ligaments – “cables” of dense regular connective tissue that hold the joint together– Relatively little stretch (can snap)

• Muscle Tone – low levels of contractile activity – more tone = more stable joints

Synovial Joint Structure

Joint Movements• Originates from muscle contraction (of course)

• Degree of joint movement is called “range of motion”

• Three main types– Gliding– Angular– Rotation

Gliding joints

• Simplest movement– One or more flat

(usually) bone surfaces glide over another• Wrist bones• Ankle bones• Between vertebrae

Angular Movement• Flexion – pulling the joint angle closed

• Extension – opening the joint angle– Hyperextension – greater than normal extension

• Abduction – moving a limb away from the median line of the body

• Adduction – moving a limb toward the median line of the body

• Circumduction – moving a limb in a cone-shaped path in space

Rotation• Turning of a bone

around its long axis– Medial rotation –

turning toward the midline

– Lateral rotation – turning away from the midline

Supination and Pronation

• Refer to movement of radius around the ulna

• With arms down at sides:– Supination is a lateral rotation of the palms (palms

anterior or up)– Pronation is a medial rotation of the palms (palms

face posteriorly, radius and ulna cross each other, forming an ‘X’)

Ankle and Foot Movement

• Dorsi flexion – moves foot up (superiorly)

• Plantar flexion – moves foot down (inferiorly)

• Inversion – sole of foot turns medially

• Eversion – sole turns laterally

Jaw movements

• Protraction and retraction – jutting jaw out and bringing it back, respectively

• Elevation and Depression – Moving a body part superiorly or inferiorly (e.g. jaw)

Synovial Joint Types• Plane (Gliding) – allow only short, gliding movements

(wrist and ankle)• Hinge (One angular direction) - allows motion only along

a single plane (flexion and extension only)• Pivot (Rotation) – allows the bone to rotate around its

axis• Condyloid (All angular directions)– Oval articulating

surfaces that permit movement in all directions• Saddle (All angular directions)– both articular surfaces

have a convex AND a concave side that articulate together

• Ball-and-Socket - (Universal movement) allows movement in all directions, including limited rotation

Knee Joint

• Very Complex– 4 bones• Femur, tibia, fibula,

patella

– Ligaments often injured in sports or accidents

Knee Injuries• Cruciate Ligaments– ACL (anterior)– PCL (posterior)

• Deep in joint cavity of knee (intracapsular)– Can tear and separate

femur from the tibia– Most often happens

when the knee is rotated during full extension

Torn ACL (Arthroscopic view)

Knee Injuries• Most dangerous

injuries are lateral blows to the fully extended knee– Torn menicsi– Torn collateral

ligaments• Tibial (Medial or

MCL)– outside hit• Fibular (Lateral or

LCL)– inside hit

Jaw Joint Problems• Jaw Joint (mandible and

mandibular fossa) is called the tempero-mandibular joint (TMJ)

• Loosely connected – has a greater range of motion than other hinge joints– Condyle of mandible can

move out of the fossa, (anterior disarticulation)