Chapter 8

Joints of the Skeletal System

Classification of Joints

Joints of the Skeletal System

• Articulations

• Functional junctions between bones

• Bind parts of skeletal system together

• Make bone growth possible

• Permit parts of the skeleton to change shape during childbirth

• Enable body to move in response to skeletal muscle contraction

Functional Classification Of Joints

• Classification=based on the amount of movement allowed

• 3 types:

• Synarthroses = immovable joints– Example = sutures of skull

• Amphiarthroses = slightly movable joints.– Example = intervertebral discs between vertebrae

• Diarthroses = freely movable joints– Examples = joints of appendicular skeleton

Structural Classification Of Joints

• Classification= Based on material, which joins bones

• 3 types:– Fibrous– Cartilaginous– Synovial

Fibrous Joints

• joints composed of fibrous tissue

• no joint cavity is present

• 3 types:– Syndesmosis– Suture– Gomphosis

Fibrous Joints cont.

• Syndesmosis = cord of fibrous tissue called a ligament – amphiarthroses with

"give" but no true movement

– Example = distal tibiofibular joint

Fibrous Joints cont.• Sutures = short

fibrous CT fibers– synarthroses– Only found in skull

Fibrous Joints cont.

• Gomphosis = tooth within its bony socket (alveolar fossa)– short periodontal

ligament

Cartilaginous Joints

• joints composed of cartilage

• no joint cavity

• 2 types:– Synchondrosis– Symphysis

Cartilaginous Joints cont.

• Synchondrosis = a plate of hyaline cartilage– sites of bone growth

during youth– eventually ossify =

synarthrotic– Examples: joint

between the first rib and manubrium and the epiphyseal plate

Cartilaginous Joints cont.

• Symphysis = pad or plate of fibrocartilage– compressible "shock

absorber"– limited movement =

amphiarthroses– Examples:

intervertebral discs and symphysis pubis

Synovial Joints

• = fluid-filled joint cavity– free movement

= diarthrosis

General Structure Of A Synovial Joint

• General Structure Of A Synovial Joint = 5 distinct features:

1. Articular cartilage = hyaline cartilage covers the surface of each bone

2. Joint cavity = a potential space between the two bones, filled with synovial fluid

3. Synovial fluid = viscous lubricating fluid within cavity – reduces friction between cartilages of 2 bones

• provide lubrication• nourish cartilage • contain phagocytes

Synovial Joints cont.4. Articular capsule = double layered capsule

surrounding cavity:– External, tough flexible fibrous capsule

(continuous with periosteum of the bones)– Synovial membrane = loose CT lining of fibrous

capsule, that also covers all internal joint surfaces excluding hyaline cartilage

5. Reinforcing ligaments = ligaments that strengthen joint– Definition: A ligament joins a bone to another

bone across a synovial joint– usually thickened portions of fibrous capsule

(intrinsic or capsular)

General Structure of a Synovial Joint

Synovial Joints cont.

• Other joint features:

• fatty pads (hip & knee)

• menisci or articular discs or that separate cavity into 2 compartments (knee, jaw, sternoclavicular)

Synovial Joints cont.

• bursa = flattened fibrous sacs with a synovial membrane and fluid that act as "ball bearings" to prevent friction on adjacent structures during joint activity– cushion the movement of one body part over

another;– located between skin and bone (where skin rubs

over bone), and between muscle, tendons, ligaments and bone.

Types Of Synovial Joints• Ball-and-socket joints

= most freely movable joints; all angular movement– The head of one bone fits

into the socket of another– Examples = hip and

shoulder

• Condyloid joints = permit all angular motion, except rotation– Examples = wrists and

knuckles

Types Of Synovial Joints cont.

• Gliding joints = cartilaginous joints– Example =

intervertebral discs

• Hinge joints = permit flexion & extension only– Examples = elbow

and knee

Types Of Synovial Joints cont.

• Pivot joints = permit rotation– Example = first

intervertebral joint (atlantoaxial joint)

• Saddle joints = thumb

Types Of Joint Movements

Introduction

• Origin = part of muscle attached to the immovable bone

• Insertion = part of a muscle attached to the movable bone

• When a muscle contracts across a joint, its insertion is pulled toward its origin

Three general types of movement

Gliding movements = when flat bone surfaces glide or slide over one another – occur at cartilaginous joints– Examples = intervertebral discs and

sternoclavicular joints

Angular movements = changes in angles between bones – occur only at synovial joints

Movement cont.• Flexion = decreasing the angle between 2

bones.– Example = head toward chest– Dorsiflexion = bringing foot closer to shin– Plantar flexion = pointing one's toe (flexion

toward the sole)

• Extension = increasing the angle between 2 bones– Example = straightening a flexed neck– Hyperextension = increasing the angle greater

than 180o

Movement cont.• Abduction = moving a limb away from the

midline.– Example = raising arm or thigh laterally;

• Adduction = moving a limb toward the midline

Movement cont.

• Circumduction = moving a limb in a circular (cone-shaped) manner

• Rotation = turning movement of a bone along its long axis.– Example = atlas over axis (i.e. “just say no”)– Example = shoulder and hip joint

Special Movements

Special Movements = those at specific joints

• supination/pronation = movements between the radius and ulna at the proximal radioulnar joint– thumb up = supination– thumb down = pronation

• inversion/eversion = movement of foot – sole inward = inversion – sole out = eversion

Special Movements cont.

• elevation/depression – shoulder shrug = elevation– mandible in opening mouth = depression

• protraction/retraction– thrust forward = protraction– pull back = retraction

Shoulder joint

• Shoulder joint (2 joints) • Ball and socket is the glenohumeral joint

– joins Glenoid cavity and head of humerus

• Syndesmosis is called the acromioclavicular joint– acromial end of clavicle and the acromion process of the

scapula

• Ball and socket is surrounded by many reinforcing ligaments and tendons collectively called the rotator cuff

• Many bursa also lubricate the shoulder• Movement can occur in any angular plane

Elbow joint

• (2 joints)

• Hinge is between trochlea of humerus and trochlear notch of ulna

• Gliding joint is between capitulum of humerus and head of radius

• Very stable joint with many reinforcing ligaments

• Only allows flexion and extension

Hip joint

• (coxal joint)

• Ball and socket between head of femur and acetabulum of coxa

• Contains many large reinforcing ligaments

• Allows same movements as shoulder, but with less range due to bony limitations

Knee• (3 joints)• Largest, most complex joint

– Functions as a hinge even though 3 joints work together

• Medial condyles of femur and tibia make one condyloid joint

• Lateral condyles of femur and tibia make another condyloid joint

• Patellar surface of femur and patella make a gliding joint– Flexion and extension with some slight rotation– Contains many reinforcing structures

Knee cont.

• Menisci– medial meniscus– lateral meniscus

• C-shaped fibrocartilage pads– Reshape the tibial condyles for a better fit– Absorb shock– Many bursae