Chapter 8: Articulations

What is an articulation?

A site where two or more bones meet

What are the two functions of joints?

Allow movement and hold the skeleton together

Why are joints considered the weakest parts of the skeleton?

They are where bones meet

What are the three structural classifications of joints?

• Fibrous

• Cartilaginous

• Synovial

What is structural classification based on?

The material binding bones together and whether a joint cavity is present

What are the three functional classifications of joints?

• Synarthroses

• Amphiarthroses

• Diarthroses

Synarthroses

Immovable

Amphiarthroses

Slightly movable

Diarthroses

Freely movable

What is functional classification based on?

The amount of movement allowed

What are the characteristics of fibrous joints?

Bones joined by fibrous connective tissue, with no joint cavity. Most are immovable.

What are the three types of fibrous joints?

Sutures, syndesmoses, and gomphoses.

Where are sutures found?

Between the bones of the skull

How are sutures structured?

Interlocking junctions filled with connective tissue fibers.

What do sutures allow during youth?

They hold skull bones tightly together while allowing growth.

What happens to skull bones in middle age?

Skull bones fuse and are called synostoses.

What is a synostosis?

A joint formed when bones fuse together.

How are syndesmoses connected?

By fibrous tissue ligaments.

How much movement do syndesmoses allow?

Immovable to slightly movable.

What are two examples of syndesmoses?

• Between the tibia and fibula

• Between the radius and ulna

What is a gomphosis?

A peg-in-socket fibrous joint between a tooth and its alveolar socket.

What connects a tooth to its alveolar socket?

The periodontal ligament.

What are the characteristics of cartilaginous joints?

• Bones are united by cartilage

• No joint cavity

What are the two types of cartilaginous joints?

Synchondroses and symphyses

What connects bones in a synchondrosis?

A bar or plate of hyaline cartilage.

What is the functional classification of all synchondroses?

Synarthrotic (immovable)

What are two examples of synchondroses?

• Epiphyseal plates in children.

• Joint between the first rib's costal cartilage and the sternum.

How are symphyses structured?

Hyaline cartilage covers the bone surfaces and is fused to an intervening pad of fibrocartilage.

What is the functional classification of symphyses?

Amphiarthrotic (slightly movable)

What are symphyses designed for?

Strength and flexibility

What are two examples of symphyses?

• Intervertebral joints (between vertebrae)

• Pubic symphysis of the pelvis

What is a synovial joint?

A joint where articulating bones are separated by a fluid-filled joint cavity

What is the functional classification of all synovial joints?

Diarthroses (freely movable)

What are examples of synovial joints?

All limb joints and most joints of the body.

What are the five structures found in all synovial joints?

1. Articular cartilage

2. Joint (synovial) cavity

3. Articular capsule

4. Synovial fluid

5. Reinforcing ligaments

What are bursae?

Flattened, fibrous sacs lined with synovial membranes and filled with synovial fluid.

Where are bursae commonly found?

Where ligaments, muscles, skin, tendons, or bones rub together.

What is a tendon sheath?

An elongated bursa that wraps completely around a tendon.

What determines synovial joint stability?

• Articular surfaces: shape determines movement.

• Ligaments: connect bones and prevent excessive movement.

• Muscle tone: keeps tendons tight to stabilize joints.

What is a muscle's origin?

Attachment to the immovable bone

What is a muscle's insertion?

Attachment to the movable bone

What planes describe joint movements?

Transverse, frontal, and sagittal

What are the four range-of-motion classifications?

• Nonaxial: slipping only.

• Uniaxial: one plane.

• Biaxial: two planes.

• Multiaxial: all three planes.

What is gliding?

One flat bone surface slips over another similar surface.

What are examples of gliding joints?

Intercarpal, intertarsal, and flat vertebral articular process joints.

What is flexion?

Decreases the joint angle.

What is extension?

Increases the joint angle; opposite of flexion.

What are dorsiflexion and plantar flexion?

• Dorsiflexion: foot moves upward

• Plantar flexion: foot moves downward

What is abduction?

Movement away from the midline

What is adduction?

Movement toward the midline.

What is circumduction?

Movement in a cone-shaped pattern.

What is rotation?

Turning a bone around its long axis.

What are examples of rotation?

Between the first two vertebrae and at the hip and shoulder joints.

What are supination and pronation?

• Supination: palm faces up

• Pronation: palm faces down

What are inversion and eversion?

• Inversion: sole turns inward (medially)

• Eversion: sole turns outward (laterally)

What are protraction and retraction?

• Protraction: scapulae move apart.

• Retraction: scapulae move together.

What are elevation and depression?

• Elevation: upward movement

• Depression: downward movement

What is opposition?

Thumb crosses the palm to touch the pinky

What are the characteristics of plane joints?

• Articular surfaces are flat

• Allow slipping or gliding only

• The only nonaxial joints

How are hinge joints structured?

A cylindrical projection of one bone fits into a trough-shaped surface of another.

What movements do hinge joints allow?

Uniaxial movement: flexion and extension in one plane

What are examples of hinge joints?

Elbow and interphalangeal (finger and toe) joints

How are pivot joints structured?

The rounded end of one bone fits into a ring formed by another bone and possibly ligaments.

What movements do pivot joints allow?

Uniaxial movement only.

What are examples of pivot joints?

• Joint between the axis and dens

• Proximal radioulnar joint

How are condyloid joints structured?

An oval articular surface fits into a matching depression; both surfaces are oval.

What movements do condyloid joints allow?

Biaxial movement, allowing all angular motions.

What are examples of condyloid joints?

Radiocarpal (wrist) and metacarpophalangeal (knuckle) joints

How are saddle joints structured?

Each articular surface has both a concave and a convex surface.

How do saddle joints compare with condyloid joints?

They are similar, but saddle joints allow greater movement.

What is an example of a saddle joint?

Carpometacarpal joint of the thumb.

How are ball-and-socket joints structured?

A spherical or hemispherical head fits into a cup-like socket

What movements do ball-and-socket joints allow?

Multiaxial movement; they are the most freely moving synovial joints.

What are examples of ball-and-socket joints?

Shoulder and hip joints

What structures stabilize the shoulder joint?

• Thin, loose joint capsule

• 4 ligaments: 1 coracohumeral and 3 glenohumeral

• Long head of biceps tendon: passes through the intertubercular groove and secures the humerus to the glenoid cavity

• Rotator cuff: 4 tendons surrounding the joint and blending with the capsule

Why is shoulder stability weak?

The joint capsule is thin and loose, providing limited stability.

What type of joint is the hip, and how is it formed?

Ball-and-socket joint; the head of the femur fits into the acetabulum.

What limits the hip joint's range of motion?

The deep socket and strong ligaments.

What structures stabilize the hip joint?

• Acetabular labrum

• Iliofemoral ligament

• Pubofemoral ligament

• Ischiofemoral ligament

• Ligamentum teres

What is a sprain?

Stretching or tearing of ligaments that reinforce a joint.

How do partially and completely torn ligaments heal?

• Partially torn: slowly repair themselves

• Completely torn: require prompt surgical repair

What are cartilage injuries?

The snap and pop of overstressed cartilage

What is a common cause or context for cartilage injuries?

They are a common aerobics injury.

How are cartilage injuries repaired?

With arthroscopic surgery

What is a dislocation?

Bones are forced out of alignment.

What commonly accompanies dislocations?

Sprains, inflammation, and joint immobilization.

What causes dislocations?

Serious falls; they are also common sports injuries.

What is a subluxation?

Partial dislocation of a joint.

What is bursitis, and what causes it?

Inflammation of a bursa, usually caused by a blow or friction.

What are the symptoms and treatments of bursitis?

• Symptoms: pain and swelling.

• Treatment: anti-inflammatory drugs; excessive fluid may be aspirated.

What is tendonitis, and what causes it?

Inflammation of tendon sheaths, typically caused by overuse.

How are tendonitis symptoms and treatments similar to bursitis?

Both cause pain and inflammation and have similar treatments.

What is arthritis?

More than 100 inflammatory or degenerative diseases that damage joints. It is the most widespread crippling disease in the U.S.

What are the symptoms of arthritis?

Joint pain, stiffness, and swelling

How are acute and chronic arthritis different?

• Acute: caused by bacteria and treated with antibiotics

• Chronic: includes osteoarthritis, rheumatoid arthritis, and gouty arthritis

What is osteoarthritis?

The most common chronic arthritis, often called “wear-and-tear” arthritis.

Who is more affected by osteoarthritis?

Women are more than men

What percentage of Americans have osteoarthritis?

85%

Who is more likely to develop OA, and what is it related to?

Older adults; it is probably related to the normal aging process.

What causes cartilage breakdown in osteoarthritis?

Years of abrasion and compression increase production of metalloproteinase enzymes, which break down cartilage.