Ch 8

Joints (Articulations)

Weakest parts of the skeleton  Articulation – site where two or more

bones meet Functions

    Give the skeleton mobility    Hold the skeleton together

Classification of Joints: Structural Structural classification focuses on the

material binding bones together and whether or not a joint cavity is present

The three structural classifications are:    Fibrous    Cartilaginous     Synovial

Classification of Joints: Functional Functional classification is based on the

amount of movement allowed by the joint

The three functional class of joints are:    Synarthroses – immovable     Amphiarthroses – slightly movable     Diarthroses – freely movable

Fibrous Structural Joints The bones are jointed by fibrous tissues There is no joint cavity Most are immovable There are three types:

Sutures Syndesmoses Gomphoses

Fibrous Structural Joints: Sutures Occur between the bones of the skull Comprised of interlocking junctions

completely filled with CT fibers Bind bones tightly together, but allow for

growth during youth In middle age, skull bones fuse and are

called synostoses

Fibrous Structural Joints: Syndesmoses Bones are connected by a fibrous tissue

ligament Movement varies from immovable to

slightly variable Examples include the connection

between the tibia and fibula, and the radius and ulna

Fibrous Structural Joints: Gomphoses The peg-in-socket fibrous joint between

a tooth and its alveolar socket The fibrous connection is the periodontal

ligament

Cartilaginous Joints

Articulating bones are united by cartilage

Lack a joint cavity Two types – synchondroses and

symphyses

Cartilaginous Joints: Synchondroses A bar or plate of hyaline cartilage unites

the bones All synchondroses are synarthrotic Examples include:

    Epiphyseal plates of children    Joint between the costal cartilage of the

first rib and the sternum

Cartilaginous Joints: Symphyses Hyaline cartilage covers the articulating

surface of the bone and is fused to an intervening pad of fibrocartilage

Amphiarthrotic joints designed for strength and flexibility

Examples include intervertebral joints and the pubic symphysis of the pelvis

Synovial Joints

Those joints in which the articulating bones are separated by a fluid-containing joint cavity

All are freely movable diarthroses Examples – all limb joints, and most

joints of the body

Synovial Joints: General Structure Synovial joints all have the following:

    Articular cartilage    Joint (synovial) cavity    Articular capsule    Synovial fluid    Reinforcing ligaments

Synovial Joints: Friction-Reducing Structures Bursae – flattened, fibrous sacs lined

with synovial membranes and containing synovial fluid

Common where ligaments, muscles, skin, tendons, or bones rub together

Tendon sheath – elongated bursa that wraps completely around a tendon

      Synovial Joints: Stability

Stability is determined by:    Articular surfaces – shape determines

what movements are possible    Ligaments – unite bones and prevent

excessive or undesirable motion Muscle tone is accomplished by:

    Muscle tendons across joints are the most important stabilizing factor

    Tendons are kept tight at all times by muscle tone

Synovial Joints: Movement Muscle attachment across a joint Origin – attachment to the immovable

bone Insertion – attachment to the movable

bone Described as movement along

transverse, frontal, or sagittal planes

Synovial Joints: Range of Motion

Nonaxial – slipping movements only Uniaxial – movement in one plane Biaxial – movement in two planes Multiaxial – movement in or around all

three planes

Gliding Movements

One flat bone surface glides or slips over another similar surface

 Examples – intercarpal and intertarsal joints, and between the flat articular processes of the vertebrae

Angular Movement

Flexion Extension Dorsiflexion and plantar flexion of the

foot Abduction Adduction Circumduction

Rotation

The turning of a bone around its own long axis

Examples:    Between first two vertebrae    Hip and shoulder joints

Special Movements

Supination and pronation Inversion and eversion Protraction and retraction Elevation and depression Opposition

Types of Synovial Joints Plane joints

    Articular surfaces are essentially flat    Allow only slipping or gliding movements    Only examples of nonaxial joints

Hinge joints    Cylindrical projections of one bone fits into a

trough-shaped surface on another    Motion is along a single plane    Uniaxial joints permit flexion and extension

only    Examples: elbow and interphalangeal joints

Pivot Joints

Rounded end of one bone protrudes into a “sleeve,” or ring, composed of bone (and possibly ligaments) of another

Only uniaxial movement allowed Examples: joint between the axis and

the dens, and the proximal radioulnar joint

Pivot Joints

Condyloid, or Ellipsoidal, Joints

Oval articular surface of one bone fits into a complementary depression in another

Both articular surfaces are oval Biaxial joints permit all angular motions Examples: radiocarpal (wrist) joints, and

metacarpophalangeal (knuckle) joints

Saddle Joints

Similar to condyloid joints but with greater movement

Each articular surface has both a concave and a convex surface

Example: carpometacarpal joint of the thumb

Ball-and-Socket Joints

A spherical or hemispherical head of one bone articulates with a cuplike socket of another

Multiaxial joints permit the most freely moving synovial joints

Examples: shoulder and hip joints

Synovial Joints: Shoulder (Glenohumeral)

Ball-and-socket joint in which stability is sacrificed to obtain greater freedom of movement

Head of humerus articulates with the glenoid fossa of the scapula

Synovial Joints: Shoulder Stability

Weak stability is maintained by:    Thin, loose joint capsule    Four ligaments – coracohumeral, and

three glenohumeral    Tendon of the long head of biceps, which

travels through the intertubercular groove and secures the humerus to the glenoid cavity

    Rotator cuff (four tendons) encircles the shoulder joint and blends with the articular capsule

Synovial Joints: Knee

Largest and most complex joint of the body

Allow flexion, extension, and some rotation

Three joints in one surrounded by a single joint cavity    Femoropatellar    Lateral and medial tibiofemoral joints

Synovial Joints: Major Ligaments and Tendons – Anterior View

Tendon of the quadriceps femoris muscle

Lateral and medial patellar retinacula Fibular collateral ligament Tibial collateral ligament Patellar ligament

Synovial Joints: Knee – Other Supporting Structures

Anterior cruciate ligament Posterior cruciate ligament Medial meniscus (semilunar cartilage) Lateral meniscus

Synovial Joints: Knee – Posterior Superficial View

Adductor magnus tendon Articular capsule Oblique popliteal ligament Arcuate popliteal ligament Semimembranosus tendon

Sprains

The ligaments reinforcing a joint are stretched or torn

Partially torn ligaments slowly repair themselves

Completely torn ligaments require prompt surgical repair

Sprain

Cartilage Injuries

The snap and pop of overstressed cartilage

Common aerobics injury Repaired with arthroscopic surgery

Cartilage Injuries

Dislocations

Occur when bones are forced out of alignment

Usually accompanied by sprains, inflammation, and joint immobilization

Caused by serious falls and are common sports injuries

Subluxation – partial dislocation of a joint

Dislocation

Dislocation

Inflammatory and Degenerative Conditions Bursitis

    An inflammation of a bursa, usually caused by a blow or friction

    Symptoms are pain and swelling    Treated with anti-inflammatory drugs;

excessive fluid may be aspirated       Tendonitis

    Inflammation of tendon sheaths typically caused by overuse

    Symptoms and treatment are similar to bursitis

Arthritis More than 100 different types of

inflammatory or degenerative diseases that damage the joints

Most widespread crippling disease in the U.S.

Symptoms – pain, stiffness, and swelling of a joint

Acute forms are caused by bacteria and are treated with antibiotics

Chronic forms include osteoarthritis, rheumatoid arthritis, and gouty arthritis

Osteoarthritis (OA)

Most common chronic arthritis; often called “wear-and-tear” arthritis

Affects women more than men 85% of all Americans develop OA More prevalent in the aged, and is

probably related to the normal aging process

Osteoarthritis: Course OA reflects the years of abrasion and

compression causing increased production of metalloproteinase enzymes that break down cartilage

As one ages, cartilage is destroyed more quickly than it is replaced

The exposed bone ends thicken, enlarge, form bone spurs, and restrict movement

Joints most affected are the cervical and lumbar spine, fingers, knuckles, knees, and hips

Osteoarthritis: Treatments OA is slow and irreversible Treatments include:

    Mild pain relievers, along with moderate activity

    Magnetic therapy     Glucosamine sulfate decreases pain and

inflammation    SAM-e (s-adenosylmethionine) builds up

cartilage matrix and regenerates tissue

Rheumatoid Arthritis (RA) Chronic, inflammatory, autoimmune

disease of unknown cause, with an insidious onset

Usually arises between the ages of 40 to 50, but may occur at any age

Signs and symptoms include joint tenderness, anemia, osteoporosis, muscle atrophy, and cardiovascular problems

The course of RA is marked with exacerbations and remissions

Rheumatoid Arthritis: Course RA begins with synovitis of the affected

joint Inflammatory blood cells migrate to the

joint, causing swelling Inflamed synovial membrane thickens

into a pannus Pannus erodes cartilage, scar tissue

forms, articulating bone ends connect The end result, ankylosis, produces

bent, deformed fingers

Rheumatoid Arthritis: Treatment Conservative therapy – aspirin, long-

term use of antibiotics, and physical therapy

Progressive treatment – anti-inflammatory drugs or immunosuppressants

The drug Embrel, a biological response modifier, removes cells that promote inflammation

Gouty Arthritis Deposition of uric acid crystals in joints

and soft tissues, followed by an inflammation response

Typically, gouty arthritis affects the joint at the base of the great toe

In untreated gouty arthritis, the bone ends fuse and immobilize the joint

Treatment – colchicine, nonsteroidal anti-inflammatory drugs, and glucocorticoids

Developmental Aspects of Joints By embryonic week 8, synovial joints resemble adult joints Few problems occur until late middle age Advancing years take their toll on joints including: Ligaments and tendons shorten and weaken Intervertebral discs become more likely to herniate OA is inevitable, and all people of 70 have some degree of

OA Prudent exercise (especially swimming) that coaxes joints

through their full range of motion is key to postponing joint problems