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 8

Joints

 

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,
and 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

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

Cartilage Injuries

•      The snap and pop of overstressed cartilage

•      Common aerobics injury

•      Repaired with arthroscopic surgery

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

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