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