10/08/2019
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 p***c 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
