Introduction to Articulations
- Articulation - site where two or more bones meet
- Functions of joints
- Give the skeleton mobility
- Hold the skeleton together
- Structural classification focuses on the material binding bones together and whether or not a joint cavity is present
- The three structural classifications are:
- Fiborus
- Cartilaginous
- Synovial
- Functional classification is based on the amount of movement allowed by the joint
- The three functional classes of joints are:
- Synarthroses - immovable
- Amphiarthroses - slightly movable
- Diarthroses - freely movable
Fibrous Joints
- Sutures occur between bones of skull and use very short connective tissue fibers to hold the bones together.
- Synostoses - fused in adult
- In syndesmoses, the bones are connected by a ligament, which is a cord or band of fibrous tissue.
- A gomphosis is a peg-in-socket fibrous joint.
- Synchondroses involve a bar or plate of hyaline cartilage uniting the bones, such as the epiphyseal plate.
- In symphyses, such as the pubic symphysis, the articular surfaces are covered with articular cartilage that is then fused to an intervening pad or plate of fibrocartilage
- 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 all have the following
- 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
- Stability is determined by:
- Articular surfaces - shape determines what movements are possible
- Ligaments - unite bones and prevent excessive or undesirable motion
- Labrums and menisci that deepen the articular surface
- Muscle tone is accomplished by:
- Muscle tendons across joints acting as stabilizing factors
- Tendons that are kept tight at all times by muscle tone
- Synovial Joints: Range of Motion
- Nonaxial - slipping movements only
- Uniaxial - movement in one plane
- Biaxial - movement in two planes
- Multiaxial - movement around all three planes
- Types of Movements
- 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 Movements
- Flexion - bending movement that decreases the angle of the joint
- Extension - reverse of flexion; joint angle is increased
- Dorsiflexion and plantar flexion - up and down movement of the foot
- Abduction - movement away from the midline
- Adduction - movement toward the midline
- Circumduction - movement describes a cone in space
- Rotation Movements
- 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
Synovial Joint Descriptions
- Knee Joint
- Largest and most complex joint of the body
- Allows flexion, extension, and some rotation
- Three joints in one surrounded by a single joint cavity
- Femoropatellar
- Lateral and medial tibiofemoral joints
- Ligaments and tendons
- Quadriceps tendon
- Lateral and medial patellar retinacula
- Fibular and tibial collateral ligaments
- Patellar ligament
- Other supporting structures
- Shoulder (Glenohumeral)
- Ball-and-socket joint - stability is sacrificed for greater freedom of movement
- Head of humerus articulates with the glenoid fossa of the scapula
- 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 that encircles the shoulder joint and blends with articular capsule
- Hip (Coxal) Joint
- Ball-and-socket joint
- Head of the femur articulates with the acetabulum
- Good range of motion, but limited by the deep socket and strong ligaments
- Stablizing structures
- Acetabular labrum
- Iliofemoral ligament
- Pubofemoral ligament
- Ischiofemoral ligament
- Ligamentum teres
Injuries
- 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
- 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
- Course of the Disease
- 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
- Treatments
- OA is slow and irreversible
- Treatments include:
- Mild pain relievers, along with moderate activity
- Magnetic therapy
- Glucosamine sulfate decreases pain and inflammation
- Rheumatoid Arthritis (RA)
- Chronic, inflammatory, autoimmune disease of unknown cause
- 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
- Course
- RA begins with synovitis of the affected joint
- Inflammatory chemicals are inappropriately released
- 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
- Treatment
- Conservative therapy - aspirin, long-term use of antibiotics, and physical therapy
- Progressive treatment - anti-inflammatory drugs or immunosuppressants
- The drug Enbrel, a biological response modifier, neutralizes the harmful properties of inflammatory chemicals
- 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
Other Conditions
Helpful Activities to do after you finish reading this chapter
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