Joints: Anatomy and Physiology

How Joints Are Classified

  • According to movability
  • According to the material binding them together

Classification of Joints

  • Fixed joints (fibrous joints or synarthroses):
    • Bound by fibers.
    • Collagen fibers from one bone penetrate the adjacent bone, anchoring it in place.
  • Semi-movable joints (cartilaginous joints or amphiarthroses):
    • Two bones joined by cartilage.
    • Slightly moveable.
  • Freely movable joints (synovial joints or diarthroses):
    • Contain a fluid-filled joint capsule.
    • Most numerous and versatile joints.

Joints: Structure and Types of Motion

Synovial Joints Structure

  • Bone
  • Articular cartilage
  • Synovial membrane
  • Articular capsule
  • Hyaluronic acid (OHOH)

Synovial Joints Components

  • Bone
  • Periosteum
  • Joint capsule
  • Synovial membrane
  • Joint cavity
  • Articular cartilage
  • Ligament

Types of Synovial Joints

  • Pivot joint:
    • A projection from one bone articulates with a ring-shaped socket of another bone, allowing rotation or pivot.
    • Examples:
      • Dens of the second cervical vertebrae turns within a ring-shaped portion of the first vertebrae, allowing head rotation.
      • Radioulnar joint (head of the radius rotates within a groove of the ulna).
  • Hinge joint:
    • Allows only back-and-forth movements (flexion and extension).
    • The convex surface of one bone (e.g., humerus) fits into a concave depression on another bone (e.g., ulna).
    • Examples: elbow, knee, and interphalangeal joints of the fingers and toes.
  • Gliding joint:
    • Two relatively flat bone surfaces slide over each other; surrounding ligaments limit movement.
    • Least mobile of all synovial joints.
    • Examples: tarsal bones of the ankle, carpal bones of the wrist, and articular processes of the vertebrae.
  • Ball-and-socket joint:
    • The ball-shaped head of one bone fits into a cuplike socket of another bone.
    • Offers the widest range of motion of all joints.
    • Examples: shoulder and hip joints.
  • Saddle joint:
    • Surfaces of both bones are shaped like a saddle: concave in one direction and convex in the other.
    • Bones move back and forth and from side to side (side-to-side motion is limited).
    • Found only in the thumbs, allowing the thumb to touch the tips of the fingers.
  • Condyloid joint:
    • An oval convex surface on one bone fits into a similarly shaped depression on another.
    • Allows flexion and extension, as well as side-to-side movement.
    • Examples: distal end of the radius with the carpal bones of the wrist and the joints at the base of the fingers.

Movements of Synovial Joints

  • Depend on the shape of the joint
  • Depend on the involvement of nearby muscles, tendons, and ligaments
  • Flexion
  • Extension
  • Hyperextension
  • Dorsiflexion
  • Plantar flexion
  • Abduction
  • Adduction
  • Circumduction
  • Internal rotation
  • External rotation
  • Supination
  • Pronation
  • Inversion
  • Eversion
  • Protraction
  • Retraction

Anatomy of Specific Joints

Shoulder

  • Consists of: Humerus, Scapula, Clavicle, and Ligaments
  • Bursae
Shoulder Dislocation
  • Most likely joint to suffer a dislocation.
  • Usually dislocates inferiorly due to downward forces; when an outstretched arm receives a blow from above.
  • Treatment:
    • Immobilize extremity.
    • Apply ice to control swelling.
    • Pain control.
    • MD may need to manipulate back into place.
    • Repeated dislocations may require surgical repair.

Elbow

  • Consists of: Humerus, Joint capsule, Tendon (cut), Radius, Bursa, Ligaments, and Ulna.

Knee

  • Consists of: Femur, Condyles, Fibular collateral ligament, Lateral meniscus, Tibial collateral ligament, Posterior cruciate ligament, Anterior cruciate ligament, Medial meniscus, Fibula, and Tibia.
Knee Injury
  • Knee has few surrounding muscles compared to the hip.
  • Common sports injuries involve the meniscus and anterior cruciate ligament.
  • Treatment: Arthroscopic surgery

Hip

  • Consists of: Ilium, Ligaments, Greater trochanter, Lesser trochanter, Femur, Pubis

Joint Replacement (Arthroplasty)

  • Surgical replacement of a joint with an artificial joint or prosthesis.

Arthritis

  • Very common; more than 100 different types.
  • People of all ages, sexes, and races can have arthritis; it is the leading cause of disability in America.
  • More than 50 million adults and 300,000 children have some type of arthritis.
  • Most common among women and occurs more frequently as people get older.
  • Common symptoms include swelling, pain, stiffness, and decreased range of motion.
  • Symptoms may come and go and can be mild, moderate, or severe.
  • Severe arthritis can result in chronic pain, inability to do daily activities, and difficulty walking or climbing stairs.
  • Can cause permanent joint changes.

Rheumatoid Arthritis

  • Autoimmune disease.
  • The body attacks the synovial membranes, leading to degeneration of the articular cartilage and thickening of the synovial membrane.
  • Synovial membrane becomes calcified.

Review Questions

  1. Which joint is most likely to be dislocated? A. Shoulder
  2. Most of the joints in the body are: B. synovial joints.
  3. Which joint offers the widest range of motion? D. Ball-and-socket joint
  4. Which joint allows flexion and extension as well as side-to-side movement? § Condyloid joint
  5. Which features of synovial joints are credited with providing friction-free movement? § Synovial membrane and articular cartilage
  6. The rotator cuff is found in the § shoulder.
  7. Osteoarthritis occurs when: § articular cartilage softens and degenerates.
  8. Which is true about rheumatoid arthritis? • It is an autoimmune disease.
  9. Movement that involves bending a joint to decrease the angle of the joint: § Flexion
  10. Foot movement that turns the sole medially, towards the other foot: § Inversion