Joint Types and Arthritis Overview

Joint Types

• Joints connect bones, providing structural strength or motion
• Solid joints are tightly connected (e.g., cranial sutures).
• Synovial joints have a space for motion.
  • Articular surfaces are made of hyaline cartilage (type II collagen).
  • The surfaces are surrounded by a joint capsule

Degenerative Joint Disease (Osteoarthritis)

• Progressive degeneration of articular cartilage
• Often due to wear and tear
• Major risk factor is age (often after 60)
• Other risk factors: obesity, trauma
• Affects a limited number of joints (e.g., hips, lower lumbar spine, knees, DIP and PIP joints)
• Morning stiffness, worsening throughout the day
• Pathologic features include:
  • Cartilage disruption and fragments within the joint space (“joint mice”)
  • Eburnation of the subchondral bone
  • Osteophyte formation (bony outgrowths), commonly at DIP and PIP joints (Heberden and Bouchard nodes)

Rheumatoid Arthritis

• Chronic, systemic autoimmune disease
• Classically affects women of childbearing age
• Associated with HLA-DR4
• Characterized by synovitis (inflammation of the joint lining), pannus (granulation tissue) formation
• Leads to cartilage destruction and joint fusion (ankylosis)
• Clinical features:
  • Morning stiffness, improving with activity
  • Symmetric involvement of joints (especially PIP joints) in fingers, wrists, elbows, ankles, and knees; DIP usually spared
  • Joint space narrowing, cartilage loss, and osteopenia are common on X-rays
  • Fever, malaise, weight loss, myalgias
  • Rheumatoid nodules, vasculitis (inflammation in blood vessels), Baker cyst, and lung involvement

Seronegative Spondyloarthropathies

• Group of joint disorders
• Lack of rheumatoid factor
• Axial skeleton involvement (spine and sacroiliac joints) and HLA-B27 association
• Typical diseases: ankylosing spondylitis, reactive arthritis, psoriatic arthritis
  • Ankylosing spondylitis: low back pain, vertebral fusion ("bamboo spine"), uveitis and aortitis; affects young adults mostly males
  • Reactive arthritis: triad of arthritis, urethritis, and conjunctivitis, follows GI or Chlamydia trachomatis infection; affects young adults, mostly males
  • Psoriatic arthritis: affects axial and peripheral joints (DIP joints), often occurs with psoriasis

Infectious Arthritis

• Arthritis due to an infectious agent (typically bacterial)
• Common causes: Neisseria gonorrhoeae (young adults), Staphylococcus aureus (older individuals)
• Symptoms include warm joint, limited range of motion, fever, elevated WBC count, elevated ESR
• Commonly affects one joint; usually the knee

Gout

• Deposition of monosodium urate crystals in joints, typically in the great toe (podagra)
• Due to hyperuricemia (high uric acid levels), either from overproduction or decreased excretion
• Primary gout: most common form, cause unknown
• Secondary gout: associated with conditions that cause increased cell turnover (e.g., leukemia)
• Acute gout: sudden pain and inflammation
• Chronic gout: tophi (urate crystals) formation in soft tissues, joint damage, and chronic renal disease

Pseudogout

• Clinically similar to gout, but caused by calcium pyrophosphate dihydrate (CPPD) crystal deposition in joints
• Synovial fluid shows rhomboid-shaped crystals with weakly positive birefringence