🦴 Osteoarthritis (OA)

  • definition Degenerative joint disease with articular cartilage loss; minimal/no inflammation.
  • epidemiology Most common arthritis; affects ≥1 joint in 80% of people >70 yr.
  • risk factors
    • Obesity, prior joint injury, diabetes, hemochromatosis, ochronosis.
    • Age-related biomechanical wear + chondrocyte injury.
  • joint distribution Weight-bearing (knees, hips, spine); often asymmetrical.
  • clinical features
    • Insidious onset: deep aching pain worsened by motion, morning stiffness <30 min.
    • Crepitus, decreased ROM, joint effusion, osteophyte nerve compression.
  • imaging Joint space narrowing, subchondral sclerosis, osteophytes (lipping), bone cysts.
  • pathology
    • Cartilage fibrillation → eburnation (polished bone).
    • Subchondral cysts, loose bodies (“joint mice”), osteophytes (bone spurs).
    • Heberden nodes: DIP osteophytes; Bouchard nodes: PIP osteophytes.
FeatureOARA
Pathophysiology“wear & tear”systemic autoimmune
Rheumatoid factor−+ (80%)
Synoviumdegenerativeproliferative pannus
Typical jointsknees, hips, hands (DIP in women)hands (PIP), feet, wrists
Symmetryasymmetricalsymmetrical
Heberden nodes (DIP) and Bouchard nodes (PIP) are pathognomonic osteophytes of OA.

🔄 Rheumatoid Arthritis (RA)

  • definition Chronic systemic inflammatory disease; progressive arthritis, RF+, extra-articular features.
  • epidemiology F:M 4:1; peak 20–50 yr; HLA-DR4/DR1 association.
  • etiology Autoimmune reaction (infectious trigger in genetically susceptible).
  • joint features
    • Symmetrical: hands (PIP, MCP), wrists, knees, ankles.
    • Morning stiffness >1 hr, improves with activity.
    • Fusiform swelling, warmth, redness.
  • imaging Juxta-articular osteoporosis, erosions, joint effusion.
  • pathology
    • Diffuse proliferative synovitis → pannus (granulation tissue over cartilage).
    • Fibrous/bony ankylosis, joint deformities.
    • Deformities: radial wrist deviation, ulnar finger deviation, swan-neck (PIP hyperext, DIP flex), boutonnière (PIP flex, DIP ext).
  • laboratory Elevated ESR, hypergammaglobulinemia. RF (IgM anti-IgG) in 80% – titer correlates with severity.
  • extra-articular
    • Necrotizing vasculitis, rheumatoid nodules (extensor surfaces, heart, lung, pleura).
    • Sjögren syndrome (15%), Felty syndrome (RA + splenomegaly + neutropenia), Caplan syndrome (RA + pneumoconiosis).
    • Secondary amyloidosis.
Baker cyst (popliteal synovial cyst) may occur in RA.

⚡ Seronegative Spondyloarthropathies

  • core features RF−, sacroiliac involvement, HLA‑B27 association.
  • ankylosing spondylitis
    • Young men, 90% HLA‑B27; sacroiliitis + spine.
    • Bamboo spine (vertebral fusion).
  • reactive arthritis
    • Triad: conjunctivitis + urethritis + arthritis (ankles/knees).
    • Male > female, age 20–30; after venereal or dysenteric infection.
  • enteropathic arthritis 10–20% of IBD patients.
  • psoriatic arthritis 5–10% of psoriasis; mild, slowly progressive, similar to RA.
Complete spinal fusion (bamboo spine) may occur in ankylosing spondylitis.

💎 Crystal Deposition Arthropathies

  • gout Hyperuricemia → monosodium urate crystals in joints.
    • Primary (90%): idiopathic, older men.
    • Secondary (10%): cell breakdown (chemo), renal underexcretion, Lesch‑Nyhan (HPRT deficiency, X‑linked).
    • Podagra (great toe), ankle, heel, wrist.
    • Synovial fluid: needle‑shaped, negatively birefringent crystals; neutrophils.
    • Tophi: crystal deposits with inflammation → joint destruction, renal calculi, renal failure.
    • Treatment: NSAIDs, colchicine, probenecid, allopurinol.
  • pseudogout (CPPD) Calcium pyrophosphate crystals.
    • Age >50, knee most common.
    • Fluid: rhomboid, weakly positive birefringent crystals.
    • Associated with metabolic diseases (diabetes, hypothyroidism, hemochromatosis, hyperparathyroidism, hypophosphatemia, hypomagnesemia).
Purine metabolism → Uric acid → Monosodium urate → Gout
Lesch‑Nyhan: X‑linked, HPRT deficiency, hyperuricemia, self‑mutilation, cognitive impairment.

🦠 Infectious Arthritis

  • suppurative arthritis Seeding via bacteremia, contiguous spread, or direct inoculation.
    • Organisms: gonococci, Staph, Strep, H. influenzae, gram‑negative bacilli.
    • Monoarticular large joints (knee, hip, shoulder).
    • Cloudy fluid, high neutrophils; Gram stain/culture positive 50‑70%.
    • Urgent antibiotics to prevent joint destruction.
  • lyme arthritis Borrelia burgdorferi (tick‑borne).
    • Erythema chronicum migrans, migratory arthritis (knees, shoulders, elbows).
    • CNS, cardiac involvement; serology may be negative early.
Lyme disease: targetoid rash + migratory arthritis; treat with doxycycline / amoxicillin.

🧠 Neuropathic Arthropathy (Charcot Joint)

  • definition Joint destruction due to loss of pain sensation and proprioception.
  • mechanism Unnoticed trauma → progressive damage, debris, deformity, dislocation.
  • associated conditions
    • Diabetes mellitus (most common) → tarsometatarsal (midfoot).
    • Syringomyelia → shoulder, elbow, wrist.
    • Tabes dorsalis (neurosyphilis) → hip, knee, ankle.
Charcot joint is a complication of diabetes, syringomyelia, or tabes dorsalis.
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