Joints and Rheumatologic Diseases

Osteoarthritis - Cartilage Crack‑Up

• Most common joint disorder; degenerative "wear & tear" arthritis leading to progressive loss of articular cartilage.
• Pathogenesis: Imbalance between cartilage degradation (↑MMPs, aggrecanases) & synthesis by chondrocytes.
  • Early: Chondrocyte proliferation & ↑ matrix production.
  • Late: Chondrocyte apoptosis, cartilage fibrillation, eburnation (polished, ivory-like bone).
• Risk Factors: Age (>50 yrs), obesity (esp. knee OA), trauma, female sex, genetics, joint malalignment.
• Clinical Features:
  • Insidious onset joint pain: worse with activity, relieved by rest.
  • Morning stiffness < 30 minutes; gelling phenomenon.
  • Crepitus, ↓ range of motion (ROM), joint instability.
  • Bony enlargements: Heberden's nodes (DIP joints), Bouchard's nodes (PIP joints).
  • No systemic symptoms.
• Commonly Affected Joints: Weight-bearing (knees, hips), hands (DIP, PIP, 1st CMC), spine (cervical, lumbar). Typically spares MCPs, wrists, elbows, ankles.
• Radiographic Findings: 📌 Mnemonic: LOSS
  • Loss of joint space (asymmetric)
  • Osteophytes (bone spurs)
  • Subchondral sclerosis
  • Subchondral cysts
• Synovial Fluid: Non-inflammatory (WBC < 2000/µL, predominantly mononuclear cells, normal viscosity).

⭐ Eburnation, where subchondral bone becomes smooth and polished like ivory due to complete cartilage loss, is a hallmark of advanced osteoarthritis visible on gross pathology and sometimes inferred from X-rays as severe sclerosis and joint space obliteration.

Rheumatoid Arthritis - Synovial Showdown

Autoimmune, chronic systemic inflammatory disease primarily targeting synovium, often leading to progressive, symmetrical joint destruction and deformity.

• Clinical Presentation:
  • Symmetrical polyarthritis: Affects small joints (MCP, PIP - spares DIP), wrists, MTPs.
  • Morning stiffness > 1 hour, improves with activity.
  • Deformities: Swan neck, Boutonniere, ulnar deviation, Z-thumb. (📌 SUBZ: Swan neck, Ulnar deviation, Boutonniere, Z-thumb)
  • Systemic: Fatigue, low-grade fever, weight loss, rheumatoid nodules (common on extensor surfaces, e.g., olecranon).
• Pathogenesis:
  • Synovial inflammation (synovitis) with T-cell, B-cell, macrophage infiltration.
  • Pannus formation: Proliferative, invasive granulation tissue eroding cartilage, bone, ligaments.
• Key Diagnostics:
  • Rheumatoid Factor (RF): Positive in ~70-80%; not specific.
  • Anti-Cyclic Citrullinated Peptide (Anti-CCP) antibodies: Highly specific (>95%).
  • ↑ESR, ↑CRP (inflammatory markers).
• Radiology:
  • Juxta-articular osteoporosis, marginal erosions, joint space narrowing.

⭐ Anti-CCP antibodies are more specific for RA diagnosis and often associated with more aggressive disease than Rheumatoid Factor.

Spondylo & Crystals - Axial Aches, Shiny Shards

• Seronegative Spondyloarthropathies (SpA): Axial inflammation, enthesitis, dactylitis; HLA-B27+; RF-.
  • Ankylosing Spondylitis (AS): Young males; sacroiliitis; morning stiffness >1hr; bamboo spine; uveitis. Improves with exercise.
  • Psoriatic Arthritis (PsA): Psoriasis; asymmetric oligoarthritis; dactylitis ("sausage digits"); "pencil-in-cup" X-ray; nail pitting.
  • Reactive Arthritis (ReA): 📌 "Can't see, can't pee, can't climb a tree"; post-GI/GU infection; asymmetric oligoarthritis.
  • Enteropathic Arthritis: Assoc. with IBD (Crohn's, UC); peripheral arthritis/sacroiliitis.
• Crystal Arthropathies: Acute, recurrent monoarthritis.
  • Gout: Monosodium Urate (MSU) crystals.
    • Needle-shaped, negatively birefringent (yellow when parallel to compensator).
    • 1st MTP (podagra), knee. Tophi.
    • Risk: ↑uric acid (diet, alcohol, diuretics).
  • Pseudogout (CPPD): Calcium Pyrophosphate Dihydrate crystals.
    • Rhomboid/rod-shaped, positively birefringent (blue when parallel to compensator).
    • Knee, wrist. X-ray: chondrocalcinosis.
    • Assoc: Hyperparathyroidism, hemochromatosis.

⭐ HLA-B27 is present in approximately 90% of patients with Ankylosing Spondylitis.

High‑Yield Points - ⚡ Biggest Takeaways

• Osteoarthritis: Degenerative; eburnation, osteophytes, Heberden's/Bouchard's nodes, asymmetrical joint involvement.
• Rheumatoid Arthritis: Autoimmune; symmetrical polyarthritis, pannus, anti-CCP (specific), HLA-DR4.
• Gout: Monosodium urate crystals (needle-shaped, negatively birefringent), podagra, tophi, hyperuricemia.
• Pseudogout (CPPD): Calcium pyrophosphate dihydrate crystals (rhomboid, positively birefringent), chondrocalcinosis.
• Ankylosing Spondylitis: HLA-B27, sacroiliitis, bamboo spine, uveitis, aortitis.
• Septic Arthritis: Usually bacterial (S. aureus), acute painful monoarthritis, synovial fluid >50,000 WBCs.
• Seronegative Spondyloarthropathies: Include AS, psoriatic arthritis, reactive arthritis; HLA-B27 association, axial skeleton involvement, enthesitis.