Musculoskeletal Conditions and Disorders
Domain 2: Musculoskeletal Conditions and Disorders
This domain tests pattern recognition: distinguishing inflammatory from mechanical disease, applying classification criteria, and knowing when to refer.
Core rules
- Osteoarthritis: activity-related pain, brief morning stiffness (<30 minutes), bony enlargement; radiographs show joint-space narrowing, osteophytes, subchondral sclerosis, and cysts. Treatment is exercise, weight management, topical/oral NSAIDs, and arthroplasty in end-stage disease.
- Rheumatoid arthritis: symmetric small-joint polyarthritis, prolonged morning stiffness (>1 hour), MCP/PIP swelling; check RF and anti-CCP, ESR/CRP. Early DMARD referral prevents erosions.
- Gout: acute monoarthritis, often first MTP; synovial fluid shows negatively birefringent needle-shaped crystals. Do not initiate or stop urate-lowering therapy during an acute flare without a plan; treat with NSAIDs, colchicine, or steroids.
- Osteoporosis: DXA T-score <= -2.5; fragility fracture; use FRAX. Atypical femoral fracture and osteonecrosis of the jaw are rare long-term bisphosphonate concerns.
- Red flags: fever, weight loss, night pain, neuro deficit, and progressive deformity warrant urgent workup.
Worked example
A 52-year-old woman has 8 weeks of bilateral hand pain and 90 minutes of morning stiffness with MCP tenderness. This is inflammatory, not osteoarthritis. Order RF, anti-CCP, ESR/CRP, and radiographs, then refer promptly for DMARD therapy.
Traps
Using a positive RF to diagnose RA in an older adult with osteoarthritis; aspirating a joint without sending crystals and culture; and missing septic arthritis because the patient has known gout.