Musculoskeletal
What you must know
Separate mechanical from inflammatory disease. Osteoarthritis is activity-related with brief morning stiffness (under 30 minutes), bony enlargement, and minimal swelling; rheumatoid arthritis is symmetric, small-joint, with prolonged morning stiffness (over an hour) and systemic features. Gout is monoarticular, abrupt, exquisitely tender, often at the first metatarsophalangeal joint; serum uric acid can be normal during an acute flare, so it does not exclude the diagnosis. Septic arthritis is the cannot-miss diagnosis: fever, an immovable joint, and risk factors such as prosthetic material, immunosuppression, or recent instrumentation.
Back pain: most is mechanical and self-limited. Red flags - age over 50 with new pain, cancer history, fever, intravenous drug use, night pain, progressive neurologic deficit, saddle anesthesia, bowel or bladder dysfunction - mandate imaging and, for cauda equina features, urgent decompression. Osteoporosis: screen with DXA; T-score of -2.5 or lower defines osteoporosis, and a fragility fracture warrants treatment regardless of score. Polymyalgia rheumatica produces proximal girdle pain and stiffness with a high ESR/CRP and dramatic response to low-dose prednisone; add temporal arteritis symptoms (headache, jaw claudication, vision loss) to the differential and treat urgently with steroids. Also know compartment syndrome, carpal tunnel syndrome, and tendon disorders.
Traps
- Giving antibiotics before aspirating a hot joint - arthrocentesis first, then treat.
- Dismissing saddle anesthesia as musculoskeletal pain.
- Using high-dose steroids for polymyalgia rheumatica.
- Assuming a normal radiograph excludes fracture.
Rule of thumb
A single hot swollen joint with fever is septic until proven otherwise: aspirate for cell count, crystals, and culture before the first antibiotic dose.