Musculoskeletal System
Core concepts
Approach joint complaints by pattern: monoarticular versus polyarticular, acute versus chronic, inflammatory versus mechanical. Osteoarthritis affects weight-bearing joints with brief morning stiffness and bony nodes; rheumatoid arthritis is symmetric, involves the metacarpophalangeal and proximal interphalangeal joints, causes prolonged morning stiffness, and is supported by anti-cyclic citrullinated peptide antibodies.
A hot swollen joint is septic until proven otherwise. Aspirate it. Gout shows needle-shaped negatively birefringent crystals, pseudogout shows rhomboid positively birefringent crystals, and septic arthritis shows a markedly elevated white count with organisms on Gram stain. Do not let a uric acid level or a fever pattern substitute for the tap.
Fracture and injury assessment relies on mechanism, neurovascular status, and targeted imaging rules such as the Ottawa ankle criteria. Compartment syndrome is the emergency to memorize: pain out of proportion, pain with passive stretch, tense compartment, paresthesias, and later pallor, paralysis, and absent pulses. Pulselessness is a late and unreliable finding.
Back pain requires red-flag screening: saddle anesthesia, bowel or bladder dysfunction, bilateral leg weakness, fever, cancer history, trauma, and age over 50 with new pain. Cauda equina syndrome needs emergent MRI and decompression.
Traps
- Diagnosing gout in a febrile patient without aspirating the joint.
- Waiting for pulselessness before calling surgery for compartment syndrome.
- Missing an open fracture or a neurovascular deficit on the first examination.
Rule of thumb
Pain with passive stretch of the toes or fingers is the earliest reliable sign of compartment syndrome; fasciotomy is decided clinically, not by compartment pressure alone in an obvious case.