AdultPediatric
Cannot miss / life threats
Cannot miss / life threats
Diagnostic flow — check first
Diagnostic flow — check first
- Knee dislocation → ABI/CTA mandatory even if reduced.
- Hot swollen joint + fever → aspirate.
- Cannot extend knee actively → think extensor mechanism rupture.
- Atraumatic effusion in adult → aspirate (gout/septic).
- Pediatric knee pain with normal knee exam → image the hip.
Differential diagnosis — checklist
0/19
Check off each diagnosis as you consider it. Tap the name for unique exam, lab/imaging clues, first-line confirmatory test, and management.
Traumatic0/8
Atraumatic0/7
Pediatric0/4
Initial ED workup
Bedside0/5
- Vitals; check for fever/systemic signs
- Inspect deformity, effusion, ecchymosis
- Active extension test (rule out extensor mechanism injury)
- Ligament tests (Lachman, varus/valgus, posterior drawer)
- Distal NV exam, popliteal pulse + ABI for any dislocation
Labs0/2
- CBC, CRP, urate
- Synovial fluid analysis if effusion + fever or atraumatic monoarthritis
Imaging0/4
- AP + lateral + sunrise XR (Ottawa knee rules)
- CT for tibial plateau
- MRI (without contrast) outpatient for ligament/meniscus
- CTA for any knee dislocation
Initial management0/4
- Knee immobilizer, crutches, ice, elevation, NSAID + acetaminophen
- Reduce dislocations; serial NV exams
- Aspirate + ortho washout for septic joint
- Vascular consult for ABI <0.9
Pearls / pitfalls
Pearls
- All knee dislocations need ABI even if reduced — popliteal artery injury can be missed.
- Apply Ottawa knee rules: age >55, isolated patella tenderness, fibular head tenderness, cannot flex 90°, cannot weight bear → XR.
- A septic knee aspirate is non-negotiable if effusion + fever + atraumatic.