What are the red flags for a knee injury that require immediate medical attention?

Red Flags for Knee Injury Requiring Immediate Medical Attention

Obtain immediate radiographs and urgent evaluation for any patient with gross deformity, inability to bear weight, inability to flex the knee to 90 degrees, or bony tenderness following acute knee trauma. 1

Absolute Red Flags Requiring Urgent Imaging and Evaluation

Clinical decision rules should NOT be applied in the following scenarios—radiographs must be obtained immediately: 1

• Gross deformity of the knee 1
• Palpable mass at the injury site 1
• Penetrating injury to the knee 1
• Prosthetic hardware present 1
• Altered mental status (head injury, intoxication, dementia) making examination unreliable 1
• Neuropathy (paraplegia, diabetic neuropathy) preventing accurate assessment 1
• Multiple injuries making clinical examination unreliable 1

Ottawa Knee Rule Criteria (Age ≥18 Years)

Obtain radiographs immediately if ANY of the following are present: 1

• Age ≥55 years 1
• Isolated patellar tenderness (no other bony tenderness) 1
• Tenderness at the head of the fibula 1
• Inability to flex knee to 90 degrees 1
• Inability to bear weight immediately after injury 1
• Inability to take 4 weight-bearing steps in the emergency department 1

Pittsburgh Decision Rule Criteria

Obtain radiographs if: 1

• Age <12 years OR >50 years with acute knee trauma 1
• Cannot take 4 weight-bearing steps in the emergency department 1

Critical Warning Signs Suggesting Septic Arthritis (Orthopedic Emergency)

Septic arthritis requires immediate orthopedic consultation, joint aspiration, and IV antibiotics: 2

• Fever with joint pain and systemic symptoms 2
• Severe pain with inability to move the joint 2
• Recent bacteremia or infection elsewhere in the body 2
• Rapid onset of swelling (within 2 hours suggests hemarthrosis from fracture or ligament rupture) 3

Signs of Severe Ligamentous Injury (Grade III Sprain)

Four findings that together indicate 96% probability of complete ligament rupture: 1

• Significant swelling 1
• Hematoma formation 1
• Pain on palpation 1
• Positive anterior drawer test 1

Common Pitfall to Avoid

Never skip radiographs even when soft tissue injury seems obvious—fractures requiring immediate intervention must be ruled out first. 4 The sensitivity of clinical examination alone is insufficient, and radiographs showing lipohemarthrosis on cross-table lateral view indicate intra-articular fracture. 1

Physician judgment supersedes all clinical decision rules—if clinical suspicion is high for serious injury, obtain imaging regardless of whether formal criteria are met. 1