Acute knee injury


Knee ligaments

  • Anterior Cruciate Ligament
    • Limits anterior translation of tibia
    • 75% of all hemarthroses are caused by disruption of ACL
  • Posterior Cruciate Ligament
    • Limits posterior translation of tibia
    • Isolated injuries are rare
  • Medial Collateral Ligament
    • Provide restraint against valgus (outward) stress
  • Lateral Collateral Ligament
    • Provide restraint against varus (inward) stress

Clinical Features

  • Acute trauma and pain to knee

Differential Diagnosis

Knee diagnoses

Acute knee injury



Ottawa knee rules

X-ray is only required in patients who have an acute injury and one or more of the following:

  • Age >55
  • Isolated tenderness of the patella
  • Tenderness at the fibular head
  • Inability flex to 90 degrees
  • Inability to walk 4 steps BOTH immediately after the injury and in the ED

Knee x-rays

  • Anteroposterior and lateral views
    • Consider sunrise if pain over patella


  • If xrays are positive (when indicated)
    • Treat underlying condition
  • If xrays are negative or not indicated Ottawa knee rules
    • Do full knee exam to check for ligamentous/meniscal instability:
      • Negative exam → RICE
      • Positive exam or unable to evaluate secondary to pain/swelling → knee brace + RICE


  • Depends on diagnosis; most often results in outpatient ortho referral

See Also


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