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    Ottawa Knee Rule

    Describes criteria for knee trauma patients so low risk as not to warrant knee imaging.
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    When to Use
    Pearls/Pitfalls
    Why Use

    The Ottawa Knee Rules should be applied to all patients aged 2 and older with knee pain/tenderness in the setting of trauma.

    The Ottawa Knee Rules were derived to aid in the efficient use of radiography in acute knee injuries.

    • Rules have been prospectively validated on multiple occasions in different populations and in both children and adults.
    • Numerous studies found sensitivities for the Ottawa Knee Rules of 98-100% for clinically significant knee fractures. One study did find a sensitivity of just 86%.
    • Specificities for the Ottawa Knee Rules typically range from 19%-50%, though the rule is not designed/intended for specific diagnosis.
    • When used appropriately, the amount of knee x-rays obtained can be reduced by around 20-30%.
    • The Ottawa Knee Rules are useful in ruling out fracture (high sensitivity) when negative, but poor for ruling in fractures (many false positives).

    Tips from the creators at University of Ottawa:

    • Tenderness of patella is significant only if an isolated finding.
    • Use only for injuries <7 days.
    • “Bearing weight” counts even if the patient limps.

    Precautions from the creators at University of Ottawa:

    • Clinical judgment should prevail if examination is ureliable:
      • Intoxication.
      • Uncooperative patient.
      • Distracting painful injuries.
      • Diminished sensation in legs.
    • Always provide written instructions.
    • Encourage follow-up in 5-7 days if pain and ability to walk is not better.
    • Patients without criteria for imaging by the Ottawa Knee Rules are highly unlikely to have a clinically significant fracture and do not need plain radiographs.
    • Application of the Ottawa Knee Rules can cut down on the number of unnecessary radiographs by 20-30%, which has proven to be cost effective for patients without reducing quality of care. (Nichol 1999)
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    ottawa knee rule

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    Next Steps
    Evidence
    Creator Insights

    Advice

    Patients who do not have any of the Ottawa Knee Rules present do not need an x-ray. If one or more of the conditions are met, then x-ray is recommended.

    Management

    For significant non-bony injuries, often crutches and a knee immobilizer can be helpful to assist with ambulation.

    Critical Actions

    Patients who do not have any of the Ottawa Knee Rules present do not need an x-ray. If one or more of the conditions are met, then x-ray is recommended.

    Many experts would consider this score “one directional.” Because the rule is sensitive and not specific, it provides a clear guide of which patients not to x-ray if all criteria are met. However if a patient fails the criteria, need for x-ray can be left to clinical judgement.

    Formula

    Series of Yes/No questions. See criteria below.

    Facts & Figures

    • A knee x-ray series is only required for knee injury patients with any of these findings:
      • Age ≥ 55, OR
      • Isolated tenderness of patella (no bone tenderness of knee other than patella), OR
      • Tenderness of head of fibula, OR
      • Inability to flex to 90°, OR
      • Inability to bear weight both immediately after injury and in the ED for 4 steps (unable to transfer weight twice onto each lower limb regardless of limping.