Enter Patient Findings
Formula Used
The Ottawa Knee Rule is a logical decision rule (no arithmetic scoring). A knee radiograph is indicated if any of the following is true:
- Age ≥ 55 years
- Isolated patella tenderness
- Tenderness at the head of the fibula
- Inability to flex the knee to 90°
- Inability to bear weight for 4 steps both immediately and in clinic/ED
Radiograph = (Age≥55) OR (PatellaTender) OR (FibulaTender) OR (Flex<90°) OR (BearWeightImmediate=No AND BearWeightClinic=No)
How to Use This Calculator
- Select whether the injury is acute (recent) and enter age if available.
- Record exam findings: isolated patella tenderness and fibular head tenderness.
- Indicate whether knee flexion to 90° is possible.
- Assess weight-bearing: ability to take 4 steps immediately and again in clinic/ED.
- Click Calculate to see the recommendation above the form.
- Use the download buttons to export a CSV or a PDF report.
Example Data Table
| Case | Age | Patella Tenderness | Fibular Head Tenderness | Flex 90° | Bear Weight (Immediate / Clinic) | Output |
|---|---|---|---|---|---|---|
| A | 62 | No | No | Yes | Yes / Yes | Radiography recommended (age criterion) |
| B | 28 | Yes | No | Yes | Yes / Yes | Radiography recommended (patella tenderness) |
| C | 41 | No | Yes | Yes | Yes / Yes | Radiography recommended (fibular head tenderness) |
| D | 33 | No | No | No | Yes / Yes | Radiography recommended (cannot flex to 90°) |
| E | 24 | No | No | Yes | No / No | Radiography recommended (cannot bear weight both times) |
| F | 37 | No | No | Yes | Yes / Yes | Not required by criteria (use judgment) |
Examples are illustrative and not clinical advice.
Downloads
After you calculate, use the buttons in the result panel to export.
- CSV includes inputs, criteria, and the recommendation.
- PDF creates a compact report suitable for records.
Clinical purpose
The Ottawa Knee Rule supports rapid decisions after acute knee trauma by focusing on bony findings that raise fracture suspicion. In day‑to‑day services, knee radiographs are frequently ordered “just in case.” Using a standardized checklist helps target imaging to higher‑risk presentations, improves flow, and can reduce avoidable radiation and cost.
Rule components
This calculator evaluates five criteria: age 55 years or older, isolated patella tenderness, fibular head tenderness, inability to flex the knee to 90°, and inability to bear weight for four steps both immediately after injury and at assessment. The logic is simple: if any criterion is positive, radiography is recommended by the rule. Select findings carefully; uncertain items should be treated as positive until clarified by repeat examination.
Weight‑bearing interpretation
Four steps means transferring weight twice on each leg, with or without limping, using usual supports if needed. A patient who can briefly stand but cannot take four steps is considered unable. The two‑time requirement matters: analgesia, splinting, and adrenaline can change performance, so the rule flags persistent inability across both time points.
Imaging efficiency
To illustrate impact, imagine a clinic audit of 200 acute knee injuries in a month. If 110 meet no criteria, the tool would suggest no radiograph for those 110, reserving imaging for 90. That is a 55% reduction in radiographs. If one radiograph episode adds about 25 minutes from ordering to review, avoiding 110 returns roughly 46 clinic hours. The exact savings vary by case‑mix and policy.
Documentation workflow
Decision rules are only useful when documented consistently. Capture each criterion as yes or no, add a short mechanism note, and record the final recommendation. Exporting to CSV supports registries, peer review, and teaching rounds. For monitoring, track the percentage of visits meeting each criterion and compare imaging use over time. The PDF report provides a compact summary for referrals, handover, or attachment to an encounter record.
Limitations and safety
The rule addresses fracture risk, not ligament, meniscal, vascular, or infectious pathology. A negative output should not override red flags such as deformity, worsening swelling, open injury, fever, numbness, or poor perfusion. If the injury is not acute, validation is weaker. Combine this output with examination, patient factors, and clear follow‑up instructions.
FAQs
1) What does a positive result mean?
A positive result means at least one Ottawa criterion was selected as yes. The rule advises obtaining a knee radiograph to assess for fracture. It does not confirm a fracture; it signals higher imaging value.
2) Can I use this for chronic knee pain?
It is designed for recent traumatic injuries. For chronic pain, atraumatic swelling, infection concern, or post-operative knees, use clinical assessment and appropriate pathways rather than this rule alone.
3) How do I interpret the four-step test?
Four steps equals two steps on each leg, with or without a limp, using usual assistance. If the patient cannot transfer weight for four steps, mark inability. The criterion is positive only when unable both immediately and at evaluation.
4) What if the patient’s age is unknown?
If age is not entered, the age criterion is treated as negative. When age might be 55 or older, enter an estimate or confirm from records so the output reflects that risk factor.
5) Does a negative result rule out serious injury?
No. A negative result reduces fracture likelihood but does not exclude ligament or meniscal tears, dislocation, vascular injury, or compartment syndrome. Persistent pain, instability, deformity, numbness, or worsening swelling warrants further evaluation.
6) Should I still follow local protocols?
Yes. Local imaging policies, clinician judgment, and patient-specific factors always apply. Use this tool to support documentation and consistency, then decide imaging and follow-up based on the full clinical picture.