Ottawa Knee Rules Calculator

Ottawa Knee Rules Calculator for Emergency. The displayed count explains how many findings contributed, but the clinical decision is any versus none, not a graded fracture probability. A patient with several findings is not assigned a severity or a specific fracture type.

For shared guidance on choosing a tool and documenting results, read the clinical calculator workflow.

How this calculator works

The Ottawa knee rule is satisfied by any one of five findings: age at least 55 years, isolated patellar tenderness, fibular-head tenderness, flexion below 90 degrees, or inability to take four weight-bearing steps at both specified times. Age and measured flexion are numeric inputs so 54.9 years and 89.9 degrees are not rounded into the wrong category.

When to use this calculator

Use in an alert adult after recent minor knee trauma when the examination is reliable. The adult, within-seven-days scope is a conservative implementation boundary, not an extension to children, repeat presentations or major multiple trauma. Assess deformity, circulation and an open wound before applying imaging decision support.

Inputs used

  • Alert adult with reliable examination, acute knee injury within 7 days and no urgent exclusion?
  • Age (years)
  • Tenderness confined to the patella, without other knee bone tenderness?
  • Fibular head tenderness?
  • Maximum assessed knee flexion (degrees)
  • Unable to take four weight-bearing steps both immediately after injury and at examination?

Clinical interpretation

The displayed count explains how many findings contributed, but the clinical decision is any versus none, not a graded fracture probability. A patient with several findings is not assigned a severity or a specific fracture type.

Worked example

An otherwise negative examination at age 55 contributes one finding and meets the rule. At age 54.9 with flexion exactly 90 degrees, neither age nor flexion contributes. Changing flexion to 89.9 degrees adds one finding and changes the result to a radiography trigger.

Limitations and safety notes

Pain may make range-of-motion assessment unreliable. A negative fracture imaging rule does not assess ligament disruption, extensor injury or a dislocation that reduced before examination. The original source cards are not reproduced and no developer endorsement or independent medical validation is claimed.

Frequently asked questions

Why is patellar tenderness described as isolated?

The relevant criterion is tenderness confined to the patella rather than patellar discomfort among several other bony sites.

Is exactly 90 degrees a trigger?

No. Inability to reach 90 degrees is the finding, so the implemented boundary is below 90.

Can I apply the result to a child?

This implementation intentionally supports adults only. Use an appropriate pediatric assessment rather than extrapolating.

References

  • OHRI developer group: adult alert recent minor trauma population. https://ohri.ca/en/find-researcher/istiell
  • Health Canada adult nursing guideline: five knee radiography findings and exact age/flexion/weight-bearing criteria. https://www.canada.ca/content/dam/hc-sc/migration/hc-sc/fniah-spnia/alt_formats/pdf/services/nurs-infirm/clini/adult/musculo-eng.pdf

Editorial review and citation methodology

Maintained by the Quick Medical Calculator Editorial Team. Content record date: September 9, 2026. A content date is not evidence of independent clinical review. Individual clinical sign-off is not recorded on this page.

  • Prefer original validation studies for scoring systems and prediction tools.
  • Use current specialty society guidance, transplant allocation policy, public health guidance, or regulator resources when they govern clinical use.
  • Include limitations and safety notes when a calculator is population-specific, context-dependent, or unsuitable as a standalone decision tool.

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