Ottawa knee rule
For: Knee fracture after an acute knee injury (need for X-ray)
Website-only page: no separate test card in the book, which discusses this in its ‘The knee’ chapter.
A break in one of the bones of the knee (the kneecap, the top of the shin bone or fibula, or the lower end of the thigh bone) after an injury. Decision rules for it decide who needs an X-ray; they do not diagnose the fracture.
Best used to rule outLikelihood ratios as pooled in the review.
These figures have not been confirmed against the full paper (checked against the abstract or a secondary source only).
How it is done
For an adult with an acute knee injury. A knee X-ray is needed if ANY one of these is present: (1) age 55 or over; (2) tenderness at the head of the fibula; (3) tenderness isolated to the kneecap (patella), with no other bony tenderness of the knee; (4) unable to bend the knee to 90°; (5) unable to bear weight for four steps both immediately after the injury and at the time of assessment. If none is present, no X-ray is needed.
What the studies found
Decision rule for knee X-ray — a rule-out tool. A negative rule makes a fracture very unlikely; a positive rule means 'X-ray', not 'fracture' (LR+ only 1.86). Figures are the pooled estimates of Sims et al. 2020 (8 studies, 7,385 adults): sensitivity 99% (95% CI 97–100%), specificity 49% (47–51%), LR+ 1.86 (1.72–2.01), LR− 0.07 (0.02–0.24). Other meta-analyses agree on high sensitivity but differ on LR−: Bachmann 2004 (6 studies, 4,249 adults) sensitivity 98.5%, specificity 48.6%, LR− 0.05; Kazemi 2023 (18 studies, 6,702 adults) sensitivity 98%, specificity 43%, LR− 0.12, with very large differences between studies. Some single studies found lower sensitivity (Richman 1997, 84.6%), and in Seaberg 1998 the rule's specificity was only 27%. In children, a meta-analysis (Vijayasankar 2009: 3 studies, 1,130 children) found sensitivity 99% and LR− 0.07, and concluded the rule can be used over age 5 but that there are not enough good data under age 5.
What the numbers mean
- Positive result: barely informative: a positive result changes little.
- Negative result: a strong rule-out: a negative result makes the diagnosis very unlikely.
The ladder: what a result does to your estimate
| If you thought | After a positive | After a negative |
|---|---|---|
| 10% | 17% | under 1% |
| 30% | 44% | 3% |
| 50% | 65% | 7% |
Calculated from the likelihood ratios above. For any other starting estimate, use the probability calculator.
Work out what a result means for your patient: probability calculator
Other tests in the library for knee fracture after an acute knee injury (need for X-ray)
Source
Sims JI, Chau MT, Davies JR. Diagnostic accuracy of the Ottawa Knee Rule in adult acute knee injuries: a systematic review and meta-analysis. Eur Radiol. 2020;30(8):4438–4446. Journal article (DOI) · meta-analysis
Also cited: Bachmann LM, Haberzeth S, Steurer J, ter Riet G. The accuracy of the Ottawa knee rule to rule out knee fractures: a systematic review. Ann Intern Med. 2004;140(2):121–124. Journal article (DOI)
Also cited: Kazemi SM, Khorram R, Fayyazishishavan E, et al. Diagnostic accuracy of Ottawa knee rule for diagnosis of fracture in patients with knee trauma; a systematic review and meta-analysis. Arch Acad Emerg Med. 2023;11(1):e30. Journal article (DOI)
Also cited: Stiell IG, Greenberg GH, Wells GA, et al. Prospective validation of a decision rule for the use of radiography in acute knee injuries. JAMA. 1996;275(8):611–615. PubMed
Also cited: Richman PB, McCuskey CF, Nashed A, Fuchs S, Petrik R, Imperato M, Hollander JE. Performance of two clinical decision rules for knee radiography. J Emerg Med. 1997;15(4):459–463. Journal article (DOI)
Also cited: Vijayasankar D, Boyle AA, Atkinson P. Can the Ottawa knee rule be applied to children? A systematic review and meta-analysis of observational studies. Emerg Med J. 2009;26(4):250–253. Journal article (DOI)
Website-only page, added to the library on 9 October 2026. Rule It In, Rule It Out discusses this but has no separate test card for it. Figures independently checked against the sources cited above; any note above says where only the abstract could be checked.
Get the book for how to do and read each knee test with published figures, and which ones to trust for the ACL, meniscus and kneecap
The ‘The knee’ chapter of Rule It In, Rule It Out discusses this, alongside how to do and read each test in the chapter.
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