Pittsburgh knee rule
For: Knee fracture after an acute knee injury (need for X-ray)
Website-only test: not part of the book.
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.
Treat with caution (see below)Likelihood ratios calculated from the published sensitivity and specificity.
Caution: Validated by the rule's own developers; independent studies found sensitivity of only 77% and 86%.
These figures have not been confirmed against the full paper (checked against the abstract or a secondary source only).
How it is done
A knee X-ray is needed if the injury was from blunt trauma or a fall AND either (a) the patient is under 12 or over 50 years old, or (b) the patient cannot walk (bear weight) at the time of assessment. If the injury was not from blunt trauma or a fall, or neither (a) nor (b) applies, 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 unlikely; a positive rule means 'X-ray', not 'fracture' (LR+ only 2.48). Seaberg 1998 enrolled a convenience sample of patients with acute, high-risk knee injuries who were already going to have an X-ray, at 3 US emergency departments; the rule could be applied in 745 (91 fractures). It missed one fracture: sensitivity 99% (95% CI 94–100%), specificity 60% (95% CI 56–64%). Because the LR− rests on a single missed fracture it is imprecise: at the lower confidence limit for sensitivity (94%) it would be about 0.10. Validated by the group that developed it. Independent studies were less reassuring: Simon 2006 (152 patients) missed 4 of 13 fractures (sensitivity 77%), and Cheung 2013 (90 patients, 7 fractures) found sensitivity 86% and specificity 51%. No meta-analysis; the Ottawa knee rule has the stronger evidence.
What the numbers mean
- Positive result: a small shift: a positive result nudges the diagnosis up, but does not settle it.
- Negative result: see the caution above before relying on this result.
The ladder: what a result does to your estimate
| If you thought | After a positive | After a negative |
|---|---|---|
| 10% | 22% | under 1% |
| 30% | 52% | under 1% |
| 50% | 71% | 2% |
Calculated from the likelihood ratios above. Read the caution above before relying on these. 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
Seaberg DC, Yealy DM, Lukens T, Auble T, Mathias S. Multicenter comparison of two clinical decision rules for the use of radiography in acute, high-risk knee injuries. Ann Emerg Med. 1998;32(1):8–13. Journal article (DOI) · single study
Also cited: Simon LV, Matteucci MJ, Tanen DA, Roos JA, Riffenburgh RH. The Pittsburgh Decision Rule: triage nurse versus physician utilization in the emergency department. J Emerg Med. 2006;31(3):247–250. Journal article (DOI)
Also cited: Cheung TC, Tank Y, Breederveld RS, Tuinebreijer WE, de Lange-de Klerk ES, Derksen RJ. Diagnostic accuracy and reproducibility of the Ottawa Knee Rule vs the Pittsburgh Decision Rule. Am J Emerg Med. 2013;31(4):641–645. Journal article (DOI)
Website-only test: added to the library on 9 October 2026 and not part of Rule It In, Rule It Out. Figures independently checked against the sources cited above; any note above says where only the abstract could be checked. If a newer or better study changes them, this page will be updated.
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
This test is in the website library only; it is not one of the tests in Rule It In, Rule It Out. The book covers the tests in its ‘The knee’ chapter: how to do each one, what counts as positive, and how to read the result.
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