Clinical decision rule
Pittsburgh Knee Rules
The Pittsburgh Knee Rules indicate a knee radiograph after blunt trauma or a fall when the patient is younger than 12 or older than 50, or cannot walk four weight-bearing steps in the emergency department — and the rule does not apply at all to any other mechanism of injury.
What the Pittsburgh Knee Rules mean
Pittsburgh Knee Rules categories describe different patterns, not increasing severity — a higher-lettered or higher-numbered category is not necessarily a worse problem. The groups below are descriptive.
- Outside the rule-1–-1
Mechanism other than blunt trauma or a fall; no recommendation either way.
- Imaging not indicated0–0
- Imaging indicated1–1
Published criteria and reliability
The published cut-offs that define this instrument, and the measured agreement between observers using it. Each is reported with the population it was derived in.
| Type | Value | Subscale | Population | Follow-up | Source |
|---|---|---|---|---|---|
| Criterion | Blunt trauma or a fall, plus age under 12 or over 50, or inability to walk four weight-bearing steps | — | Adults and children presenting to the emergency department with acute knee injury | — | Seaberg DC 1994 |
| Criterion | Sensitivity approximately 99% with specificity around 60%, giving higher specificity than the Ottawa knee rule at comparable sensitivity | — | Multicentre comparison in emergency department patients with acute knee injury | — | Seaberg DC 1998 |
Criterion is a published cut-off, definition or performance figure belonging to a classification or decision rule — it is not a change score and should not be read as one.
How the score is calculated
Stated in full so the calculation can be independently checked, and reproduced by hand if needed.
The rule is applied only to knee injuries caused by blunt trauma or a fall. Within that group, a radiograph series is indicated if either of two criteria is present: the patient is younger than 12 years or older than 50 years, or the patient is unable to bear weight for four steps in the emergency department. If neither criterion is present, no radiograph is indicated by the rule. If the mechanism was anything other than blunt trauma or a fall, the rule does not apply and makes no recommendation — imaging is then decided on clinical grounds alone. The rule is deliberately narrower than the Ottawa knee rule, which has five criteria and no mechanism gate, and the narrowness is the point: it sends fewer patients for radiography at a similar sensitivity.
Instrument profile
- Developer
- David C. Seaberg and Richard Jackson
- Institution
- University of Pittsburgh, United States
- First published
- 1994
- Items
- 3
- Response format
- One entry condition and two criteria
- Score range
- 0 to 1
- Direction
- Categories are not ranked by severity
- Completion time
- About 1 minutes
- Age range
- Children and adults
- Regions
- Knee
- Conditions
- Acute knee injury, Knee fracture, Patellar fracture, Tibial plateau fracture
- Procedures
- Knee radiography
- Validity
- Derived and validated for clinically significant knee fractures in emergency department patients. Its practical advantage over the Ottawa knee rule is specificity: both miss very few fractures, but the Pittsburgh rule sends a smaller proportion of patients for radiography.
- Reliability
- The criteria are objective — a date of birth and an observed walking test — so agreement between clinicians is high. The weight-bearing test has to be performed rather than inferred from the history.
When to use the Pittsburgh Knee Rules
Well suited to
- Deciding whether to radiograph an acutely injured knee in the emergency department after blunt trauma or a fall.
- Reducing unnecessary knee radiography where departmental volume makes the difference in specificity worth having.
- Children with knee injury, who fall outside the Ottawa knee rule’s derivation population but are within this one.
Limitations and poor fits
- Any mechanism other than blunt trauma or a fall — including penetrating injury, an atraumatic effusion or an injury presenting more than a week later.
- Patients in whom the examination is unreliable: intoxication, a distracting injury, altered sensation in the leg or an inability to cooperate.
- As a rule-in test. It identifies who should be imaged, not who has a fracture; most patients it sends for radiography will have none.
- Suspected ligament or meniscal injury, which plain radiographs will not show whatever the rule says.
Pittsburgh Knee Rules compared with other instruments
Instruments measuring a related construct, with the practical difference between them.
| Instrument | Items | Range | What it adds |
|---|---|---|---|
| Ottawa Knee Rule | 5 | 0–1 | The Ottawa Knee Rule determines whether an acute knee injury requires radiographs using five criteria — age 55 or over, isolated patellar tenderness, fibular head tenderness, inability to flex to 90 degrees, and inability to bear weight for four steps — and is close to 99% sensitive for clinically significant fractures. |
| Schatzker | 1 | 1–6 | The Schatzker classification sorts tibial plateau fractures into six types by the plateau involved and the fracture pattern, where types I to III involve the lateral plateau and carry a better prognosis, and types IV to VI are higher-energy injuries with medial, bicondylar or metaphyseal-diaphyseal involvement. |
| Ottawa Ankle Rules | 7 | 0–1 | The Ottawa Ankle Rules determine whether an acute ankle or midfoot injury requires radiographs, based on bone tenderness at four specific sites and the ability to bear weight for four steps; they are approximately 98% sensitive for clinically significant fractures. |
| NEXUS | 5 | 0–1 | The NEXUS low-risk criteria allow the cervical spine to be cleared without imaging after blunt trauma when all five findings are absent — midline cervical tenderness, focal neurological deficit, altered alertness, intoxication and a distracting injury — with a reported sensitivity of about 99% for clinically significant injury. |
Copyright and permitted use
Published openly because it is the question every clinician and researcher asks before using an instrument, and almost nobody answers it.
A published clinical decision rule. No licence is required.
References
- Seaberg DC, Jackson R. Clinical decision rule for knee radiographs. American Journal of Emergency Medicine. 1994.
- 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. Annals of Emergency Medicine. 1998.
Editorial status
This page has not yet been signed off by a named clinical reviewer. The scoring logic is stated in full above so it can be independently verified, and every threshold is traceable to its source. See our editorial methodology.