Emerg Med J 29:77-78 doi:10.1136/emermed-2011-200980
  • Best Evidence Topic reports

BET 1: Predicting the need for knee radiography in the emergency department: Ottawa or Pittsburgh rule?

Report by: Bryony Patrick

Search checked by: Richard Body

Institution: University of Manchester, Manchester, UK

Clinical scenario

A 30-year-old man presents to the emergency department (ED) after twisting his knee. You suspect a soft tissue injury and are aware that the Ottawa knee rule could be used to help determine whether radiography is necessary. A colleague suggests that you should use the Pittsburgh rule instead. You wonder which rule has greater sensitivity (thus missing fewer fractures) and greater specificity (thus reducing the need for unnecessary radiography).

Three-part question

In (adult patients presenting to the emergency department with traumatic knee pain) does the (Ottawa knee rule or the Pittsburgh knee rule) have (greater sensitivity and specificity for knee fractures)?

Search strategy

We searched MEDLINE 1948 to Week 3 October 2011 and EMBASE 1980–2011 Week 44 using the Ovid interface. We also searched the Cochrane Database of Systematic Reviews on 7th November 2011.

MEDLINE and EMBASE: (exp Knee/ OR exp Knee Joint/ OR AND ((Ottawa AND Pittsburgh) OR decision rules).af. Limit to humans and English language.


We identified 31 papers in MEDLINE, 35 in EMBASE and 5 in the Cochrane database. We identified two papers that addressed the three-part question.


The Ottawa rule recommends radiography if any of 5 features are present: (1) Age ≥55 years; (2) Isolated tenderness of the patella; (3) Tenderness at the fibular head; (4) Inability to flex the knee to 90 degrees; (5) Inability to bear weight both immediately and in the ED (limping is acceptable). The Pittsburgh rule recommends radiography if the mechanism of injury is blunt trauma or a fall and either (1) age is <12 years or >50 years, or (2) the patient cannot complete four weight-bearing steps in the ED.

We identified two cohort studies (see table 1) that have directly compared the diagnostic accuracy of these two clinical decision rules. The studies demonstrate that the rules have similar sensitivity. Both rules would miss some fractures when used alone. In the larger study, the Pittsburgh rule had a sensitivity of 99% with significantly superior specificity compared to the Ottawa rule (60% vs 27%). Thus, while the Ottawa knee rule has been more extensively investigated in both cohort studies and randomised controlled trials of clinical implementation (Bachmann et al 2004, Stiell et al 1997), the evidence presented here suggests that the Pittsburgh rule may be a viable alternative and could lead to less use of radiography without lowering sensitivity. Randomised controlled trials are now necessary to definitively answer this question.

Table 1

Clinical bottom line

The Ottawa and Pittsburgh rules appear to have similar sensitivity, although the Pittsburgh rule may have higher specificity and could therefore lead to less unnecessary radiography. Neither rule has perfect sensitivity so clinical judgement should still be exercised. Randomised controlled trials are necessary to definitively answer this question.

▶ Bachmann L, Haberzeth S, Steurer J, et al. The accuracy of the Ottawa knee rule out fractures. Ann Intern Med 2004;140:121–4.

▶ Stiell IG, Wells GA, Hoag RH, et al. Implementation of the Ottawa knee rule for the use of radiography in acute knee injuries. J Am Med Assoc 1997;278:2075–9.

▶ Richman P, McCuskey C, Nahed A, et al. Performance of two clinical decision rules for knee radiography. J Emerg Med 1997;15:459–63.

▶ Seaberg D, Yealy D, Lukens T, et al. Multicenter comparison of two clinical decision rules for the use of radiography in acute, high risk knee injuries. Ann Emerg Med 1998;32:8–13.


  • Linked articles 200981, 200982, 200983, .

  • Provenance and peer review Commissioned; internally peer reviewed.

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