This Ottawa knee rules calculator checks whether the patient needs knee x-ray imaging performed due to knee and ankle pain. Below the form you can find more details about the score and how to interpret the accurate Ottawa rules.

Age above 55 years

Unable to bear weight both immediately and in ED

Unable to flex knee to 90 degrees

Isolated tenderness of the patella

Tenderness at the fibular head

How does this Ottawa knee rules calculator work?

This health tool helps clinicians decide whether there is need for radiography in patients with trauma to the knee based on patient bedside data. This is based on the original accurate Ottawa score and comprise of the 5 criteria described below as follows:

■ Age above 55 - this being one of the risk factors for likelihood of fractures in case of symptoms in the area of the knee.

■ Isolated tenderness of the patella (significant when no other bone tenderness).

■ Tenderness at the fibular head.

■ Unable to flex knee to 90 degrees.

■ Unable to bear weight both immediately and in ED (inability to take four steps, for example two steps on each leg, regardless of limping).

Both Ottawa rules have been validated in numerous studies both in children (although it is not recommended to be used as a sole decision rule) and adults and also on different populations, in most studies the sensitivity being found over 86%. However, clinical judgment needs to prevail, especially in cases where the criteria evaluation has not been consistent or the patient has not been cooperative.

The only criticism of the model is related to the low specificity and the possibility of false positives proved in several occasions.

There are also some counter indications to applying the knee injury rule in children, for injuries that are older than 7 days, in patients with altered levels of consciousness or who simply don’t collaborate or in cases presenting with several other fractures or injuries of both the articulation and the soft tissues.

Ottawa Knee Rules

Picture source: Ottawa Hospital Research Institute.

Ottawa rule interpretation

This Ottawa knee rules calculator allows the user to quickly check if either of the criteria is met and offers the result on the spot on whether there is need for knee x-ray or the patient can still be monitored before doing that.

This comes as an improvement in the management of acute knee injury as it allows physicians to cut on resources that were often used unnecessary in some cases in order to rule out any serious injury that could lead to disabilities.

The model sais that if one of the criteria is met, then radiography might prove necessary and as the factors taken in consideration are consistent with serious injuries, the Ottawa score is said to be at around 98% for relevant knee fractures.

At the same time, as the factors taken into consideration are extremely relevant, it is highly unlikely that a patient not displaying any of them to be suffering from a significant fracture. And as acute knee injuries are a common presentation in the emergency departments, the application of the model, allowed a more efficient streamline of patients and as well cut resources spend on radiographs by up to 30% in most clinical settings where it had been used and changed the routine management procedure of knee injuries.

This rule model comes after the implementation of a similar model, the Ottawa rules for ankle which provided similar outcomes of ruling out x-ray necessity in common ankle injuries.


1) Stiell IG, Greenberg GH, Wells GA, McKnight RD, Cwinn AA, Cacciotti T, McDowell I, Smith NA. (1995) Derivation of a decision rule for the use of radiography in acute knee injuries. Ann Emerg Med; 26(4):405-13.

2) Stiell IG, Greenberg GH, Wells GA, McDowell I, Cwinn AA, Smith NA, Cacciotti TF, Sivilotti ML. (1996) Prospective validation of a decision rule for the use of radiography in acute knee injuries. JAMA; 275(8):611-5.

3) Stiell IG, Wells GA, Hoag RH, Sivilotti ML, Cacciotti TF, Verbeek PR, Greenway KT, McDowell I, Cwinn AA, Greenberg GH, Nichol G, Michael JA. (1997) Implementation of the Ottawa Knee Rule for the use of radiography in acute knee injuries. JAMA; 278(23):2075-9.

4) Bachmann LM, Haberzeth S, Steurer J, ter Riet G. (2004) The accuracy of the Ottawa knee rule to rule out knee fractures: a systematic review. Ann Intern Med; 140(2):121-4.

12 Sep, 2015