The Ottawa Knee Rule: A Clinical Decision Tool for Acute Knee Injuries
The Ottawa Knee Rule (OKR) is a validated clinical decision-making tool designed to reduce unnecessary radiographic imaging in patients presenting with acute knee trauma. Developed in the mid-1990s, the rule has become a cornerstone in emergency medicine, helping clinicians identify patients at low risk for knee fractures and avoid excessive use of radiography.
Radiographs of the knee are indicated if any of the following criteria are present¹:
Age ≥55 years
Isolated tenderness of the patella (no other bony tenderness)
Tenderness at the head of the fibula
Inability to flex the knee to 90°
Inability to bear weight both immediately after injury and in the emergency department (defined as four steps, regardless of limping)
These criteria are applied to patients with blunt trauma to the knee and are not intended for use in cases involving penetrating injuries, altered consciousness, or multiple traumas.
The OKR was derived in a 1995 multicenter prospective cohort study led by Dr. Ian Stiell and colleagues, published in Annals of Emergency Medicine². The study enrolled 1,047 adult patients with acute knee injuries and evaluated 23 clinical variables. Recursive partitioning was used to identify predictors of fracture. The final rule demonstrated 100% sensitivity for identifying clinically significant fractures, with a specificity of 49%².
The rule was prospectively validated in a 1996 study published in JAMA, which confirmed its 100% sensitivity for knee fractures³. A subsequent implementation study in 1997 showed that applying the OKR led to a 26.4% reduction in radiography use without missing any fractures⁴.
A 2004 systematic review and meta-analysis pooled data from multiple studies and found the OKR to have a pooled sensitivity of 98.5% and specificity of 48.6%⁵. These findings support the rule’s reliability across diverse clinical settings and patient populations.
The OKR has significantly improved efficiency in emergency departments by:
Reducing unnecessary imaging by up to 28–43%⁴⁶
Lowering healthcare costs and patient wait times⁴
Maintaining high diagnostic accuracy and patient satisfaction⁴
Despite its effectiveness, studies have shown variable compliance among clinicians, often due to medico-legal concerns or lack of familiarity with the rule⁶.
While highly sensitive, the OKR has limitations:
It does not account for ligamentous injuries, which may require advanced imaging
Accuracy depends on clinician palpation and interpretation, introducing variability
It is not recommended for children under 18, although some studies suggest it may be safe in children over 5⁷
The Ottawa Knee Rule exemplifies the power of evidence-based medicine. Its derivation, validation, and widespread adoption have led to safer, more efficient care for patients with knee injuries. When applied correctly, the rule minimizes unnecessary imaging while preserving diagnostic accuracy—making it a vital tool in emergency clinical practice.
Ottawa Knee Rules - Physiopedia. https://www.physio-pedia.com/Ottawa_Knee_Rules. Accessed July 27, 2025.
Stiell IG, Greenberg GH, Wells GA, et al. Derivation of a decision rule for the use of radiography in acute knee injuries. Ann Emerg Med. 1995;26(4):405–413.
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.
Stiell IG, Wells GA, Hoag RH, et al. Implementation of the Ottawa Knee Rule for the use of radiography in acute knee injuries. JAMA. 1997;278(23):2075–2079.
Bachmann LM, Haberzeth S, Steurer J, et al. The accuracy of the Ottawa knee rule to rule out knee fractures: a systematic review. Ann Intern Med. 2004;140(2):121–124.
Sims JI, Chau M, Davies J. Validation of the Ottawa Knee Rule in adults: A single centre study. J Med Radiat Sci. 2020;67(3):193–198.
Bulloch B, Neto G, Plint A, et al. Validation of the Ottawa Knee Rule in children: a multicenter study. Ann Emerg Med. 2003;42(1):48–55.