The Ottawa Ankle Rules (OAR) are a standardized medical screening tool used globally to manage acute ankle and midfoot injuries. These guidelines help clinicians determine if a patient presenting with pain following trauma requires an X-ray to diagnose a potential fracture. By focusing on specific physical examination findings, the OAR quickly and accurately assess the likelihood of a clinically significant fracture. The rules are highly sensitive, meaning they reliably identify nearly all patients who have a fracture.
Why the Rules Were Developed
Before the Ottawa Ankle Rules (OAR) were developed in the early 1990s, standard practice was to order an X-ray for nearly all patients presenting with an ankle sprain. Physicians did this to avoid missing a fracture, even though less than 15% of ankle sprains seen in emergency departments involved a bone break. This resulted in a significant number of unnecessary radiographic examinations.
The high volume of unnecessary imaging increased healthcare costs, wasted emergency department time, and exposed patients to needless low-dose radiation. A team of physicians in Ottawa, Canada, sought to create a safe and effective way to identify the small percentage of patients who truly needed an X-ray. Their goal was to maintain near-perfect accuracy in detecting fractures while drastically reducing the overall number of images taken.
The Five Specific Criteria
The Ottawa Ankle Rules specify five distinct physical findings that collectively indicate the need for an X-ray examination. The first criterion assesses the patient’s ability to bear weight. An X-ray is required if the patient is unable to bear weight immediately after the injury and for a distance of four steps during the clinical assessment.
The remaining four criteria involve checking for tenderness at specific anatomical locations on the ankle and foot bones. The ankle assessment focuses on the posterior edge or tip of the lateral malleolus (the outer ankle bump). Tenderness must be present along the distal six centimeters of this area of the fibula.
The second ankle location is the posterior edge or tip of the medial malleolus (the inner ankle protrusion). Tenderness must be present along the distal six centimeters of this section of the tibia. These two points target the most common sites for ankle fractures.
To assess for a midfoot fracture, the final two criteria focus on bony points near the arch of the foot. The fourth criterion is bone tenderness located at the base of the fifth metatarsal (near the outer edge of the foot). The fifth criterion is bone tenderness over the navicular bone (on the top and inner side of the midfoot).
Using the Rules for Diagnosis
The application of the Ottawa Ankle Rules follows a clear decision-making pathway. If a patient presents with pain in the malleolar or midfoot zone, the clinician systematically checks all five criteria. If the patient tests positive for any one of these five criteria—either the inability to bear weight or tenderness at one of the four specified bone points—an X-ray is required.
Conversely, if the patient can bear weight for four steps and reports no tenderness at any of the four bony locations, the OAR are considered negative. A negative result means a fracture is highly unlikely, as studies show the rules possess a sensitivity of nearly 100% for detecting clinically important fractures. In these cases, an X-ray is usually deemed unnecessary, and the injury is managed as a sprain.
The OAR come with specific exclusions and limitations that govern their proper use. The rules are not reliable for children under 18, as growth plates can complicate fracture detection. They also cannot be accurately applied to patients who are intoxicated, have significant distracting injuries, or have chronic injuries older than 10 days. These exclusions ensure the integrity of the assessment.