Ottawa Ankle Rules Calculator

The Ottawa Ankle Rules are a rule-out instrument, built to be highly sensitive rather than accurate. Ankle radiographs are indicated if there is bone tenderness along the distal 6 cm of the posterior edge or tip of either malleolus, or if the patient cannot bear weight for four steps both immediately after the injury and in the department. A separate foot series is indicated if there is bone tenderness at the base of the fifth metatarsal or over the navicular, or the same weight-bearing failure. The anatomical targets are chosen because those are the sites where clinically important fractures actually occur: distal fibular and medial malleolar fractures, fifth metatarsal base avulsions, and navicular fractures. The 6 cm boundary matters - palpating the ligament bellies or the anterior malleolar surface produces tenderness in ordinary sprains and destroys specificity. Across validation work the pooled sensitivity is about 98 percent and specificity roughly 30 to 50 percent, so the rules are designed to over-refer. That asymmetry is intentional: with a negative-likelihood ratio near 0.1 and a fracture prevalence of about 15 percent in ankle injury presentations, a fully negative examination drops post-test fracture probability to roughly 1 to 2 percent, and the rare missed injuries are small avulsion fragments treated the same as a sprain. Applied consistently, the rules cut ankle and foot radiography by roughly 30 to 40 percent. They should not be used when pain assessment is unreliable - intoxication, head injury, distracting injuries, peripheral neuropathy from diabetes - nor in children under about 5 years.

The rules were derived by Ian Stiell and colleagues in the emergency department of the Ottawa Civic Hospital in Ontario, and published in Annals of Emergency Medicine in 1992, with an implementation study in JAMA that same period. The team prospectively examined several hundred adults with acute ankle injuries, recorded dozens of candidate clinical variables before radiography, and used recursive partitioning to find the smallest set of findings that retained 100 percent sensitivity for significant fracture in the derivation cohort. The motivation was concrete: more than 95 percent of ankle radiographs ordered at the time showed no fracture. Stiell published a prospective multicentre validation in the BMJ in 1995 covering eight Canadian hospitals, and later a refined version extending applicability. The rules then spread further than almost any other decision instrument in emergency medicine. A 2003 systematic review by Lucas Bachmann and colleagues in the BMJ pooled 27 studies with more than 15,000 patients and confirmed sensitivity near 98 percent across adults and children over 5. Subsequent work validated application by triage nurses, physiotherapists, and paramedics rather than physicians only. Stiell went on to apply the same derivation methodology to other imaging questions, producing the Ottawa Knee Rule in the mid-1990s and the Canadian C-Spine Rule and Canadian CT Head Rule around 2001, establishing a template for evidence-based clinical decision rule development.