Clinical Decision-Making

Ottawa Rules: Choose the Correct Region Before Ordering an X-Ray

Quick Medical Calculator Editorial Team · Reading label 25 August 2026 · 3 min read

Retrospective study sequence, not publication date

The Ottawa ankle, foot, and knee rules answer a narrow question after an acute injury: is radiography indicated to look for fracture? A negative result does not diagnose a sprain, exclude tendon or ligament injury, or overrule an unreliable examination.

Ankle and Foot Are Separate Decisions

For the ankle rule, first establish pain in the malleolar zone. Radiography is indicated when this is accompanied by posterior-edge or tip tenderness of either malleolus, or inability to take four weight-bearing steps both immediately after injury and during assessment. The posterior-edge examination covers the distal 6 cm.

For the foot rule, first establish pain in the midfoot zone. Navicular tenderness, tenderness at the base of the fifth metatarsal, or the same four-step limitation makes the foot rule positive. Do not replace these anatomical sites with "tender ankle." NSW Emergency Care Assessment and Treatment: ankle rules.

A Walking Patient Can Still Need Imaging

A fictional patient can walk four steps after twisting an ankle but has focal tenderness at the fifth-metatarsal base and midfoot pain. The foot rule is positive despite walking. An ankle-only film is not a substitute for assessing the injured foot. Conversely, inability to walk is not a reason to skip the location-specific examination.

The original refined ankle rules identified all fractures in their second-stage validation sample, but their confidence intervals did not establish zero risk in every future patient. Imaging reductions were estimates in a particular study, not guaranteed savings for every department. Primary validation study.

The Knee Rule Uses Different Triggers

In an eligible adult with acute knee injury, any of these supports knee radiography: age at least 55; isolated patellar tenderness; fibular-head tenderness; inability to flex to 90 degrees; or inability to take four weight-bearing steps both immediately after injury and during assessment. NSW Emergency Care Assessment and Treatment: knee rules. The adult prospective validation included 1,096 patients and identified 63 clinically important fractures. Knee-rule validation.

When a Negative Rule Is Not Enough

Do not use these rules to withhold investigation in deformity, open injury, neurovascular compromise, or an examination made unreliable by altered consciousness or sensory impairment. Persistent or worsening symptoms require reassessment.

The blanket claim that Ottawa ankle rules require closed growth plates is incorrect. ACR addresses their use in eligible adults and children aged five or older; younger children and unreliable examinations need another pathway. That does not automatically extend every adult knee-rule assumption to children. ACR acute ankle trauma criteria.