2. Ottawa Ankle Rules Applied to a Real Patient Scenario

Case Presentation

A 34-year-old recreational basketball player presents to the urgent care clinic approximately two hours after an inversion injury to the right ankle sustained while landing from a rebound. He describes the mechanism as the foot rolling inward beneath him with immediate onset of lateral pain. He is able to bear weight with a noticeable limp but reports pain over the lateral malleolus. There is visible swelling over the lateral aspect of the ankle and mild ecchymosis beginning to appear inferior to the lateral malleolus. He denies any prior ankle injury, and there is no open wound, gross deformity, or neurovascular compromise. Distal pulses are palpable, capillary refill is under two seconds, and sensation is intact in all dermatomes of the foot.

The clinical question is straightforward: does this patient require radiography? The Ottawa Ankle Rules (OAR) were developed precisely to answer this question in the acute setting, reducing unnecessary radiation exposure and emergency department costs without missing clinically significant fractures. Applying them correctly requires disciplined palpation of specific bony landmarks and an honest assessment of weight-bearing status — not a general impression of "it looks swollen."

The Decision Structure of the Ottawa Ankle Rules

The OAR apply to adults aged 18–55 with acute blunt ankle trauma presenting within ten days of injury. They do not apply to pregnant patients, patients with diminished sensation (e.g., neuropathy), patients with distracting injuries, or those who are intoxicated. For the ankle series specifically, radiography is indicated if either of the following is present:

• Bone tenderness at the posterior edge or tip of the lateral malleolus, assessed over the distal 6 cm of the fibula.
• Bone tenderness at the posterior edge or tip of the medial malleolus, assessed over the distal 6 cm of the tibia.
• Inability to bear weight both immediately after the injury and in the clinic (four steps, two on each foot, even if limping).

Note the anatomical precision: tenderness must be bone tenderness at the posterior edge or tip of the malleolus, not diffuse soft tissue tenderness over the anterior joint line or the deltoid ligament. The 6 cm boundary is measured from the tip of each malleolus proximally. The weight-bearing criterion requires failure at both time points — a patient who could not walk immediately but now takes four limping steps does not meet the weight-bearing criterion.

Applying the Rules to This Patient

Palpation is performed with the patient seated and the leg supported, using the thumb or index finger to press firmly along the posterior border of the lateral malleolus from its tip proximally for 6 cm, then the same for the medial malleolus. In this patient:

The weight-bearing criterion is not met because the patient passed the in-clinic test, but the lateral malleolus criterion alone is sufficient. The OAR are a rule-in rule: a single positive criterion mandates radiography. The decision is therefore to obtain an ankle series (AP, mortise, and lateral views).

Documenting the Decision

The clinical record must make the reasoning auditable. A defensible note captures the mechanism, the specific tender zones with their anatomical boundaries, the weight-bearing status at both time points, and the resulting decision. A concise example:

Mechanism: inversion injury, right ankle, ~2 h prior.
OAR eligibility: age 34, acute blunt trauma, within 10 days. No neuropathy,
  intoxication, distracting injury, or pregnancy.
Palpation:
  - Lateral malleolus: focal bone tenderness at tip and posterior edge,
    within distal 6 cm of fibula. POSITIVE.
  - Medial malleolus: no bone tenderness; soft tissue tenderness over
    deltoid ligament only. NEGATIVE.
Weight-bearing:
  - Immediately post-injury: unable (assisted off court). FAILED.
  - In clinic: 4 steps with limp. PASSED.
Decision: OAR positive (lateral malleolus criterion). Ankle radiography
  ordered — AP, mortise, lateral views.

Verification and Pitfalls

The rule is validated to be highly sensitive for clinically significant ankle fractures (near 100% in the original derivation and subsequent validation studies), which is why a negative OAR is a strong basis for withholding radiography. Its specificity is lower, meaning many patients who are OAR-positive will have normal films — that is an accepted trade-off. The practical verification step is to confirm that the documented tender zone matches the anatomical definition and that weight-bearing status was tested at both time points. If a colleague reviewing the note cannot reconstruct which landmark was tender and whether the patient walked, the documentation has failed even if the decision was correct.

Two failure modes deserve emphasis. First, misattributing soft tissue tenderness to bone: pressing over the anterior talofibular ligament and calling it lateral malleolar tenderness inflates the positive rate. Second, collapsing the two weight-bearing time points: a patient who now walks but could not immediately after injury has not satisfied the weight-bearing criterion, and a patient who could walk immediately but now cannot has likewise not satisfied it. In this case the lateral malleolus criterion carried the decision independently, so the mixed weight-bearing result did not change the outcome — but the note should still record both time points accurately, because the next clinician may rely on them.

Quick Reference Card

For this patient, the lateral malleolus criterion is positive and the decision is to obtain an ankle series. The weight-bearing result is mixed and does not alter the outcome, but it is documented for completeness and for the next clinician's reference.