Ottawa Ankle Rules
The most extensively validated clinical decision rule in emergency medicine. Determines the need for radiography after ankle and midfoot injuries using targeted palpation and weight-bearing assessment — safely reducing unnecessary X-rays by 30–40% without missing clinically significant fractures.
Ottawa Ankle Rule — Malleolar Zone
An ankle X-ray series is indicated if there is pain in the malleolar zone AND any one of the following findings. Palpate the posterior edge and tip of each malleolus over the distal 6 cm. For midfoot pain, use the foot X-ray assessment below.
Ottawa Ankle Rule — Midfoot Zone
A foot X-ray series is indicated if there is pain in the midfoot zone AND any one of the following findings. Palpate the navicular bone and the base of the 5th metatarsal specifically. For malleolar zone pain, use the ankle X-ray assessment above.
The Ottawa Ankle Rules apply to adults and children over 5 years of age presenting with acute blunt ankle or midfoot injury. They do not apply to: patients presenting more than 10 days after injury, isolated skin injuries, patients referred back with previously interpreted X-rays, patients with diminished sensation due to neurological deficit, or patients with obvious deformity suggesting fracture or dislocation (in whom X-ray is indicated regardless). Pregnant patients can be assessed using the rules — the rules determine the need for X-ray, and the minimal radiation from extremity films is generally considered safe.
Understanding the Ottawa Ankle Rules
The Ottawa Ankle Rules (OAR) were developed by Ian Stiell and colleagues at the Ottawa Civic Hospital and first published in 1992. They represent one of the most successful clinical decision rules in medical history — derived from a prospective study of 750 patients, then validated in multiple subsequent studies involving over 40,000 patients across multiple countries. The rules have been independently validated more than any other clinical decision rule in emergency medicine.
The fundamental insight behind the rules is that the vast majority of ankle and foot injuries seen in the emergency department are soft tissue injuries (sprains, contusions), not fractures. Before the rules’ implementation, virtually every patient with an ankle injury received X-rays, even though only approximately 15% had fractures. The OAR identify the clinical features that reliably distinguish patients who need imaging from those who do not.
Ankle X-Ray Series Required If:
Pain in the malleolar zone AND any of:
- Bone tenderness at the posterior edge or tip of the lateral malleolus (distal 6 cm)
- Bone tenderness at the posterior edge or tip of the medial malleolus (distal 6 cm)
- Inability to weight-bear 4 steps immediately after injury AND in the ED
Foot X-Ray Series Required If:
Pain in the midfoot zone AND any of:
- Bone tenderness at the base of the 5th metatarsal
- Bone tenderness at the navicular bone
- Inability to weight-bear 4 steps immediately after injury AND in the ED
Key concept — two separate rules, two separate X-ray series: The Ottawa Ankle Rules are actually two independent assessments — one for the malleolar (ankle) zone and one for the midfoot zone. A patient may need an ankle series only, a foot series only, both, or neither. Each zone should be assessed independently. The zones overlap slightly, so a patient with pain spanning both areas should have both rules applied.
Interpretation & Rule Performance
The Ottawa Ankle Rules are “rule-out” tools with near-perfect sensitivity. They are designed to identify patients who can safely forgo radiography, not to diagnose fractures.
| Metric | Ankle (Malleolar) Rule | Foot (Midfoot) Rule |
|---|---|---|
| Sensitivity | 98.5–100% | 98.0–100% |
| Specificity | ~40–49% | ~37–47% |
| Negative predictive value | ~99.6% | ~99.6% |
| X-ray reduction | 30–40% | 30–40% |
| Missed fracture rate | <1.4% (mostly avulsion fractures <3 mm) | <2% (mostly avulsion fractures) |
The very rare fractures “missed” by the Ottawa Ankle Rules are almost exclusively small avulsion fractures (<3 mm) at the tip of the malleolus that do not require operative treatment and are managed identically to a severe sprain. No study has identified a clinically significant fracture requiring operative intervention that was missed by correct application of the rules. The rules are designed to catch all fractures that would change management — they are not designed to detect every radiographic abnormality.
The weight-bearing criterion requires inability to take 4 steps at both timepoints: immediately after the injury AND at the time of ED assessment. If the patient was able to walk immediately after the injury but cannot now, or vice versa, the criterion is not met. Limping counts as weight-bearing — the patient does not need to walk normally, only to transfer weight onto the injured limb for 4 consecutive steps. Many patients with significant swelling and pain can still manage 4 limping steps.
Examination Technique & Anatomy
Accurate application of the Ottawa Ankle Rules requires precise palpation of specific bony landmarks. Understanding the anatomy and examination technique is critical for reliable results.
The malleolar zone encompasses the distal 6 cm of the fibula (lateral malleolus) and the distal 6 cm of the tibia (medial malleolus), including their posterior edges and tips. The key is to palpate the bone, not the soft tissues overlying it.
Lateral malleolus: Begin at the tip of the lateral malleolus and press firmly on the bone. Then move your fingertip along the posterior edge of the fibula, maintaining bone contact, up to 6 cm proximal to the tip. Apply firm pressure at multiple points along this posterior edge. The anterior aspect of the malleolus is not part of the rule — tenderness confined to the anterior talofibular ligament (ATFL) alone does not meet the criterion.
Medial malleolus: Similarly, palpate the tip and posterior edge of the medial malleolus up to 6 cm proximal. The deltoid ligament lies inferior and anterior to the medial malleolus — tenderness isolated to the deltoid area does not meet the criterion.
The critical distinction is between bone tenderness (pain when pressing directly on the malleolar bone) and ligament/soft tissue tenderness (pain when pressing on the soft tissue structures around the malleolus). Only bone tenderness counts. Swelling alone, tenderness over the ATFL, or generalised ankle puffiness does not satisfy the rule.
The midfoot zone assessment requires palpation of two specific bones:
Base of the 5th metatarsal: The styloid process of the 5th metatarsal is the bony prominence on the lateral (outer) border of the midfoot. It is easily located by running your finger along the lateral border of the foot from the little toe proximally — the first prominent bump you encounter is the base of the 5th metatarsal. This is a common fracture site (avulsion fracture or Jones fracture) in inversion injuries. Press firmly on the bone and ask about pain.
Navicular bone: The navicular is located on the medial (inner) side of the midfoot, just distal to the talar head. It can be located by palpating the medial longitudinal arch — the navicular forms the apex of the arch on the medial side. An alternative landmark: the navicular tuberosity is palpable approximately 2.5 cm distal and inferior to the medial malleolus. Navicular fractures are uncommon but clinically significant — they can be stress fractures in athletes or avulsion fractures in acute trauma.
As with the malleolar zone, the distinction between bone tenderness and soft tissue tenderness is critical. Only tenderness elicited by direct pressure on the bone satisfies the criterion.
The weight-bearing criterion is frequently misapplied. The correct assessment requires both a history component and an examination component:
History component: Ask the patient (or witnesses): “Were you able to walk at all immediately after the injury?” Any ambulation counts — walking to the car, walking off the sports field, limping to a chair. If the answer is yes, the patient was able to weight-bear immediately after injury, and this half of the criterion is not met.
Examination component: In the ED, ask the patient to take 4 steps. They may use a walking aid, hold onto furniture, or limp — the key is whether they can transfer weight onto the injured limb for 4 consecutive steps. Do not insist on normal gait. If the patient is too anxious or refuses to try, this should generally be counted as unable to weight-bear, and imaging should be obtained.
Both conditions must be met: Inability to weight-bear at both timepoints. If the patient walked immediately after injury but cannot now (common with progressive swelling), the criterion is not met — and X-ray may not be needed (assuming no bone tenderness is present).
The Ottawa Ankle Rules define two distinct anatomical zones, each with its own set of criteria and its own radiographic series:
Malleolar zone: Extends from the tips of both malleoli, including the distal 6 cm of the posterior edge of both the fibula and tibia, and the soft tissues surrounding the malleoli. Pain in this region triggers the ankle (malleolar) assessment, and a positive result indicates an ankle X-ray series (AP, mortise, and lateral views).
Midfoot zone: The area between the malleoli and the metatarsal heads, encompassing the navicular, cuboid, cuneiforms, and the bases of the metatarsals. Pain in this region triggers the midfoot assessment, and a positive result indicates a foot X-ray series (AP, oblique, and lateral views).
The two zones overlap in the region of the talonavicular and calcaneocuboid joints. Patients with pain that spans both zones should have both rules applied independently. Note that the hindfoot (calcaneus and posterior talus) is not well covered by either rule — calcaneal fractures have different injury mechanisms (typically falls from height) and require separate clinical assessment.
Inversion injury (most common): The foot rolls inward. This typically injures the lateral ligaments (ATFL most commonly, then calcaneofibular ligament). If severe, can cause an avulsion fracture of the lateral malleolus tip, a fracture of the base of the 5th metatarsal (avulsion or Jones fracture), or an anterior process calcaneal fracture.
Eversion injury: The foot rolls outward. Injures the deltoid ligament medially. A significant eversion force can cause a medial malleolus fracture, a Maisonneuve fracture (proximal fibula fracture with disruption of the interosseous membrane), or a syndesmotic (high ankle) sprain.
Rotational mechanism: External rotation of the foot relative to the tibia. Common in falls and sports. Can cause a range of ankle fractures following the Lauge-Hansen classification — from isolated lateral malleolus fractures to complex bimalleolar or trimalleolar patterns.
Direct blow/crush: Localised injury to the point of impact. May cause fractures at atypical locations that do not follow the usual sprain patterns. The Ottawa rules still apply — palpation of the specific bony landmarks will identify most significant fractures.
Special Populations & Considerations
The Ottawa Ankle Rules have been validated across diverse populations, but certain groups require additional consideration.
The OAR have been validated in children from age 5 upward, with similar sensitivity and specificity to adults. In children under 5, the rules should not be applied — skeletal immaturity, difficulty cooperating with examination, and the risk of Salter-Harris physeal injuries make clinical assessment less reliable. For children aged 5–12, note that physeal (growth plate) injuries can present with tenderness over the malleolar tip or distal fibula that may mimic ligament injury. When bone tenderness is present, X-ray appropriately — the OAR will capture these cases.
The OAR perform well in elderly patients and have been validated in this population. However, elderly patients have a higher prevalence of osteoporosis, and fractures may occur with lower-energy mechanisms. The rules appropriately capture most of these through the bone tenderness and weight-bearing criteria. Be aware that elderly patients may have pre-existing pain or difficulty weight-bearing unrelated to the acute injury — use the acute change from baseline as the relevant finding.
Athletes with ankle injuries may have a higher pain threshold and may attempt weight-bearing despite significant injury. They also have a higher incidence of syndesmotic (high ankle) sprains and osteochondral lesions of the talar dome — injuries not specifically targeted by the OAR. The rules still apply, but if an athlete has persistent pain, mechanical instability, or difficulty returning to sport despite normal initial X-rays, further evaluation with MRI or stress views should be considered at follow-up.
The OAR rely on the patient’s ability to perceive and report bone tenderness. Patients with peripheral neuropathy (diabetic, alcoholic, or other causes) may not reliably localise or report bony pain, potentially leading to false-negative assessments. The rules explicitly exclude patients with diminished sensation due to neurological deficit. For patients with known significant neuropathy, a lower threshold for imaging is appropriate — consider X-ray if there is any clinical concern regardless of the OAR result.
Clinical takeaway: The OAR can be applied to most patients aged 5 and over with acute ankle or midfoot injuries. The main populations where caution is needed are children under 5, patients with peripheral neuropathy, and patients who cannot reliably cooperate with the examination. In these groups, clinical judgement and a lower threshold for imaging should prevail.
Common Pitfalls & Limitations
The single most common error in applying the Ottawa Ankle Rules is palpating the anterior talofibular ligament (ATFL) or deltoid ligament and interpreting tenderness as a positive finding. The rules specifically require bone tenderness at the posterior edge or tip of each malleolus — not anterior soft tissue tenderness. The ATFL is the most commonly injured structure in ankle sprains, and it is located anterior and inferior to the lateral malleolus. A patient with isolated ATFL tenderness but no posterior bony tenderness does not meet the criteria for an ankle X-ray. This distinction is critical — failing to differentiate bone from ligament tenderness will result in unnecessary imaging and negate the rule’s purpose.
Technique tip: place your fingertip directly on the malleolar bone and press. Then move along the posterior edge, maintaining bone contact. The posterior edge is the key palpation area — not the anterior surface or the ligamentous structures below the malleolus.
The Ottawa Ankle Rules perform best when applied after the initial acute pain has subsided slightly — typically at the time of ED presentation, which is usually 30 minutes to several hours post-injury. Very early assessment (within minutes of injury) may produce unreliable results because acute pain and guarding can make palpation assessment difficult, and the patient may be unable to attempt weight-bearing due to pain alone rather than mechanical instability. Conversely, the rules should not be applied more than 10 days after injury — at that point, significant soft tissue healing has occurred and the clinical findings may no longer reliably predict the initial injury pattern.
The Maisonneuve fracture is an important injury that the Ottawa Ankle Rules may not directly identify. This injury involves a fracture of the proximal fibula (not the distal 6 cm assessed by the rules), disruption of the interosseous membrane, and deltoid ligament rupture or medial malleolus fracture — constituting an unstable ankle injury despite potentially normal ankle X-rays. The OAR will typically catch this injury through medial malleolus bone tenderness or inability to weight-bear, but if the medial side injury is purely ligamentous (deltoid tear without fracture), the bony tenderness criterion may not be met.
Clinical tip: in any eversion/external rotation mechanism with medial ankle tenderness, palpate the full length of the fibula to its head at the knee. Tenderness over the proximal fibula should prompt a dedicated proximal fibula/knee X-ray to exclude a Maisonneuve fracture — this is a separate clinical assessment from the OAR.
Many clinicians apply the ankle (malleolar) rule but forget to separately assess the midfoot zone. The ankle and foot rules are independent assessments — a patient with a normal ankle rule may still need a foot X-ray if they have midfoot tenderness over the navicular or 5th metatarsal base. Base-of-5th-metatarsal fractures (avulsion fractures and Jones fractures) are common, clinically significant, and easy to miss if the midfoot is not specifically examined. Always palpate both zones in any patient presenting after an ankle or foot injury, and document which rules were applied.
The Ottawa Ankle Rules were designed to detect common fractures of the malleoli, 5th metatarsal base, and navicular. Several important injuries fall outside the rules’ primary targets:
- Talar dome osteochondral lesions: May present with vague ankle pain and clicking; often missed on initial X-ray and require MRI for diagnosis.
- Lisfranc (tarsometatarsal) injuries: Midfoot pain with inability to weight-bear may prompt foot X-rays, but subtle Lisfranc injuries can be missed on standard views. Weight-bearing foot X-rays or CT are often needed.
- Calcaneal fractures: The hindfoot is not specifically assessed by the OAR. Falls from height with heel pain should prompt calcaneal imaging regardless of the rules.
- Syndesmotic (high ankle) sprains: Injury to the tibiofibular syndesmosis may present with pain above the malleolar zone. Not specifically targeted by the OAR — the squeeze test and external rotation stress test are needed.
- Achilles tendon rupture: Presents with posterior ankle pain and weakness. Clinically distinct from bony injury — Thompson test is the key assessment.
A negative Ottawa Ankle Rule means the patient does not need an X-ray — it does not mean the patient has a trivial injury. Significant ligament sprains (grade II–III), syndesmotic injuries, and tendon injuries can all produce a negative OAR. Patients cleared by the rules should still receive appropriate treatment for their soft tissue injury: RICE (rest, ice, compression, elevation), analgesia, and weight-bearing guidance. They should also receive safety-netting advice: if symptoms are not improving by 5–7 days, or if weight-bearing remains very difficult at 10–14 days, reassessment and further imaging may be needed. Failure to provide adequate follow-up guidance is a common source of patient dissatisfaction after a “no X-ray” decision.
Quick Reference Summary
| Zone | X-Ray If Pain + Any Of: | Series Ordered |
|---|---|---|
| ANKLE (MALLEOLAR) ZONE | ||
| Malleolar zone pain | Bone tenderness — posterior edge/tip of lateral malleolus (distal 6 cm) | Ankle X-ray series (AP, mortise, lateral) |
| Bone tenderness — posterior edge/tip of medial malleolus (distal 6 cm) | ||
| Inability to weight-bear 4 steps (immediately + in ED) | ||
| FOOT (MIDFOOT) ZONE | ||
| Midfoot zone pain | Bone tenderness — base of the 5th metatarsal | Foot X-ray series (AP, oblique, lateral) |
| Bone tenderness — navicular bone | ||
| Inability to weight-bear 4 steps (immediately + in ED) | ||
Palpate bone, not ligaments. Posterior edge, not anterior. 4 steps at both timepoints. The Ottawa Ankle Rules are deceptively simple but depend entirely on precise examination technique. Bone tenderness at the specific landmarks — posterior malleolar edges (distal 6 cm), navicular, and 5th metatarsal base — is the critical finding. Soft tissue tenderness, swelling, or ecchymosis alone does not indicate the need for radiography. When the rules are negative, treat the soft tissue injury and provide clear follow-up advice.
Disclaimer & References
For Educational Purposes Only. This calculator and the accompanying clinical information are intended as educational tools for healthcare professionals. They do not replace clinical judgement. Results should be interpreted in the full clinical context. Lab reference ranges vary by institution — verify with your own laboratory. Drug dosages should be confirmed against current prescribing information.
References
- Stiell IG, Greenberg GH, McKnight RD, et al. A study to develop clinical decision rules for the use of radiography in acute ankle injuries. Ann Emerg Med. 1992;21(4):384–390. DOI: 10.1016/S0196-0644(05)82656-3
- Stiell IG, Greenberg GH, McKnight RD, et al. Decision rules for the use of radiography in acute ankle injuries: refinement and prospective validation. JAMA. 1993;269(9):1127–1132. DOI: 10.1001/jama.1993.03500090063035
- Stiell IG, McKnight RD, Greenberg GH, et al. Implementation of the Ottawa Ankle Rules. JAMA. 1994;271(11):827–832. DOI: 10.1001/jama.1994.03510350037034
- Bachmann LM, Kolb E, Koller MT, Steurer J, ter Riet G. Accuracy of Ottawa ankle rules to exclude fractures of the ankle and mid-foot: systematic review. BMJ. 2003;326(7386):417. DOI: 10.1136/bmj.326.7386.417
- Dowling S, Spooner CH, Liang Y, et al. Accuracy of Ottawa Ankle Rules to exclude fractures of the ankle and midfoot in children: a meta-analysis. Acad Emerg Med. 2009;16(4):277–287. DOI: 10.1111/j.1553-2712.2008.00333.x
- Stiell IG, Wells GA. Methodologic standards for the development of clinical decision rules in emergency medicine. Ann Emerg Med. 1999;33(4):437–447. DOI: 10.1016/S0196-0644(99)70309-4
- Pijnenburg AC, Glas AS, De Roos MA, et al. Radiography in acute ankle injuries: the Ottawa Ankle Rules versus local diagnostic decision rules. Ann Emerg Med. 2002;39(6):599–604. DOI: 10.1067/mem.2002.123646
- Leddy JJ, Smolinski RJ, Lawrence J, Snyder JL, Priore RL. Prospective evaluation of the Ottawa Ankle Rules in a university sports medicine center. Am J Sports Med. 1998;26(2):158–165. DOI: 10.1177/03635465980260020201