Do I need an X-ray for this ankle?
Ankle sprains are among the most common injuries seen in emergency departments and urgent care clinics. Before the 1990s, most patients had an X-ray, yet fewer than 15% had a fracture. Ian Stiell and colleagues at the University of Ottawa studied which findings predicted a fracture and published simple rules in 1992 and 1993. Applied correctly, they reduce ankle X-rays by about 30 to 40% while missing almost no significant fractures.
The ankle rule
An ankle X-ray series is needed if there is pain in the malleolar zone and any one of:
- Bone tenderness along the back edge or tip of the lateral malleolus (the outer ankle bone), over its lower 6 cm.
- Bone tenderness along the back edge or tip of the medial malleolus (the inner ankle bone), over its lower 6 cm.
- Inability to bear weight, meaning to take four steps, both immediately after the injury and at the time of the examination.
The foot rule
A foot X-ray series is needed if there is pain in the midfoot zone and any one of:
- Bone tenderness at the base of the fifth metatarsal, on the outer edge of the foot.
- Bone tenderness at the navicular bone, on the inner side of the midfoot.
- Inability to bear weight as defined above.
Limping still counts as bearing weight. The four steps do not have to be normal.
Worked example
A person rolls their ankle playing basketball. The outer ankle is painful and swollen, but pressing on the back edge and tip of both malleoli is not painful. They could not walk after the injury and still cannot take four steps in the clinic. The ankle rule is positive because of the inability to bear weight, so an ankle X-ray is indicated. There is no midfoot pain, so the foot rule does not apply.
Using the rules safely
- The rules apply to adults and have also been validated in children over about 5 years.
- They do not apply with intoxication, a head injury, multiple injuries, reduced sensation in the legs, pregnancy, or injuries more than 10 days old.
- They rule out fractures; they do not diagnose sprains. A badly sprained ankle without fracture still needs rest, compression and a follow-up if it does not improve within a week.
- Pressing exactly on the bone, not on the soft tissue in front of it, is the key to applying them correctly.
This calculator is for general information and education. It is not medical advice and does not replace the judgment of a doctor, nurse or pharmacist who knows the full clinical picture.