Is it a sprain or a fracture? When an ankle injury needs an X-ray

It’s the first question after any twisted ankle: is it broken? A dramatically swollen, purple ankle can be “just” a sprain, and a fracture can look surprisingly mild. What separates them is a short set of checks called the Ottawa ankle rules.

The Ottawa ankle rules

Emergency physicians in Ottawa developed these rules to decide who needs an X-ray after an ankle or midfoot injury. An X-ray is needed if there is pain in the ankle or midfoot and any of these:

Ankle:

• tenderness along the back edge or tip of the outer ankle bone (lateral malleolus), or
• tenderness along the back edge or tip of the inner ankle bone (medial malleolus), or
• being unable to take four steps, both right after the injury and when examined.

Midfoot:

• tenderness at the base of the fifth metatarsal (the bony bump halfway along the outer edge of the foot), or
• tenderness over the navicular (the bony bump on the inner side of the midfoot), or
• being unable to take four steps.

“Four steps” means four steps taken on each foot, even with a limp.

How accurate are they?

Very good at their job, which is ruling fractures out. A systematic review of 27 studies and more than 15,000 patients found that when the rules were negative, the chance of a fracture was very small, and using them could avoid many unnecessary X-rays.^[1] A later meta-analysis confirmed high sensitivity for both the ankle and midfoot rules.^[2] They work in children too.^[1]

The trade-off is that a positive result doesn’t mean there is a fracture, only that an X-ray is worth taking. Many people with positive rules turn out to have a sprain.

Injuries the rules can miss

The rules are built for the ankle and midfoot. They don’t cover everything:

• Fractures elsewhere, such as the toes or the heel.
• High ankle sprains and other ligament injuries between the shin bones.
• Lisfranc injuries of the midfoot, which can look mild on the day.^[3]
• Cartilage injuries inside the ankle joint, which don’t show on regular X-rays.
• Stress fractures, which build up over weeks rather than from one twist.

That’s why pain that isn’t improving over a week or two deserves another look, even after a normal X-ray. See fractures and trauma.

What to do right now

• If any Ottawa sign is present, get an X-ray. We can take it at the office; call us.
• If none is present, treat it as a sprain: protect, ice, elevate and start moving as pain allows. Our guide to sprained ankle recovery takes you through it week by week.
• If it’s not improving after one to two weeks, see us.

When to see a podiatrist