The Ottawa Ankle Rules are a simple set of physical exam criteria that help determine whether an ankle or midfoot injury needs an X-ray. Developed in the early 1990s, they give clinicians a reliable way to rule out fractures without imaging every sprained ankle that walks through the door. They catch roughly 91 to 99% of fractures while cutting down on unnecessary X-rays, saving time, money, and radiation exposure.
How the Rules Work
The Ottawa Ankle Rules divide the lower leg and foot into two zones: the ankle (malleolar zone) and the midfoot. Each zone has its own set of criteria. If any single criterion is positive in a given zone, an X-ray of that area is recommended. If none are positive, imaging can safely be skipped.
For the ankle zone, an X-ray is indicated if there is pain near either ankle bone (the bony bumps on each side of your ankle) along with any of the following:
- Bone tenderness along the back edge or tip of the outer ankle bone. The examiner presses along the last 6 centimeters (roughly 2.5 inches) of the outer leg bone, from the bump down toward the tip.
- Bone tenderness along the back edge or tip of the inner ankle bone. Same technique on the inside of the ankle.
- Inability to bear weight for four steps. This applies both right after the injury and again at the time of the exam. Limping counts as bearing weight; the test is whether you can take four steps at all, even painfully.
For the midfoot zone, an X-ray is indicated if there is midfoot pain along with bone tenderness at the base of the fifth metatarsal (the bony bump on the outside edge of your foot, about halfway between heel and little toe) or at the navicular bone (on the inside of the foot, just in front of the ankle).
Age also factors in. Patients 55 and older are flagged for imaging regardless, since fracture risk increases with age and bone density changes.
Why These Specific Spots Matter
The palpation points aren’t random. They correspond to the areas where fractures most commonly occur in twisting or rolling injuries. The posterior edges of the ankle bones are thinner and more vulnerable to avulsion fractures, where a ligament pulls a chip of bone away during a sprain. The base of the fifth metatarsal is a classic fracture site because a strong tendon attaches there that can yank the bone apart during an inversion injury (when your foot rolls inward). The navicular, meanwhile, sits in a high-stress area of the arch.
Pressing directly on bone rather than on surrounding soft tissue is key. Swelling and bruising from a ligament sprain can make the entire ankle tender, but tenderness that’s sharpest right on the bone surface suggests the bone itself may be damaged.
How Accurate Are They?
The Ottawa Ankle Rules are designed to be highly sensitive, meaning they catch nearly all fractures. An earlier systematic review found pooled sensitivity of 97.3% in adults. A more recent meta-analysis reported sensitivity of 91%, though individual studies have found rates as high as 99.4%. The important number for patients is the negative likelihood ratio: when the rules say you don’t need an X-ray, the chance of a missed fracture is extremely low.
Specificity is lower, around 25 to 37% depending on the study. In practical terms, this means the rules will send some people for X-rays who turn out not to have fractures. That’s an intentional tradeoff. The rules are built to be cautious, to avoid missing a broken bone, not to perfectly predict one. The accuracy holds regardless of whether a doctor, nurse practitioner, or other trained clinician performs the exam.
Impact on Emergency Care
Before the Ottawa Ankle Rules existed, most people who came to an emergency department with an ankle injury got X-rayed as a matter of routine, even though only about 15% of those images revealed a fracture. The rules gave clinicians a structured reason to skip imaging when the exam findings didn’t warrant it. Studies in both adult and pediatric populations have shown statistically significant drops in X-ray rates after the rules were adopted, without any increase in missed fractures.
Use in Children
The rules were originally developed and validated in adults, but research has confirmed they work in children too. A prospective study of children ages 1 to 15 at a pediatric emergency department found sensitivity of 98.3% and specificity of 46.9%. Implementing the rules reduced the X-ray rate from about 64% to 57% of pediatric ankle injury visits, a statistically significant drop. Only one fracture was missed in each group (before and after implementation), confirming the rules don’t compromise safety in younger patients.
What the Rules Don’t Cover
The Ottawa Ankle Rules apply specifically to blunt ankle and midfoot injuries, the kind you get from rolling your ankle on a curb or landing wrong during a basketball game. They are not designed for injuries more than 10 days old, open wounds over the ankle, patients with reduced sensation in their legs (from diabetes-related nerve damage, for example), or injuries caused by significant trauma like car accidents. In those situations, imaging is typically ordered regardless of exam findings.
The rules also don’t assess injury severity beyond the fracture question. A negative Ottawa screen means a fracture is very unlikely, but it doesn’t mean the injury is minor. Severe ligament sprains, tendon tears, and cartilage damage won’t trigger the rules but can still require weeks of treatment and rehabilitation.