You get a sprained ankle when your foot rolls or twists beyond its normal range of motion, stretching or tearing the ligaments that hold the joint together. About 85% of ankle sprains happen when the foot rolls inward, a motion called inversion, which damages the ligaments on the outside of the ankle. It takes surprisingly little to make it happen: a misstep off a curb, an awkward landing after a jump, or simply walking on uneven ground.
What Happens Inside the Ankle
Your ankle joint is held in place by bands of tough tissue called ligaments. On the outer side, three ligaments connect your leg bone to your foot bones. On the inner side, a thicker, stronger set of ligaments does the same job. This difference in strength is exactly why inward rolls are so much more common and damaging than outward rolls. The outer ligaments are thinner and easier to overstretch.
When your foot rolls inward, those outer ligaments absorb the force. If the roll is forceful or sudden enough, the fibers stretch beyond their limit and begin to tear. An outward roll, where the foot turns away from the body, is less common precisely because the inner ligaments are thicker and more resistant. When outward-roll sprains do occur, they often involve more significant structural damage because it takes greater force to injure those stronger ligaments.
There’s also a less common type called a high ankle sprain, which involves the ligaments higher up, between the two bones of the lower leg. This happens through a different mechanism: an outward twisting of the foot combined with the foot bending upward toward the shin. High ankle sprains typically result from sudden cutting, turning, or falling motions and take considerably longer to heal than standard sprains.
The Most Common Ways It Happens
Ankle sprains don’t require a dramatic event. The Mayo Clinic lists four primary causes: a fall that twists the ankle, landing awkwardly after jumping or pivoting, walking or exercising on uneven surfaces, and having another person step or land on your foot during sports. That last one is especially common in basketball and soccer, where feet are constantly competing for the same patch of ground.
Sports that involve jumping, sudden direction changes, or foot rotation carry the highest risk. Basketball, tennis, football, soccer, and trail running are all frequent culprits. But plenty of sprains happen outside of sports entirely. Stepping off a sidewalk at a slight angle, catching your foot on a stair, or losing your balance on a wet floor can generate enough force to roll the ankle and tear a ligament.
Risk Factors That Make Sprains More Likely
Certain conditions make your ankles more vulnerable. Uneven terrain is an obvious one, but footwear plays a bigger role than many people realize. Shoes that don’t fit properly, aren’t designed for the activity you’re doing, or have high heels all increase your risk. Research on older tennis players found that wearing running shoes during lateral movements led to greater inward ankle angles compared to wearing court-specific tennis shoes. The extra cushioning in running shoes may feel comfortable, but it can reduce lateral stability and increase the chance of a roll during side-to-side movements.
The single biggest risk factor, though, is a previous sprain. A study in BMJ Open Sport and Exercise Medicine found a recurrence rate of about 26% among professional football players who had already sprained an ankle. One of the most notable findings: the severity of the original sprain didn’t predict whether a second one would happen. Grade I sprains were just as likely to recur as more severe injuries. What did matter was rehabilitation time. Players who returned to activity faster had a higher risk of reinjury, and most recurrences happened between 2 and 12 months after the initial sprain.
How Sprains Are Graded
Not all sprains are the same. They’re classified into three grades based on how much ligament damage has occurred.
- Grade 1: The ligament is stretched or slightly torn. You’ll notice mild tenderness, some swelling, and stiffness, but the ankle feels stable. Walking with minimal pain is usually possible.
- Grade 2: A more significant but still incomplete tear. Expect moderate pain, swelling, and bruising. The injured area is tender to touch, and walking hurts. The ankle may feel somewhat unstable.
- Grade 3: A complete tear of one or more ligaments. This brings severe swelling, bruising, and intense pain. The ankle feels unstable and gives out, making walking extremely difficult or impossible.
How to Tell If It’s a Sprain or a Fracture
This is the question most people are really asking when they’re sitting on the ground holding their ankle. Doctors use a set of guidelines called the Ottawa Ankle Rules to determine whether an X-ray is needed. You likely need imaging if you can’t bear weight on the ankle at all, if you can’t take four steps, or if there’s point tenderness directly over certain bony landmarks (the knobs on either side of the ankle, the heel bone, or the bone on top of the foot).
If you can hobble on it and the pain is more spread out across the soft tissue rather than sharply focused on bone, a sprain is more likely. That said, moderate and severe sprains can feel just as painful as fractures in the first few hours, so the inability to walk alone isn’t a reliable way to distinguish them.
What Recovery Looks Like
Grade 1 sprains typically need several days to a few weeks of rest, with gentle range-of-motion exercises starting as soon as pain allows. The goal is to restore flexibility and strength before the joint stiffens up. Grade 2 sprains follow a similar path but on a longer timeline, often requiring several weeks before normal activity feels comfortable again.
Grade 3 sprains are more complex. Most heal with conservative treatment (rest, bracing, and structured rehabilitation), but some high-level athletes with complete ligament tears opt for surgical repair to get back to full performance more quickly. Regardless of grade, starting rehabilitation exercises early and completing them fully appears to be one of the most important factors in preventing reinjury. The research on recurrence rates suggests that cutting rehab short, even when the ankle feels better, significantly increases the odds of spraining it again within the following year.
Ankle braces or taping during sports can reduce risk for people with a history of sprains. Choosing activity-appropriate footwear, particularly shoes designed for lateral stability during court sports or hiking, addresses one of the most controllable risk factors.