Cause

Ankle sprains occur when ligaments that connect the bones in the foot, ankle, and lower leg stretch or tear.

An inversion injury, the most common cause of ankle sprains, occurs when the ankle rolls outward and the foot turns inward. It results in stretching and tearing of the ligaments on the outside of the ankle.

In an eversion injury, the ankle rolls inward and the foot turns outward, damaging the ligaments at the inside of the ankle.

In a "high" ankle sprain, a less common type of injury, ligaments that join the two lower leg bones together above the ankle, called the syndesmosis, are injured. This usually happens if the foot is forced up, or if the leg is forcefully twisted while the foot is planted. This injury can occur either by itself or with an inversion or eversion sprain. If the ligaments of the syndesmosis are injured, the sprain is more severe and takes longer to heal.

See a picture of types of ankle sprains.

Damage to the ligament varies from simply stretched or slightly torn to completely torn. Your doctor will grade your sprain accordingly.

• Grade I is stretching or slight tearing of the ligament with mild tenderness, swelling, and stiffness. The ankle feels stable, and it is usually possible to walk with minimal pain.
• Grade II is a larger but incomplete tear with moderate pain, swelling, and bruising. The ankle sometimes feels stable, but the damaged areas are tender to the touch, and walking is painful.
• Grade III is a complete tear of the affected ligament or ligaments with severe swelling and bruising. The ankle is unstable and may feel "wobbly." Walking is usually not possible, because the ankle gives out and there is intense pain, although initial pain may quickly subside. See a picture of an ankle sprain.