Ankle sprain: A common musculoskeletal injury in which the ligaments of the ankle partially or completely tear due to sudden stretching. This typically occurs when the ankle is suddenly "twisted" in a sports activity or by stepping off an uneven surface. The pain is initially severe and can be associated with a "popping" sensation. Immediate swelling over the area of injury often occurs as the injured blood vessels leak fluid into the local tissue. Partial tears retain some ankle stability, whereas complete tears lose stability because the strapping ligaments no longer brace the ankle joint.

Initial treatment is with ice, rest, and limiting the amount of walking and weight bearing on the injured ankle. The leg can be elevated to reduce swelling, and crutches are often recommended to avoid further trauma to the injured ligaments. Antiinflammatory medications can be given to reduce local inflammation. Severe injuries are placed in immobilization casts. Surgery may be needed for complete tears. Physical therapy programs are part of the rehabilitation process, incorporating strengthening exercises of the lower leg muscles.