Twisting

• One of the more common causes of a bimalleolar ankle fracture is simply twisting your ankle. Due to the awkward nature of this type of rotation, the bones located on either side of your ankle may sustain a break. It usually affects the lateral malleolus of your fibula (which is located on the outside of your ankle) and the medial malleolus of the tibia (the protrusion on the inside of your ankle), but it may also cause a problem along the distal portion of your tibia instead. With this type of injury, it's also quite possible to sustain a strain or tear within the ligament of your ankle during the course of the awkward rotation, further exacerbating the severity of the injury.
  
  

Rolling

• While twisting your ankle may be one of the more common causes for a bimalleolar fracture, you can often suffer this type of injury due to a rolling of the ankle, which essentially means that an incorrect foot placement has caused the foot itself to roll on its side. This triggers an irregular rolling motion within your ankle that can produce a break at the base of your fibula and tibia, resulting in this "double" fracture. As soon as it happens, you'll frequently lose your footing and find it difficult to place weight on the affected joint.
  
  

Impact

• Besides twisting and rolling your ankle, which are actions that can occur during any type of physical exertion, it's also possible to suffer a bimalleolar ankle fracture from a direct blow to this particular joint. Car accidents are by far the most prevalent culprit, as the velocity of the impact can distribute a great deal of force up through your foot and into the ankle, causing it to fracture in more than one place. But, you may also suffer from a bimalleolar fracture as a result of any sort of trauma to the bones of your ankle. After the injury, you'll regularly see some deformity within the ankle itself that is soon followed by swelling of the joint.
  
  

Weakening

• Though not necessarily as common as the other causes of bimalleolar fracture, you may suffer from this type of ankle injury as a result of weakening or deterioration to the ligaments of the ankle. When this tissue suffers any sort of damage, the overall stability of your ankle is inevitably compromised, increasing the potential of a bimalleolar fracture.