Edited by Lance Silverman, MD
The ankle joint is formed by three bones (Figure 1):
- The Tibia. The large bone forming the top and inside (media aspect) of the ankle joint.
- The Fibula. The smaller bone making up the outside (lateral aspect) of the ankle joint.
- The Talus. The dome-shaped lower bone of the ankle joint.
An “ankle fracture” (broken ankle) occurs when one or both of the bones (fibula or tibia) making up the top part of the ankle joint are broken. Most commonly, this is the bone on the outside of the ankle (the fibula).
Ankle fractures can be broadly divided into two groups:
- Stable Ankle Fractures: The ankle joint remains intact (Figure 2)
- Unstable Ankle Fractures: The ankle joint is displaced (Figure 3)
Figure 1: Normal Ankle x-ray
Figure 2: Stable Ankle Fracture
Figure 3: Unstable Ankle Fracture
Ankle injuries routinely fall into predictable patterns based on how they happen. Understanding the mechanism of injury helps doctors to treat the fractures, making the decision to proceed to surgery or attempt non-surgical treatment easier.
Most ankle fractures occur following an acute twisting injury; the foot is planted on the ground and the body rotates around it, (ex. Figure 4). When the foot rotates outward, the bone on the outside of the ankle (the fibula), breaks first. If the rotation continues, the structures on the inside of the ankle, the medial malleolus or the deltoid ligament will break or tear respectively.
Conversely, if the foot rotates inward, either the ankle ligaments will sprain or the medial malleolus will break first, followed by the fibula as the rotation continues.
Sometimes a twisting injury tears the syndesmosis, (the strong fibrous tissue that holds the two bones of the lower leg together at the ankle), which can lead to a fibula fracture higher up the leg.
Figure 4: Twisting mechanism causing an Ankle Fracture
A stable ankle fracture (Figure 2) occurs when only the outside bone (fibula) is broken and the other ligaments and bones that make up the ankle are undamaged. Stable ankle fractures are most often treated non-operatively by limiting twisting stress to the ankle joint until the bones heal (typically 6 weeks). Sometimes stability is hard to assess initially. Orthopaedic surgeons will ask patients to return in less than 10 days to see if the fracture displaces or is truly stable.
An unstable ankle fracture (Figure 3) occurs with different injury patterns. Either isolated injury to the medial (inside) ankle bones, or injury to both the outside bone (fibula) and other structure, (medial malleolus, deltoid ligament, or syndesmosis) is injured. these injuries disrupt the containment of the talus bone and benefit from surgery to speed healing and decrease the risk of ankle arthritis, (Figure 5). While surgery has risks, the risks of arthritis or failure to heal the bones without surgery is much higher.
Following an ankle fracture, some patients heal and return to full function without a problem. Unfortunately, even with ideal treatment, some patients develop ankle arthritis.
Figure 5: Unstable Ankle Fracture stabilized with surgery
Edited on September 22, 2018