Edited by Daniel Charlick, MD
The ankle joint is formed by three bones (Figure 1):
- The Tibia. The large bone forming the top and inside (media and posterior malleolus) of the ankle joint.
- The Fibula. The smaller bone making up the outside (lateral malleolus) of the ankle joint.
- The Talus. The dome-shaped lower bone of the ankle that moves up and down within the 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.
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 when 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.
If the foot rotates inward, either the ankle ligaments will sprain or the medial malleolus will break first, followed by a fracture of the fibula as the rotation continues.
Sometimes a twisting injury will tear the syndesmosis, the strong fibrous tissue that holds the fibula and tibia together at the ankle, which can lead to a fibula fracture closer to the knee.
It is very important for a fracture of the ankle to be well aligned. If the ankle fracture heals with even 1 mm of shifting out of place, the result can be the development of ankle arthritis, with pain and stiffness of the joint. This may severe enough to require surgical treatment including Ankle Arthrodesis (Ankle Fusion) or Ankle Arthroplasty (Ankle Replacement).
A stable ankle fracture (Figure 2) occurs when the broken bones and ligament damage is mild enough that the ankle does not displace with weight bearing. This can occur if the fractures are lower than the joint surface or sometimes when only the outside bone (fibula) or outside bone (tibia) is broken and the ligaments that stabilize 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. A cast or walking boot is typically applied and the patient is allowed to bear weight on the injured leg as tolerated. The Orthopaedic Surgeon will ask the patient to return in less than 10 days to see if the fracture displaces. If it does, it is unstable. If not, non-operative treatment can continue.
An unstable ankle fracture (Figure 3) occurs when the injury has disrupted the containment of the talus and it shifts, either to the side or to the front or back. This usually happens when there is injury to more than one bone or ligament of the ankle. Unstable ankle fractures typically benefit from surgery to realign the ankle joint and hold it in place while it heals, decrease the risk of ankle arthritis (Figure 4). While ankle fracture surgery has risks, the risks of arthritis or failure to heal the bones without surgery is usually much higher.
Following an ankle fracture, some patients heal and return to full function without a problem. Unfortunately, even with ideal treatment, some patients may develop ankle arthritis as a result of the severity of the joint damage.
Figure 4: Unstable Ankle Fracture stabilized with surgery
Edited on May 30, 2020