The ankle joint is where the bones of the leg (the tibia and fibula) meet with the bones on the hindfoot (talus) to form a joint that allows the foot to bend up and down. The ankle joint is susceptible to injury and one common type of injury is called an ankle fracture. Ankle fractures can occur from many types of trauma including slips on the ice, a fall down stairs, sports injuries, and car crashes.
When people talk about ankle fractures, they are usually referring to an injury to the bones of the tibia and fibula. The ends of these bones commonly called the medial malleolus (end of the tibia) and lateral malleolus (end of the fibula), are the bony bumps that you feel on the inner and outer side of the ankle. While other bones around the ankle joint can be injured as well, a common ankle fracture occurs to the end of the tibia and/or the end of the fibula.
There are different types of ankle fractures that can occur, and one of the more serious types is called a bimalleolar ankle fracture--an injury to both the inner and outer side of the ankle. Bimalleolar ankle fractures almost always require surgical treatment. Only in rare circumstances, usually because of poor patient health or limited function, would a bimalleolar ankle fracture be treated without surgery.
An ankle fracture can be caused in many ways, and because of that, each individual injury is slightly different and the treatment and recovery may vary significantly from one injury to another. Some people are confused when they have an ankle fracture that requires surgery and prolonged therapy when someone else they know just wore a brace for a few weeks. While both of these injuries were ankle fractures, they were clearly very different and had different timelines for recovery.
Most bimalleolar and trimalleolar ankle fractures are serious injuries. They often occur from high energy injuries such as falls and motor vehicle collisions. In addition to the force of impact, there is often a significant force of rotation on the ankle seen in sports injuries and serious falls. Sometimes these fractures can occur due to a weakening of the bone, most commonly in people with osteoporosis. That's not to say that people who have these injuries have weak bone—sometimes the force of injury is just too much for even the strongest bone. However, in people with underlying conditions that weaken the bone, these injuries can occur with less force than in other people.
Bimalleolar Ankle Fractures
When a bimalleolar ankle fracture occurs, there is an injury to both the medial malleolus (inner side of the ankle) and the lateral malleolus (outer side of the ankle). Because both sides are injured, the ankle joint becomes unstable. An unstable injury occurs when the fracture disrupts the structural integrity of the ankle (joint). Because the joint is unstable, it is susceptible to damage and early ankle arthritis if left untreated. Therefore, the typical treatment is to surgically repair the fracture to stabilize the ankle joint.
Bimalleolar Equivalent Ankle Fractures
One special subset of these fractures is called a bimalleolar equivalent fracture. This typically occurs when there is a fracture of the lateral malleolus and a ligament injury on the inner side of the ankle (the deltoid ligament)1. While this particular injury does not involve a bone injury on the inner side of the ankle, the ligament injury that has occurred causes the ankle joint to become unstable and requires surgical treatment to stabilize the joint.
Bimalleolar equivalent fractures need to be considered any time a lateral malleolus fracture has occurred. If there is pain or swelling on the inner side of the ankle, a bimalleolar ankle fracture may be present. Special x-rays, called stress x-rays, can be performed to look for signs of instability of the ankle joint.
Trimalleolar Ankle Fractures
Another variant of this type of injury is called a trimalleolar ankle fracture. The typical bimalleolar fracture involves bone injury to the inner and outer side of the ankle. People who sustain a trimalleolar ankle fracture also have a bone injury at the back of the tibia (posterior malleolus fracture) near the ankle joint.2 Often this does not change the treatment from that of a bimalleolar ankle fracture. However, if the bone injury in the back of the tibia, called the posterior malleolus, causes instability of the ankle joint, it may need to also be repaired at the time of surgery.
Treatment of Complex Ankle Fractures
Treatment of all of these injuries is similar, and almost always requires surgery. The surgical procedure is performed to repair the bones, most often with metal plates and screws3. These implants repair the bones to restore the stability of the ankle joint. It is very important to repair the bones with proper alignment; if not lined up perfectly there is a higher chance of developing early ankle arthritis.
One of the concerns of these complex ankle fractures is that they are usually accompanied by significant ankle swelling. Often this swelling can be serious, and may even cause blisters (called fracture blisters) to form on the skin. Surgery is frequently delayed days or weeks if there is significant swelling. Severe swelling not only makes the surgery more difficult to perform but can dramatically increase the risk of infection and healing problems after surgery.
As mentioned, infection and wound complications are the most worrisome concerns associated with ankle fracture surgery. Other common complications include stiffness and long-term swelling. Many patients notice swelling after ankle fracture surgery for six months, and may always have some increased swelling. Another concern is that because the bone is directly under the skin, metal plates and screws are sometimes bothersome and require removal. Lastly, even with appropriate care, surgical repair, and proper rehabilitation, ankle arthritis can occur.
A Word From Verywell
Bimalleolar and trimalleolar ankle fractures are typically unstable injuries that require surgical intervention in order to adequately restore alignment and stability to the ankle joint. Surgical treatment can be complicated by a tenuous soft tissue envelope surrounding the ankle joint causing the potential for complications such as infection and healing problems. Because of this, surgeons often proceed cautiously, allowing soft tissue to dictate the timing of surgical intervention. While most people fully recover, long-term mobility in the strength of the ankle joint can be an issue after these injuries