A bimalleolar fracture is a severe injury involving the ankle joint, the connection point between the leg and the foot. This type of break is characterized by fractures on both sides of the ankle, making the joint highly unstable. The injury typically results from a traumatic event requiring a significant amount of force.
Defining the Bimalleolar Fracture
The term “bimalleolar” refers to a fracture involving two of the bony prominences, or malleoli, that form the ankle mortise. The ankle joint is composed of the tibia, the fibula, and the talus. A bimalleolar fracture specifically involves the distal ends of the tibia and fibula.
The break includes the medial malleolus (the bump on the inner side of the ankle and the end of the tibia) and the lateral malleolus (the bump on the outer side of the ankle and the end of the fibula). Since the injury affects both sides of the joint, it disrupts the ankle’s ring structure, making the joint unstable.
The ankle’s stability is maintained by the syndesmosis, a group of strong ligaments connecting the lower ends of the tibia and fibula. Injury to these ligaments, or a fracture of the posterior portion of the tibia, often accompanies a bimalleolar break. The involvement of these structures contributes to the joint’s instability and dictates the complexity of treatment.
Mechanisms of Injury
Bimalleolar fractures most often result from rotational and twisting forces applied to the ankle joint. This occurs when the foot is planted and the body rotates violently over the ankle, causing a severe twisting motion. Common scenarios include rolling the ankle during sports or stepping onto uneven ground, leading to forced inversion or eversion of the joint.
The most frequent mechanism is supination-external rotation, where the foot turns inward while the lower leg twists outward. This action places intense stress on the ankle structures, often breaking the lateral malleolus first and then the medial malleolus.
High-impact trauma is another cause, often seen in motor vehicle accidents or falls from heights. These high-energy events can create complex fracture patterns. In older adults, falls may cause this injury even with less force, particularly if bone strength is compromised.
Treatment Pathways and Surgical Considerations
Treatment for a bimalleolar fracture is determined by whether the ankle joint remains stable after the injury. Stable fractures are rare for this injury type and may be managed without surgery if the bones are minimally displaced and the ankle mortise remains aligned. Non-operative treatment involves a period of non-weight bearing, typically in a cast or boot for six to eight weeks, with repeat X-rays to ensure the bones do not shift.
Most bimalleolar fractures are unstable due to the disruption of the ankle ring, almost always requiring surgical intervention. An unstable fracture means the talus has shifted out of its normal position, which can lead to poor long-term function.
The standard procedure for unstable bimalleolar fractures is Open Reduction Internal Fixation (ORIF). This surgery involves opening the skin to manually reposition the broken bone fragments into their correct anatomical alignment. Once aligned, the fragments are held in place using metal hardware, such as plates, screws, or wires.
A more complex variation is a trimalleolar fracture, which involves the medial, lateral, and posterior malleoli. The involvement of the posterior malleolus increases the fracture’s complexity and instability, nearly always requiring an ORIF procedure. The goal of surgical fixation is to restore the ankle mortise to its precise position to minimize the risk of developing post-traumatic arthritis.
Recovery and Rehabilitation
Following surgical fixation, the initial recovery phase mandates a period of strict non-weight bearing lasting approximately six to twelve weeks. During this time, the patient must use crutches or a knee scooter to prevent pressure on the healing bones, as bearing weight too early can displace the fixed fragments. Swelling is common and can persist for up to a year after the injury.
Physical therapy (PT) is a major component of the post-operative process and begins after the non-weight bearing period is complete. PT focuses on regaining the ankle’s full range of motion, which is often limited by stiffness after immobilization. Progressive exercises are then introduced to restore strength in the surrounding muscles and re-establish a normal gait pattern.
Full recovery can take six months to a year, and long-term consequences are possible with such a severe joint injury. Post-traumatic arthritis is a common concern, with an estimated incidence of 20 to 40% following an ankle fracture. Factors like residual joint misalignment and the degree of initial cartilage damage contribute to the risk of future stiffness and pain.