Bimalleolar Ankle Fractures

Etiology

According to the Lauge Hansen classification, supination and external rotation injuries are the most common cause of bimalleolar fractures. Eversion is considered the most common reason which can cause all damage.[5]

Epidemiology

Ankle fractures account for 9% of all fractures. In the United States, ankle fractures are the most common lower limb fractures and are the most frequent fracture or injury in the emergency room. The bimalleolar fracture accounts for 60% of all ankle fractures, with an incidence of 187 fractures per 100,000 people. This fracture has a bimodal distribution and most commonly affects older women and young males. Ankle fracture is the third most common fracture overall; in athletes, it is the most frequently encountered fracture. Also, this is the third most frequent fracture in patients over 60.[3][2] 

History and Physical

A focused and thorough history should be obtained to identify any comorbidities or conditions that may be detrimental to healing. Important findings include diabetes with or without peripheral neuropathy, peripheral vascular disease, osteopenia, alcohol use, tobacco use, and malignancy. Chronic medications such as corticosteroids can also cause prolonged healing. So, it is necessary to ask about medication history. These should be identified before any physical exam takes place. The patient history should investigate multiple aspects of the injury, including time from injury to presentation, pain location, and possibly the mechanism of injury. It can be helpful if the patient can describe the injurious event, the force directed toward the ankle, along with the intensity of this force. Higher levels of force should raise the suspicion of more complications.

On physical examination, the clinician should begin with the affected limb by examining for gross deformity and skin changes that may indicate a change in neurovascular status or open wounds that may indicate an open fracture. It is also important to examine the knee, fibula, tibia, ankle, and foot and look for any signs of fracture like swelling, redness, hematoma formation, and lateral or medial tenderness malleolus or the proximal head of the fibula. The inability to bear weight on the injured foot indicates a fracture, and palpation can identify the fracture's exact location. The clinician must ensure that the foot and ankle's neurovascular state is intact, including palpating pedal pulses and assessing the motor function, sensation, capillary refill time, and pulses at the injury site. Examine both the active and passive range of motion of the joint and weight-bearing status. Also, any signs of open wounds or compartment syndrome should be assessed.[1][7][11]

Anatomy

The ankle joint is classified as a mortise and tenon joint. As stated above, the ankle is composed of the tibia, fibula, and talus articulating with each other, and these articulations are supported by strong ligamentous support on either side. The medial collateral ligament, or deltoid ligament, is a triangular-shaped ligamentous complex composed of 4 ligaments that stabilize the medial aspect of the ankle by anchoring the tibia to the foot. These 4 ligaments are named the anterior tibiotalar ligament, posterior tibiotalar ligament, tibiocalcaneal ligament, and tibionavilcuar ligament, and they are divided into 2 portions: superficial and deep.[6]

The superficial fibers extend from the medial malleolus to the navicular, sustentaculum tali of the calcaneus and the talus. The deep portion is the strongest and extends from the medial malleolus to the talus. The deltoid ligament is the most common ligamentous injury during the medial malleolar fracture, causing joint instability. When the deltoid ligament ruptures instead of the medial malleolus fracturing during a bimalleolar ankle fracture, it is known as a "bimalleolar equivalent" fracture.[7] The most common mechanism of injury that damages this ligament is foot eversion or an external rotation force due to the intense medial stresses these forces produce. The lateral collateral ligaments comprise 3 ligaments: the anterior talofibular ligament, calcaneofibular ligament, and posterior talofibular ligament. These secure the lateral aspect of the ankle by anchoring the fibula to the foot. These ligaments restrict inversion and internal rotation forces.[8]

The syndesmosis is a long interosseous membrane that holds the fibula and tibia together and comprises 4 ligaments at its most distal end. These ligaments are the anterior inferior tibiofibular ligament, the posterior inferior tibiofibular ligament, the inferior transverse ligament, and the interosseous ligament, which is the most distal aspect of the interosseous membrane. These ligaments hold the fibular within the incisura of the tibia and help keep the integrity of the ankle joint. Syndesmotic tears or sprains can result from hyper-dorsiflexion trauma and rotational injuries.[9][4][5][6][7][8]

Evaluation

According to the Ottawa Ankle Rules, the clinician should not order ankle radiographs unless there is pain or tenderness in the ankle malleoli along with 1 of the following:

• The presence of tenderness at the tip of lateral or medial malleolus within or 6 cm above these structures
• Patients should not be able to tolerate weight-bearing after injury.

Radiological Features

Plain-film Radiographs

Ankle X-ray is the best initial investigation, requiring 3 views:

• Anterior-posterior view: assesses the soft tissue swelling and checks for any subtle fractures.
• Mortise view: this view is done by putting the foot in 15 to 20 degrees of internal rotation. It evaluates the talus positioning and the syndesmosis widening.
• Lateral view: serves to assess fractures in the lateral view and for determining any effusion in the ankle joint

Sometimes the tenderness is present in the proximal leg in addition to the widening of the syndesmosis, without obvious fracture in the ankle; however, there is a fracture in the proximal fibula. It provides a clue to the rupture of the syndesmosis. This presentation calls for a radiograph of the proximal tibia and fibula to diagnose a specific injury called a Maisonneuve fracture, which is a spiral fracture in the proximal third of the fibula.

Usually, weight-bearing films, if possible, are the best option to diagnose syndesmotic injuries.

CT

• CT is mostly for potential posterior malleolar fractures and to give an idea about the degree of impact. 

MRI

• MRI is only indicated to assess soft tissues, ie, cartilage or ligament injuries.

Ultrasound

• Ultrasound is also sometimes useful for ligament assessment, but the results are user-dependent[1][10][11]

Classifications

The most common classification systems used to explain ankle fractures are the Lauge-Hansen and Danis-Weber systems. Each has its uses in classifying these fractures to identify the best way to treat the injury. The Lauge-Hansen classification attempts to identify the fracture pattern based on the motion of the talus in the ankle joint. The classification system is broken into 4 groups: supination-adduction, pronation-abduction, supination-external rotation, and pronation-external rotation. Each mechanism of injury is associated with specific fracture patterns.[12] The Danis-Weber divides the lateral malleolus into 3 distinct areas and classifies the fracture of the lateral malleolus based on where the fibula was fractured. This classification is more basic and is more relevant when it comes to operative decision-making.[12]

Treatment / Management

In treatment, assessment of the patient and the injury should proceed systematically according to ATLS guidelines. The primary survey should come first, ruling out any life-threatening injuries. Then, the examiner can manage the ankle fracture, first checking for any neurovascular damage that requires an urgent ankle reduction to regain the foot's vascularity and avoid long-term sequence. A skin integrity examination is essential because open fractures can be treated primarily by external fixators. Open fractures can lead to delayed union, infection, and skin necrosis. Most bimalleolar fractures are unstable fractures and require treatment with open reduction internal fixation. The management plan can be for either operative or non-operative treatment.

Non-operative 

Uses a below-knee cast for 6 weeks or a total contact cast for 3 months in patients with diabetes; indicated if the fracture is stable or when the patient cannot tolerate surgical fixation. It needs repeat ankle X-rays in a week to check for any displacement. Also, patients should be on thromboprophylaxis. 

Operative

Open reduction internal fixation is indicated when the fracture is unstable, such as in a talar shift. The technique uses fibula fixation using plates and screws (lateral malleolus) and medial malleolus fixation using cannulated screws or tension band wiring or plate over medial malleolus in certain types of medial malleolus fractures (Lauge-Hansen supination-adduction fracture pattern). The syndesmosis should be inspected for injury once the medial and lateral malleoli are reduced and fixated. If there is a syndesmotic injury, syndesmotic screws should be inserted (there are some intraoperative tests to check syndesmosis integrity, 1 of them called the Cotton test). If the posterior malleolus fracture is more than 25%, a CT scan is necessary, and it requires posterior fixation using cannulated screws or, in some situations, plating. In the 2 options, thromboprophylaxis is necessary until the patient achieves full weight bearing to avoid the risk factor of DVT.[2][13][14][15][1] Previously, surgeons stated that reducing the lateral malleolus was critical in treating ankle fractures. Today, it is accepted that the deep deltoid ligament is the primary ankle stabilizer that prevents lateral talar shift and external rotation of the talus.[16](A1)

Differential Diagnosis

• Ankle sprain
• Osteoarthritis
• Osteosarcoma
• Osteomyelitis
• Achilles rupture
• Septic arthritis
• Tendon dislocation
• Rheumatoid arthritis
• Osteoid osteoma
• Charcot joint
• Pathologic fracture
• Ewing sarcoma
• Gout

Prognosis

Depending on the patient and operation, the bimalleolar fracture can have a poor prognosis. Those at higher risk are the elderly, persons with diabetes, peripheral neuropathy, peripheral vascular disease, and tobacco users. In general, full weight-bearing takes time and can begin after 5 to 6 weeks of immobilization. However, this is different for each patient depending on the injury's severity, bone quality, and reduction's stability. With operative intervention, the mortality 1 year after the surgery is 12% in patients older than 65, increasing to 50% for patients over 95.[2][1][14][17]

Complications

Complications of a bimalleolar ankle fracture can range in severity and include wound infection, wound hematoma, delay of wound healing, dislocation, arthrosis, inadequate reduction, complex regional pain syndrome, compartment syndrome, impingement syndrome, limited range of motion, malunion, malunion, and Charcot arthropathy, mainly in diabetic patients. The long-term complications include deformity, infection, ulceration, ankle osteoarthritis, and amputation. Until the patient reaches full weight-bearing, they must take thromboprophylaxis to prevent the development of DVT or pulmonary embolism.[1][15]