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Ankle Fractures (Tibia and Fibula)

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Description

Ankle fractures involve the bony prominence of the distal tibia or fibula (the so- called malleolus), or, occasionally, the shaft of the fibula as well. Ankle fractures range from a simple injuries of a single bone to complex ones involving multiple bones and ligaments.  Twisting with the foot planted on the ground and the body rotating around it is the most common mechanism of injury. (Compression is more apt to produce a fractures of the weight-bearing surface of the distal tibia, the plafond; these are designated as “pilon fractures", and are considered distinctly.)  Ankle fractures can be broadly divided into stable or unstable injuries. Stable fractures are typically amenable to non-operative management. Some residual arthrosis is not uncommon even if the bone heals perfectly. 

Structure and function

Ankle anatomy

The ankle joint is made up of the tibia, fibula, and talus. The tibia forms the superior and medial aspects of the joint, and the fibula its lateral aspect.  The talus is a dome-shaped lower bone that sits above the calcaneus and below the tibial plafond.  The distal ends of the fibula and tibia that overlap the talus are known as the malleoli (“little hammers”): the lateral malleolus is the distal end of the fibula, whereas the medial and posterior malleoli are part of the tibia. A fracture affecting both the medial and lateral malleoli is called a bimalleolar fracture, and one involving the medial, lateral, and posterior malleoli is called a trimalleolar fracture.

The ankle joint also contains three important ligaments: the deltoid ligament medially, connecting the tibia to the talus and calcaneus;  the talo-fibular and calcaneo-fibular ligaments (collectively the lateral collateral ligaments); and the syndesmosis which connects the distal tibia and fibula above the tibio-talar joint line.

 

Figure: Anatomy of the ankle joint. Medially, the deltoid ligament (shown in red) connects the tibia to the talus and calcaneus; laterally the calcaneofibular (green)  and talofibular (yellow) ligaments stabilize the joint. The syndesmosis (red) between the tibia and fibula holds them together.  

 

The tibial plafond, lateral malleolus, and medial malleolus form a mortise, a socket in which the talus sits.  Although the ligaments are needed to give the ankle its full stability, the bony congruity of the mortise and the talus is a necessary component. When the mortise is disrupted by a fracture, the talus is free to move more than it should. This abnormal motion leads to focal loading on the points of contact between the bones and thereby injures the joint surface.

Figure: The ankle forms a mortise and tenon. The mortise (the socket) comprises the  lateral malleolus, the  tibial plafond, and the medial malleolus. The tenon (or tongue) is the talus. As seen, the talus is wedged into a space just big enough to hold it.

Classification of ankle fractures

There are many methods of classifying ankle fractures, some of which are very simple, and other that may provide more detailed information yet can be unwieldy or unreliable (PMID: 2071659)

 

 

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 The simplest way to classify ankle fractures is purely descriptive. Important points come from gross examination and radiographic imaging and should include the bony structures involved (i.e., isolated medial/lateral malleolar, bimalleolar, trimalleolar, etc.), whether the fracture is open or closed, and the condition of the soft tissue (i.e., swelling, bruising).

 

Figure: Example of a bimalleolar fracture x-ray. Note the lateral malleolus (arrowhead) and medial malleolus (arrow) are broken and displaced, and that the talar body has subluxed laterally. Credit: http://en.wikipedia.org/wiki/Ankle_fracture#mediaviewer/File:Bimalleolar_fracture_legend.jpg

Stable versus Unstable Classification of Ankle Fractures

Another classification method is based on the stability of the joint. Ankle fractures are classified as stable if the fracture is non-displaced or minimally displaced and the medial structures (deltoid ligament and medial malleolus) are intact. This occurs if the fracture affects only the lateral malleolus, with the medial malleolus, deltoid ligament, and syndesmosis intact. This type of injury allows the talus to remain within the mortise, preventing displacement of the joint. Ankle fractures are classified as unstable if the injury also disrupts structures on the medial aspect of the ankle including the medial malleolus or deltoid ligament. This type of injury allows the talus to be loose and potentially poorly positioned within the ankle joint.  In some patients an unstable ankle fracture is only diagnosed after the ankle is "stress" under x-ray revealing the lateral displacement of the talus and therefore disruption of the deltoid ligament.

 

Figure: Plain x-ray of a stable ankle fracture. Note the space between the talus and tibia remains consistent. Credit: http://www.footeducation.com/stable-ankle-fracture

 

Figure: Plain x-ray of an unstable ankle fracture. Note how the talus is displaced laterally away from the tibial plafond. Credit: http://www.footeducation.com/ankle-fracture

 

There are also more systematized classification methods for ankle fractures. These include the Weber classification and the Lauge-Hansen classification.

Weber Classification of Ankle fractures

The Weber system classifies ankle fractures into three types based on the location of the fibular fracture relative to the syndesmosis. Type A fractures occur below the syndesmotic ligament (infra-syndesmotic) usually from an avulsion mechanism, Type B fractures exit the medial fibula at level of the joint  (transsyndesmotic), and Type C fractures exit the medial aspect of the fibula well above the joint level and cause disruption of the syndesmotic ligaments  (suprasyndesmotic).

 

Figure: Weber classification of ankle fractures. Credit: http://www.orthopaedicsone.com/display/Clerkship/Ankle+fractures

Lauge-Hansen Classification of Ankle Fractures

The Lauge-Hansen (L-H) system classifies ankle fractures based on fracture patterns observed from a series of experiments in which cadaveric ankles were placed in different positions (supination or pronation) and subsequently loaded to failure by different deforming forces (external rotation, adduction, or abduction). Different combinations of positions and motions led to unique and predictable patterns of injury. In general, the side of the ankle where structures are under most tension is injured first and then injuries progress around the ankle in a sequential manner.

The L-H system defines four stereotypical fracture patterns: supination external rotation (SER), supination adduction (SAD), pronation external rotation (PER), and pronation abduction (PAB). Each of these fracture patterns has additional numerical designations that describe the sequential failure of anatomic structures as the deforming force progresses. It is important to note that in these injuries, a given ligament may rupture or that ligament may remain intact and cause an avulsion fracture at its insertion. Due to the predictable locations of the fibular fractures, L-H classifications SAD, SER/PAB, and PER are virtually equivalent to Weber classifications A, B, and C, respectively.

The most common fracture pattern in the L-H system is supination external rotation (SER). This injury initially ruptures the anterior inferior tibiofibular ligament and is essentially a high ankle sprain (SER 1). As the leg continues to rotate, the talus collides with the distal fibula leading to an oblique/spiral fibular fracture at the level of the plafond or syndesmosis (SER 2). SER2 fractures are the most commonly encountered ankle fracture. If the rotation continues, it will involve either rupture of the posterior inferior tibiofibular ligament or an avulsion fracture of the posterior malleolus (SER 3). These will likely continue to the final stage (SER4) and involve a transverse fracture of the medial malleolus or rupture of the deltoid ligament.

 

Figure: Supination external rotation (Weber Type B) fracture. Credit: http://www.orthopaedicsone.com/display/Clerkship/Ankle+fractures

 

Another common fracture pattern is supination adduction (SAD). This injury will initially create tension at the lateral collateral ligaments that either results in a talofibular sprain or a transverse avulsion fracture of the lateral malleolus below the syndesmosis (SAD 1). If the rotation continues the talus will collide with the tibia, leading to a vertical fracture of the medial malleolus (SAD 2). The syndesmosis is not involved in SAD injuries.

 

Figure: Supination adduction (Weber Type A) fracture. Credit: http://www.orthopaedicsone.com/display/Clerkship/Ankle+fractures

 

Pronation external rotation (PER) injuries are different in that they start medially. In the pronated position, the foot experiences greatest tension medially. A PER 1 injury results in either a transverse fracture of the medial malleolus or a rupture of the deltoid ligament. As the talus continues to rotate laterally, it stresses the anterior-inferior tibial fibular ligament, resulting in its rupture or an avulsion fracture of the anterior tibia or fibula (PER 2). Continued rotation will result in an oblique or spiral fibular fracture above the level of the joint (PER 3). PER 4 will additionally involve rupture of the posterior tibiofibular ligament or an avulsion fracture of the posterior malleolus.

 

Figure: Pronation external rotation (Weber Type C) fracture. Credit: http://www.orthopaedicsone.com/display/Clerkship/Ankle+fractures

 

Pronation abduction (PAB) injuries also start medially. PAB 1 injuries begin with a fracture of the medial malleolus or rupture of the deltoid ligament. Further abduction will drive the talus into the fibula, resulting in failure of the anterior tibiofibular ligament (PAB 2). This will further progress to a short oblique fracture of the fibula at or above the ankle joint (PAB 3).

 

Tibial plafond fractures

Tibial plafond fractures (pilon fractures) are a unique type of ankle fracture with a different mechanism of injury. Pilon fractures often occur as a result of a high-energy axial (compression) load to the foot, like falling from height or a motor vehicle accident. They are relatively uncommon but very severe ankle injuries that affect the distal part of the tibia known as the tibial plafond. The tibial plafond, along with the medial and lateral malleoli, forms the mortise that articulates with the dome of the talus. In a pilon fracture, a major load to the foot drives the talus into the tibial plafond. In other words, the foot gets jammed into the lower part of the tibia. This results in a serious fracture that extends into and involves the weight-bearing surface of the ankle joint. Tibial plafond fractures are severe injuries that produce extensive damage to the soft tissues, direct injury to the articular cartilage of the ankle joint, and fracturing of the  the bones of the ankle.

There are various classification schemes for pilon fractures including the Ruedi-Allgower classification and the AO/OTA classification. The Ruedi and Allgower system classifies pilon fractures according to the size and displacement of the articular fragments. Type A fractures have no comminution or displacement of the joint fragments. Type B fractures have displacement but no comminution. Type C fractures have both displacement and comminution and/or impaction. The AO/OTA system classifies pilon fractures according to the extent of involvement of the articular surface of the tibial plafond. Type A fractures are tibial metaphyseal injuries that do not extend into the articular surface. Type B fractures are partial intra-articular while Type C fractures involve the entire articular surface of the plafond.

 

Patient presentation

Patients with ankle fractures usually present with immediate and severe pain, swelling, and bruising following an acute ankle injury. The hallmark difference between ankle fractures and ankle sprains is an inability to bear weight on the injured foot, although this is not always the case. Deformity may be evident if the ankle joint has been dislocated in the case of an unstable ankle fracture. In some stable fractures presenting early after injury, there may be minimal swelling and no deformity.

Patients typically describe an acute twisting injury in which the foot is planted on the ground and the body rotates around it. The direction of rotation and the orientation of the foot while planted will determine the order in which structures are broken. While this is useful information to obtain, it is often the case that the patient cannot recall or describe exactly what happened.

The history is important in making an accurate diagnosis of a pilon fracture, as patients will often describe an acute high-impact injury forcing a major load against the ankle joint.  Falls from a great height and motor vehicle crashes are the most common causes of these fractures.  Patients with pilon fractures will present with extreme discomfort, marked pain and swelling, deformity, crepitus about the ankle joint, and an inability to bear weight. In addition to significant injury to the tibial shaft at the weight-bearing portion of the ankle joint, pilon fractures often involve extensive soft tissue injury to the knee and foot. 


Objective evidence

The Ottawa Ankle Rules were designed to aid physicians in determining the patients with ankle pain who are most likely to have a fracture and thus warrant the added, and otherwise unnecessary, expense of radiological evaluation. According to these rules, ankle radiographs are only necessary if there is (1) pain at a malleolus that is accompanied by either (2a) bony tenderness associated with the posterior aspect of the lateral or medial malleolus or (2b) inability to bear weight (take four steps). Unless these criteria are met, ankle x-rays are unnecessary as they will be negative nearly 100% of the time.

In cases that do satisfy these criteria, patients should have anterior-posterior (AP), lateral, and oblique (mortise) x-rays. These views should be evaluated for the integrity of the bones as well as proper alignment between joint surfaces. The malleoli should be examined for fracture lines at, above, and below the syndesmosis.

 

Figure: Common x-ray views of the ankle. You can check the alignment of the talus within the mortise in the mortise and lateral views. Credit: http://www.orthopaedicsone.com/display/Clerkship/Ankle+fractures

 

On the AP view, the medial clear space is the distance from the lateral border of the medial malleolus to the medial border of the talus. If this space is >4mm or greater than the superior clear space (distance between superior border of the talus and inferior border of the tibial plafond), it indicates lateral dislocation of the talus. Additionally, tibiofibular overlap <10mm or tibiofibular clear space >5mm indicates injury to the syndesmosis. On the lateral view, the talus should appear directly underneath the tibia. On the mortise view, the clear space between the talus and the mortise should be symmetric.

Pilon fractures require additional radiographs of the foot, leg, and knee to evaluate for soft tissue or bony involvement of these areas. CT scans are helpful and often necessary to visualize the various fracture lines, since fracture patterns vary considerably from patient to patient.

 

Figure: CT scan of a pilon fracture. Note how the fracture extends into the weight-bearing portion of the tibia. Credit: http://en.wikipedia.org/wiki/Pilon_fracture#mediaviewer/File:Volkmann_gro%C3%9F.png

 

Epidemiology

According to Lin et al (PMID: 21655420), ankle fractures occur in the USA with an incidence of approximately 187 fractures per 100,000 people per year. The incidence of ankle fractures has risen dramatically over the last two decades, likely due to the growth of the elderly population. Fracture incidence is bimodal, with men typically having higher rates as young adults and women having higher rates as elderly adults. The highest incidence is found in elderly white women. 

The most common type of ankle fracture is an isolated fibular fracture, comprising about half of all ankle fractures. One-fourth of ankle fractures are bimalleolar, while trimalleolar fractures and isolated medial malleolar fractures are less common. Only 2% of ankle fractures are open.  

According to Mauffrey et al, pilon fractures are relatively rare and account for only 5-7% of tibial fractures (PMID: 21954749). The incidence of pilon fractures is on the rise due to mandatory air bags in cars and the resulting increased survival rates after major motor vehicle accidents. The typical patient who suffers a pilon fracture is a 35-40 year old male. Despite their relative rarity, pilon fractures are significant because they have a high complication rate, require a prolonged period of non-weight-bearing, and are associated with a high rate of long-term ankle arthritis..

 

Differential diagnosis

In any case of acute ankle injury, it is necessary to discern which ligaments are sprained and which bones are broken. These injuries are not exclusive; ankle fractures are often accompanied by sprains to the supporting ligaments of the foot and leg. According to Boyce et al (PMID: 15496699), ankle injuries are common in the emergency department. In fact, 22% of sports injuries presenting to the emergency room involve the ankle, but sprains constitute the majority of these injuries and are far more common than fractures (sprain-to-fracture ratio is 8:1).

Injuries that cause ankle fractures may also cause damage outside of the ankle joint that cannot be seen on a standard ankle x-ray. For example, damage to the medial ankle joint (e.g., medial malleolar fracture or rupture of the deltoid ligament) may be part of an injury complex whereby the force of the injury passes through the syndesmosis and interosseous membrane disrupting these structures and eventually leading to a fracture in the proximal fibula near the knee (Maisonneuve fracture).  A Maisonneuve fracture is a type of Weber C ankle fracture.

 

Figure: Maisonneuve fracture in the proximal fibula accompanying a medial malleolus fracture (not shown in x-ray). Credit: http://en.wikipedia.org/wiki/Maisonneuve_fracture#mediaviewer/File:Maisonneuve_fracture_Malleolus.jpg

 

It is also possible that injuries outside of the ankle joint will cause ankle pain. For example, an injury to the Lisfranc joint (tarsometatarsal joint) in the midfoot can mimic the symptomatology of an ankle fracture. Radiographic imaging and careful examination to find the area of maximal tenderness can differentiate a Lisfranc injury from a true ankle fracture.

 

Red flags

It is important to determine if a non-displaced fracture of the fibula also involves a medial injury as this will indicate an unstable fracture and change the treatment and prognosis. Radiographic stress imaging is often necessary in this case, as physical examination revealing medial tenderness has been shown to have poor predictive value for significant deltoid injury.

On examination, look for an open wound. Blood on the skin is suggestive of an open fracture and any break in the skin associated with an ankle fracture should be considered an open fracture until proven otherwise.  Open fractures require administration of antibiotics and tetanus prophylaxis as indicated. Formal irrigation and debridement should be performed in the operating room by a specialist, however, basic wound management (cleaning the wound with saline and applying a dressing and splint) should not await the arrival of a specialist.

Rapid reduction should be performed on any ankle fracture with dislocation.

If a patient presents with severe ankle pain following an acute injury but x-rays are normal, they may have an injury to the foot and not the ankle, such as a Lisfranc joint disruption or navicular fracture. It is important to evaluate the midfoot to catch any injuries that might mimic the presentation of an ankle fracture.

Diabetic patients who fracture their ankles pose a unique challenge, especially if their diabetes is uncontrolled (HgA1C >7%).  They have a much higher risk of developing a post-operative infection if surgery is indicated.  Additionally, they are at high risk for developing a Charcot ankle arthropathy which is a destructive arthritis associated with neuropathy. 

If the patient’s growth plates are still open, they should be evaluated for growth plate injury.  

If a pilon fracture is suspected, it is important to look for possible associated injuries that may require urgent intervention, such as neurovascular injury or compartment syndrome. The knee joint should also be evaluated for soft tissue damage or bony disruption. Given the severity of the injury, it is not uncommon for pilon fractures to be open. In these cases, expedited surgical treatment is necessary to minimize the risk of infection.

 

Treatment options and outcomes

Initial management of all ankle fractures should consist of reduction in the case of a dislocated fracture and basic wound management (sterilization, dressing, and prophylactic antibiotics) in the case of an open fracture. The ankle should then be immobilized with a splint and elevated to minimize swelling.

After initial management, decisions regarding definitive treatment can be made. If the fracture is stable and not displaced, non-operative treatment may suffice. This is often the case when the injury is limited to the lateral malleolus at or below the syndesmosis without injury to the medial malleolus, deltoid ligament, or syndesmosis. Non-operative treatment consists of casting or the use of a walker boot for 4-6 weeks with a brief period of protective weight bearing and crutches. Frequent radiographs are necessary to monitor for displacement and to ensure that proper alignment is maintained over the course of treatment. Following adequate bone healing, physical therapy will be necessary to help the patient regain strength, range of motion, and proprioceptive function.

Operative fixation will be necessary if there is displacement of the bone fragments or disruption of the mortise architecture. This is often the case when the fracture affects the medial malleolus, the fibula above the syndesmosis (Weber Type C), or if the injury is bimalleolar, trimalleolar, intra-articular (pilon), or open. Operative fixation normally occurs days after the injury to allow the swelling to go down and reduce the risk of soft tissue complications. Surgery generally consists of making incisions at the affected malleoli, re-positioning the bony fragments to their appropriate positions, and holding them in place with screws and plates. The hardware can be left in the joint permanently unless it causes irritation, in which case it can be removed once the fracture has healed.

 

Figure: Fibula fracture with laterally displaced talus pre-surgery. Note the increase in medial clear space between medial border of talus and medial malleolus suggesting lateral dislocation. Credit: http://www.footeducation.com/wp-content/uploads/2010/08/Ankle-Fracture-ORIF-Figure-1.jpg

 

 

Figure: Displaced fibula fracture post-surgery. Credit: http://www.footeducation.com/wp-content/uploads/2010/08/Ankle-Fracture-ORIF-Figure-2.jpg

 

 

Outcomes for stable fractures treated non-operatively are generally excellent. Ankle fractures treated with operative fixation heal uneventfully in approximately 85% of the cases. Not surprisingly, outcomes improve with more accurate reduction. Factors that negatively affect outcomes include involvement of the posterior malleolus, impaction of the talus, severe talar dislocation, and diabetic status of the patient. Recovery time will depend on the severity of the initial injury but it often takes a year or more before patients reach their point of maximal improvement. Even then, mild to moderate symptoms may persist for years despite complete radiographic healing.      

Complications of ankle fractures include malunion, non-union, stiffness, and wound complications. Even with optimal treatment, some ankle fractures may result in post-traumatic ankle arthrosis.  A history of a previous ankle or tibia fracture is present in 75% of patients with severe ankle arthritis.  It is possible that these cases involved damage to the articular surface, leading to chondrocyte death or dysfunction. In the case of sub-optimal reduction, the joint may be misaligned, promoting the development of arthrosis. Another possible, albeit rare, complication of ankle fractures is complex regional pain syndrome (CRPS) which was previously known as reflex sympathetic dystrophy syndrome. This uncommon but debilitating condition is characterized by burning or throbbing pain, sensitivity to cold or touch, weakness, stiffness, and changes in skin color, temperature, or texture.

Outcomes for pilon fractures are good in approximately 75% of cases, but this will vary significantly depending on the complexity and severity of the fracture. Due to the severe nature of most pilon fractures, they have a reasonably high complication rate. Post-traumatic ankle arthrosis is the most common complication of pilon fractures. Axial load injuries, such as those that lead to pilon fractures, can cause cartilage damage that will promote arthritis regardless of good anatomic reconstruction. Other complications include infection, wound healing problems, painful prominent hardware, and non-union or delayed union.

 

Figure: Pilon fracture. Note the numerous fracture lines and how the fracture extends into the weight-bearing portion of the tibia. Credit: http://www.footeducation.com/wp-content/uploads/2010/09/Figure-1-Pilon-Fracture-X-Ray.png

 

 

Figure: Pilon fracture after operative treatment. Note how the ankle joint is restored to as close to a normal position as possible and fixed with plates and screws. Credit: http://www.footeducation.com/wp-content/uploads/2010/09/Figure-2-Pilon-Fracture-Following-Surgery.png

 

Risk factors and prevention

Valtola et al and Honkanen et al (PMID: 11792591, 9692074) found that primary risk factors for ankle fracture are cigarette smoking and a high body mass index. According to Seeley et al (PMID: 8864910), although low bone density is a risk factor for other fractures, it is not considered a major risk factor for ankle fractures.

 

Miscellany

Ankle injuries are among the most common sports-related injuries.

Clinical pearls: If an ankle fracture is suspected, palpate the proximal fibula for tenderness to look for a Maissoneuve fracture. You can visualize lateral talar dislocation on a mortise view of the ankle if the distance between the medial malleolus and medial border of the talus is > 4mm. The squeeze test – compression of the proximal tibia and fibula to elicit pain at the syndemosis – should be performed to test for syndesmotic injury. Assess neurovascular function before and after treatment. In particular, assess the motor and sensory functions of the tibial, superficial peroneal, deep peroneal, saphenous, and sural nerves.

There is still disagreement on indications for surgical stabilization of ankle fractures, especially stable lateral malleolar and posterior malleolar fractures.

Avulsion fractures are visualized as small flecks of bone on radiographs just distal to a malleolus. The fragment is a small part of bone that was pulled off its insertion by its corresponding ligament. These fractures are not structurally significant but they do inform the viewer that an ankle sprain is present.

Race horses are sometimes in the news for “ankle fractures.” However, their injuries are actually to the metatarsophalangeal joint, also known as the “fetlock.”

 

Key terms

Ankle fracture

Stable ankle fracture

Unstable ankle fracture

Bimalleolar ankle fracture

Maissoneuve fracture

Lateral malleolus

Medial malleolus

Posterior malleolus

Ottawa Ankle Rules

Mortise

Deltoid ligament

Lateral collateral ligament

Syndesmosis

Tibial plafond

Pilon fracture

Medial clear space

Tibiofibular overlap

Lauge-Hansen Classification

Weber Classification

 

Skills  

Physically examine an injured ankle and determine the extent of injury and structures involved

Apply the Ottawa Ankle Rules to decide which patients require radiographic evaluation

Describe radiographic findings and use radiographs to identify fractures, infer ligamentous injuries, and recognize instability and displacement

Differentiate between stable and unstable ankle fractures

Provide first-line treatment to open fractures (wound management) and dislocations (gross reduction and splinting)