1.1 Epidemiology

Ankle fractures are one of the most common fractures and in the lower limb are second in frequency only to proximal femoral fractures. Ankle fractures have a bimodal age distribution of young men and elderly women. There is a noticeable increase in ankle fractures among the elderly.

1.2 Special characteristics

Malleolar injuries are articular fractures. Treatment is aimed at restoring normal joint anatomy and providing sufficient stability for early movement. Stable, undisplaced fracture patterns can be treated by closed methods. Anatomical restoration and stable fixation of the unstable, displaced fracture is best achieved by open reduction and internal fixation.

The decision to operate is not based on the fracture pattern alone. The condition of the soft tissues is paramount. Patient factors, such as age, diabetes, and osteoporosis, may alter the indications and fixation techniques for ankle fracture.

2.1 Case history and physical examination

Ankle fractures are often isolated injuries and a case history of the mechanism of injury, deformity, and ability to bear weight after injury should be obtained from the patient. Ankle fractures most often result from low-energy twisting injuries. The position of the foot and ankle at the time of injury will often dictate the fracture pattern. A case history of higher-energy trauma should indicate the possibility of greater soft-tissue involvement and the development of compartment syndrome. Higher-energy mechanisms may indicate that the fracture may be a tibial plafond fracture.

It is important to determine the presence of comorbidities, such as diabetes, peripheral vascular disease, neuropathy, and smoking. A social history determining the preinjury mobility and functional aspirations of the patient may aid treatment decision making.

Physical examination should look for any open wounds, swelling, deformity, bruising, and tenderness. Skin discoloration and blanching may indicate skin compromise and the need for prompt reduction. The neurovascular status of the foot should be carefully assessed.

2.2 Imaging

Three radiographic views of the ankle are required: the AP view, the AP view obtained in 20° angle of internal rotation to bring the transmalleolar axis parallel to the plate (mortise view), and the lateral view. It is important to look for shortening of the fibula, which is best evaluated by a step in the alignment of the subchondral plates of the tibial plafond and the lateral malleolus ( Fig 6.9-1 ). The talocrural angle is 83° plus or minus 4° ( Fig 6.9-2 ). If the angle is greater or lesser, then that indicates instability, change in fibular length, or displacement of the mortise. The joint space between the talus and plafond should equal the space between the medial malleolus and medial talus.

Widening of the medial joint space is indicative of mortise displacement.

The lateral view demonstrates the pattern of fibular fracture and any anterior or posterior translation of the talus. Computed tomographic (CT) scanning is rarely required for malleolar fractures. However, if in doubt as to the exact fracture pattern or mechanism of injury, a CT scan can be useful in identifying ankle fractures that are a pilon fracture variant, with a large posterior cortical (Volkmann) fragment in association with a fibular fracture. Occasionally, with the supination-adduction infrasyndesmotic fractures, a CT scan can also help to clearly elucidate the medial tibial articular impaction to allow comprehensive preoperative planning. Stress x-rays or views are only useful in the fully anesthetized patient and when compared to the normal side ( Fig 6.9-3 ).

3.1 Inferior tibiofibular complex (syndesmosis)

The distal tibia and fibula are held together to provide a tight elastic ankle mortise and this syndesmotic bond consists of three elements ( Fig 6.9-4 ):

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  The anterior syndesmotic (anterior tibiofibular) ligament joins the anterior tibial tubercle (tubercle of Tillaux-Chaput) to the lateral malleolus.

  
  
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  The posterior syndesmotic (posterior tibiofibular) ligament is stronger and joins the lateral malleolus to the posterior tibial tubercle.

  
  
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  The interosseous ligament binds the tibia to the fibula in the tibial notch (incisura fibularis tibiae), and is continuous with the interosseous membrane proximal to the syndesmotic ligaments.

3.2 Collateral ligament complexes

The collateral ligaments prevent varus/valgus tilting of the talus in the ankle mortise. The lateral collateral ligament complex consists of three distinct elements ( Figs 6.9-4 – 5 ):

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  The anterior talofibular ligament originates from the anterior border of the fibula and inserts just anterior to the lateral malleolar facet of the talus.

  
  
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  The calcaneofibular ligament originates at the tip of the fibula and runs posteriorly and distally underneath the peroneal tendons to insert at the calcaneus.

  
  
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  The posterior talofibular ligament originates from the posterior aspect of the distal fibula and inserts posteriorly at the talus.

The medial collateral ligament complex, or deltoid ligament, consists of two parts:

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  The tibiocalcaneal ligament is superficial and fan-shaped.

  
  
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  The deep anterior and posterior talotibial ligaments.

3.3 Mortise congruity

The talus remains in close contact with the entire articular surface of the mortise in all positions of dorsiflexion and plantar flexion.

This intimate contact is important for an even distribution of load at the ankle [1] and must be restored after injury. Biomechanical studies [2, 3] have shown that ankle congruity is maintained not by movement as a hinge but by a combination of sliding and rotation of the talus, coupled with translational movement of the fibula, in all positions of dorsal and plantar flexion.

Plantar flexion of the ankle is accompanied by internal rotation of the talus. Dorsiflexion results in external rotation of the talus and combined posterolateral translation and external rotation of the fibula. This fibular motion at the syndesmosis is an essential part of normal ankle function. The total congruity of the articulation is the most important element in protecting the thin articular cartilage of the ankle from high strain and secondary degeneration.

Disturbances of ankle congruity reduce the contact area and may lead to overload of the articular cartilage [4].

4.1 AO/OTA Fracture and Dislocation Classification

The AO/OTA Fracture and Dislocation Classification was developed to enable surgeons to recognize and to describe the x-ray appearance of fracture patterns in a detailed and comparable way. On this basis, the three main types of ankle fractures may be classified according to the level of the fibular fracture as A, B, or C with increasing instability of the mortise ( Fig 6.9-6 ) [5].

As ligament complexes do not appear on x-rays, the surgeon needs to be able to diagnose ligamentous injuries from the fracture pattern to fully understand the anatomy of the injury.

A transverse fibular fracture below the level of the ankle joint implies an adduction injury with the fibula fracturing in tension and the syndesmotic ligament remaining intact ( Fig 6.9-7a–c ). With foot supination and talar external rotation, the fibular fracture is oblique or spiral and starts anteriorly at the level of the ankle joint with possible partial disruption of the anterior syndesmotic ligament ( Fig 6.9-8c ). The interosseous membrane, as a rule, remains intact. The posterior syndesmotic ligament has remained completely intact, or it is intact but has avulsed a fragment of the posterior tibial articular lip (Volkmann triangle) ( Fig 6.9-8d ).

An indirect fibular shaft fracture that is above the syndesmotic ligaments implies that both the medial collateral ligament and syndesmotic complexes have been disrupted and that there is likely to be major instability ( Fig 6.9-9i–j ). The interosseous membrane, from the ankle joint proximally to at least the level of the fibular fracture and the syndesmotic ligaments, will either be ruptured or avulsed with their bone attachments. Although this is the common and potentially more serious implication of this pattern, a spiral fracture above the syndesmosis may occur from a pure external rotation of the fibula. This will disrupt only the anterior tibiofibular ligament, resulting in a more stable pattern as the fibula rotates externally on the intact interosseous membrane and posterior tibiofibular ligament.

The unique nature of the complexity of malleolar fractures and the necessity of distinguishing them from vertical compression injuries of the tibial pilon required the allocation of a specific code. As an exception to the rest of the AO/OTA Fracture and Dislocation Classification, for this bone region the code 4 is used. Malleolar fractures are therefore categorized as 44.

4.2 Classification and mechanism of injury

The position of the foot and the direction of the deforming force set the pattern of failure of the osseoligamentous mortise. The position of the foot determines which structures are tight at the onset of the deformation and therefore most likely to fail first and to fail under tension. If the foot is supinated (inverted), the lateral structures are tight and the medial structures relaxed. In contrast, in pronation (eversion) the medial structures are tight and fail first. The deforming force can be rotational, usually external, or translational in abduction or adduction. The resulting specific fracture patterns of the lateral malleolus form the basis of classification ( Fig 6.9-6 ) as originally proposed by Weber [6].

4.2.1 The infrasyndesmotic injury (type A fracture)

With the foot supinated and an adduction deforming force applied to the talus, the first injury will occur on the lateral side, which is under tension. This will either rupture the lateral ligament, or cause osseoligamentous avulsion, or result in a transverse fracture of the lateral malleolus at or just below the level of the tibial plafond ( Fig 6.9-7a–c ). If the deforming force still continues, the talus tilts and this will cause a shearing, compression fracture of the medial malleolus ( Fig 6.9-7d , Fig/Animation 6.9-10 ).

4.2.2 The transsyndesmotic injury (type B fracture)

The most common pattern of injury occurs with axial loading of a supinated foot.

By virtue of the obliquity of the axis about which subtalar movement occurs, inversion results in external rotation of the talus ( Fig 6.9-11 ). First, the fibula fails, producing an oblique fracture starting at the level of the ankle joint and extending proximally from anterior to posterior ( Fig 6.9-8a ). Progressive talar external rotation ( Fig 6.9-8b ) causes posterior displacement, resulting in either an injury to the posterior syndesmotic ligament or fracture of the posterior malleolus ( Fig 6.9-8c ). Finally, as the talus subluxes posteriorly, the medial complex fails in tension, either by rupture of the deltoid ligament ( Fig 6.9-8d ) or by a transverse fracture of the medial malleolus ( Fig 6.9-8e , Fig/Animation 6.9-12 ).

4.2.3 The suprasyndesmotic injury (type C fracture)

A third type of injury occurs when the foot is in pronation, the medial structures are under tension, and an external rotation force is applied ( Fig 6.9-9a–c ). The first injury will occur on the tensioned medial side in form of a deltoid ligament rupture ( Fig 6.9-9d ) or a medial malleolar avulsion fracture ( Fig 6.9-9e ). This allows the medial side of the talus to translate anteriorly. As the talus rotates externally, it forces the fibula to twist about its vertical axis. This results in a rupture of the anterior syndesmotic ligament first, and then of the interosseous ligament ( Fig 6.9-9f–h ). At this point, the tibia dislocates medially off the rotating talus, forcing separation (diastasis) of the fibula from the tibia. This causes failure of the posterior syndesmotic ligament (or rarely avulsion of the posterior malleolus), and finally an indirect fracture of the fibular shaft, the level of which depends on how far proximally the interosseous membrane ruptures ( Fig 6.9-9i–j , Fig/Animation 6.9-13 ).