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Acute Osseous Injury to the Ankle and Foot
Overview
Of all of the major weight-bearing joints in the body, the ankle is the most frequently injured. In athletes, foot and ankle injuries account for up to one fourth of sports-related injuries, with the ankle ranking first as the most common cause of time lost in sports competition. In otherwise healthy patients, ankle injuries may be complicated by chronic joint instability and pain. Female gender, obesity (elevated body mass index), and diabetes with associated comorbidities have been reported to be significant risk factors for ankle fractures, with the last associated with an increased risk of posttreatment complications, including infection, nonunion, malunion, and Charcot-type neuroarthropathy. In contrast to other sites commonly involved by fracture such as the hip, wrist, and spine, osteoporosis is not considered a risk factor in ankle fracture. Ankle injuries are often complex, encompassing injuries to tendons, ligaments, and bones.
However, acute fracture-dislocations of the foot can be overlooked because changes may be subtle or patients may present with clinical features suggesting an ankle sprain. Anterior calcaneal process fractures, talar dome fractures, lateral and posterior talar process fractures, cuboid fractures, and fractures of the fifth metatarsal base are among the injuries that may present as ankle sprains.
Anatomy
Ankle
For practical purposes, the ankle may be regarded as a ringlike bony structure supported by numerous ligaments; disruption and instability result when the ring is broken in two places, as a result of bony and/or ligamentous injury.
The bony structures that make up the ankle include the distal tibia, distal fibula, and talus. The ankle mortise is formed by the medial malleolus, distal tibial articular surface, and lateral malleolus, within which the talus should be symmetrically centered. The ankle joint proper is composed of the tibiotalar articulation and the distal tibiofibular articulation. The ankle joint is a synovial hinge joint with a single axis (transverse between the malleoli through the body of the talus) about which the only naturally occurring motions are flexion (plantarflexion) and extension (dorsiflexion).
The important landmarks of the distal tibia include the medial malleolus, the laterally located fibular groove, the anterior and posterior processes, and the plafond, which comprises the inferior tibial articular surface.
The medial malleolus is defined as the medial process of the distal tibia, which is composed of two colliculi: anterior and posterior. The anterior process of the tibia forms its caudal anterior edge and may be referred to by some as the anterior malleolus. Anterolaterally, the anterior process gives rise to the anterior tibial tubercle, also known as the tubercle of Chaput. The posterior tibial process of the tibia refers to its caudal posterior edge and may be referred to by some as the posterior malleolus. Posterolaterally, this terminates as the posterior tibial tubercle. The space outlined by this and the tubercle of Chaput is referred to as the fibular groove. The distal fibula is the lateral malleolus and demonstrates a convex articular surface.
The talus articulates with the medial and lateral malleoli and tibial plafond to comprise the ankle joint. The posterior tibial process or posterior malleolus does not limit movement of the talus as the medial and lateral malleoli do but does contribute significantly to the overall weight-bearing surface at the ankle joint.
Three sets of ligamentous structures facilitate osseous support about the ankle. These include the medial collateral ligamentous complex (deltoid), lateral collateral ligamentous complex (consisting of the anterior talofibular, posterior talofibular, and calcaneofibular ligaments), and the syndesmotic ligamentous complex of the distal tibiofibular articulation. The last consists of the anterior tibiofibular ligament, posterior tibiofibular ligament, and interosseous membrane.
The deltoid ligament has superficial and deep components. Superficially, three bands take origin from the anterior tibial colliculus. These attach to the navicular/spring ligamentous complex (plantar calcaneonavicular ligament), the sustentaculum tali of the calcaneus, and the medial tubercle of the talus. The superficial fibers provide little overall stability to the ankle joint. The deep component is composed of anterior and posterior tibiotalar ligaments, the latter being the principal stabilizer of the mortise.
The syndesmotic ligamentous complex is composed of the anterior and posterior tibiofibular ligaments, which attach, respectively, to anterior tibiofibular tubercles and posterior tibiofibular tubercles, the inferior transverse ligament, and the interosseous ligament, which is a cranial thickening of the tibiofibular interosseous membrane. The latter comprises the roof of the syndesmosis.
The lateral collateral ligamentous complex has three components. The anterior talofibular ligament attaches the lateral neck of the talus to the fibula just distal to its anterior tubercle. The calcaneofibular ligament extends posteriorly and caudally from the distal aspect of the posterior fibula to the lateral calcaneus. The posterior talofibular ligament extends axially from the fibula to the posterior process of the talus; its orientation readily facilitates visualization on axial cross-sectional imaging of the ankle.
Hindfoot
Hindfoot is composed of talus and calcaneus. The calcaneus is the most frequently fractured tarsal bone. Treatment of fractures and dislocations about the calcaneus frequently result in significant long-term disability. The talus is the second most commonly fractured tarsal bone. Certain talar fractures (talar dome and talar process) may be difficult to detect, resulting in delay in diagnosis and management.
Talus
The talar articulations account for the majority (>90%) of the motion in the foot and ankle. Therefore, it is critical to stabilize this structure after injury.
The blood supply of the talus is tenuous because 60% of the surface is covered by articular cartilage and there are no muscle or tendon insertions on its surface. The superior articular surface, the trochlea, articulates with the tibia superiorly. Articular cartilage extends medially and laterally in a plantar direction to articulate with the medial and lateral malleoli forming the ankle mortise. The inferior articular surface is complex, forming three articulations with the calcaneus. The anterior and posterior facets articulate with similarly named calcaneal facets. The middle facet is just posterior to the anterior facet and articulates with the sustentaculum tali. The talar sulcus lies between the anterior and middle facets, forming the roof of the tarsal sinus. The interosseous talocalcaneal ligament lies within the tarsal sinus ( eFig. 31-1 ).
The talar neck is angled 15 to 20 degrees and has a coarse surface due to ligament attachments and vascular supply. The distal aspect of the talus (head of the talus) articulates with the tarsal navicular and is contiguous with the spring ligament and sustentaculum tali inferiorly and the deltoid ligament medially (see eFig. 31-1 ).
The talus has lateral and posterior processes. The posterior process is divided by a groove for the flexor hallucis longus tendon into medial and lateral tubercles. The os trigonum is a common variant that arises from a separate ossification center posterior to the lateral tubercle. When fusion of this ossification center occurs, it forms the Stieda process. The ossicle remains unfused in up to 50% of patients. The lateral talar process is a wedge-shaped structure that articulates with the distal fibula superiorly and a portion of the posterior calcaneal articulation inferiorly ( eFig. 31-2 ).
Talar fractures and fracture-dislocations are discussed separately. However, Table 31-1 summarizes fracture types, incidence, and mechanism of injury.
TABLE 31–1
Ottawa Ankle Rules
| Accepted Indications: Ankle Radiographs | Accepted Indications: Midfoot Radiographs |
|---|---|
| Point tenderness about the inferior or posterior aspect of either malleolus (to include the distal 6 cm of the lateral malleolus) | Point tenderness about the navicular or the base of the fifth metatarsal |
| Inability to bear weight at the time of injury and/or clinical evaluation (four independent steps) | Inability to bear weight at the time of injury and/or clinical evaluation (four independent steps) |
Talar Neck Fractures
Talar neck fractures are uncommon compared with all skeletal injuries but account for 30% to 50% of talar fractures. Depending on the type of fracture, complication rates may be high. Talar neck fractures most commonly occur with hyperdorsiflexion of the foot on the tibia (see eTable 31-1 ).
eTABLE 31–1
Talar Fracture and Fracture-Dislocations *
| Type | Incidence (% Talar Injuries) | Mechanism of Injury |
|---|---|---|
| Talar neck | 30%–50% | Hyperdorsiflexion of the foot on the tibia |
| Talar body | 40% | |
| Talar dome | 1%–6% | Inversion, eversion, twisting injuries |
| Lateral process | Rare | Dorsiflexion and inversion of the foot |
| Posterior process | Rare | Avulsion, direct compression |
| Crush fractures | 28%–33% | Axial compression |
| Talar head | Rare | Extreme plantarflexion |
| Subtalar dislocation | 15% | Inversion (medial) eversion (lateral) |
| Total dislocation | Rare | Extreme inversion or eversion |
Although originally described in pilots, most are due to motor vehicle accidents or falls from a significant height. The injury is most common in young males. Open fractures are common (16% to 25%) when there is significant displacement of the talar body. Open fractures have poor results and a high incidence of infection.
Talar neck fractures have been associated with a high incidence of complications, including osteonecrosis, infection, skin necrosis, malunion, nonunion, and posttraumatic arthritis.
Hawkins classified talar neck fractures and associated subluxation-dislocations ( Fig. 31-1 ). This classification (see eTable 31-2 ) is useful for long-term prognosis and management ( Fig. 31-2 ). Complications are common despite adequate reduction, increase in severity as the classification level increases, and include skin necrosis, infection, delayed and nonunion, malunion, avascular necrosis, and posttraumatic arthrosis.
eTABLE 31–2
Talar Neck Fractures: Hawkins Classification *
| Type | Definitions | Incidence |
|---|---|---|
| I | Nondisplaced neck fracture | 11%–21% |
| II | Displaced neck fracture with subluxation or dislocation of the subtalar joint | 10%–24% |
| III | Displaced neck fracture with subluxation/dislocation of the ankle and subtalar joint | 23%–47% |
| IV | Type III plus dislocation of the talonavicular joint | 5% |
Delayed union is more common with Hawkins types II to IV injuries, which is likely related to the higher incidence of avascular necrosis. The incidence of delayed union approaches 13%. Nonunion (no evidence of healing for 6 months) is uncommon, but malunion may be evident in 45% to 77% of displaced neck fractures.
Avascular necrosis is uncommon (0% to 13%) with Hawkins type I fractures (see eTable 31-2 ). Osteonecrosis develops in 20% to 50% of type II and 83% to 100% of type III fractures (see Figs. 31-1 and 31-2 ).
Talar Body Fractures
There are a wide range of talar body fractures ranging from osteochondral fractures to comminuted crush or shear fractures (see eTable 31-1 ). eTable 31-1 summarizes talar body fractures, their incidence, and the mechanism of injuries.
Talar dome fractures result from inversion, eversion, and twisting injuries of the ankle. Both the medial and lateral aspects of the talar dome may be involved. Lateral talar dome fractures are more often acute. These injuries are associated with inversion or inversion-dorsiflexion trauma. These lesions usually are shallow or flakelike. Medial lesions are more often deeper, and when acute they are associated with lateral rotation on a plantarflexed ankle.
The most commonly used classification of these injuries was devised by Berndt and Harty ( Figs. 31-3 and 31-4 ).
Stage I lesions are compressions of the talar dome without associated ligament injury, and the overlying cartilage is intact. Stage II lesions are incomplete osteochondral fractures with partial elevation of the fragment. Stage III lesions are complete fractures without displacement, and stage IV lesions are complete fractures with displacement.
Lateral Process Fractures
Fractures of the lateral talar process are easily overlooked on radiographs. These fractures result from inversion and dorsiflexion of the foot. In recent years, this fracture has been commonly seen in snowboarders, hence the name “snowboarder's fracture.” Hawkins classified these fractures into three groups: (1) chip fractures, (2) a single large fragment involving the talofibular and subtalar joints, and (3) comminuted fractures involving both articular surfaces.
Persistent symptoms, nonunion, and eventual resection or subtalar fusion are more common when the subtalar joint is involved.
Posterior Process Fractures
The posterior process consists of medial and lateral tubercles separated by the groove for the flexor hallucis longus tendon.
Both tubercles have articular cartilage on the plantar surface forming the posterior margin of the posterior subtalar facet. The lateral tubercle remains unfused in 50% of patients (os trigonum) (see eFig. 31-2 ). The lateral tubercle is fractured by forced plantarflexion or avulsion (posterior talofibular ligament avulsion) ( eFig. 31-3 ). Pronation and dorsiflexion may cause avulsion of the deltoid ligament attachment.
Comminuted Talar Body Fractures
Complex fractures of the talar body ( Fig. 31-5 ) may be related to crush or shearing injuries. These fractures are much more uncommon than talar neck fractures. There is a high incidence of avascular necrosis, malunion, and posttraumatic arthrosis with these injuries.
Talar Head Fractures
Fractures of the talar head ( Fig. 31-6 ) are rare (see eTable 31-1 ). The fracture line extends into the talonavicular joint. Compression forces with plantarflexion of the foot cause this injury. Associated talar dislocations have also been reported with talar head fractures.
Talar Dislocations
Subtalar dislocations may be medial or lateral. Medial dislocations occur with inversion and lateral dislocations with eversion injuries.
Subtalar dislocations account for 15% of talar injuries but only 1% of all dislocations (see Fig. 31-2 ). It is not surprising that associated osteochondral fractures of the talus, calcaneus, and navicular occur in 45% of patients.
Total talar dislocation is rare ( Fig. 31-7 ). This injury is caused by extreme supination (total medial dislocation) and extreme pronation (total lateral dislocation). Most injuries are open with a high incidence of infection and avascular necrosis.
Detenbeck and Kelly reported an 89% incidence of infection requiring eventual talectomy.
Calcaneus
Calcaneal Fracture-Dislocations
Fractures and dislocations of the calcaneus present significant short- and long-term treatment challenges.
The calcaneus is the largest tarsal bone, with three facets on the anterosuperior surface for articulation with the talus (see eFig. 31-1 ). The cortex is thickened posteriorly at the Achilles attachment. Medially, the sustentaculum tali projects from the body of the calcaneus. This structure contains the middle facet. The flexor hallucis longus tendon passes inferior to the sustentaculum tali (see eFig. 31-1 ). The medial position of the flexor tendons and neurovascular structures places them at risk after fracture or during reduction.
Laterally, the peroneal tubercle and retinaculum contain the peroneal tendons. The lateral ankle ligament complex (anterior talofibular, calcaneofibular, and posterior talofibular) provide important support laterally. The deltoid ligament complex provides medial support to the ankle.
There are two critical angle measurements that are routinely evaluated on lateral radiographs. Bohler's angle (normal, 25-40 degrees) is a useful measurement for evaluating calcaneal height.
This angle is formed by a line from the posterior calcaneal margin to the margin of the posterior facet and a second line from the margin of the posterior facet to the superior margin of the anterior calcaneal process ( eFig. 31-4 ).
The crucial angle of Gissane (normal about 100 degrees) is formed by a line along the posterior facet and a second line along the anterior calcaneal process (see eFig. 31-5 ).
The calcaneus is the most commonly fractured tarsal bone but accounts for only 2% of all fractures. Calcaneal fractures may be extra-articular or intraarticular or may result in fracture-dislocations. Seventy-five percent of fractures are intraarticular and 25% are extra-articular.
Extra-articular fractures occur from a multitude of mechanisms, including falls and twisting injuries. Intraarticular fractures result from compression injuries due to significant falls (>8 feet) or motor vehicle accidents.
Two fracture patterns occur with intraarticular fractures due to shearing or compression forces. A shear fracture line occurs in the sagittal plane involving the posterior facet with extension that may reach the calcaneocuboid articulation. This fracture separates the calcaneus into sustentacular (anteromedial) and tuberosity (posterolateral) fragments. Compression fracture lines cause displacement of the anterolateral calcaneus into the angle of Gissane. Fractures result in loss of calcaneal height, widening of the calcaneus, and articular deformity in the posterior facet (see eFigs. 31-4 and 31-5 ).
Intraarticular Fractures
Numerous fracture classifications have been used over the years based on radiographic features and the extent of articular involvement. However, CT is the accepted technique for determining the extent of injury and most appropriate surgical approach. It is generally agreed that CT scans are the gold standard to analyze calcaneal fractures and other fractures of the foot. Therefore, CT classifications are most commonly used by orthopedic surgeons. CT systems include the Crosby-Fitzgibbons classification based on coronal CT images of the posterior facet; the Sanders classification, which is similar to the Crosby-Fitzgibbons but more complex; and the Hannover classification.
The Sanders classification, based on reformatted CT images, is most commonly used (see eFig. 31-6 ).
Type I fractures are undisplaced. Type II fractures (a single fracture line) involve the posterior facet and are further subdivided (IIA to IIC) depending on the location of the fracture (A, lateral; B, mid posterior facet; C, medial posterior facet). Medial fractures (type IIC) are more difficult to detect and reduce surgically. Type III fractures (two fracture lines in the posterior facet) result in three fragments with a central depressed fragment. Type IV fractures are comminuted with four or more articular fragments.
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