Ankle
Andrew Pennock
Maya Pring
INTRODUCTION
In 1898, John Poland wrote Traumatic Separation of the Epiphyses and noted that ankle injuries in children differed from those in adults in three important ways:
The growth plate forms a plane of weakness directing fracture lines in patterns different from those of adults.
Ligaments are stronger than bone so that ligamentous injuries are less common in children.
Certain injuries will affect growth.
“Education is the most powerful weapon which you can use to change the world”
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 Figure 16-1 Ankle anatomy. AITFL, anterior inferior tibiofibular ligament; ATFL, anterior talofibular ligament; ATTL, anterior talotibial ligament; CFL, calcaneofibular ligament; PITFL, posterior inferior tibiofibular ligament; PTFL, posterior talofibular ligament; PTTL, posterior talotibial ligament; TCL, tibiocalcaneal ligament; TNL, tibionavicular ligament. |
 Figure 16-2 Progression of normal distal tibial physeal closure at puberty. A. Begins centrally. B. Spreads medially. C. Then laterally. D. Until complete closure. |
Mortise Joint
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French = “mortaise”
Spanish = “mortaja”
Arabic = “al-mortáz”
A cavity, socket, groove, slot, or hole. Usually rectangular into which is received a structure of complementary shape to form a joint.
Source: Diab M. Lexicon of orthopaedic etymology. Amsterdam, The Netherlands: Harwood Academic Publishers; 1999.
ANATOMY
The ankle joint is composed of the talus, which articulates with the ankle mortise (formed by the distal tibia, the lateral and medial malleolus). The three major groups of ligaments (deltoid, tibiofibular, tibiotalar) originate on an epiphysis (Fig. 16-1) and provide stability for the articulation.
The distal tibia physis closes around the age of 14 years in girls and 16 in boys. The asymmetric closure of the physis is responsible for many of the fractures that will be discussed in this chapter (Fig. 16-2). Closure proceeds in two directions from an initial site in the near central area, which has been coined “Kump’s bump” after W. Kump’s 1966 paper on the topic. This is followed by fusion of the posteromedial and finally the anterolateral segments of the growth plate. The distal fibula physis closes approximately 1 year later.
Kump’s Bump
Warren Kump, a Minneapolis radiologist, first described the mound-shaped medial undulation on the distal tibial physis, now referred to as “Kump’s bump.” Kump noted that natural physeal closure begins “medio-centrally” in this area. The medial physis closes earlier than the lateral, predisposing to the Tillaux-type fracture.
Others believe that this prominence may be prone to shear injury with a physeal fracture, predisposing to premature physeal closure.
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When the foot is forced into an abnormal position, tension and compression forces are generated across the ankle. The structure of the ankle appears to permit tension injuries most frequently with the result that avulsion injuries of the epiphyses are common. Compression fractures are relatively unusual except with axial loading, which can be seen when a child jumps or falls from a height.
ASSESSING THE PATIENT
Gross deformity of the ankle (dislocation) should be reduced before sending a patient to the x-ray suite or transferring the patient to another facility. In-line traction will usually realign severe deformity quickly, improve patient comfort, allow for better x-ray assessment of the fracture anatomy, and will decrease the risk of neurovascular problems by taking tension off the neurovascular bundles (Fig. 16-3).
There may be significant swelling with ankle fractures and dislocations, although this swelling is distal to the muscle compartments of the leg, swelling under the extensor retinaculum as is frequently seen with Salter-Harris injuries can cause numbness in the first web space and loss of extensor hallucis longus (EHL) and extensor digitorum communis (EDC) function; this indicates need for urgent surgical release of the extensor retinaculum. Neurovascular exam is critical when evaluating an ankle fracture.
There is minimal soft tissue padding around the distal tibia and fibula; the medial and lateral malleoli are subcutaneous, so it is important to check the skin carefully for signs of open fracture.
Always palpate the proximal tibia and fibula and examine the knee. It is easy to focus on the ankle fracture and miss the high fibula fracture indicating a syndesmotic injury (Maisonneuve fracture).
RADIOGRAPHIC ISSUES
Many people assume that there is no fracture if the x-ray appears normal. However, nondisplaced physeal separations may reveal no fracture lucency. The clinical signs and localized soft tissue swelling on the x-ray should be sufficient to lead to the correct diagnosis. On occasion, there may be widening of the physis when comparison is made with x-rays of the uninjured ankle.
Fractures about the ankle can be missed when only two views of the ankle are obtained (Fig. 16-4). We feel strongly that a mortise view should always be performed (Table 16-1). The term mortise describes the fitting of the talus into the “socket” formed by the distal fibula and medial malleolus. The mortise x-ray is taken from anterior to posterior with the foot internally rotated 20 degrees; on this view, the outline of the talus is visualized with a symmetric space around it. Asymmetry indicates ligamentous injury and ankle instability.
 Figure 16-3 Do not transfer a patient with a dislocated joint; this fracture dislocation was sent from another facility, leaving the ankle dislocated for greater than 6 hours. |
 Figure 16-4 This fracture is much more visible in the mortise view than the AP view. The mortise view shows a Type IV fracture that will require surgical reduction. |
Table 16-1 The Mortise X-ray | ||||||||||||||||
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X-ray measurements of the tibiofibular line, talocrural angle, talar tilt, medial clear space, and tibia-fibular overlap can be made from the standard mortise view to help determine stability and plan treatment.
CLASSIFICATION
The pattern of injury to the ankle depends on many factors, including the age of the patient, the quality of the bone, the position of the foot at the time of injury, and the direction, magnitude, and rate of the loading forces. In children, the Salter-Harris method still remains the most widely accepted classification system for ankle fractures (Table 16-2).
Table 16-2 The Salter-Harris Classification | ||||||||||||||||||
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Much of our current understanding of the mechanisms of ankle injury (Fig. 16-5) is derived from the work of Lauge-Hansen who emphasized the influence that the position of the foot (supination or pronation) and the direction that the deforming forces (adduction, external rotation, or abduction) have on the fracture pattern. These adult descriptions are often used to describe children’s fractures (with only partial success—the terminology appears to be too complex for everyday use).
 Figure 16-5 Supination and adduction of the foot causes the top injury. Pronation and external rotation causes the bottom injury. |
An alternative classification scheme that may be used in older adolescents is the Danis-Weber system (Fig. 16-6), which classifies the distal fibula fracture based on its level relative to the ankle joint and provides information regarding the stability of the syndesmosis.
NON-ARTICULAR FRACTURES OF THE TIBIA
Salter-Harris Type I Injury of the Distal Tibia
Salter-Harris Type I injuries are usually non-displaced; diagnosis is based on clinical exam more than x-ray. The child will have tenderness and swelling directly over the physis. Sometimes the injury cannot be recognized on radiographs until subperiosteal new bone appears after 3 weeks. If you do not see a fracture on x-ray, rule out infection before placing the child in a cast. Once you are convinced that the pain is just a Salter-Harris I fracture, a short leg walking cast for 3-4 weeks will allow healing of the fracture. X-rays are typically taken when the cast is removed, but often no callus is noted. The true incidence of Salter-Harris I fracture versus ligament injury is poorly understood. A simple walking cast treats either nicely.
 Figure 16-6 The Danis-Weber classification is based on the relationship between the fibular fracture and the mortise. |
 Figure 16-7 Salter-Harris II injury of the distal tibia treated with open reduction and K-wire fixation. |
 Figure 16-8 This is the same patient from Figure 16-7 at 6 months post-op. Note the symmetric Harris growth line, which confirms physeal growth. |
 Figure 16-9 Periosteal entrapment can block reduction in a Salter-Harris II distal tibia fracture. It may need to be removed surgically as seen here. |
The rare displaced fracture requires reduction and a longer period of immobilization (up to 6 weeks), and we will typically limit any weight bearing for the first 3-4 weeks.
Salter-Harris Type II Injury of the Distal Tibia
Type II injuries typically result from higher-energy mechanisms; the force is most commonly supination-plantar flexion or abduction (Fig. 16-7). Gross displacement sometimes produces ischemia of the foot, which should be relieved, prior to transfer or definitive treatment, by partially reducing the fracture with the help of longitudinal traction and splinting. Usually this initial step leads to improved circulation to the foot with pulses evaluated by finger palpation or Doppler exam.
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