Laboratory Studies
No laboratory studies are necessary for patients with isolated ankle fracture when caused by a plausible mechanism. However, repeated ankle fracture or fracture caused by simple, low-force trauma may require investigation for osteoporosis, Charcot-Marie-Tooth disease, arthritis, connective tissue disease, or peripheral vascular disease.
Imaging Studies
Routinely obtaining radiographs following an ankle injury is not cost-effective, because less than 15% of affected patients have a fracture. Patients without fracture are identified reliably on physical examination. Stress radiographs assess the ankle during stress testing; however, results of this test generally are not sought for immediate ED management. The Shetty test is a valid clinical screening tool that can help the emergency physician decide whether simple radiography is indicated for foot and ankle injuries. It is a simple, quick, and reproducible test. [13]
Indications for ankle radiographs for patients with acute ankle pain include pain in the ankle region plus one of the following [14] :
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Bony tenderness at the distal 6 cm of the posterior edge of the medial malleolus
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Bony tenderness at the distal 6 cm of the posterior edge of the lateral malleolus
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Inability to bear weight both immediately and in the ED (defined as 4 steps)
Diagnostic guidelines for suspected ankle fracture are available in the American College of Radiology (ACR) Appropriateness Criteria. [15]
ACR Appropriateness Criteria for acute trauma to the ankle include the following [16] :
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Use of 3-view (anteroposterior, lateral, and mortise) radiographic evaluation for patients meeting the criteria of the Ottawa Ankle Rules
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Cross-sectional imaging as a tool for preoperative planning and as a problem-solving technique for patients with persistent symptoms in whom occult fracture is suspected
The Ottawa Ankle Rules have been developed to predict the necessity of radiographs for acute ankle injuries, with the goal of protecting patients from unnecessary radiation exposure. [4] These rules provide practical guidelines for selecting patients for radiographic studies. [17, 18]
Application of the Ottawa Ankle Rules to patients younger than 18 years is controversial. Although some advocate that the rules can be applied to children old enough to talk and walk, others use the age of 5 or 6 as a cut-off. [19]
Confounding variables to the Ottawa rules are (1) underlying neurologic deficit affecting the lower limb(s), (2) altered mental status, and (3) multisystem trauma.
Radiography
Perform a standard 3-view radiographic examination (anteroposterior [AP], lateral, and mortise views) of the ankle. In the mortise view, the foot is rotated approximately 15° internally, allowing better visualization of the ankle mortise. Check the radiograph for the headset sign (ie, tibia sits atop the talus, resembling a headpiece on a receiver). Normally, the space between the cradle and the handle should be equal. Lack of symmetry suggests injury.
The ankle joint usually adheres to the ring axiom (eg, a fracture in one part of the ring often is associated with a second injury). Always look for an associated medial malleolar fracture when a spiral fracture of the fibula proximal to the ankle mortise is seen. A vertical fracture of the medial malleolus is associated with either a lateral malleolar fracture or rupture of the lateral ligaments.
Accessory ossicles frequently appear adjacent to the medial and lateral malleoli and may mimic fracture. Clinical correlation is important. Accessory ossicles demonstrate well-corticated margins, whereas fracture fragments exhibit less-defined borders.
Radiographic examination of the foot is not required for patients with an isolated ankle complaint. Although an occult fracture of the base of the fifth metatarsal may occur, this should be detected with an adequately performed ankle radiograph. [20]
Externally rotated lateral radiographic projections can provide surgeons with additional information regarding the presence, size, and displacement of posterior malleolar ankle fractures, according to one study. In this study, posterior malleolar fractures were accurately identified on 86.67% (26/30) of standard lateral radiographs and on 100% (30/30) of externally rotated lateral radiographs. In addition, surgeons described the fracture with greater precision and had greater interclass correlation coefficient values regarding sagittal plane displacement (0.977 vs 0.939) and percentage of involvement of the tibial plafond (0.972 vs 0.775) with an externally rotated lateral projection, as compared to a standard lateral projection. [21]
Other imaging tools
Computed tomography (CT) and magnetic resonance imaging (MRI) studies may be performed as part of outpatient management when imaging features documented by other modalities are equivocal. [22]
Advanced imaging is most useful for diagnosing talar dome and triplane fractures, for distinguishing pilon from trimalleolar fractures, and for differentiating an accessory ossicle from an avulsion fracture. Occasionally, these tests are used to assess the complexity of the fracture and associated ligamentous and intra-articular injuries.
A bone scan rarely is indicated emergently. It may be useful for diagnosing and localizing stress fractures, infections, and neoplastic lesions.
A study of patients who presented to an urban level 1 trauma center with acute ankle injuries found that the sensitivity of bedside ultrasonography for detecting foot and/or ankle fractures was 100% and that the specificity of the Ottawa Foot and Ankle Rules increased from 50% to 100% with the addition of ultrasonography. Negative predictive value was 100%, and positive predictive value was 100%. [23]
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Maisonneuve injury. Mortise view shows transverse fracture of the medial malleolus and widening of the tibiofibular syndesmosis without a fracture of the fibula. This injury is suggestive of a proximal fibula fracture (Maisonneuve fracture).
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Pilon fracture in a 35-year-old man who fell 20 ft. Anteroposterior radiograph shows at least 2 fracture lines extending to the articular surface (plafond) of the tibia.
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A 13-year-old girl with triplane fracture. Anteroposterior radiograph shows a sagittal component through the distal tibia epiphysis.
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An 11-year-old girl with juvenile Tillaux fracture. Mortise view shows fracture involving the lateral portion of tibial epiphysis.
