DOI: 10.1148/radiol.2313021096
(Radiology 2004;231:789-790.)
© RSNA, 2004
The Ankle Teardrop Sign1
Justin P. Dodge, MD
1 From the Department of Radiology, Tripler Army Medical Center, 1 Jarrett White Rd, Honolulu, HI 96859. Received September 5, 2002; revision requested November 6; revision received January 2, 2003; accepted January 15. Address correspondence to the author (e-mail: justin.p.dodge@us.army.mil).
Index terms: Ankle, abnormalities, 463.254 • Ankle, injuries, 463.486 • Joints, fluid, 463.254, 463.486 • Signs in Imaging
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APPEARANCE
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The teardrop sign (1) is a teardrop-shaped opacity that extends anteriorly from the talotibial joint and continues along the neck of the talus on lateral radiographs of the ankle (Fig 1).
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Figure 1. Lateral radiograph of the ankle shows the teardrop sign (*) caused by a posttraumatic effusion secondary to a fracture. The fracture of the distal fibula is not clearly evident in this projection.
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EXPLANATION
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The teardrop-shaped opacity represents fluid in the inferior space of the anterior compartment of the ankle joint. A lateral radiograph of the ankle is the optimum projection for depicting the teardrop sign and confirming ankle effusion (1–3). The reason for this is directly related to the anatomy of the ankle. Because the articular capsule is tightly bound—medially by the deltoid ligament and laterally by the talofibular ligament—the articular capsule restricts joint fluid to anterior and/or posterior extension only (1,2). Positioning of the foot in the neutral position is important because dorsiflexion increases false-positive findings, and plantar flexion decreases sensitivity (4).
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DISCUSSION
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Ankle effusion, an excess of fluid in the synovial space, has been associated with several local and systemic disorders. The differential diagnosis of ankle effusion includes common causes, such as gout, infectious arthritis, rheumatoid arthritis, synovitis, and trauma-associated hemorrhage. Less common causes include allergic reaction, bone neoplasm, hemophilia, juvenile chronic arthritis, leukemia, lymphoma, neuropathic joint disease, pseudogout, and acute rheumatic fever (5). A review of the patient’s medical history and a physical examination are very important in narrowing the differential diagnosis into at least one of four broad categories: infectious, inflammatory, traumatic, and metabolic. Aspiration of the joint can be very useful if the patient’s medical history is unclear. Other radiographic abnormalities can be helpful, as well.
The amount of fluid required for radiographic visualization of ankle effusion has been reported as 5 mL (1,2). Sonography and magnetic resonance (MR) imaging (Fig 2) are increasingly sensitive in detection of smaller effusions of 2 mL and 1 mL, respectively (2). If the detection of small effusion is clinically important, the use of these modalities may be warranted, although both sonography and MR imaging can also demonstrate effusion in asymptomatic and otherwise healthy individuals (6,7).
In summary, the teardrop sign, which can be seen on the standard lateral radiograph of the ankle in the neutral position, is useful in diagnosing ankle effusions of 5 mL or larger.
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FOOTNOTES
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A trainee (resident or fellow) wishing to submit a manuscript for Signs in Imaging should first write to the Editor for approval of the sign to be prepared, to avoid duplicate preparation of the same sign.
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REFERENCES
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- Towbin R, Dunbar JS, Towbin J, Clark R. Teardrop sign: plain film recognition of ankle effusion. AJR Am J Roentgenol 1980; 134:985-990.[Abstract]
- Jacobson JA, Andresen R, Jaovisidha S, et al. Detection of ankle effusions: comparison study in cadavers using radiography, sonography, and MR imaging. AJR Am J Roentgenol 1998; 170:1231-1238.[Abstract/Free Full Text]
- Hall FM. More on detection of ankle effusions (letter). AJR Am J Roentgenol 1998; 171:1428.[Medline]
- Hall FM. Pitfalls in the diagnosis of ankle joint effusion (letter). AJR Am J Roentgenol 1981; 136:637.[Medline]
- Reeder MM. Gamuts in radiology New York, NY: Springer-Verlag, 1993.
- Nazarian LN, Rawool NM, Martin CE, Schweitzer ME. Synovial fluid in the hindfoot and ankle: detection of amount and distribution with US. Radiology 1995; 197:275-278.[Abstract/Free Full Text]
- Schweitzer ME, van Leersum M, Ehrlich SS, Wapner K. Fluid in normal and abnormal ankle joints: amount and distribution as seen on MR images. AJR Am J Roentgenol 1994; 162:111-114.[Abstract/Free Full Text]
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