Teardrop Sign

1. High-Yield Overview & Pathognomonic Essence

• Radiographic Appearance: A teardrop-shaped or elliptically bulging water-density soft-tissue mass extending anteriorly from the talocrural joint line and draping over the dorsal neck of the talus on the lateral ankle radiograph, causing displacement and effacement of the normally crisp, radiolucent triangular pretalar fat pad stripe.
• Pathognomonic Significance: Represents capsular distension of the anterior talocrural synovial recess secondary to ankle joint effusion or acute hemarthrosis, quantitatively defined on non-weightbearing lateral radiographs as anterior capsular distension of 5 mm or greater or total anteroposterior (AP) capsular distension of 13 mm or greater.
• Diagnostic & Clinical Utility: In acute ankle trauma with normal routine three-view radiographs, a positive teardrop sign exhibits a 72% to 80% positive predictive value for a radiographically occult intra-articular fracture (predominantly talar dome osteochondral lesions, lateral process of the talus, anterior process of the calcaneus, or posterior malleolus), mandating rigid non-weightbearing immobilization and urgent cross-sectional imaging (CT or MRI) rather than discharge as a simple sprain.

2. Diagnostic Sign Summary Matrix

3. Clinical Case Imaging & Standardized Figures

Standardized diagnostic evaluation of the teardrop sign requires correlation between the pathological capsular distension and normal baseline anatomy on well-positioned lateral ankle projections.

For comparative diagnostic assessment, an anatomically normal lateral ankle projection illustrates the expected tight adherence of the capsular boundary along the anterior margin of the joint space without pretalar bulging.

4. Pathophysiology & Biomechanical Mechanism

The radiographic appearance of the teardrop sign is governed by the functional anatomy of the talocrural joint capsule, the mechanical compliance of the anterior synovial recess, and the hydraulic behavior of intra-articular fluid collections under pressure.

Anterior Capsular Anatomy and Regional Architecture: The talocrural fibrous joint capsule exhibits distinct regional variations in thickness and structural compliance. Medially and laterally, the joint is reinforced by dense, non-compliant ligamentous complexes (the deltoid ligament medially and the anterior talofibular, calcaneofibular, and posterior talofibular ligaments laterally) that resist multidirectional mechanical displacement. In contrast, the anterior and posterior aspects of the capsule are thin, membranous, and pliable, designed to facilitate a wide sagittal arc of motion (approximately 45 to 50 degrees of total dorsiflexion and plantarflexion). Proximally, the anterior fibrous capsule attaches 5 to 8 mm superior to the anterior articular rim of the distal tibial plafond, creating an anatomically distinct anterior synovial pouch (recessus tibio-talaris anterior). Distally, it inserts into the dorsal cortex of the talar neck, several millimeters proximal to the talonavicular articulation.

Pretalar Fat Pad Effacement: Positioned immediately anterior to this pliable fibrous capsule is the pretalar fat pad. On a true lateral radiograph, this structure appears as a well-defined triangular or teardrop-shaped radiolucency. The space is bounded posteriorly by the fibrous anterior talocrural capsule, superiorly by the distal tibia, anteriorly by the deep crural fascia and overlying extensor tendon sheaths (tibialis anterior, extensor hallucis longus, and extensor digitorum longus), and inferiorly by the dorsal talar neck and navicular bone. In the physiological state, the anterior capsule conforms tightly against the subchondral bone, preserving the crisp lucency of the fat stripe. When intra-articular fluid accumulates, it encounters minimal resistance from the pliable anterior capsular membrane. The capsule balloons forward into the loose areolar and adipose tissue of the pretalar space, displacing the fat pad anteriorly and replacing its radiolucent profile with a homogenous soft-tissue water density.

Joint Volume Kinetics and Intracapsular Pressure: The physiological resting volume of synovial fluid within the adult talocrural joint is minimal, typically between 1.0 and 2.5 mL. The ankle joint exhibits a non-linear pressure-volume compliance curve. Small increases in volume (up to 3 or 4 mL) are accommodated within resting synovial folds with negligible increases in intracapsular hydrostatic pressure. However, once intra-articular fluid volume reaches or exceeds 5.0 mL, the joint enters the steep portion of its compliance curve. Intracapsular hydrostatic pressure rises sharply, driving progressive outward distension of both the anterior and posterior capsular recesses. At volumes between 10 and 15 mL or greater, maximal capsular excursion occurs. Because the posterior recess is constrained by the robust flexor hallucis longus tendon and posterior talofibular ligament, the pliable anterior capsule undergoes preferential displacement along the path of least mechanical resistance, creating the pathognomonic teardrop configuration draping over the dorsal talar neck.

Hemarthrosis versus Serous Effusion: Acute traumatic joint distension is almost invariably caused by hemarthrosis resulting from intra-articular vascular disruption. Forces that induce ankle trauma (inversion, eversion, external rotation, and axial loading) impose severe tension or shear stresses across the articular surface and subchondral bone. Cortical microfractures, osteochondral impaction injuries, capsular sleeve avulsions, or cancellous fractures of the subchondral bone plate rupture high-pressure intraosseous and subsynovial capillary beds, pouring whole blood into the joint cavity within 1 to 2 hours of injury. When an intra-articular fracture breaches the medullary canal of the distal tibia, talus, or calcaneus, marrow fat droplets enter the joint fluid. Because lipid has a lower specific gravity than serum and red blood cells, it floats to the non-dependent surface, creating lipohemarthrosis, which serves as absolute confirmation of an intra-articular skeletal breach. In contrast, atraumatic effusions resulting from inflammatory synovitis or early pyogenic infection develop more gradually as an inflammatory transudate or exudate driven by hypervascular synovial proliferation, cytokine-mediated vascular permeability, or bacterial colonization, lacking the rapid high-pressure onset and marrow lipid components of acute traumatic hemarthrosis.

5. Modality-Specific Imaging Findings

Plain Radiography

Plain radiography represents the initial diagnostic modality for identifying the teardrop sign, evaluated exclusively on the non-weightbearing lateral ankle projection.

• Technical Positioning and Projection Geometry: A true lateral projection is mandatory. The radiographic beam must be centered directly over the talocrural joint line with the foot positioned at 90 degrees of neutral dorsiflexion relative to the tibia. Strict superimposition of the medial and lateral trochlear domes of the talus is required. If the domes are separated by more than 2 to 3 mm of rotational parallax, the anterior capsular shadow and pretalar fat space become distorted, introducing diagnostic error.
• Quantitative Diagnostic Thresholds: Anterior capsular distension is measured as the maximum perpendicular distance from the anterior cortical margin of the talar neck to the outer convex border of the teardrop soft-tissue shadow. An anterior distension of 5.0 mm or greater is considered definitive for significant joint effusion. An anterior capsular distension greater than 3.0 mm offers 81% sensitivity, whereas distension greater than 5.0 mm achieves 92% specificity and an 80% positive predictive value for an intra-articular fracture.
• Combined Anteroposterior (AP) Capsular Distension: Calculated by summing the anterior capsular distension and the posterior capsular distension (measured from the posterior articular rim of the distal tibia to the outer margin of the posterior capsular bulge). A combined AP distension of 13.0 mm or greater is 100% specific for joint effusion, correlating directly with an aspirated joint fluid volume of 5.0 mL or greater.
• Secondary Skeletal Landmarks: Identification of a teardrop sign requires meticulous scrutiny of accompanying AP and 15-to-20-degree mortise views for subtle fracture flakes, including osteochondral talar dome lesions, fractures of the lateral process of the talus (snowboarder’s fracture), avulsion fractures of the anterior process of the calcaneus, and subtle posterior malleolar fragments.

Computed Tomography

Computed tomography (multidetector CT or extremity cone-beam CT) provides definitive multiplanar cross-sectional evaluation of the traumatized ankle joint, resolving diagnostic ambiguity and identifying occult osseous injuries.

• Occult Fracture Detection: In acute ankle trauma presenting with a radiographic teardrop sign but negative standard radiographs, CT reveals radiographically occult intra-articular fractures in 72% to 80% of patients. CT accurately delineates fracture line orientation, fragment size, degree of comminution, and articular step-off.
• Characteristic Occult Sites: Volumetric multiplanar reformations (axial, coronal, sagittal) systematically capture osteochondral defects of the medial or lateral talar dome, fractures of the lateral process of the talus, fractures of the posterior malleolus (Volkmann’s fragment), anterior calcaneal process fractures, and syndesmotic avulsion fractures (Tillaux-Chaput and Wagstaffe fragments).
• Tissue Attenuation Quantification: Simple serous or transudative fluid collections demonstrate low attenuation ranging from 0 to 18 Hounsfield Units (HU). In contrast, acute hemarthrosis displays hyperdense or intermediate attenuation between 30 and 60 HU due to high cellularity and clot formation. Lipohemarthrosis displays a pathognomonic fat-fluid level within the anterior synovial pouch, characterized by non-dependent negative attenuation (-30 to -100 HU) floating over dependent hyperdense blood.

Magnetic Resonance Imaging & Ultrasound

Cross-sectional soft tissue imaging modalities offer superior diagnostic accuracy for characterizing non-osseous pathology, capsular integrity, and subtle cartilage injuries.

• High-Resolution Ultrasound: Point-of-care ultrasound utilizing a 10 to 18 MHz linear transducer aligned longitudinally over the anterior talocrural joint line provides rapid, cost-effective evaluation. An anterior capsule-to-bone distension greater than 3.0 mm (or side-to-side asymmetry greater than 1.5 to 2.0 mm compared to the contralateral uninjured ankle) yields 92.5% to 94% sensitivity and 95.1% specificity for joint effusion. Traumatic hemarthrosis presents as complex, hypoechoic to echogenic fluid with swirling internal debris upon dynamic transducer compression, distinguishing it from anechoic simple effusion and vascularized synovial pannus.
• Magnetic Resonance Imaging (MRI): Standard 1.5T or 3.0T multiplanar protocols (sagittal, coronal, and axial T1-weighted, T2-weighted fat-suppressed, and STIR sequences) demonstrate marked high T2/STIR hyperintensity expanding the anterior and posterior synovial pouches. MRI provides unmatched sensitivity for detecting occult trabecular bone contusions (bone bruises), subchondral microfractures, chondral delamination, and full-thickness tears of the anterior talofibular ligament (ATFL), calcaneofibular ligament (CFL), and distal tibiofibular syndesmosis.
• Evaluation of Capsular Decompression: MRI is the definitive modality for verifying capsular integrity. In high-energy trauma where the teardrop sign is unexpectedly absent despite gross joint swelling, MRI confirms extensive capsular rupture with extravasation of hemarthrosis into periarticular soft-tissue planes.

6. Diagnostic Utility, Sensitivity & Specificity

The diagnostic value of the teardrop sign has been rigorously analyzed across prospective cohort studies, anatomical distension investigations, and comparative cross-sectional imaging trials.

Landmark Diagnostic Validation: In their foundational work, Towbin et al. (1980) evaluated 150 clinical ankles (100 normal controls, 50 with documented effusion) alongside cadaveric joint distension models. They established that an anterior capsular distension of 5.0 mm or greater or a total AP capsular distension of 13.0 mm or greater is highly specific for ankle effusion, correlating directly with an aspirated joint fluid volume of 5.0 mL or greater.

Positive Predictive Value for Occult Fractures: Clark et al. (1995) investigated 100 consecutive acute ankle trauma patients presenting with normal standard three-view radiographs. In patients exhibiting a positive radiographic teardrop sign (capsular distension >= 5.0 mm), subsequent tomography and CT revealed radiographically occult intra-articular fractures in 72%, establishing a positive predictive value of 72%. Clark et al. (1996) subsequently refined these diagnostic cutoffs in 112 consecutive acute ankle trauma cases: an anterior capsular distension greater than 3.0 mm exhibited 81% sensitivity and 78% specificity for occult fracture, whereas increasing the threshold to greater than 5.0 mm raised the specificity to 92% and the positive predictive value to 80% for hemarthrosis-producing osteochondral or avulsion fractures.

Impact on Emergency Clinical Decision-Making: Ho et al. (1996) demonstrated in a prospective cohort of 94 emergency department patients that plain film recognition of an ankle effusion and teardrop sign directly altered clinical management in 40.4% of patients. Identifying this sign converted presumed simple lateral sprains into appropriately managed fracture pathways requiring rigid cast immobilization or orthopaedic surgical referral. Furthermore, contemporary comparative diagnostic studies by Allen et al. (2020) and Li et al. (2026) confirmed that while plain radiography detects approximately 68% of subtle effusions, high-resolution ultrasound and extremity CT increase diagnostic sensitivity to 92.5% to 94%, matching 3.0T MRI (inter-modality agreement kappa = 0.89).

Radiographic Pitfalls and Operator Dependency: Technical execution and biomechanical factors can introduce diagnostic errors that clinicians must actively anticipate:

• Rotational Obliquity (Hall, 1981): Achieving a true lateral projection is essential. Rotational obliquity causes the anterior cortex of the fibula or medial malleolus to project across the pretalar space, artificially mimicking capsular distension (false positive) or obscuring a genuine effusion (false negative). Precise superimposition of the talar trochlear domes eliminates this artifact.
• Overlying Soft-Tissue Artifacts (Hall, 1981): Severe subcutaneous edema, direct anterior contusion, or extensor digitorum and tibialis anterior tenosynovitis can obscure the margin of the pretalar fat pad, creating an illusion of intracapsular distension.
• The Capsular Rupture False-Negative Pitfall (Hall, 1998): In severe, high-energy rotational trauma with complete rupture of the anterior joint capsule or collateral ligament complexes, intra-articular hemarthrosis immediately decompresses into the surrounding subcutaneous and subfascial compartments of the lower leg and foot. Under these conditions, the joint cavity is deflated, resulting in a flat or minimally distended capsular shadow (< 3 mm). Clinicians must recognize that an absent teardrop sign in a grossly swollen, unstable ankle does not exclude severe intra-articular trauma.

7. Differential Diagnosis & Radiographic Mimics

Distinguishing classic post-traumatic hemarthrosis from infectious, inflammatory, and extra-articular mimics is critical for guiding immediate clinical triage and definitive management.

8. Clinical Significance & Management Implications

The clinical identification of a teardrop sign fundamentally alters the diagnostic and therapeutic approach to acute ankle injuries, preventing the underdiagnosis of unstable intra-articular skeletal trauma.

Emergency Department Triage and Risk Stratification: Acute ankle injuries represent up to 10% of all emergency department presentations. Although the vast majority are benign lateral ligament sprains, misdiagnosing an occult intra-articular fracture as a simple sprain leads to chronic instability, nonunion, osteochondral necrosis, and accelerated post-traumatic osteoarthritis. The detection of a teardrop sign (capsular distension >= 5.0 mm) on routine lateral radiographs must immediately elevate the injury from a “routine sprain” to a “presumed occult fracture”, prompting definitive immobilization rather than discharge with elastic wrapping.

Immediate Immobilization Protocol: Patients presenting with a post-traumatic teardrop sign should be placed immediately into rigid immobilization:

• Immobilization Device: A rigid posterior plaster or fiberglass splint with stirrups, or a non-weightbearing pneumatic controlled ankle movement (CAM) walking boot locked at neutral (90 degrees).
• Weightbearing Restrictions: Strict non-weightbearing status with crutches or a knee scooter until advanced cross-sectional imaging or specialist orthopaedic follow-up is completed.
• Avoidance of Premature Rehabilitation: Aggressive range-of-motion exercises and early weightbearing must be withheld until occult fracture lines, syndesmotic instability, or osteochondral lesions are definitively excluded.

Advanced Imaging Pathways: When a teardrop sign is identified on initial radiographs without an obvious fracture, second-line cross-sectional imaging is indicated. Non-contrast multidetector CT is the primary modality of choice within 24 to 72 hours to detect cortical fractures, displaced osteochondral fragments, and articular step-off. If CT is negative but significant pain, mechanical locking, or inability to bear weight persists, MRI is recommended to evaluate for radiographically occult chondral shear injuries, trabecular contusions, or high-grade syndesmotic tears.

Indications and Technique for Arthrocentesis: Diagnostic arthrocentesis is mandatory whenever an atraumatic, acute joint effusion raises suspicion for septic arthritis or crystalline arthropathy. In acute traumatic settings, therapeutic arthrocentesis is indicated for tense, excruciatingly painful hemarthrosis. Evacuation of intra-articular blood provides rapid pain relief, relieves capsular tension ischemia, and prevents cartilage degradation driven by free iron and inflammatory mediators from lysed red blood cells. Arthrocentesis is performed via an anteromedial approach: with the ankle in slight plantarflexion, a 18-to-20-gauge needle is introduced immediately medial to the tibialis anterior tendon and directed posterolaterally into the talocrural joint space under strict sterile conditions.

Preoperative Planning and Surgical Indications: Uncovering radiographically occult fractures permits timely surgical intervention before symptomatic malunion or avascular necrosis occurs. Specific surgical indications include:

• Displaced fractures of the lateral process of the talus (> 2 mm displacement or articular involvement > 1 cm), requiring open reduction and internal fixation (ORIF) or fragment excision to prevent subtalar arthritis.
• Unstable or displaced osteochondral lesions of the talar dome (Ferkel Stage III or IV), requiring arthroscopic debridement, bone marrow stimulation (microfracture), or retrograde drilling / fixation.
• Displaced posterior malleolar or syndesmotic avulsion fractures necessitating anatomic reduction and rigid screw fixation to restore tibiotalar contact kinematics.

9. Master Class Pro-Tip

Master Class Pro-Tip: In the evaluation of acute ankle trauma, never dismiss a lateral radiograph displaying an anterior capsular teardrop distension of 5 mm or greater as a routine lateral ligament sprain, even if standard three-view radiographs show no cortical breach. In nearly three out of four patients, this distinct capsular displacement represents acute hemarthrosis driven by a radiographically occult intra-articular fracture—most commonly of the talar dome, lateral process of the talus, or anterior calcaneal process. Convert the patient immediately to strict non-weightbearing in a rigid boot or posterior splint, and obtain non-contrast CT imaging. Conversely, beware the false-negative trap: in high-energy injuries with gross swelling, complete capsular and collateral ligament rupture can decompress hemarthrosis into the subcutaneous tissue, obliterating the teardrop sign despite severe articular disruption.

Master Class Radiological Pearl: Teardrop Sign and Occult Ankle Trauma

10. Evidence-Based Synthesis

11. References

1. Towbin R, Dunbar JS, Towbin J, Clark R. Teardrop sign: plain film recognition of ankle effusion. AJR Am J Roentgenol. 1980;134(5):985-990. DOI [Level IV: Diagnostic Cohort & Anatomical Arthrogram Investigation]
2. Dodge JP. The Ankle Teardrop Sign. Radiology. 2004;231(3):701-702. DOI [Level V: Radiological Review & Landmark Sign Analysis]
3. Clark TW, Janzen DL, Ho K, Grunfeld A, Connell DG. Detection of radiographically occult ankle fractures following acute trauma: positive predictive value of an ankle effusion. AJR Am J Roentgenol. 1995;164(5):1185-1189. DOI [Level II: Prospective Diagnostic Cohort Study]
4. Clark TW, Janzen DL, Logan PM, Ho K, Connell DG. Improving the detection of radiographically occult ankle fractures: Positive predictive value of an ankle joint effusion. Clin Radiol. 1996;51(9):632-636. DOI [Level II: Prospective Diagnostic Validation Study]
5. Ho K, Connell DG, Janzen DL, Grunfeld A, Clark TW. Using Tomography to Diagnose Occult Ankle Fractures. Ann Emerg Med. 1996;27(5):600-604. DOI [Level II: Prospective Diagnostic Comparison Study]
6. Allen GM, Wilson DJ, Bullock SA, Watson MS. Extremity CT and ultrasound in the assessment of ankle injuries: occult fractures and ligament injuries. Br J Radiol. 2020;93(1105):20180989. DOI [Level II: Prospective Multimodality Comparative Diagnostic Study]
7. Li W, Zuo Y, Xie Y, Zhang Y. Diagnostic performance of ultrasound and magnetic resonance imaging in ankle injuries: a retrospective cohort study. BMC Musculoskelet Disord. 2026;27:268. DOI [Level III: Retrospective Comparative Diagnostic Study]
8. Hall FM. Pitfalls in the diagnosis of ankle joint effusion. AJR Am J Roentgenol. 1981;136(3):637. DOI [Level V: Diagnostic Methodology & Technical Pitfalls Analysis]
9. Hall FM. More on detection of ankle effusions. AJR Am J Roentgenol. 1998;171(5):1426-1427. DOI [Level V: Diagnostic Biomechanics Commentary]
10. Ho K, Clark TW, Janzen DL, Connell DG, Beaver PF. Occult ankle fracture detected by an ankle effusion on plain radiography: A case report. J Emerg Med. 1996;14(4):463-466. DOI [Level V: Clinical Diagnostic Case Report & Protocol Integration]