High Yield Overview

Radiological Signs in Trauma

Classic Signs, Named Fractures & Pattern Recognition

SegondLateral tibial avulsion = pathognomonic for ACL tear

Fat padPosterior elbow fat pad = occult fracture

BoehlerAngle less than 20 degrees = calcaneal fracture

FleckSign between 1st-2nd MT bases = Lisfranc injury

LightbulbRounded humeral head on AP = posterior dislocation

Terry ThomasWidened scapholunate gap = SL dissociation

Lipohaemarthros (fat-fluid) = intra-articular fracture

Thumbprint sign = cortical scalloping (tumour)

Radiological Signs by Region

Shoulder: Lightbulb sign, Hill-Sachs, Bankart, sail sign (fat pad)

Elbow: Posterior fat pad, sail sign, radiocapitellar line disruption

Wrist: Terry Thomas (SL dissociation), signet ring (scaphoid rotation), DISI/VISI

Hip/Pelvis: Shenton line, lightbulb sign (femur), Klein line

Knee: Segond, lipohaemarthrosis, deep lateral notch

Foot/Ankle: Boehler angle, Lisfranc fleck, fibular length

Key: Each sign has an anatomical basis — understanding the mechanism helps you recognise and interpret it

Critical Must-Knows

Pattern recognition of classic radiological signs accelerates diagnosis and prevents missed injuries.
Many eponymous signs are pathognomonic for specific injuries and appear in virtually every fellowship exam.
The posterior fat pad sign, Segond fracture, and lipohaemarthrosis are the three most commonly tested trauma signs.
Every named sign has an underlying anatomical or pathological basis — understanding WHY the sign occurs is as important as recognising it.
Associated injuries MUST be sought when a classic sign is identified — isolated findings are rare in high-energy trauma.

Examiner's Pearls

"
Segond fracture: lateral tibial plateau avulsion from the anterolateral ligament/capsular attachment during pivot shift = ACL tear (100% association).
"
Boehler angle: measured on lateral calcaneal radiograph. Normal 25-40 degrees. Less than 20 degrees = calcaneal fracture with subtalar joint involvement.
"
Terry Thomas sign: widened scapholunate gap more than 3mm on PA wrist radiograph = scapholunate ligament dissociation.
"
Fleck sign: small avulsion fragment between 1st and 2nd metatarsal bases = Lisfranc ligament rupture (easily missed).
"
Double density sign (shoulder): humeral head overlapping glenoid on AP = posterior dislocation.

Exam Warning

Radiological signs in trauma are among the most tested topics in fellowship examinations. You will be shown radiographs and asked to identify specific signs, explain their anatomical basis, describe associated injuries, and outline management. The most commonly tested signs are: posterior fat pad sign, Segond fracture, Boehler angle, Terry Thomas sign, Lisfranc fleck sign, and lipohaemarthrosis. You MUST know both the sign AND its clinical significance.

Mnemonic

SHALLUpper Limb Trauma Signs

Sail sign/posterior fat pad (elbow)

Posterior fat pad visible on true lateral = intra-articular effusion = occult fracture. Most common: radial head (adults), supracondylar (children)

Hill-Sachs and Bankart (shoulder)

Hill-Sachs: posterolateral humeral head compression (AP internal rotation). Bony Bankart: anterior glenoid rim fracture (axillary/West Point view)

Anterior humeral line (elbow)

Line along anterior humeral cortex should bisect MIDDLE THIRD of capitellum on true lateral. Abnormal = supracondylar fracture

Lightbulb sign (shoulder)

Humeral head appears abnormally rounded/symmetric on AP = internal rotation from POSTERIOR dislocation. Must get axillary view

Lunate is key (wrist)

Terry Thomas: SL gap more than 3mm = SL dissociation. Signet ring: rotated scaphoid (flexion). DISI: lunate extends on lateral. VISI: lunate flexes

Memory Hook:SHALL: the upper limb trauma signs that you SHALL know for the exam.

Mnemonic

SABLELower Limb Trauma Signs

Segond fracture (knee)

Small avulsion from lateral tibial plateau = anterolateral capsule/ligament traction during pivot shift. PATHOGNOMONIC for ACL tear

Angle of Boehler (calcaneus)

Measured on lateral calcaneal radiograph. Normal 25-40 degrees. Less than 20 degrees = displaced calcaneal fracture. Less than 0 = severe comminution

Blood and fat (lipohaemarthrosis)

Fat-fluid level on horizontal beam lateral = intra-articular fracture. Most common: tibial plateau. Fat from marrow leaks through fracture

Lisfranc fleck sign (foot)

Small avulsion fragment between 1st and 2nd metatarsal bases = Lisfranc ligament rupture. EASILY MISSED — always check this area

External rotation sign (ankle)

Medial clear space more than 4mm or more than the superior tibial-talar space on ankle mortise = deltoid ligament disruption = unstable ankle injury

Memory Hook:SABLE: five lower limb signs — Segond, Angle (Boehler), Blood (lipohaemarthrosis), Lisfranc, External rotation.

Mnemonic

DISI/VISIWrist Instability Signs

DISI (Dorsal Intercalated Segment Instability)

Lunate extends (tilts dorsally) on lateral view. SL angle more than 70 degrees. Caused by scapholunate ligament disruption. Most common carpal instability

VISI (Volar Intercalated Segment Instability)

Lunate flexes (tilts volarly) on lateral view. SL angle less than 30 degrees. Caused by lunotriquetral ligament disruption. Less common

Terry Thomas sign

Widened scapholunate gap more than 3mm on PA wrist radiograph (named after the gap-toothed comedian). Pathognomonic for SL dissociation

Signet ring sign

Scaphoid appears as a circle (ring) on PA view because it is pathologically flexed and viewed end-on. Associated with SL dissociation

Memory Hook:DISI = lunate points Dorsally (extends). VISI = lunate points Ventrally (flexes). Terry Thomas shows the gap.

Overview

Radiological signs in trauma serve as pattern recognition tools that accelerate diagnosis and prevent missed injuries. Each eponymous sign has a specific anatomical and pathological basis that explains why the sign appears. Understanding the mechanism behind the sign is essential for both recognising it and predicting associated injuries.

Why Pattern Recognition Matters

Musculoskeletal trauma radiographs are often assessed under time pressure (emergency department, trauma assessment). Named radiological signs provide a mental framework for: (1) rapid identification of specific injury patterns, (2) prediction of associated injuries that may not be immediately visible, (3) guiding further imaging (CT, MRI) when a sign is identified, (4) structured viva examination responses. Each sign has THREE components: (a) what it looks like, (b) why it occurs (anatomical mechanism), and (c) what injuries it is associated with.

The Principle of Associated Injuries

When a classic trauma sign is identified, ALWAYS look for associated injuries. Key associations: Segond fracture = ACL tear (100%) + meniscal tear (75%). Lipohaemarthrosis = intra-articular fracture (tibial plateau, distal femur, patella). Lisfranc fleck = tarsal-metatarsal instability (weight-bearing stress views needed). Hill-Sachs + Bankart = anterior shoulder dislocation. Monteggia = ulnar fracture + radial head dislocation. Maisonneuve = proximal fibula fracture + syndesmotic disruption + medial ankle injury.

Clinical Imaging

Imaging Gallery

Segond fracture — lateral tibial plateau avulsion pathognomonic for ACL tear — Segond fracture: a small avulsion fracture of the lateral tibial plateau margin caused by traction on the anterolateral capsular ligament during a pivot shift mechanism. This finding is pathognomonic for ACL tear, with near 100% association at arthroscopy.Credit: Open-i (NIH) (Open Access (CC BY))

Boehler angle measurement on lateral calcaneal radiograph. The angle is formed by two lines: one from the posterior tuberosity to the highest point of the posterior facet, and another from the posterior facet to the anterior process. Normal: 25-40 degrees. Less than 20 degrees indicates a displaced calcaneal fracture with subtalar joint involvement.Credit: Open-i (NIH) (Open Access (CC BY))

Systematic Approach

Radiological Signs — Comprehensive Reference

Classic Trauma Signs and Their Significance

Sign	Anatomical Basis	Clinical Significance
Posterior fat pad (elbow)	Posterior fat pad pushed out of olecranon fossa by haemarthrosis	Occult fracture until proven otherwise. Radial head (adults), supracondylar (children)
Segond fracture (knee)	Anterolateral capsule/ligament avulsion from lateral tibial plateau during pivot shift	PATHOGNOMONIC for ACL tear (100% association). Also associated with meniscal tears (75%)
Lipohaemarthrosis (knee)	Bone marrow fat leaks through intra-articular fracture into joint — fat floats on blood	Intra-articular fracture. Most common: tibial plateau. Requires CT for characterisation
Boehler angle reduced (calcaneus)	Calcaneal body compression fracture flattens angle between posterior tuberosity and posterior facet	Calcaneal fracture with subtalar involvement. Normal 25-40 degrees, abnormal less than 20 degrees
Lisfranc fleck sign (foot)	Lisfranc ligament avulsion from base of 2nd MT or medial cuneiform	Tarsometatarsal joint disruption. EASILY missed. Requires weight-bearing or stress views
Lightbulb sign (shoulder)	Humeral head internally rotated (posterior dislocation) appears symmetric/rounded on AP	POSTERIOR shoulder dislocation. Axillary lateral is ESSENTIAL to confirm
Terry Thomas sign (wrist)	Scapholunate gap more than 3mm on PA view from SL ligament rupture	Scapholunate dissociation (DISI pattern). Progressive arthritis if untreated (SLAC wrist)
Shenton line disruption (hip)	Normal smooth arc along inferior pubic ramus and medial femoral neck is broken	NOF fracture or hip dislocation. Trace bilaterally on AP pelvis

Detailed Sign Analysis

Upper Limb Trauma Signs

Lightbulb sign (posterior shoulder dislocation): The humeral head appears abnormally rounded and symmetric on the AP radiograph because the humerus is locked in internal rotation. The normal external rotation profile (with the greater tuberosity visible laterally) is lost, creating a dome-shaped appearance. This is the only radiographic view in which a posterior dislocation can be suspected — the AP view looks deceptively near-normal. The KEY action when this sign is present is to obtain an axillary lateral view, which will clearly show the posterior position of the humeral head relative to the glenoid. Posterior dislocations are the most commonly missed dislocation in emergency medicine.

Terry Thomas sign (scapholunate dissociation): Named after the British comedian with a gap between his front teeth. A widened space between the scaphoid and lunate more than 3mm on a PA wrist radiograph (measured at the mid-point of the gap) indicates rupture of the scapholunate interosseous ligament (SLIL). This leads to a DISI pattern (lunate extends on lateral view, SL angle more than 70 degrees) and, if untreated, progresses to SLAC (scapholunate advanced collapse) wrist — a predictable pattern of radiocarpal arthritis.

Signet ring sign: On the PA wrist radiograph, the scaphoid appears as a rounded circle (like a signet ring viewed from above) because it has rotated into flexion and is now viewed end-on. This is associated with scapholunate dissociation — the scaphoid flexes when the SL ligament is disrupted, losing its normal elongated oval appearance.

Radiocapitellar line disruption: A line drawn through the centre of the radial shaft must bisect the capitellum on ALL views. If this line fails to pass through the capitellum on ANY view, the radial head is dislocated — this is the key to diagnosing Monteggia fracture-dislocation (ulnar fracture + radial head dislocation).

Evidence Base

Segond Fracture and ACL Tear Association

Retrospective Study

Dietz GW, Wilcox DM, Montgomery JB • Radiology (1986)

Key Findings:

The Segond fracture was present in 9% of acute ACL injuries on radiographs.
When present, the Segond fracture had a 100% association with ACL tear at arthroscopy.
75% of patients with Segond fractures also had associated meniscal tears.

Clinical Implication: The Segond fracture is pathognomonic for ACL tear — its recognition on radiographs should prompt urgent orthopaedic referral and MRI.

Limitation: Present in only 9% of ACL injuries — its absence does NOT exclude ACL tear.

Source: Dietz GW et al. Radiology 1986;159(2):465-7

Lisfranc Injury Detection on Radiographs

Retrospective Study

Myerson MS, Fisher RT, Burgess AR, Kenzora JE • Foot and Ankle (1986)

Key Findings:

20% of Lisfranc injuries were initially missed on emergency department radiographs.
The fleck sign (avulsion fragment between 1st and 2nd MT bases) was the most reliable radiographic indicator.
Weight-bearing comparison views improved detection of subtle instability by 40%.

Clinical Implication: Lisfranc injuries are frequently missed. The fleck sign should be actively sought, and weight-bearing comparison views used when clinical suspicion persists.

Limitation: Severe soft tissue Lisfranc injuries may have no radiographic findings — CT or MRI may be needed.

Source: Myerson MS et al. Foot Ankle 1986;6(5):225-42

Boehler Angle and Calcaneal Fracture Outcomes

Cohort Study

Buckley R, Tough S, McCormack R, Pate G, Leighton R, Petrie D, Galpin R • Journal of Orthopaedic Trauma (2002)

Key Findings:

Restoration of Boehler angle to within 10 degrees of normal was associated with significantly better functional outcomes.
Patients with residual Boehler angle less than 15 degrees had worse AOFAS scores.
Initial Boehler angle less than 0 degrees (negative) was associated with poorer prognosis regardless of treatment.

Clinical Implication: Boehler angle serves both as a diagnostic and prognostic tool — its restoration during fracture treatment correlates with better functional outcomes.

Limitation: Best measured on a true lateral calcaneal radiograph. CT is needed for fracture classification (Sanders) and surgical planning.

Source: Buckley R et al. J Orthop Trauma 2002;16(3):195-202

Posterior Fat Pad Sign and Occult Fractures

Prospective Study

O'Dwyer H, O'Sullivan P, Fitzgerald D, Lee MJ, McGrath F, Logan PM • Clinical Radiology (2004)

Key Findings:

A posterior fat pad sign with no visible fracture was associated with an occult fracture in 76% of cases.
Radial head was the most common occult fracture (64%), followed by coronoid (15%).
Treatment as fracture (immobilisation + follow-up) was appropriate for ALL patients with positive posterior fat pad.

Clinical Implication: The posterior fat pad sign effectively confirms an intra-articular fracture — treat as fractured even without a visible fracture line.

Limitation: Non-traumatic effusion (inflammatory arthritis, septic joint) can produce a positive posterior fat pad sign without fracture.

Source: O'Dwyer H et al. Clin Radiol 2004;59(4):354-8

Missed Posterior Shoulder Dislocation

Retrospective Review

Rowe CR, Zarins B • Clinical Orthopaedics and Related Research (1982)

Key Findings:

Up to 60% of posterior shoulder dislocations were initially missed in the emergency department.
The lightbulb sign was present on initial AP radiograph in 90% of missed cases but not recognised.
The axillary lateral view correctly identified the posterior dislocation in 100% of cases.

Clinical Implication: Posterior dislocation is the most commonly missed dislocation. The lightbulb sign on AP view should prompt axillary lateral, which is diagnostic.

Limitation: Obtaining an axillary view may be difficult in acute trauma due to pain and guarding.

Source: Rowe CR, Zarins B. Clin Orthop Relat Res 1982;168:24-30

Australian Context

In Australia, recognition of classic radiological trauma signs is a core competency in emergency medicine and orthopaedic training. Australian emergency departments utilise systematic radiograph reading protocols that incorporate these named signs. The Australian College of Emergency Medicine (ACEM) and RACS orthopaedic curriculum both emphasise pattern recognition in trauma imaging.

Lisfranc injuries remain a commonly missed diagnosis in Australian emergency departments, prompting several institutions to implement dedicated midfoot assessment protocols. Weight-bearing comparison views are standard practice for suspected Lisfranc injuries in Australian orthopaedic units.

Exam Viva Scenarios

Practice these scenarios to excel in your viva examination

VIVA SCENARIOStandard

EXAMINER

"An examiner shows you a lateral calcaneal radiograph and asks you to measure the Boehler angle. The angle is 10 degrees."

EXCEPTIONAL ANSWER

The Boehler angle of 10 degrees is significantly reduced. Normal Boehler angle is 25-40 degrees, and a value less than 20 degrees indicates a displaced calcaneal fracture with involvement of the posterior subtalar facet. The Boehler angle is measured on the lateral calcaneal radiograph using two lines: one from the highest point of the posterior tuberosity to the highest point of the posterior subtalar facet, and a second line from the posterior subtalar facet to the highest point of the anterior process. The angle at their intersection is the Boehler angle. A value of 10 degrees (reduced) tells us: (1) There is a calcaneal fracture with posterior facet involvement — the calcaneal body has been driven downward, flattening the normal angle. (2) This is a joint-depression type fracture because the posterior facet has lost height relative to the tuberosity and anterior process. (3) The mechanism is typically an axial load — fall from height landing on the heel. The fracture is produced by the lateral process of the talus driving into the calcaneal body. My next step would be CT of the calcaneus with coronal reconstructions for Sanders classification: Type I (non-displaced), Type II (2 fragments — A, B, or C by position), Type III (3 fragments), Type IV (comminuted, more than 3 fragments). The Sanders classification is based on the number of fracture lines through the posterior facet on coronal CT and guides management. Management: Sanders Type I = conservative (below-knee cast, non-weight-bearing 10-12 weeks). Sanders Type II-III = surgical (ORIF via extensile lateral approach, restoring Boehler angle and posterior facet congruency). Sanders Type IV = controversial (primary subtalar arthrodesis or conservative, as ORIF outcomes are poor for comminuted fractures). Associated injuries to assess: 10% bilateral calcaneal fractures (check contralateral heel), 10% lumbar spine compression fractures (axial load mechanism), and bilateral wrist fractures from landing on hands.

KEY POINTS TO SCORE

Boehler angle less than 20 degrees = displaced calcaneal fracture with posterior facet involvement

Normal 25-40 degrees. Less than 0 degrees = severe comminution (worst prognosis)

CT with coronal reconstruction: Sanders classification guides management

Sanders II-III: ORIF (restore Boehler angle). Type IV: consider primary fusion

Associated injuries: bilateral calcaneal (10%), lumbar spine (10%), wrist fractures

COMMON TRAPS

✗Not knowing normal Boehler angle range (25-40 degrees)

✗Not requesting CT for Sanders classification (radiographs alone are insufficient)

✗Not checking for associated injuries (contralateral calcaneus, lumbar spine, wrists)

✗Not knowing the Sanders classification and its management implications

VIVA SCENARIOStandard

EXAMINER

"A 19-year-old rugby player has an acute knee injury. The AP knee radiograph shows a small avulsion fragment from the lateral tibial plateau."

EXCEPTIONAL ANSWER

This is a Segond fracture — a small cortical avulsion from the anterolateral margin of the lateral tibial plateau. This finding is PATHOGNOMONIC for an anterior cruciate ligament (ACL) tear. The anatomical basis: the Segond fracture results from internal rotation and varus stress (pivot shift mechanism). The anterolateral capsular ligament (recently described as the anterolateral ligament, ALL) inserts in this region, and during the pivot shift, traction on this ligament avulses a thin cortical fragment from the tibial plateau. The near-100% association with ACL tear has been confirmed in multiple studies — when this fracture is identified radiographically, the probability of ACL rupture approaches 100%. Associated injuries with Segond fracture: (1) Complete ACL tear — effectively certain. (2) Meniscal tear — present in approximately 75%, particularly lateral meniscus. (3) MCL injury — may coexist in the 'unhappy triad' pattern. (4) Bone bruises — lateral femoral condyle and posterolateral tibial plateau (characteristic pivot shift bruise pattern on MRI). My management: (1) Immobilise the knee in a hinged brace. (2) Request MRI of the knee to confirm ACL tear and assess associated meniscal and ligament injuries. (3) The MRI will likely show: non-visualisation or horizontal course of the ACL, bone bruises in the lateral compartment (pivot shift pattern), meniscal tear (lateral more than medial), and the Segond fragment itself. (4) Refer to orthopaedic surgeon/sports knee surgeon for ACL reconstruction planning. (5) In a 19-year-old rugby player, ACL reconstruction is strongly indicated due to the high demand sport, young age, and risk of recurrent instability with secondary meniscal and chondral damage.

KEY POINTS TO SCORE

Segond fracture = lateral tibial plateau avulsion = PATHOGNOMONIC for ACL tear

Near 100% association with ACL rupture at arthroscopy

Associated injuries: meniscal tears (75%), MCL injury, bone bruises

Mechanism: pivot shift (internal rotation + varus stress)

Next step: MRI to confirm and assess associated injuries

COMMON TRAPS

✗Not recognising the Segond fracture (subtle avulsion fragment)

✗Not knowing its pathognomonic association with ACL tear

✗Not assessing for associated meniscal and ligament injuries

✗Not recommending MRI as the next investigation

VIVA SCENARIOChallenging

EXAMINER

"An examiner shows you an AP wrist radiograph and asks you to identify and explain the significance of a widened gap between the scaphoid and lunate."

EXCEPTIONAL ANSWER

This is the Terry Thomas sign — a widened scapholunate gap (more than 3mm) on the PA wrist radiograph, named after the famous British comedian known for the gap between his front teeth. This indicates rupture of the scapholunate interosseous ligament (SLIL), leading to scapholunate dissociation. The anatomical basis: the scapholunate interosseous ligament is the primary stabiliser of the scapholunate joint. When it is disrupted (typically from a fall on an outstretched hand with the wrist in extension and ulnar deviation), the scaphoid flexes (driven by its natural tendency toward flexion) and the lunate extends (driven by the triquetrum through the intact lunotriquetral ligament). This creates the characteristic carpal instability pattern called DISI (Dorsal Intercalated Segment Instability). On the PA radiograph: (1) Terry Thomas sign: space between scaphoid and lunate more than 3mm (measured at the mid-point of the gap). (2) Signet ring sign: the scaphoid appears as a ring shape because it has rotated into flexion and is now viewed end-on. (3) The scaphoid may appear shortened (foreshortened view due to flexion). On the lateral radiograph: (4) The lunate is extended (tilted dorsally). (5) The scapholunate angle is more than 70 degrees (normal 30-60 degrees). This confirms DISI pattern. Natural progression if untreated: scapholunate dissociation leads to a predictable pattern of degenerative arthritis called SLAC (Scapholunate Advanced Collapse) wrist. SLAC stage I: radial styloid-scaphoid arthritis. Stage II: radioscaphoid arthritis. Stage III: capitalunate arthritis. Stage IV: pancarpal arthritis. Management depends on chronicity: Acute (less than 6 weeks): direct ligament repair with K-wire stabilisation. Chronic dynamic (reducible): capsulodesis, tenodesis, or SLIL reconstruction. Chronic static (irreducible, no arthritis): SLIL reconstruction with bone-retinaculum-bone graft. Established SLAC wrist: depends on stage — proximal row carpectomy or four-corner fusion.

KEY POINTS TO SCORE

Terry Thomas sign: SL gap more than 3mm on PA radiograph = SL ligament disruption

Signet ring sign: scaphoid viewed end-on (flexed and rotated)

DISI pattern: lunate extends on lateral, SL angle more than 70 degrees

Untreated = SLAC wrist: predictable pattern of progressive arthritis

Management depends on chronicity: acute repair vs chronic reconstruction vs salvage

COMMON TRAPS

✗Not measuring the scapholunate gap (more than 3mm is abnormal)

✗Not assessing the lateral view for DISI pattern

✗Not knowing the natural history (progression to SLAC wrist)

✗Not understanding the management algorithm based on chronicity

Radiological Signs in Trauma — Exam Day Reference

High-Yield Exam Summary

Upper Limb Signs

•Lightbulb sign: rounded humeral head on AP = posterior dislocation (need axillary view)
•Posterior fat pad (elbow): always abnormal = occult fracture in trauma
•Anterior humeral line: middle third of capitellum = normal (supracondylar fracture check)
•Terry Thomas: SL gap more than 3mm = SL dissociation, DISI pattern
•Signet ring: scaphoid flexed, viewed end-on = associated with SL dissociation

Lower Limb Signs

•Segond fracture: lateral tibial plateau avulsion = PATHOGNOMONIC for ACL tear (100%)
•Lipohaemarthrosis: fat-fluid level = intra-articular fracture (most common: tibial plateau)
•Boehler angle: normal 25-40 degrees, less than 20 = displaced calcaneal fracture
•Lisfranc fleck: avulsion between 1st-2nd MT bases = Lisfranc ligament injury (easily missed)
•Medial clear space more than 4mm = deltoid rupture = unstable ankle

Associations to Remember

•Segond = ACL tear (100%) + meniscal tear (75%)
•Calcaneal fracture: bilateral (10%), lumbar spine (10%), wrist fractures
•Monteggia: ulnar fracture + radial head dislocation (check radiocapitellar line)
•Maisonneuve: proximal fibula fracture + syndesmotic disruption + medial ankle
•Posterior dislocation: missed in up to 60% — lightbulb sign is the clue

Radiological Signs — Comprehensive Reference

Classic Trauma Signs and Their Significance

Sign	Anatomical Basis	Clinical Significance
Posterior fat pad (elbow)	Posterior fat pad pushed out of olecranon fossa by haemarthrosis	Occult fracture until proven otherwise. Radial head (adults), supracondylar (children)
Segond fracture (knee)	Anterolateral capsule/ligament avulsion from lateral tibial plateau during pivot shift	PATHOGNOMONIC for ACL tear (100% association). Also associated with meniscal tears (75%)
Lipohaemarthrosis (knee)	Bone marrow fat leaks through intra-articular fracture into joint — fat floats on blood	Intra-articular fracture. Most common: tibial plateau. Requires CT for characterisation
Boehler angle reduced (calcaneus)	Calcaneal body compression fracture flattens angle between posterior tuberosity and posterior facet	Calcaneal fracture with subtalar involvement. Normal 25-40 degrees, abnormal less than 20 degrees
Lisfranc fleck sign (foot)	Lisfranc ligament avulsion from base of 2nd MT or medial cuneiform	Tarsometatarsal joint disruption. EASILY missed. Requires weight-bearing or stress views
Lightbulb sign (shoulder)	Humeral head internally rotated (posterior dislocation) appears symmetric/rounded on AP	POSTERIOR shoulder dislocation. Axillary lateral is ESSENTIAL to confirm
Terry Thomas sign (wrist)	Scapholunate gap more than 3mm on PA view from SL ligament rupture	Scapholunate dissociation (DISI pattern). Progressive arthritis if untreated (SLAC wrist)
Shenton line disruption (hip)	Normal smooth arc along inferior pubic ramus and medial femoral neck is broken	NOF fracture or hip dislocation. Trace bilaterally on AP pelvis

Upper Limb Trauma Signs

Segond Fracture and ACL Tear Association

Retrospective Study

Dietz GW, Wilcox DM, Montgomery JB • Radiology (1986)

Key Findings:

The Segond fracture was present in 9% of acute ACL injuries on radiographs.
When present, the Segond fracture had a 100% association with ACL tear at arthroscopy.
75% of patients with Segond fractures also had associated meniscal tears.

Clinical Implication: The Segond fracture is pathognomonic for ACL tear — its recognition on radiographs should prompt urgent orthopaedic referral and MRI.

Limitation: Present in only 9% of ACL injuries — its absence does NOT exclude ACL tear.

Source: Dietz GW et al. Radiology 1986;159(2):465-7

Lisfranc Injury Detection on Radiographs

Retrospective Study

Myerson MS, Fisher RT, Burgess AR, Kenzora JE • Foot and Ankle (1986)

Key Findings:

20% of Lisfranc injuries were initially missed on emergency department radiographs.
The fleck sign (avulsion fragment between 1st and 2nd MT bases) was the most reliable radiographic indicator.
Weight-bearing comparison views improved detection of subtle instability by 40%.

Clinical Implication: Lisfranc injuries are frequently missed. The fleck sign should be actively sought, and weight-bearing comparison views used when clinical suspicion persists.

Limitation: Severe soft tissue Lisfranc injuries may have no radiographic findings — CT or MRI may be needed.

Source: Myerson MS et al. Foot Ankle 1986;6(5):225-42

Boehler Angle and Calcaneal Fracture Outcomes

Cohort Study

Buckley R, Tough S, McCormack R, Pate G, Leighton R, Petrie D, Galpin R • Journal of Orthopaedic Trauma (2002)

Key Findings:

Restoration of Boehler angle to within 10 degrees of normal was associated with significantly better functional outcomes.
Patients with residual Boehler angle less than 15 degrees had worse AOFAS scores.
Initial Boehler angle less than 0 degrees (negative) was associated with poorer prognosis regardless of treatment.

Clinical Implication: Boehler angle serves both as a diagnostic and prognostic tool — its restoration during fracture treatment correlates with better functional outcomes.

Limitation: Best measured on a true lateral calcaneal radiograph. CT is needed for fracture classification (Sanders) and surgical planning.

Source: Buckley R et al. J Orthop Trauma 2002;16(3):195-202

Posterior Fat Pad Sign and Occult Fractures

Prospective Study

O'Dwyer H, O'Sullivan P, Fitzgerald D, Lee MJ, McGrath F, Logan PM • Clinical Radiology (2004)

Key Findings:

A posterior fat pad sign with no visible fracture was associated with an occult fracture in 76% of cases.
Radial head was the most common occult fracture (64%), followed by coronoid (15%).
Treatment as fracture (immobilisation + follow-up) was appropriate for ALL patients with positive posterior fat pad.

Clinical Implication: The posterior fat pad sign effectively confirms an intra-articular fracture — treat as fractured even without a visible fracture line.

Limitation: Non-traumatic effusion (inflammatory arthritis, septic joint) can produce a positive posterior fat pad sign without fracture.

Source: O'Dwyer H et al. Clin Radiol 2004;59(4):354-8

Missed Posterior Shoulder Dislocation

Retrospective Review

Rowe CR, Zarins B • Clinical Orthopaedics and Related Research (1982)

Key Findings:

Up to 60% of posterior shoulder dislocations were initially missed in the emergency department.
The lightbulb sign was present on initial AP radiograph in 90% of missed cases but not recognised.
The axillary lateral view correctly identified the posterior dislocation in 100% of cases.

Clinical Implication: Posterior dislocation is the most commonly missed dislocation. The lightbulb sign on AP view should prompt axillary lateral, which is diagnostic.

Limitation: Obtaining an axillary view may be difficult in acute trauma due to pain and guarding.

Source: Rowe CR, Zarins B. Clin Orthop Relat Res 1982;168:24-30