High-yield overview
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.
Clinical 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.
Clinical 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
S
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)
H
Hill-Sachs and Bankart (shoulder)
Hill-Sachs: posterolateral humeral head compression (AP internal rotation). Bony Bankart: anterior glenoid rim fracture (axillary/West Point view)
A
Anterior humeral line (elbow)
Line along anterior humeral cortex should bisect MIDDLE THIRD of capitellum on true lateral. Abnormal = supracondylar fracture
L
Lightbulb sign (shoulder)
Humeral head appears abnormally rounded/symmetric on AP = internal rotation from POSTERIOR dislocation. Must get axillary view
L
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
Hook:SHALL: the upper limb trauma signs that you SHALL know for the exam.
Mnemonic
SABLELower Limb Trauma Signs
S
Segond fracture (knee)
Small avulsion from lateral tibial plateau = anterolateral capsule/ligament traction during pivot shift. PATHOGNOMONIC for ACL tear
A
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
B
Blood and fat (lipohaemarthrosis)
Fat-fluid level on horizontal beam lateral = intra-articular fracture. Most common: tibial plateau. Fat from marrow leaks through fracture
L
Lisfranc fleck sign (foot)
Small avulsion fragment between 1st and 2nd metatarsal bases = Lisfranc ligament rupture. EASILY MISSED — always check this area
E
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
Hook:SABLE: five lower limb signs — Segond, Angle (Boehler), Blood (lipohaemarthrosis), Lisfranc, External rotation.
Mnemonic
DISI/VISIWrist Instability Signs
D
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
V
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
T
Terry Thomas sign
Widened scapholunate gap more than 3mm on PA wrist radiograph (named after the gap-toothed comedian). Pathognomonic for SL dissociation
S
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
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 Atlas
Systematic Approach
Radiological Signs — Comprehensive Reference
| 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 |
Differential Diagnosis — Mimics & Look-alikes
Several normal variants and non-traumatic findings imitate classic trauma signs. The exam favourite is being asked "what else could this be?" — knowing the mimics prevents both over-call and missed injury.
| Sign / appearance | True traumatic cause | Mimic to exclude | Discriminator |
|---|---|---|---|
| Elbow effusion / posterior fat pad | Occult intra-articular fracture (radial head, supracondylar) | Septic or inflammatory effusion; technically non-true-lateral film | Trauma history + true lateral with overlapping condyles; aspirate if sepsis suspected |
| Lateral tibial fleck (Segond) | Anterolateral ligament/capsular avulsion = ACL injury | Reverse Segond (medial avulsion, PCL/medial injury); arcuate avulsion (fibular head, posterolateral corner) | Location: Segond is lateral tibia; reverse Segond is medial tibia; arcuate is fibular styloid |
| Fat-fluid level (lipohaemarthrosis) | Intra-articular fracture leaking marrow fat | None benign — always implies fracture, but level only seen on horizontal-beam film | Requires cross-table/horizontal beam; absence on AP does not exclude fracture |
| Rounded humeral head (lightbulb) | Posterior dislocation (locked internal rotation) | Normal internally rotated arm; poor positioning | Trough line, rim sign, over 6 mm joint widening; confirm with axillary/scapular-Y |
| Gap between bones at midfoot | Lisfranc ligament avulsion (fleck sign) | Normal physis in children; os intermetatarseum accessory ossicle | Smooth corticated ossicle vs jagged avulsion; compare contralateral and weight-bear |
| Widened scapholunate space | SL ligament rupture (Terry Thomas) | Normal in young children; clenched-fist artefact; ulnar-deviation positioning | Need over 3 mm on neutral PA, ideally with contralateral comparison; correlate with DISI on lateral |
Controversies & Areas of Uncertainty
Does the Segond fragment need fixation?
The Segond fracture itself is rarely fixed — it is treated as a marker injury and management is directed at the ACL and associated meniscal/anterolateral structures. The contested question is whether anterolateral structures (ALL reconstruction or lateral extra-articular tenodesis) should be added to ACL reconstruction in high pivot-shift knees, revisions and young pivoting athletes. Evidence (including the ALL anatomical and clinical literature) increasingly supports lateral augmentation in selected patients, but routine use remains debated.
Operative vs nonoperative calcaneus
The landmark Buckley RCT showed equivalent unstratified outcomes but a real surgical benefit in defined subgroups. Modern debate has shifted toward minimally invasive/percutaneous and sinus-tarsi approaches to reduce the high wound-complication rate of the extensile lateral approach, and toward primary subtalar arthrodesis for Sanders IV. There is still no universal consensus on which displaced fracture mandates surgery.
Imaging threshold for occult injury
A positive fat pad sign, lipohaemarthrosis or subtle Lisfranc fleck reliably implies fracture, but how aggressively to pursue CT or MRI varies. MRI detects far more bone and soft-tissue injury than radiographs (as in the elbow fat pad data), yet in several series the extra findings did not change management — so routine advanced imaging for every positive sign is not universally accepted.
Reliability of the measurements
Several "objective" signs depend on technique and reader. Bohler angle, scapholunate gap and medial clear space all vary with projection, rotation and weight-bearing, and inter-observer agreement is imperfect. Contralateral comparison views and correlation with clinical examination remain essential rather than relying on a single threshold number.
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
Evidence
Segond Fracture: Lateral Capsular Ligament Avulsion
Dietz GW, Wilcox DM, Montgomery JB • Radiology (1986)
Key Findings:
- The Segond fragment is a small avulsion from the directly lateral surface of the lateral tibial condyle, produced by excessive tension on the lateral capsular ligament.
- The fragment is remarkably constant: elliptical (about 10 x 3 mm), separated by a longitudinal fracture line, lying roughly 4 mm distal to the subarticular cortex.
- A knee haemarthrosis is consistently visible, and the fracture carries a strong association with anterior cruciate ligament rupture.
Clinical implication: The Segond fracture is substantial radiographic evidence of major lateral capsular injury and ACL rupture — its recognition on the AP knee radiograph should prompt MRI and orthopaedic referral.
Limitation: A descriptive radiographic series, not a prospective diagnostic-accuracy study; the fragment is subtle and its absence does NOT exclude an ACL tear.
Source: Dietz GW et al. Radiology 1986;159(2):467-9
Evidence
Anatomy of the Anterolateral Ligament (Segond Substrate)
Claes S, Vereecke E, Maes M, Victor J, Verdonk P, Bellemans J • Journal of Anatomy (2013)
Key Findings:
- The anterolateral ligament (ALL) was identified as a discrete, well-defined structure in 40 of 41 cadaveric knees (97%), distinct from the joint capsule and iliotibial band.
- It originated at the lateral femoral epicondyle and inserted on the anterolateral tibia midway between Gerdy tubercle and the fibular head — the exact site of the Segond fracture.
- By its location it is hypothesised to control internal tibial rotation and modulate the pivot shift, providing the anatomical basis for the Segond fracture.
Clinical implication: The ALL is the anatomical substrate avulsed in a Segond fracture, explaining why this bony fleck is a surrogate marker of anterolateral rotatory injury and ACL rupture.
Limitation: Cadaveric anatomical study; biomechanical function and the clinical value of ALL reconstruction were not directly tested here.
Source: Claes S et al. J Anat 2013;223(4):321-8
Evidence
Lisfranc Fracture-Dislocation: Outcome Depends on Reduction
Myerson MS, Fisher RT, Burgess AR, Kenzora JE • Foot & Ankle (1986)
Key Findings:
- Across 76 tarsometatarsal fracture-dislocations, only 49% achieved an excellent or good result, with quality of initial reduction the major determinant of outcome.
- Open reduction and Kirschner-wire internal fixation yielded the best results; direct crush injuries did poorly (1 of 8 good or excellent).
- More than 2 mm of residual displacement or a talometatarsal angle over 15 degrees after closed reduction mandated open reduction.
Clinical implication: Anatomical reduction is the key prognostic factor in Lisfranc injuries; even small residual diastasis (over 2 mm) warrants operative reduction and fixation.
Limitation: Retrospective single-centre series with a high proportion of polytrauma patients; predates routine CT and modern fixation constructs.
Source: Myerson MS et al. Foot Ankle 1986;6(5):225-42
Evidence
Operative vs Nonoperative Displaced Intra-articular Calcaneal Fractures
Buckley R, Tough S, McCormack R, Pate G, Leighton R, Petrie D, Galpin R • J Bone Joint Surg Am (2002)
Key Findings:
- Landmark multicentre RCT (424 patients, 471 fractures): without stratification, overall functional outcomes (SF-36, VAS) were equivalent between operative and nonoperative care.
- After excluding Workers' Compensation patients, defined subgroups did significantly better with surgery — younger patients, women, comminuted fractures, and those with a moderately low Bohler angle (0-14 degrees).
- Anatomical reduction or a post-reduction step-off of 2 mm or less predicted significantly higher functional scores after surgery.
Clinical implication: Surgery is not mandatory for all displaced calcaneal fractures; benefit is concentrated in selected patients, and where ORIF is performed, restoring articular reduction and Bohler angle drives outcome.
Limitation: Two-year primary endpoint; Workers' Compensation status strongly confounded the unstratified result, and surgical technique/implants have since evolved.
Source: Buckley R et al. J Bone Joint Surg Am 2002;84(10):1733-44
Evidence
Elbow Fat Pad Sign and Radiographically Occult Fracture (MRI)
O'Dwyer H, O'Sullivan P, Fitzgerald D, Lee MJ, McGrath F, Logan PM • J Comput Assist Tomogr (2004)
Key Findings:
- In 20 adults with a post-traumatic elbow effusion but no visible fracture, MRI revealed a radiographically occult fracture in 75%.
- Most occult fractures were in the radial head (86.6%), with lateral epicondyle and olecranon each accounting for 6.7%; 90% showed bone marrow oedema.
- Effusion size (anterior or posterior fat pad displacement) did NOT correlate with the likelihood of an underlying fracture.
Clinical implication: A post-traumatic elbow effusion (positive fat pad sign) with no visible fracture should be treated as an occult intra-articular fracture — most often of the radial head.
Limitation: Small prospective series (n=20); additional MRI findings did not change management in this cohort.
Source: O'Dwyer H et al. J Comput Assist Tomogr 2004;28(4):562-5
Evidence
The Often Overlooked Posterior Shoulder Dislocation
Hatzis N, Kaar TK, Wirth MA, Rockwood CA • Texas Medicine (2001)
Key Findings:
- More than 60% of posterior shoulder dislocations are misdiagnosed at initial presentation, with correct diagnosis often delayed for months or years.
- Triggers (seizure, electric shock, fall onto a flexed adducted arm) plus loss of external rotation and abduction should raise suspicion.
- A radiographic trauma series in the scapular plane (with CT if needed) is required to exclude posterior dislocation.
Clinical implication: Posterior dislocation is the classic missed shoulder injury; the lightbulb sign on the AP view must trigger an axillary or scapular-Y view to confirm.
Limitation: Narrative review rather than a primary diagnostic-accuracy study; no DOI is indexed for this article.
Guidelines, Registries & Global Practice
Recognition of classic radiological trauma signs is a core competency in every major orthopaedic and emergency-medicine curriculum worldwide (FRCS Tr&Orth, FRACS, EBOT/FEBOT, ABOS, DNB/MS, MRCS, SICOT). Missed injuries on trauma radiographs are a leading source of medicolegal claims internationally, which is why structured "search pattern" reading and named-sign checklists are emphasised across systems.
Global Epidemiology
- Missed diagnoses are common and systematic. Posterior shoulder dislocation is misdiagnosed in over 60% of cases at first presentation; Lisfranc injuries and the Segond fracture are repeatedly cited among the most frequently overlooked findings on initial radiographs.
- Mechanism-driven incidence: Segond/ACL injuries cluster in young pivoting athletes; calcaneal and thoracolumbar burst fractures cluster in fall-from-height and road-trauma populations; posterior shoulder dislocation is over-represented in seizure, electrocution and high-energy direct trauma.
Side-by-Side Guidance
| Body / Region | Position relevant to named signs |
|---|---|
| AAOS / OTA (US) | Advocate CT for articular fractures (tibial plateau, calcaneus, pilon) once a sign or effusion is seen; Sanders CT classification guides calcaneal management |
| BOA / BOAST (UK) | BOAST standards mandate adequate orthogonal views and senior review; open-fracture and spinal-clearance standards stress not relying on a single inadequate film |
| AO Foundation | Promotes systematic ABCs search pattern (Adequacy, Bone, Cartilage/joints, Soft tissue) and CT for intra-articular extension and pre-operative planning |
| NICE (UK) | Trauma imaging guidance favours CT in significant blunt/polytrauma and supports MRI for occult injury where radiographs are equivocal |
| ESSR / ACR (Europe & US radiology) | Appropriateness criteria endorse weight-bearing/stress views for suspected Lisfranc and syndesmotic injury and MRI for radiographically occult fracture |
Registry & Practice Variation
- Registry relevance: Implant registries (NJR, AJRR, AOANJRR, Swedish/Norwegian/NZJR) do not catalogue radiological signs directly, but the downstream conditions they track — post-traumatic OA, SLAC-wrist salvage, post-calcaneal arthrodesis, post-traumatic knee arthroplasty — quantify the long-term cost of injuries first announced by these signs (e.g. an unrecognised Segond/ACL injury or a malreduced calcaneus).
- High-resource settings: Ready access to CT and MRI means a positive sign (effusion, fleck, lipohaemarthrosis) is promptly characterised with cross-sectional imaging; weight-bearing and stress views for Lisfranc/syndesmosis are routine.
- Limited-resource settings: Plain radiography may be the only modality available, which raises rather than lowers the value of named-sign recognition; contralateral comparison views, stress views and clinical correlation become the principal tools, and a positive sign is treated as the injury until proven otherwise.
Clinical Decision Scenarios
Practise clinical reasoning and management decisions out loud
Viva scenarioStandard
Clinical prompt
“An examiner shows you a lateral calcaneal radiograph and asks you to measure the Boehler angle. The angle is 10 degrees.”
Practical approach
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 clinical points
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 pitfalls
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
Further questions
“What is the Sanders classification? What is the extensile lateral approach? What are the complications of calcaneal ORIF?”
Viva scenarioStandard
Clinical prompt
“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.”
Practical approach
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 clinical points
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 pitfalls
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
Further questions
“What is the anterolateral ligament? What are the MRI signs of ACL tear? What are the indications for ACL reconstruction?”
Viva scenarioChallenging
Clinical prompt
“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.”
Practical approach
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 clinical points
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 pitfalls
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
Further questions
“What is SLAC wrist? What is the Watson test? What is a four-corner fusion? What is a proximal row carpectomy?”
Viva scenarioChallenging
Clinical prompt
“A 34-year-old man presents after a seizure with a painful shoulder held in internal rotation. He cannot externally rotate the arm. The AP radiograph shows a humeral head that looks abnormally rounded and symmetric, overlapping the glenoid.”
Practical approach
The history (seizure), the locked internal-rotation posture with loss of external rotation, and the rounded, symmetric 'lightbulb' humeral head overlapping the glenoid are the classic features of a POSTERIOR shoulder dislocation. The trap is that the AP view looks deceptively near-normal, which is exactly why posterior dislocation is the most commonly missed shoulder dislocation — misdiagnosed at first presentation in over 60% of cases, often delayed for months. The mechanism here is the violent, unopposed internal-rotator contraction during a seizure (the same applies to electric shock and a fall onto a flexed, adducted arm). Confirmatory radiographic features I would look for: (1) the lightbulb sign (loss of the normal external-rotation greater-tuberosity profile), (2) the rim sign (widening of the glenohumeral space over 6 mm), and (3) the trough line sign (a dense vertical line from an anteromedial humeral head impaction fracture, the reverse Hill-Sachs). The KEY action is to obtain orthogonal imaging the AP cannot replace: an axillary lateral view or a scapular-Y view, which directly shows the head posterior to the glenoid. If positioning is too painful, a CT scan is definitive and also quantifies the reverse Hill-Sachs defect. Management: reduce urgently under adequate sedation or general anaesthesia with traction, adduction and gentle external rotation, taking care not to fracture the head if it is impacted. After reduction, reassess stability and the size of the reverse Hill-Sachs defect on CT. A defect under about 25% of the articular surface is usually stable after reduction and a period of immobilisation in external rotation; 25-50% may need a McLaughlin procedure (subscapularis transfer) or modified McLaughlin (lesser tuberosity transfer into the defect); over 50% or chronic locked dislocations may require allograft reconstruction, arthroplasty, or rotational osteotomy. I would also screen for the underlying cause of the seizure and check for bilateral injury, since seizure-related posterior dislocations can be bilateral.
Key clinical points
Seizure/shock + locked internal rotation + lightbulb sign = posterior dislocation until proven otherwise
Most commonly missed shoulder dislocation (misdiagnosed in over 60% at first presentation)
AP is deceptive — confirm with axillary or scapular-Y view, or CT
Look for rim sign (over 6 mm) and trough line (reverse Hill-Sachs)
Management by defect size: immobilisation, McLaughlin/modified McLaughlin, or reconstruction
Common pitfalls
Calling the AP normal and missing the dislocation
Not obtaining an axillary or scapular-Y view (or CT) to confirm
Not quantifying the reverse Hill-Sachs defect before deciding treatment
Forgetting to look for bilateral injury and the seizure cause
Further questions
“What is the trough line sign? What is the McLaughlin procedure? How does reverse Hill-Sachs size change management?”
Viva scenarioChallenging
Clinical prompt
“A 28-year-old sustains a midfoot crush injury. The non-weight-bearing AP foot radiograph shows a tiny bony fleck between the bases of the first and second metatarsals and you are unsure whether the joint is aligned.”
Practical approach
The small avulsion fragment between the bases of the first and second metatarsals is the fleck sign, indicating avulsion of the Lisfranc ligament (the strong oblique band from the medial cuneiform to the base of the second metatarsal). It is dangerous because it is one of the most frequently missed injuries on initial radiographs — the static, non-weight-bearing film can look almost normal even with significant instability, and a missed Lisfranc injury leads to midfoot collapse, chronic pain and post-traumatic arthritis. Outcome is determined chiefly by the quality of reduction, so it must not be under-treated. Radiographic checks I would make: on the AP view the medial border of the second metatarsal should align with the medial border of the middle cuneiform; on the oblique view the medial border of the fourth metatarsal should align with the medial border of the cuboid. Any diastasis over 2 mm between the first and second metatarsal bases is abnormal. To unmask instability I would obtain weight-bearing views of both feet for comparison (or abduction stress views), and CT to define the fracture pattern and any subtle subluxation; MRI can assess the ligament directly when radiographs and CT are equivocal but suspicion is high. Management: a truly stable, non-displaced injury (no diastasis on weight-bearing views) can be treated non-operatively in a non-weight-bearing cast with repeat weight-bearing films to confirm it stays reduced. Any displacement, diastasis over 2 mm, or demonstrable instability requires anatomical open reduction and stable fixation — transarticular screws or dorsal bridge plating for the medial/middle columns, with the lateral column often stabilised temporarily with K-wires. Primary arthrodesis of the medial columns is an accepted option, particularly for purely ligamentous Lisfranc injuries, where it may give more reliable outcomes than ORIF. The cornerstone, whichever construct is chosen, is anatomical reduction.
Key clinical points
Fleck sign between 1st-2nd MT bases = Lisfranc ligament avulsion
Easily missed on static films — diastasis over 2 mm is abnormal
Confirm with weight-bearing comparison/stress views and CT
Outcome depends on anatomical reduction (Myerson)
Unstable/displaced = ORIF or primary arthrodesis (ligamentous injuries)
Common pitfalls
Clearing the foot on a normal-looking non-weight-bearing film
Mistaking an os intermetatarseum or open physis for an avulsion
Not obtaining weight-bearing or stress comparison views
Under-treating instability and accepting non-anatomical reduction
Further questions
“What are the radiographic alignment lines of the midfoot? When is primary arthrodesis preferred over ORIF? What are the columns of the midfoot?”
Exam day cheat sheet
Radiological Signs in Trauma — Exam Day Reference
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