High Yield Overview
Classic Radiological Signs: Paediatric
—CRITOE Sequence
—Elbow ossification ages
—Klein's Line
—SCFE detection
—Shenton's Line
—DDH assessment
—Crescent Sign
—Perthes collapse
Paediatric Hip Signs Overview
DDH: Shenton's line, acetabular index, Hilgenreiner's line
SCFE: Klein's line, Trethowan sign, slip angle
Perthes: Crescent sign, sagging rope, pillar classification
Key: Always compare with contralateral side in paediatric imaging
Critical Must-Knows
- CRITOE: Elbow ossification order (Capitellum, Radial head, Internal epicondyle, Trochlea, Olecranon, External epicondyle)
- Klein's line: Should intersect epiphysis - abnormal in SCFE
- Shenton's line disruption: DDH or hip fracture/dislocation
- Crescent sign: Subchondral fracture in Perthes
Examiner's Pearls
- "CRITOE before CRITOL: Internal epicondyle before Trochlea
- "Galeazzi sign: Apparent femur shortening in DDH
- "Sagging rope sign: Lateral pillar collapse in Perthes
- "Steel's rule of thirds: Atlantoaxial space components
Exam Warning
Paediatric radiological signs are commonly tested in fellowship exams. Know CRITOE for elbow ossification, the triad of DDH lines (Hilgenreiner, Perkin, Shenton), Klein's line for SCFE, and the crescent sign for Perthes. Always remember the child's age affects normal appearances.
Elbow Ossification Signs
Mnemonic
CRITOEElbow Ossification Order
C
C = Capitellum (1 year)
R
R = Radial head (3 years)
I
I = Internal (medial) epicondyle (5 years)
T
T = Trochlea (7 years)
O
O = Olecranon (9 years)
E
E = External (lateral) epicondyle (11 years)
Memory Hook:The key clinical point is that the Internal epicondyle ALWAYS ossifies before the Trochlea. If you see an 'apparent' trochlear ossification without internal epicondyle, it is actually a displaced internal epicondyle fragment.
Elbow Trauma Signs
| Sign | Description | Significance |
|---|---|---|
| Displaced internal epicondyle | Internal epicondyle in joint space | Often mimics trochlea; surgical indication |
| Hourglass deformity | Entrapped medial epicondyle in joint | Requires open reduction |
| Baumann's angle abnormal | Less than 70° or greater than 15° difference | Supracondylar fracture malreduction |
| Carrying angle loss | Cubitus varus on follow-up | Supracondylar fracture malunion |
The CRITOL Trap
Some texts use CRITOL (with Lateral epicondyle before Olecranon). The standard sequence is CRITOE with External (lateral) epicondyle ossifying LAST. The crucial point for exams is that Internal epicondyle ALWAYS appears before Trochlea - this is the clinically important relationship for identifying displaced medial epicondyle fragments.
DDH (Developmental Dysplasia of Hip) Signs
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DDH Radiological Lines and Signs
| Sign/Line | Description | Significance |
|---|---|---|
| Hilgenreiner's line | Horizontal line through Y-cartilages | Reference for other measurements |
| Perkin's line | Vertical from lateral acetabular edge | Femoral head should be in inferomedial quadrant |
| Shenton's line | Smooth arc from femoral neck to obturator foramen | Disrupted in DDH or hip pathology |
| Acetabular index | Angle of acetabular roof to Hilgenreiner's | Greater than 30° abnormal after 6 months |
| Centre-edge angle | Lateral coverage of femoral head | Less than 20° abnormal in older children |
Ultrasound Graf Classification
For infants less than 4-6 months, ultrasound is preferred (no ossified femoral head). Graf classification uses alpha angle (bony acetabulum) and beta angle (labrum). Type I: Normal (alpha greater than 60°). Type II: Immature/dysplastic. Type III: Subluxed. Type IV: Dislocated.
SCFE (Slipped Capital Femoral Epiphysis) Signs
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SCFE Radiological Signs
| Sign | Description | Significance |
|---|---|---|
| Klein's line | Line along superior femoral neck should intersect epiphysis | Fails to intersect in SCFE |
| Trethowan sign | Klein's line sign (same as above) | Positive when line doesn't intersect epiphysis |
| Steel's blanch sign | Increased density at metaphysis | Due to overlapping slipped epiphysis |
| Widened physis | Physeal widening/irregularity | Pre-slip or early slip |
| Pistol grip deformity | Flattened femoral head-neck junction | Healed SCFE, CAM impingement |
| Slip angle | Angle of epiphysis to shaft | Quantifies severity of slip |
Klein's Line
Draw a line along the superior border of the femoral neck on the AP view. Normally, this line should intersect a portion of the femoral epiphysis. In SCFE, the epiphysis has slipped posteriorly and inferiorly, so Klein's line passes superior to the epiphysis without intersecting it. Always compare to the contralateral hip - bilateral SCFE occurs in 20-40%.
Frog Lateral View
The frog lateral is MORE sensitive than AP for detecting early SCFE as the slip is primarily posterior. However, it should be AVOIDED if there is any suspicion of an unstable slip (acute severe pain, inability to bear weight) as the positioning could worsen the slip.
Perthes Disease Signs
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Perthes Disease Radiological Signs
| Sign | Stage | Description |
|---|---|---|
| Crescent sign | Fragmentation | Subchondral lucent line (subchondral fracture) |
| Sagging rope sign | Fragmentation | Lateral epiphyseal collapse, rope-like density |
| Head within head | Reossification | New bone within old necrotic bone |
| Gage sign | Fragmentation | V-shaped radiolucency at lateral epiphysis |
| Lateral calcification | Fragmentation | Calcification lateral to epiphysis |
| Coxa magna | Healed | Enlarged femoral head |
| Coxa plana | Healed | Flattened femoral head |
Mnemonic
CLOGSPerthes Catterall Signs (Head at Risk)
C
C = Calcification lateral to epiphysis
L
L = Lateral subluxation of femoral head
O
O = Gage sign (lateral V-shaped lucency)
G
G = Growth plate horizontalization
S
S = Sagging rope sign (lateral pillar collapse)
Memory Hook:These 'head at risk' signs suggest poor prognosis and may influence treatment towards containment
Crescent Sign
The crescent sign is a subchondral lucent line best seen on the frog lateral view. It represents a subchondral fracture through avascular bone and marks the transition from the avascular to fragmentation stage. Its presence indicates structural weakening of the femoral head.
Paediatric Fracture Signs
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Mnemonic
SALTERSalter-Harris Classification
S
S = Slipped (Type I) - Through physis only
A
A = Above (Type II) - Physis + metaphysis
L
L = Lower (Type III) - Physis + epiphysis
T
T = Through/Two (Type IV) - Metaphysis + physis + epiphysis
E
ER = Erasure/Rammed (Type V) - Crush injury to physis
Memory Hook:Types III and IV are intra-articular and require anatomical reduction. Type V may not be visible initially.
Non-Accidental Injury Signs
Certain fracture patterns suggest NAI: Classic metaphyseal lesions (corner/bucket handle), posterior rib fractures, multiple fractures of different ages, skull fractures (especially multiple or complex), and fractures in non-ambulatory infants. A skeletal survey is mandatory when NAI is suspected.
Spine Signs
Paediatric Spine Signs
| Sign | Description | Condition |
|---|---|---|
| Scotty dog sign | Normal pars interarticularis on oblique | Collar/fracture = spondylolysis |
| Atlantodens interval widening | ADI greater than 5mm in children | Atlantoaxial instability (Down syndrome, JIA) |
| SCIWORA | Spinal cord injury without radiographic abnormality | Paediatric spinal cord injury |
| Vertebra plana | Complete vertebral body collapse | LCH, eosinophilic granuloma |
| Schmorl's nodes | Disc herniation into vertebral endplate | Scheuermann's disease, trauma |
| Wedge vertebrae | Anterior height less than posterior | Scheuermann's, compression fracture |
Steel's Rule of Thirds
At the atlantoaxial level, the spinal canal space is divided into thirds: 1/3 odontoid, 1/3 spinal cord, 1/3 'space of Steel' (CSF/safety zone). This explains why significant ADI increase is tolerated before neurological compromise in some patients.
Other Paediatric Signs
Miscellaneous Paediatric Signs
| Sign | Description | Condition |
|---|---|---|
| Wimberger sign | Metaphyseal destruction/irregularity | Congenital syphilis |
| Celery stalk metaphysis | Longitudinal striations in metaphysis | Rubella, CMV |
| Fraying/cupping metaphysis | Widened, irregular metaphysis | Rickets |
| Erlenmeyer flask | Undermodelled metaphysis (flask shape) | Gaucher's, osteopetrosis |
| Bone-in-bone | Inner bone outline within outer | Osteopetrosis, lead poisoning |
| Lead lines | Dense metaphyseal bands | Lead poisoning, heavy metal |
| Leukemic lines | Transverse radiolucent metaphyseal bands | Leukaemia |
Exam Viva Scenarios
Practice these scenarios to excel in your viva examination
VIVA SCENARIOStandard
EXAMINER
"A 12-year-old obese boy presents with knee pain and a limp. Hip examination shows limited internal rotation. X-ray of the hip shows Klein's line failing to intersect the femoral epiphysis."
EXCEPTIONAL ANSWER
This is slipped capital femoral epiphysis (SCFE). The clinical scenario is classic: adolescent, obesity, referred knee pain (obturator nerve), and limited internal rotation. Radiological confirmation: (1) Klein's line (Trethowan sign) - a line along the superior femoral neck should normally intersect a portion of the epiphysis; in SCFE, the epiphysis has slipped posteriorly and inferiorly, so the line passes above it. (2) Steel's blanch sign - increased metaphyseal density due to overlapping slipped epiphysis. (3) Widened/irregular physis - physeal widening is an early sign. (4) Slip angle can be measured on the frog lateral to quantify severity. The contralateral hip must also be examined as bilateral SCFE occurs in 20-40% of cases.
KEY POINTS TO SCORE
Klein's line fails to intersect epiphysis
Obese adolescent classic presentation
Knee pain from referred hip pathology
Limited internal rotation on examination
Check contralateral hip (20-40% bilateral)
COMMON TRAPS
✗Missing the diagnosis by not examining the hip
✗Not checking the contralateral side
✗Ordering frog lateral in unstable slip (dangerous)
VIVA SCENARIOStandard
EXAMINER
"A 6-year-old boy presents with a limp. X-ray shows a subchondral lucent line in the femoral head on the frog lateral view."
EXCEPTIONAL ANSWER
This is the crescent sign, pathognomonic for Perthes disease (Legg-Calvé-Perthes disease). The crescent sign represents a subchondral fracture through the avascular bone. It is best seen on the frog lateral view and indicates the transition from the avascular/necrotic stage to the fragmentation stage. The sign appears as a curvilinear lucency parallel to and just beneath the articular surface. Clinical correlation: Age 4-10 years (peak 5-7), male 4:1, often presents with limp and hip/knee pain. The presence of the crescent sign indicates structural weakening and precedes collapse. Prognosis depends on the extent of femoral head involvement and presence of 'head at risk' signs.
KEY POINTS TO SCORE
Crescent sign = subchondral fracture
Best seen on frog lateral view
Marks transition to fragmentation stage
Perthes: Age 4-10, male predominance
Look for other head-at-risk signs
COMMON TRAPS
✗Missing the sign on AP view (frog lateral more sensitive)
✗Not recognising early Perthes
✗Confusing with other causes of AVN
VIVA SCENARIOStandard
EXAMINER
"A 7-year-old child presents after a fall with elbow pain. X-ray appears to show a trochlear ossification centre without a visible internal (medial) epicondyle."
EXCEPTIONAL ANSWER
This is a displaced medial epicondyle fracture mimicking the trochlea. Using the CRITOE sequence (Capitellum 1, Radial head 3, Internal epicondyle 5, Trochlea 7, Olecranon 9, External epicondyle 11), the internal (medial) epicondyle ALWAYS ossifies BEFORE the trochlea. If you see what appears to be a trochlear ossification centre without a visible medial epicondyle, the 'trochlea' is actually a displaced medial epicondyle fragment that has migrated into or near the joint. This is a surgical emergency as the fragment may be incarcerated in the joint, preventing reduction and causing long-term complications. Check for ulnar nerve function and obtain comparison views of the contralateral elbow if uncertain.
KEY POINTS TO SCORE
Internal epicondyle ALWAYS before trochlea (CRITOE)
Apparent trochlea without medial epicondyle = displaced medial epicondyle
Fragment may be incarcerated in joint
Surgical indication if fragment in joint
Check ulnar nerve function
COMMON TRAPS
✗Accepting apparent trochlea as normal
✗Not knowing CRITOE sequence
✗Missing the incarcerated fragment
Evidence Base
Normal Variants vs Pathology
4
4
Hip Development
3
Clinical Relevance
3
Key Evidence Points
- CRITOE ages: Standardised ossification sequence (1, 3, 5, 7, 9, 11 years)
- Shenton line: Continuous arc from medial femoral neck to inferior pubic ramus
- Normal variants: Multiple accessory ossification centres are normal, not fractures
- Systematic approach: Essential to avoid missing subtle paediatric fractures
Paediatric Signs Quick Reference
High-Yield Exam Summary
CRITOE (Elbow Ossification)
- •C = Capitellum (1 year)
- •R = Radial head (3 years)
- •I = Internal epicondyle (5 years)
- •T = Trochlea (7 years)
- •O = Olecranon (9 years)
- •E = External epicondyle (11 years)
DDH Signs
- •Shenton's line disruption
- •Perkin's line (femoral head inferomedial)
- •Acetabular index greater than 30°
- •Graf alpha angle for ultrasound
SCFE Signs
- •Klein's line fails to intersect epiphysis
- •Steel's blanch sign (metaphyseal density)
- •Widened/irregular physis
- •Frog lateral more sensitive (avoid if unstable)
Perthes Signs
- •Crescent sign (subchondral fracture)
- •Sagging rope sign (lateral collapse)
- •Head at risk: CLOGS mnemonic
- •Coxa magna/plana in healed stage