High-yield overview
DDH, SUFE, Perthes & Growth Plate Assessment
KleinLine tangent to femoral neck — fails to intersect epiphysis in SUFE
PerkinsVertical line from lateral acetabular edge for DDH assessment
HilgenreinerHorizontal line through triradiate cartilages for DDH
ShentonArc disruption in DDH and NOF fractures
SHSalter-Harris classification I-V for growth plate injuries
SALTRMnemonic for Salter-Harris types
USSPrimary modality for DDH before 6 months
HerringLateral pillar classification for Perthes prognosis
Paediatric Orthopaedic Imaging Signs
DDH: Hilgenreiner + Perkins lines, acetabular index, Shenton line, Graf USS
SUFE: Klein line, frog lateral (best view), Southwick angle
Perthes: Catterall classification, Herring lateral pillar, Gage sign, head-at-risk
Growth plate: Salter-Harris I-V (SALTR mnemonic)
NAI: Metaphyseal corner fractures, multiple fractures of different ages
Key: The Klein line for SUFE and Perkins/Hilgenreiner for DDH are the most tested paediatric signs
Critical Must-Knows
- Klein line: a line drawn along the superior femoral neck on AP radiograph should intersect the lateral epiphysis. Failure = SUFE.
- DDH assessment: Perkins line (vertical from lateral acetabular edge) and Hilgenreiner line (horizontal through triradiate cartilage) create four quadrants — femoral head should be in the inferomedial quadrant.
- Salter-Harris classification (SALTR): Slip (I), Above (II), Lower (III), Through (IV), Rammed (V) — describes growth plate fracture pattern.
- Perthes disease staging: Catterall classification (4 groups by extent of head involvement) and Herring lateral pillar classification (A, B, C by lateral pillar height preservation).
- Ultrasound is the primary imaging modality for DDH screening before 6 months (Graf classification). AP pelvis radiograph after 6 months.
Clinical Pearls
- “The Klein line is the single most important radiographic sign for SUFE — always check it on AP views of skeletally immature patients with hip or knee pain.
- “SUFE can present as knee pain (referred via the obturator nerve) — always examine and image the hip when a child presents with knee pain.
- “Perthes: the Herring lateral pillar classification is the best prognostic indicator. Group A (full height) = good prognosis. Group C (less than 50% height) = poor prognosis.
- “Salter-Harris Type II is the MOST COMMON growth plate fracture (commonly quoted as ~75%; 54% in the population-based Olmsted County series). Type V may be radiographically occult — diagnosed retrospectively by growth arrest.
- “The metaphyseal corner fracture (bucket-handle) in an infant is highly specific for non-accidental injury (NAI).
Clinical Warning
Paediatric radiological signs are among the most frequently tested topics. You must be able to: draw and interpret the Klein line (SUFE), construct Perkins and Hilgenreiner lines for DDH assessment, classify growth plate injuries using Salter-Harris, stage Perthes disease, and recognise the radiographic features of non-accidental injury. Classic traps: missing a mild SUFE by not drawing the Klein line, and not imaging the hips when a child presents with isolated knee pain.
Mnemonic
SALTRSalter-Harris Classification
S
Slip (Type I) — through the physis only
Fracture plane through the growth plate only. Radiograph may appear normal (widened physis is the only sign). Diagnosed clinically (tenderness at physis)
A
Above (Type II) — physis + metaphysis
Fracture through the physis with a metaphyseal fragment (Thurston-Holland fragment). MOST COMMON type (75%). Usually excellent prognosis
L
Lower (Type III) — physis + epiphysis
Fracture through the physis extending into the epiphysis (intra-articular). Requires anatomical reduction to restore articular surface and growth plate alignment
T
Through (Type IV) — physis + metaphysis + epiphysis
Fracture crosses all three zones. Most prone to growth disturbance (bone bridge formation). Requires ORIF for anatomical reduction
R
Rammed/cRush (Type V) — compression injury
Crush injury to the growth plate without visible fracture. Often diagnosed RETROSPECTIVELY when growth arrest becomes apparent. Worst prognosis for growth
Hook:SALTR: Slip, Above, Lower, Through, Rammed — the five Salter-Harris types in order of increasing severity.
Mnemonic
PHASDDH Radiographic Assessment Lines
P
Perkins line (vertical)
Vertical line drawn from the lateral edge of the acetabulum, perpendicular to the Hilgenreiner line. The femoral head ossification centre should lie MEDIAL to this line
H
Hilgenreiner line (horizontal)
Horizontal line through both triradiate cartilages (Y-cartilage at the base of each acetabulum). The femoral head should lie BELOW and MEDIAL in the inferomedial quadrant
A
Acetabular index
Angle between the Hilgenreiner line and a line drawn from the triradiate cartilage to the lateral acetabular edge. Normal: less than 30 degrees at birth, decreasing with age. Increased = acetabular dysplasia
S
Shenton line (arc)
Smooth arc along the inferior border of the superior pubic ramus and medial femoral neck. DISRUPTED in DDH (hip subluxation/dislocation) and femoral neck fractures
Hook:PHAS: Perkins, Hilgenreiner, Acetabular index, Shenton — the four lines/measurements for DDH assessment on AP pelvis.
Mnemonic
KISSSUFE Radiographic Assessment
K
Klein line (CRITICAL)
Line along superior femoral neck on AP view should intersect the lateral epiphysis. In SUFE: the epiphysis has slipped posteriorly and the line passes ABOVE the epiphysis (fails to intersect)
I
Ice cream falling off the cone
On the frog lateral view, the slipped epiphysis resembles ice cream sliding off a cone — the metaphysis (cone) is visible above the displaced epiphysis (ice cream)
S
Southwick angle for severity
Measured on the frog lateral view. Normal: approximately 12 degrees. Mild slip: less than 30 degrees. Moderate: 30-50 degrees. Severe: more than 50 degrees
S
Symmetry check (compare sides)
Always compare with the contralateral hip — bilateral SUFE occurs in 20-40% of cases. The Klein line should be assessed on BOTH sides
Hook:KISS: Klein line, Ice cream sign, Southwick angle, Symmetry — the four components of SUFE radiographic assessment.
Overview
Radiological signs in paediatric orthopaedics are fundamental examination topics that test pattern recognition, understanding of growth plate anatomy, and knowledge of specific paediatric conditions. The key principle is that the developing skeleton has unique anatomical features (growth plates, ossification centres, developing joint morphology) that create both diagnostic challenges and specific pathological patterns not seen in adults.
Why Paediatric Imaging Is Different
The paediatric skeleton differs from the adult in: (1) Growth plates (physes) are cartilaginous and radiolucent — fractures through them may be invisible on radiographs (Salter-Harris I, V). (2) Ossification centres appear sequentially and can be confused with fractures (CRITOE in the elbow). (3) The periosteum is thicker and more metabolically active — greenstick and torus (buckle) fractures are unique to children. (4) Joints are more cartilaginous — ultrasound is needed before ossification occurs (DDH screening). (5) Remodelling potential is greater but depends on direction of angulation and proximity to the growth plate.
The Klein Line — Most Important Paediatric Sign
The Klein line is the single most important and most commonly tested radiographic sign in paediatric orthopaedics. HOW TO DRAW IT: on the AP pelvis or hip radiograph, draw a line along the superior cortex of the femoral neck and extend it laterally. In NORMAL hips, this line should intersect (cut through) the lateral portion of the femoral head epiphysis. In SUFE: the epiphysis has slipped posteriorly (and often inferiorly), so the Klein line passes ABOVE or TANGENTIAL to the epiphysis without intersecting it. ALWAYS CHECK BOTH SIDES. CRITICAL PITFALL: SUFE can present with isolated KNEE pain (referred pain via the obturator nerve). ALWAYS image the hips when assessing a child with atraumatic knee pain.
Clinical Imaging
Imaging Atlas
Systematic Approach
Paediatric Radiological Signs Assessment
| Condition | Key Radiological Sign(s) | Clinical Significance |
|---|---|---|
| DDH (infants) | USS: Graf classification (alpha/beta angles). AP pelvis (more than 6mo): Perkins + Hilgenreiner lines, acetabular index, Shenton line | Femoral head in superolateral quadrant = subluxation/dislocation. Acetabular index more than 30 degrees = dysplasia |
| SUFE | Klein line fails to intersect epiphysis on AP. Frog lateral: ice cream off cone. Southwick angle for severity | Any positive Klein line = SUFE. Check BOTH sides (bilateral in 20-40%). Non-weight-bearing until surgical fixation |
| Perthes disease | Catterall: extent of head involvement (groups I-IV). Herring: lateral pillar height (A, B, C). Head-at-risk signs: Gage sign, lateral calcification | Herring A = good prognosis. Herring C = poor. Head-at-risk signs indicate need for containment treatment |
| Salter-Harris fractures | SALTR: I (physis only — may be normal radiograph), II (physis + metaphysis — most common), III (physis + epiphysis), IV (all three), V (crush — retrospective) | Type I: clinical diagnosis (tenderness at physis). Type III-IV: need anatomical reduction (ORIF). Type V: worst growth outcome |
| Non-accidental injury | Metaphyseal corner fractures (bucket-handle), multiple fractures of different ages, posterior rib fractures, complex skull fractures | Metaphyseal corner fractures in infants are HIGHLY SPECIFIC for NAI. Skeletal survey is mandatory |
| Congenital limb anomalies | Proximal femoral focal deficiency (PFFD), fibular hemimelia, limb length discrepancy | Aitken classification for PFFD. Scanogram for limb length. Planning for reconstruction or amputation |
Differential Diagnosis of the Limping / Painful Paediatric Hip by Age
| Age band | Most likely diagnoses | Discriminating radiological / clinical clue |
|---|---|---|
| 0-3 years (infant/toddler) | DDH, septic arthritis/osteomyelitis, toddler's fracture, NAI | DDH: disrupted Shenton line, head superolateral. Septic: effusion on USS, raised inflammatory markers. NAI: metaphyseal corner fracture, fractures of different ages |
| 4-10 years (child) | Transient synovitis, Perthes disease, septic arthritis, JIA | Perthes: sclerotic/fragmented epiphysis, lateral pillar collapse. Transient synovitis: normal radiograph, small effusion, well child. Septic: Kocher criteria positive |
| 10-16 years (adolescent) | SUFE, septic arthritis, apophyseal avulsion, JIA, tumour | SUFE: positive (modified) Klein line, posterior slip on frog lateral. Avulsion: displaced apophysis (AIIS, ischium). Tumour: aggressive periosteal reaction, soft-tissue mass |
| Any age — RED FLAGS | Septic arthritis, malignancy (leukaemia, osteosarcoma, Ewing), NAI | Fever, night pain, systemic upset, weight loss, refusal to bear weight, raised CRP/ESR — escalate urgently, do not assume benign cause |
Clinical Warning
The two most dangerous misses are SEPTIC ARTHRITIS (a surgical emergency — use the Kocher criteria: non-weight-bearing, fever over 38.5C, ESR over 40, WCC over 12) and SUFE presenting as knee pain. Transient synovitis is a diagnosis of EXCLUSION in a well child with a normal radiograph — never apply it to an unwell or febrile child.
Detailed Condition Assessment
DDH Radiographic and Ultrasound Assessment
Before 6 months (ultrasound): The femoral head has not ossified, making radiographs unreliable. Ultrasound (hip USS) is the primary imaging modality. The Graf classification uses the alpha angle (bony acetabular coverage) and beta angle (cartilaginous coverage): Type I (normal): alpha more than 60 degrees. Type IIa (physiologically immature, under 3 months): alpha 50-59 degrees. Type IIb (delayed ossification, over 3 months — treat): alpha 50-59 degrees. Type III (subluxation): alpha less than 43 degrees. Type IV (dislocation): alpha less than 43 degrees, femoral head displaced.
After 6 months (radiograph): Four key assessments on AP pelvis radiograph (PHAS): (1) Perkins line (vertical from lateral acetabular rim) — femoral head ossification centre should be MEDIAL. (2) Hilgenreiner line (horizontal through triradiate cartilages) — femoral head should be INFERIOR. Together, these create four quadrants — the femoral head should be in the INFEROMEDIAL quadrant (any other location is abnormal). (3) Acetabular index — angle between Hilgenreiner line and the acetabular roof line. Normal: less than 30 degrees (decreases with age). More than 30 degrees = dysplastic. (4) Shenton line — smooth arc disrupted in subluxation/dislocation.
Additional DDH signs: Centre-edge angle of Wiberg (used in older children and adolescents): normal more than 25 degrees. Less than 20 degrees = dysplasia. Tonnis classification for acetabular coverage and subluxation grading in older patients.
Evidence Base
Evidence
Herring Lateral Pillar Classification for Perthes
Herring JA, Kim HT, Browne R • Journal of Bone and Joint Surgery (American) (2004)
Key Findings:
- Prospective multicentre study of 438 patients (451 hips), 345 hips followed to skeletal maturity across five treatment groups.
- The modified lateral pillar classification and age at onset were both strong, independent predictors of outcome (p less than 0.0001 and p = 0.0001).
- Lateral pillar group B (and B/C border) hips in children over 8 years at onset did significantly better with surgery than non-operative care; group C hips did poorly regardless of treatment.
- Group B hips in children 8 years or younger did equally well with operative and non-operative treatment.
Clinical implication: The lateral pillar classification combined with age at onset is the most reliable prognostic framework for Perthes disease and identifies the subgroup (group B/B-C border, over 8 years) that benefits from containment surgery.
Limitation: The lateral pillar height can only be graded during the fragmentation stage; it cannot be assessed in the initial or healed stages, and an intermediate B/C border group was needed to improve reliability.
Source: Herring JA et al. JBJS Am 2004;86(10):2121-34
Evidence
Loder Stability Classification for SUFE
Loder RT, Richards BS, Shapiro PS, Reznick LR, Aronson DD • Journal of Bone and Joint Surgery (American) (1993)
Key Findings:
- 55 hips (in 54 patients) that would classically be labelled 'acute' were reclassified by physeal stability: 30 unstable, 25 stable.
- Avascular necrosis developed in 14 of 30 unstable hips (47%) and in NONE of the 25 stable hips (0%).
- Satisfactory outcome was reached in 47% of unstable versus 96% of stable hips.
- No association could be demonstrated between early reduction and the development of AVN.
Clinical implication: Physeal stability (ability to weight-bear, with or without crutches) is the dominant prognostic classification for SUFE — unstable slips carry a markedly higher AVN risk and worse outcomes than the chronicity-based classification predicts.
Limitation: Single-centre retrospective series of 55 hips; weight-bearing ability is a clinical surrogate that can be difficult to assess reliably in young or distressed children.
Source: Loder RT et al. JBJS Am 1993;75(8):1134-40
Evidence
Graf Sonographic Hip Screening — Prospective Validation
Falliner A, Hahne HJ, Hassenpflug J • Journal of Pediatric Orthopaedics B (1999)
Key Findings:
- Prospective study of 6,548 neonates examined both clinically and sonographically using Graf's technique.
- 84.6% of hips were mature (Graf type I), 14.3% physiologically immature (type IIa), and 1.1% dysplastic; 63% of sonographically dysplastic hips were clinically normal.
- 89% of type IIa hips matured spontaneously, while 11% required abduction treatment.
- All 68 dysplastic hips normalised (alpha and acetabular index angles) after a maximum of 80 days of abduction, though six hips deteriorated again by 1 year.
Clinical implication: Graf's sonographic technique reliably diagnoses infantile DDH before the femoral head ossifies and detects clinically silent dysplasia, but regular orthopaedic review is needed to catch secondary deterioration of treated hips.
Limitation: Operator-dependent technique; the high proportion of clinically normal dysplastic hips raises the question of over-detection, and hips should be assessed in defined standard planes.
Source: Falliner A et al. J Pediatr Orthop B 1999;8(2):112-7
Evidence
Modified Klein Line Improves SCFE Sensitivity
Green DW, Mogekwu N, Scher DM, Handler S, Chalmers P, Widmann RF • Journal of Pediatric Orthopaedics (2009)
Key Findings:
- Five observers assessed 30 AP and 30 frog-leg lateral radiographs of unilateral SCFE on two occasions.
- The CLASSIC Klein line (failure of the line to intersect the epiphysis) identified only 40.3% of slips — missing roughly 60%.
- A MODIFIED method (measuring the width of epiphysis lateral to Klein's line, with a 2 mm side-to-side difference indicating a slip) improved sensitivity to 79%.
- Head/shaft (Southwick) angle and percent epiphyseal displacement on the frog-leg lateral were reliable and reproducible, clearly separating slipped from control hips (p less than 0.001).
Clinical implication: The classic Klein line is highly specific but insensitive for mild SCFE; comparing the epiphyseal width lateral to Klein's line between hips (modified method) and adding the frog-leg lateral substantially reduces missed slips.
Limitation: Single-institution study of unilateral slips; a 2 mm threshold may be less applicable in bilateral disease where both hips are abnormal.
Source: Green DW et al. J Pediatr Orthop 2009;29(5):449-53
Evidence
Physeal Fracture Epidemiology (Olmsted County)
Peterson HA, Madhok R, Benson JT, Ilstrup DM, Melton LJ • Journal of Pediatric Orthopaedics (1994)
Key Findings:
- Population-based study identifying every physeal fracture in Olmsted County, Minnesota over 1979-1988: 850 children sustained 951 physeal fractures.
- Age- and sex-adjusted incidence was 279 per 100,000 person-years; boys outnumbered girls 2:1, with peaks at 11-12 years (girls) and 14 years (boys).
- The phalanges of the fingers were the most common site (37% of all physeal fractures).
- Salter-Harris type II was the commonest pattern (54%), but 16% of fractures did not fit the Salter-Harris scheme, prompting Peterson's expanded classification.
Clinical implication: Physeal injuries are common (around 18-30% of paediatric fractures in population data), peak around the adolescent growth spurt, and most often involve the distal radius and phalanges; type II predominates but the Salter-Harris system does not capture every pattern.
Limitation: Single defined population (predominantly white, North American); incidence and site distribution may differ in other regions and activity patterns, and outcome/growth-arrest data are reported in companion papers rather than here.
Source: Peterson HA et al. J Pediatr Orthop 1994;14(4):423-30
Evidence
Metaphyseal Corner Fractures in NAI — Radiologic-Histopathologic Basis
Kleinman PK, Marks SC, Blackbourne B • AJR American Journal of Roentgenology (1986)
Key Findings:
- Combined pre- and post-mortem radiographs with histology of metaphyses from four abused infants explained the classic metaphyseal lesion.
- The underlying injury is a subepiphyseal planar series of microfractures through the most immature metaphyseal bone, isolating a mineralised disc.
- Depending on size, peripheral involvement and projection, the SAME lesion appears as a 'bucket-handle' fracture, a 'corner' fracture, or a metaphyseal lucency.
- Some radiographs were normal despite significant histologic injury, and the germinal cartilage layers were spared in the specimens examined.
Clinical implication: The classic metaphyseal lesion (corner / bucket-handle fracture) is a single distinctive injury that is highly specific for non-accidental injury in infants and mandates a full child-protection work-up including a skeletal survey.
Limitation: Very small autopsy series (four infants); radiographs can underestimate the injury, and rare metabolic bone disease can mimic these lesions, so multidisciplinary assessment is essential.
Source: Kleinman PK et al. AJR Am J Roentgenol 1986;146(5):895-905
Guidelines, Registries & Global Practice
Paediatric radiological signs are interpreted within national screening and child-protection frameworks that differ in detail but share the same imaging principles worldwide.
Global Epidemiology
- DDH: clinically significant dysplasia in roughly 1-3 per 1,000 live births, but sonographic immaturity/instability is far more common (Graf type IIa in ~14% of neonates). Risk factors: female sex, breech presentation, family history, firstborn, oligohydramnios, swaddling practices.
- SUFE: incidence ~10 per 100,000 children, rising with the global increase in childhood obesity; peak age 10-16 years; more common in boys and in some Pacific Islander, African and Hispanic populations; bilateral in 20-40%.
- Perthes: incidence varies markedly by region (roughly 1-20 per 100,000 children under 15), higher in Northern Europe and lower in some Asian and Black populations; boys affected 4-5 times more than girls.
- Physeal fractures: account for ~18-30% of paediatric long-bone fractures, peaking around the adolescent growth spurt (Olmsted County incidence 279/100,000 person-years).
Side-by-Side Guideline Comparison
| Body / Region | DDH screening stance | Imaging emphasis |
|---|---|---|
| AAOS / POSNA (US) | Clinical exam for all newborns; selective ultrasound (6 weeks to 6 months) for risk factors or abnormal exam, rather than universal USS | USS before femoral head ossifies; AP pelvis once ossific nucleus present |
| UK (BSCOS / NIPE / public-health screening) | Universal newborn and 6-8 week clinical examination; selective USS by ~6 weeks for risk factors (breech, family history) or abnormal exam | Graf/Harcke USS; radiograph reserved for older infants |
| Austria / Germany (Graf model) | Universal sonographic screening of all newborns (Graf method) | Static Graf alpha/beta angles in a standardised coronal plane |
| USPSTF (US preventive task force) | Concludes evidence is insufficient to recommend FOR or AGAINST routine screening (I statement) — reflecting over-treatment concern | Highlights high spontaneous resolution of immature hips |
| AO Foundation / paediatric trauma consensus | Not a screening body; standardises physeal fracture description and management | Salter-Harris classification; CRITOE for elbow ossification |
Registry and Practice Variation
- Registries: dedicated paediatric registries are fewer than adult arthroplasty registries, but regional DDH and Perthes datasets (e.g. UK BSCOS studies and Nordic/Australasian DDH cohorts) inform screening policy and late-presentation rates. The debate between universal (Graf, German-speaking Europe) and selective (US/UK) ultrasound screening turns on cost, over-treatment of self-resolving immature hips, and late-diagnosis rates.
- High-resource settings: ready access to ultrasound, MRI for occult physeal/Perthes assessment, and arthrography-guided reduction.
- Limited-resource settings: reliance on clinical examination and plain radiographs; DDH and SUFE often present late, increasing rates of open reduction, osteotomy, and established avascular necrosis. The same radiographic signs (Klein, Perkins/Hilgenreiner, Shenton, Salter-Harris) remain the diagnostic backbone everywhere because they require only a plain film.
- Child protection: suspected non-accidental injury triggers a standardised skeletal survey worldwide; mandatory reporting and exact survey protocols vary by jurisdiction, but the metaphyseal corner fracture, posterior rib fractures and fractures of differing ages are universally recognised red flags.
Controversies & Areas of Uncertainty
Universal vs Selective DDH Screening
The biggest unresolved debate. Universal sonographic screening (Graf model, German-speaking Europe) detects more dysplasia but treats many hips that would resolve spontaneously (~89% of type IIa hips mature without intervention), risking over-treatment and Pavlik-related AVN. Selective screening (US/UK) targets risk factors but misses some late-presenting dysplasia. The USPSTF issued an "insufficient evidence" (I) statement. There is no internationally agreed gold-standard policy.
Limits of the Klein Line
The classic Klein line misses up to 60% of slips (sensitivity ~40%). Over-reliance on a single AP sign is a recognised cause of missed/delayed SUFE diagnosis. The modified Klein line (interhip epiphyseal-width comparison) and routine frog-leg lateral views improve detection, but no single radiographic measurement is both highly sensitive and specific for mild slips.
Prophylactic Fixation of the Contralateral Hip in SUFE
Whether to pin the asymptomatic contralateral hip is contested. Arguments for: 20-40% become bilateral, sequential slip can be silent, and second slips can be unstable. Arguments against: morbidity of a second procedure in hips that may never slip. Prophylactic fixation is more widely favoured in younger children, those with open triradiate cartilage, and underlying endocrine/metabolic disease.
Timing of Perthes Containment Surgery
The Herring multicentre data show benefit from containment surgery only in a specific subgroup (lateral pillar B/B-C border, onset over 8 years); group A does well regardless and group C does poorly regardless. The optimal procedure (femoral varus vs innominate osteotomy) showed no significant difference, leaving surgeon and patient preference to guide choice.
Clinical Decision Scenarios
Practise clinical reasoning and management decisions out loud
Viva scenarioStandard
Clinical prompt
“A 12-year-old obese boy presents with a 3-week history of left knee pain. He walks with an antalgic gait. There is no history of trauma.”
Practical approach
The most likely diagnosis is a SUFE (Slipped Upper Femoral Epiphysis). This classic presentation — an obese adolescent (10-16 years, during the growth spurt) with atraumatic hip or KNEE pain — should trigger immediate suspicion for SUFE. The CRITICAL teaching point is that SUFE commonly presents with KNEE pain due to referred pain via the obturator nerve. This is one of the most important pitfalls in paediatric orthopaedics — any child with unexplained knee pain MUST have the hip examined and imaged. The radiographic sign I would look for is the Klein line. On the AP pelvis radiograph, I would draw a line along the superior cortex of the femoral neck on both sides and extend it laterally. In a normal hip, this line intersects the lateral femoral head epiphysis. In SUFE: the epiphysis has slipped posteroinferiorly, so the line passes above or tangential to the epiphysis without intersecting it. I would compare both sides, because bilateral SUFE occurs in 20-40% of cases. I would also request a frog lateral view of both hips. This view shows the posterior slip most clearly — the 'ice cream falling off the cone' appearance. On the frog lateral, I would measure the Southwick angle to grade severity: mild (less than 30 degrees), moderate (30-50 degrees), severe (more than 50 degrees). I would classify the SUFE as stable (able to weight-bear) or unstable (unable to weight-bear) — this is the most important prognostic classification. Unstable SUFE has 47% AVN risk. Management: immediate non-weight-bearing (crutches or wheelchair), urgent orthopaedic referral for in-situ screw fixation. The contralateral hip should also be assessed for prophylactic fixation if risk factors are present (endocrine disorder, very young age, severe slip on the affected side).
Key clinical points
SUFE presents with KNEE pain (referred via obturator nerve) — always image the hip
Klein line: line along superior femoral neck should intersect lateral epiphysis. Fails = SUFE
Frog lateral view shows posterior slip most clearly ('ice cream off cone')
Stable vs unstable classification: unstable = 47% AVN risk
Bilateral in 20-40% — always check BOTH sides
Common pitfalls
Not imaging the hip when a child presents with isolated knee pain
Not drawing the Klein line (subtle slips are easily missed)
Not requesting the frog lateral view (best view for SUFE)
Not assessing the contralateral hip
Further questions
“What is the Southwick angle? What is the treatment for unstable SUFE? What endocrine conditions predispose to SUFE? When do you consider prophylactic fixation of the contralateral side?”
Viva scenarioStandard
Clinical prompt
“A 6-month-old infant is brought for DDH assessment. The paediatrician has noted asymmetric skin folds and limited left hip abduction.”
Practical approach
At 6 months of age, the femoral head ossification centre is typically just beginning to appear. At this transitional age, BOTH ultrasound and radiograph may provide useful information, though radiograph becomes the standard modality after the femoral head ossification centre is clearly visible. I would request an AP pelvis radiograph as the primary investigation at this age. Radiographic assessment using PHAS: (1) PERKINS line — I draw a vertical line from the lateral edge of each acetabulum, perpendicular to the Hilgenreiner line. The femoral head ossification centre (or its expected position) should lie MEDIAL to this line. If the ossification centre is LATERAL to the Perkins line, this indicates lateral subluxation or dislocation. (2) HILGENREINER line — I draw a horizontal line through both triradiate cartilages. Combined with the Perkins line, this creates four quadrants. The femoral head should be in the INFEROMEDIAL quadrant. If it is in the superolateral quadrant, this represents subluxation or dislocation. (3) ACETABULAR INDEX — the angle between the Hilgenreiner line and a line from the triradiate cartilage to the lateral acetabular edge. At 6 months, normal is approximately 25-28 degrees. More than 30 degrees indicates acetabular dysplasia. I compare both sides. (4) SHENTON LINE — a smooth arc along the inferior border of the superior pubic ramus and the medial femoral neck. Disruption on the left side would confirm hip subluxation. Additional assessments: femoral head ossification centre — is it present bilaterally and symmetric? A delayed or smaller ossification centre on the affected side may indicate altered blood supply from the abnormal hip position. If DDH is confirmed: management at 6 months is typically a Pavlik harness trial (for stable reducible hips) or closed/open reduction under anaesthetic if the hip is irreducible. Follow-up imaging with serial radiographs to monitor acetabular development.
Key clinical points
At 6 months, AP pelvis radiograph is the appropriate imaging modality
PHAS: Perkins (vertical), Hilgenreiner (horizontal), Acetabular index, Shenton line
Normal: femoral head in INFEROMEDIAL quadrant of Perkins/Hilgenreiner grid
Acetabular index more than 30 degrees = acetabular dysplasia
Disrupted Shenton line confirms subluxation/dislocation
Common pitfalls
Not knowing when to use USS vs radiograph (USS before 6 months, radiograph after)
Not drawing all four assessment lines (PHAS)
Not comparing both sides for symmetry
Not knowing the normal acetabular index values
Further questions
“What is the Graf classification? When do you switch from USS to radiograph? What is the management algorithm for DDH at different ages?”
Viva scenarioChallenging
Clinical prompt
“An examiner asks you to describe the Salter-Harris classification and its clinical implications.”
Practical approach
The Salter-Harris classification describes five patterns of physeal (growth plate) fractures in children. It is clinically important because the type of fracture determines management (conservative vs surgical), prognosis for growth disturbance, and follow-up requirements. Type I (Slip — S): the fracture plane passes ENTIRELY through the physis (growth plate). There is no metaphyseal or epiphyseal fracture component. Radiographs may be NORMAL — the only finding may be widening of the physis. Diagnosis is often CLINICAL (point tenderness at the growth plate + inability to weight-bear/use the limb). Management: immobilisation. Growth disturbance risk is LOW (less than 2%). Type II (Above — A): the fracture passes through the physis and exits through the METAPHYSIS, creating a triangular metaphyseal fragment called the Thurston-Holland fragment. This is the MOST COMMON type (75% of all physeal fractures). The periosteum remains intact on the metaphyseal fragment side, acting as a hinge that aids reduction. Management: closed reduction and immobilisation. Growth disturbance risk is LOW (less than 2% if anatomically reduced). Type III (Lower — L): the fracture passes through the physis and extends into the EPIPHYSIS, creating an intra-articular fracture. This disrupts the articular surface. Management: anatomical reduction is ESSENTIAL for both articular congruity and growth plate alignment — often requires ORIF. Growth disturbance risk is MODERATE (approximately 10%). Type IV (Through — T): the fracture crosses ALL three zones — metaphysis, physis, and epiphysis. This creates the highest risk of bone bridge formation (bone growing across the damaged physis, tethering growth). Management: ORIF with anatomical reduction of both the articular surface and the growth plate. Growth disturbance risk is HIGH (approximately 25%). Type V (Rammed/Crush — R): a CRUSH injury to the growth plate without a visible fracture. This is the RAREST type and is often diagnosed RETROSPECTIVELY when growth arrest becomes apparent months later. The mechanism is characteristic of axial loading forces. Management: supportive. Prognosis: WORST for growth (crush injury destroys the germinal layer). Growth disturbance may result in angular deformity (partial growth arrest) or limb shortening (complete arrest).
Key clinical points
SALTR mnemonic: Slip, Above, Lower, Through, Rammed
Type I may have NORMAL radiographs — diagnosed clinically (physis tenderness)
Type II is MOST COMMON (75%). Thurston-Holland fragment is the key finding
Types III-IV require ORIF for articular surface and growth plate alignment
Type V is diagnosed RETROSPECTIVELY — worst prognosis, crush mechanism
Common pitfalls
Not listing all five types and their distinguishing features
Not knowing that Type II is the most common (75%)
Not emphasising that Type V is often radiographically occult
Not knowing the growth disturbance rates for each type
Further questions
“What is a Thurston-Holland fragment? How do you manage a physeal bar (bone bridge)? What is the remodelling potential of physeal fractures?”
Viva scenarioChallenging
Clinical prompt
“A 7-year-old boy presents with a 4-month history of a painless limp and reduced left hip abduction and internal rotation. Radiographs show a fragmented, partially flattened left femoral head.”
Practical approach
The presentation — a boy aged 4-8 years with an insidious painless limp, restricted abduction and internal rotation, and a fragmented femoral head — is classic for Legg-Calve-Perthes disease (idiopathic avascular necrosis of the proximal femoral epiphysis). I would stage it radiographically through its phases: initial/necrosis (sclerosis, possible subchondral crescent sign), fragmentation (the stage shown here, with mixed lysis and sclerosis), reossification, and healed (potentially aspherical — coxa magna/plana). For PROGNOSIS, the single most useful tool is the Herring lateral pillar classification, applied during the fragmentation stage: group A (full lateral pillar height) good prognosis, group B (more than 50% preserved) intermediate, B/C border, and group C (50% or less preserved) poor prognosis. The Herring multicentre study showed that the lateral pillar group and age at onset are the strongest predictors of outcome, and that containment surgery benefits the group B / B-C border hips in children over 8 years. The older Catterall classification grades the extent of head involvement (I-IV) and describes head-at-risk signs: Gage sign (V-shaped lateral lucency), lateral calcification, lateral subluxation/uncovering, a horizontal physis, and metaphyseal cysts. Crucially, this is a UNILATERAL process — so my differential for a flattened/fragmented femoral head must exclude conditions that are typically BILATERAL and SYMMETRIC. These include multiple epiphyseal dysplasia and spondyloepiphyseal dysplasia (symmetric epiphyseal changes in multiple joints), and hypothyroidism (fragmented, stippled epiphyses). I would also consider sickle-cell or steroid-related avascular necrosis, Meyer dysplasia (dysplasia epiphysealis capitis femoris — a benign mimic in younger children), and septic/post-septic sequelae. Bilaterality, family history, short stature, or symmetric multi-joint involvement should prompt a skeletal survey, thyroid function and skeletal dysplasia work-up rather than a diagnosis of Perthes.
Key clinical points
Perthes = idiopathic AVN of the proximal femoral epiphysis, boys 4-8 years, painless limp
Herring lateral pillar classification (A/B/B-C/C) graded in the fragmentation stage is the best prognostic tool
Head-at-risk signs (Catterall): Gage sign, lateral calcification, lateral subluxation, horizontal physis, metaphyseal cysts
Bilateral/symmetric epiphyseal changes suggest a skeletal dysplasia or hypothyroidism, NOT Perthes
Containment surgery benefits lateral pillar B / B-C border hips in children over 8 years
Common pitfalls
Calling bilateral symmetric epiphyseal disease 'Perthes' (think MED, SED, hypothyroidism)
Trying to apply the lateral pillar classification outside the fragmentation stage
Forgetting that age at onset is an independent prognostic factor
Missing the head-at-risk signs that change management toward containment
Further questions
“What is the difference between Catterall and Herring classifications? What is the Stulberg outcome classification? How does Meyer dysplasia differ from Perthes? What is the principle of containment treatment?”
Exam day cheat sheet
Paediatric Radiological Signs — Exam Day Reference
DDH Assessment (PHAS)
- Perkins: vertical line from lateral acetabular edge
- Hilgenreiner: horizontal line through triradiate cartilages
- Together create 4 quadrants — femoral head should be INFEROMEDIAL
- Acetabular index: normal less than 30 degrees. More = dysplasia
- USS: before 6 months (Graf). Radiograph: after 6 months
SUFE Assessment (KISS)
- Klein line: along superior femoral neck — fails to intersect lateral epiphysis = SUFE
- Frog lateral: best view. Ice cream falling off cone appearance
- Southwick: mild (less than 30), mod (30-50), severe (more than 50 degrees)
- ALWAYS image hips for isolated knee pain in children
- Bilateral in 20-40%. Unstable = 47% AVN risk
Salter-Harris (SALTR)
- I (Slip): physis only — may be normal radiograph. Clinical diagnosis
- II (Above): physis + metaphysis — MOST COMMON (75%). Thurston-Holland fragment
- III (Lower): physis + epiphysis — intra-articular. ORIF for anatomical reduction
- IV (Through): all three zones — highest bone bridge risk. ORIF essential
- V (Rammed): crush — WORST prognosis. Diagnosed RETROSPECTIVELY
Perthes and NAI
- Herring lateral pillar: A (good), B (moderate), C (poor prognosis)
- Head-at-risk signs: Gage sign, lateral subluxation, lateral calcification
- NAI: metaphyseal corner fractures, posterior ribs, multiple ages
- NAI: skeletal survey MANDATORY. Mandatory reporting