SUFE and paediatric hip comparisons

Clinical Presentation & The Trap of Referred Knee Pain

• Demographics & Risk Factors: Typically occurs during the rapid pubertal growth spurt (boys aged 12 to 15 years, girls aged 10 to 13 years). Strongly associated with obesity (increased mechanical shear forces on the oblique pubertal growth plate) and underlying endocrinopathies (hypothyroidism, growth hormone deficiency, hypogonadism) in young or bilateral cases.
• Presentation: An antalgic limp and poorly localized aching pain. In up to 50% of cases, pain is referred exclusively to the medial distal thigh or knee via the obturator and femoral nerves. Examining only the knee without evaluating the hips is the most frequent medical negligence error in paediatric orthopaedics, causing catastrophic diagnostic delays.
• Hallmark Physical Examination Findings:
  • Marked reduction in internal rotation, abduction, and flexion of the affected hip.
  • Obligatory External Rotation on Hip Flexion: When the clinician passively flexes the hip from extension to $90^\circ$, the thigh automatically and involuntarily rotates externally into an abducted and externally rotated position. This sign is virtually pathognomonic of SUFE.
  • Stability Classification: Stable SUFE (child is able to bear weight, even with crutches; low risk of AVN, $< 5\%$); Unstable SUFE (child is completely unable to bear weight even with crutches; carries a high risk of avascular necrosis, up to $30\%\text{ to }50\%$).

Diagnostic Radiological Evaluation

• Mandatory imaging: Bilateral AP and frog-leg lateral pelvic radiographs (if unstable SUFE is suspected, perform true cross-table lateral instead of frog-leg to avoid displacing an unstable slip).
• Klein's Line & Trethowan's Sign:
  • On the AP pelvic radiograph, draw a line along the superior/lateral border of the femoral neck (Klein's line).
  • In a normal hip, Klein's line intersects the lateral aspect of the femoral epiphysis.
  • In SUFE, because the femoral head has slipped posteriorly and medially, Klein's line fails to intersect the epiphysis (or intersects a significantly smaller portion compared to the contralateral side), a finding termed Trethowan's sign.
• Other radiographic signs: Metaphyseal blanch sign of Steel (crescentic radiodense band across the metaphysis caused by the overlapping posterior slip on the AP view); widening and irregularity of the physis.

Emergency Management

1. Strict Mandatory Non-Weight Bearing: Immediately place the patient on a bed, stretcher, or wheelchair. The child must not take another single step, as weight-bearing can convert a stable slip into a catastrophic unstable slip, tearing the fragile retinacular blood vessels.
2. Emergency Orthopaedic Surgical Fixation:
   • Percutaneous In-Situ Cannulated Screw Fixation: A single cannulated screw is inserted centrally across the physis into the centre of the epiphysis under fluoroscopic guidance to achieve physeal closure and prevent further slippage.
   • Avoid Closed Manipulation: Vigorous or forceful closed reduction is strictly contraindicated; attempting to reduce the chronic slip causes kinking and thrombosis of the lateral retinacular vessels, directly causing catastrophic avascular necrosis and chondrolysis.
   • Contralateral Prophylactic Pinning: Bilateral involvement occurs in up to 20% to 40% of cases (often presenting months later). Prophylactic screw fixation of the contralateral normal hip is routinely performed in young children ($< 10$ years), patients with underlying endocrine disorders, or those with non-compliant follow-up.

Clinical comparison: Differential Diagnosis of Paediatric Hip Conditions

• Septic Arthritis: Typical Age Cohort: Any age (peak $< 3\text{ years}$); Primary Presentation: Acute acute pain, refusal to bear weight, toxic appearance; Physical Examination Hallmarks: Fever $> 38.5^\circ\text{C}$; joint held flexed/abducted; extreme pain on all movement; Key Diagnostic Findings: Ultrasound: capsular distension; aspirate: WBC $> 50,000/\mu\text{L}$, pos Gram stain; Definitive Management Plan: Emergency surgical arthrotomy & washout; IV flucloxacillin or cefazolin
• Transient Synovitis: Typical Age Cohort: $3\text{ to }8\text{ years}$ (male $>$ female); Primary Presentation: Acute limp following recent viral infection (1-2 weeks prior); Physical Examination Hallmarks: Afebrile or low-grade; weight-bearing preserved; mild loss of internal rotation; Key Diagnostic Findings: Ultrasound: small sterile effusion; ESR $< 40$, CRP $< 20$, normal WBC; Definitive Management Plan: Conservative: bed rest, oral NSAIDs, mandatory clinical review in 48 to 72 hours
• Perthes Disease: Typical Age Cohort: $4\text{ to }8\text{ years}$ (male $>$ female 4:1); Primary Presentation: Insidious, painless or mildly aching limp; referred knee pain; Physical Examination Hallmarks: Antalgic limp; disuse thigh atrophy; restricted internal rotation and abduction; Key Diagnostic Findings: Pelvic X-rays: subchondral crescent sign, flattening, patchy sclerosis of epiphysis; Definitive Management Plan: Containment: observation ($< 6\text{y}$); surgical femoral/pelvic osteotomy ($> 6\text{y}$)
• Slipped Epiphysis (SUFE): Typical Age Cohort: $10\text{ to }15\text{ years}$ (overweight adolescent); Primary Presentation: Antalgic limp; dull groin or isolated referred knee pain; Physical Examination Hallmarks: Loss of internal rotation; obligatory external rotation on hip flexion; Key Diagnostic Findings: Pelvic X-rays: Klein's line fails to intersect epiphysis; blanch sign of Steel; Definitive Management Plan: Strict non-weight bearing; urgent percutaneous in-situ cannulated screw fixation
• JIA: Typical Age Cohort: Persistent inflammatory joint symptoms; Primary Presentation: ANA may be positive or negative and helps uveitis risk assessment; Physical Examination Hallmarks: Paediatric rheumatology and risk-based eye surveillance

Primary references (checked 7 October 2026): RCH limp assessment.