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Diagram 1 - SCFE Anatomy (The Slip)

• Epiphysis slips posteriorly, medially, and inferiorly relative to the neck
• Slip occurs through the hypertrophic zone of the physis (zone of Ranvier)
• Neck moves anteriorly and superiorly (NOT the head moving - the neck rides up)
• Mnemonic: "Ice cream slides off the cone"

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Diagram 2 - Klein's Line / Trethowan's Sign (AP X-ray)

• Klein's line = drawn along the superior border of femoral neck on AP view
• Normal: line intersects at least 1/5th of femoral head
• SCFE: line passes entirely above the head - Trethowan's sign positive
• Additional signs: widened physis, metaphyseal blanch sign (Steel's sign), decreased head-neck offset

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Diagram 3 - Grading + In-Situ Pinning Treatment

• Stable - can weight bear (with or without crutches) → AVN risk ~0%
• Unstable - cannot weight bear → AVN risk up to 47%

• Single cannulated 7.3 mm screw
• Entry point: anterior on femoral neck (to account for posterior slip)
• Tip: central position in femoral head
• Crosses physis perpendicularly (aim for centre-centre position)
• Do NOT attempt forceful reduction → dramatically increases AVN risk

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Quick Answer Framework for 10 Marks

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SLIPPED CAPITAL FEMORAL EPIPHYSIS (SCFE)

Structured Answer - KNRUHS MS Ortho Theory Exam

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DEFINITION

Technically a Salter-Harris Type I fracture-separation through the hypertrophic zone of the physis.

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INCIDENCE / EPIDEMIOLOGY

• Most common hip disorder of adolescence
• Age: 10-16 years (during rapid growth spurt, Risser grade 0)
• Sex: Males > Females (2:1)
• Race: Twice as common in African than European descent
• Bilateral in 25-40% of cases; second slip usually within 12-18 months
• Left side more commonly involved (65%) when unilateral
• Elevated serum leptin levels associated regardless of BMI

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AETIOLOGY / RISK FACTORS

Mechanical factors:

• Obesity (increased shear at physis)
• Increased obliquity of physis with growth
• Thinning of perichondrial ring
• Decreased neck-shaft angle (coxa vara)
• Femoral retrotorsion + acetabular retroversion

Hormonal / systemic factors:

Rule: Any child < 10 years with SCFE - mandatory endocrine workup.

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PATHOANATOMY

• Slip occurs through the hypertrophic zone of the physis (zone of provisional calcification)
• The perichondrial ring is weakened by hormonal/mechanical factors
• The neck moves anteriorly and rotates externally (NOT the head moving posteriorly)
• Mnemonic: "Ice cream sliding off the cone"
• Reliable orientation of lateral epiphyseal vessels adjacent to the tubercle explains the low rate of AVN in stable, chronic slips

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CLINICAL FEATURES

Symptoms:

• Pain in groin, hip, medial thigh, or knee (referred via obturator nerve - missed diagnosis!)
• Limp (antalgic + Trendelenburg gait)
• Chronic: mild shortening, fixed external rotation deformity

Signs:

Diagnostic trap: SCFE should be suspected in any obese 10-16 year old with knee pain - always examine the hip!

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CLASSIFICATION

1. Loder Classification (MOST IMPORTANT - prognostic)

2. Temporal Classification (descriptive, no prognostic value)

• Acute: symptoms < 3 weeks
• Chronic: symptoms > 3 weeks
• Acute-on-chronic: acute exacerbation of chronic symptoms

3. Southwick Grading (% of slippage on frog-leg lateral)

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INVESTIGATIONS

X-Ray (first-line investigation):

• Frog-leg lateral is MORE sensitive - do not skip it
• Cross-table lateral for unstable slips (avoid positioning)

AP Radiograph Signs:

Frog-leg lateral:

• Best view to demonstrate degree of slip (Southwick angle measured here)
• Shows posterior displacement clearly

MRI:

• Pre-slip: physeal edema on T2
• Assess femoral head perfusion (unstable slips)
• Rule out additional hip pathology

CT:

• Check if physis is closed
• Pre-operative planning for complex osteotomies

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TREATMENT

Principle: Stabilize, do NOT reduce forcefully

Forceful reduction causes AVN - absolutely contraindicated in chronic slips.

A. In-Situ Pinning (Treatment of choice for ALL grades, stable and unstable)

1. Patient supine on fracture/radiolucent table
2. Image intensifier (C-arm) for AP + true lateral views
3. Entry point: anterior on femoral neck (to account for posterior slip)
4. Single 7.3 mm cannulated screw, perpendicular to physis
5. Tip: central position in femoral head (centre-centre) - no closer than 4 mm from subchondral bone
6. Confirm on multiple fluoroscopic views - avoid screw penetration

• Stabilize the epiphysis
• Promote closure of proximal femoral physis
• Prevent further slippage

B. Unstable SCFE - Additional considerations:

• Urgent stabilization within 24 hours
• Capsulotomy to decompress the haemarthrosis (reduces AVN risk)
• Gentle "finger reduction" if possible - avoid forceful manipulation
• Modified Dunn technique (surgical hip dislocation) for severe unstable slips

C. Modified Dunn (Subcapital Realignment):

• Surgical hip dislocation via Ganz approach
• Neck shortening + periosteal retinacular flap preservation
• For moderate-severe chronic slips with deformity
• Preserves blood supply via trochanteric flip osteotomy

D. Osteotomies (for residual deformity/FAI):

E. Prophylactic Pinning of Contralateral Hip:

• Age < 10 years (female) or < 12 years (male)
• Endocrine abnormality present
• Posterior sloping angle > 12 degrees
• Open triradiate cartilage
• Unreliable follow-up
• Hypothyroidism, low Vit D, DM, GH use history

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COMPLICATIONS

1. Avascular Necrosis (AVN) - Most feared

• Stable slips: practically 0% risk
• Unstable slips: 24-47% risk
• Due to disruption of the retinacular vessels (lateral epiphyseal vessels)
• Anterior physeal separation on imaging is a sign of high AVN risk (Ballard sign)
• Management: core decompression, vascularized fibular graft, THA in adults

2. Chondrolysis

• Diagnosis: joint space < 3 mm (normal 4-6 mm) + decreased ROM
• Incidence decreased from 7% to 1% with improved surgical technique
• Causes: pin penetration, prolonged immobilization, immune-mediated
• Management: NSAIDs, physiotherapy, joint distraction

3. Femoroacetabular Impingement (FAI)

• Cam-type FAI from residual neck deformity
• Leads to early osteoarthritis
• 22% of hips coming to THA in North America had SCFE-associated OA

4. Other:

• Premature physeal closure + limb length discrepancy
• Coxa vara
• Femoral neck fracture (post-pinning complication)
• Degenerative osteoarthritis (long term)

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DIFFERENTIALS (to mention briefly)

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EXAM-READY SUMMARY BOX

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