Slipped Upper Femoral Epiphysis (SUFE)

1. Clinical Overview

Summary

Slipped Upper Femoral Epiphysis (SUFE), also known as Slipped Capital Femoral Epiphysis (SCFE), is the most common hip disorder affecting adolescents during the pubertal growth spurt. The condition represents a Salter-Harris type I physeal fracture through the proximal femoral growth plate, where the femoral neck (metaphysis) displaces anteriorly and superiorly while the epiphyseal head remains seated in the acetabulum. [1,2]

The incidence ranges from 0.33 per 100,000 in Asian populations to 50.5 per 100,000 in high-risk populations, with marked ethnic variation. [3] The condition predominantly affects obese males aged 10-16 years, with the highest burden observed in Maori and Pacific Islander populations—4.2 and 5.6 times higher than European Caucasian populations respectively. [4]

SUFE is an orthopaedic emergency requiring urgent surgical stabilization to prevent catastrophic complications, particularly avascular necrosis (AVN) of the femoral head. The Loder classification (stable vs unstable) is the most important prognostic indicator: unstable slips carry up to 47% risk of AVN compared to less than 10% in stable slips. [5,6]

Key Facts

• "The Ice Cream Analogy": The femoral head is the scoop of ice cream, the neck is the cone. In SUFE, the cone slips forward and upward, while the scoop stays in the acetabulum.
• Knee Pain Trap: Up to 50% of patients present with knee pain alone due to referred pain via the obturator nerve. Hip examination is mandatory in all adolescents with knee pain. [7]
• Stability is Destiny: The Loder classification based on weight-bearing ability is the single most important prognostic factor, surpassing slip angle or chronicity. [5]
• Seasonal Variation: SUFE demonstrates significant seasonal clustering with peak incidence in late summer months (August) in Northern Hemisphere populations above 40°N latitude, potentially related to growth hormone and vitamin D fluctuations. [8]

Clinical Pearls

"Drehmann's Sign is Pathognomonic": When flexing the affected hip, the leg obligatorily externally rotates. This occurs because the posteriorly displaced epiphysis impinges on the posterior acetabular rim, forcing external rotation to avoid impingement.

"Never Forcefully Reduce a Chronic Slip": Attempted closed reduction of chronic slips can tear the delicate lateral epiphyseal vessels (retinacular arteries), precipitating AVN. The mantra is "fix it where it lies" (in situ fixation). [9]

"Check the Thyroid in Atypical Cases": Children younger than 10 years, thin patients, or those outside the pubertal growth spurt should be screened for endocrine disorders—particularly hypothyroidism, growth hormone deficiency, hypogonadism, or renal osteodystrophy. [10]

"The Contralateral Hip is Never Safe": 20-40% of patients develop contralateral slip, with highest risk in those with endocrine disorders, age less than 10 years, or bilateral physeal abnormalities on imaging. [11]

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2. Epidemiology

Incidence and Prevalence

The global incidence of SUFE shows remarkable geographic and ethnic variation:

The weighted pooled incidence across 15 international studies is 9.62 per 100,000 children. [3]

Demographics

Age Distribution

• Peak Age: 10-16 years, correlating with pubertal growth spurt
• Mean Age at Presentation: 12.0 years (SD 0.4) [3]
• Boys: Peak at 13-14 years
• Girls: Peak at 11-12 years (earlier physeal closure)
• Atypical Age (< 10 or 16 years): Strongly suggestive of underlying endocrinopathy [10]

Sex Distribution

• Male:Female Ratio: Ranges from 1.43:1 to 3.12:1 across populations [3]
• Classic Ratio: 2:1 (male predominance)
• Possible Mechanisms: Greater body mass in males, hormonal influences on physeal strength, biomechanical differences in activity levels

Ethnic Variation

• Highest Risk: Pacific Islanders, Maori, African Americans
• Intermediate Risk: Hispanic populations
• Lower Risk: Asian populations (Japanese, Korean)
• Caucasian: Baseline reference risk

Maori children present younger (p=0.002) and more frequently with bilateral involvement (p=0.05) compared to European populations. [4]

Temporal Trends

Seasonal Clustering

Recent cosinor regression analysis of 21,428 cases demonstrated significant seasonal variation in populations above 40°N latitude (p< 0.0001):

• Peak Month: August (482 cases)
• Nadir Month: February (293 cases)
• Pattern: Late summer to early fall peak
• Hypothesized Mechanisms: Growth hormone surges, vitamin D fluctuations, increased summer activity levels [8]

Increasing Incidence

SUFE incidence is rising globally, paralleling childhood obesity epidemic. Swedish data shows incidence increased from 4.0 to 50.5 per 100,000 over recent decades. [3]

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3. Risk Factors

Major Risk Factors

1. Obesity (Dominant Risk Factor)

• Prevalence in SUFE Patients: 66-67.6% overweight/obese in Western populations [3]
• Mechanism: Increased shear force across physis due to elevated body mass index
• Biomechanics: Obesity increases the force vector perpendicular to the physis during weight-bearing
• Leptin Hypothesis: Emerging evidence suggests elevated leptin levels may independently contribute to physeal weakening, regardless of obesity status [3]

2. Endocrine Disorders (10-15% of cases) [10]

3. Previous Radiation Therapy

• Cranial radiation for brain tumors
• Pelvic radiation for malignancy
• Mechanism: Direct physeal damage with disrupted growth plate architecture

4. Genetic and Familial Factors

• Family history increases risk (exact inheritance pattern unclear)
• COL2A1 gene polymorphisms implicated in some studies
• Syndromic associations: Down syndrome, Marfan syndrome

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4. Pathophysiology

Normal Physeal Anatomy

The proximal femoral physis (growth plate) consists of distinct histological zones:

1. Resting Zone: Chondrocyte reservoir
2. Proliferative Zone: Active cell division
3. Hypertrophic Zone: Enlarged chondrocytes, weakest structural area
4. Zone of Provisional Calcification: Mineralization frontier

Critical Point: SUFE occurs through the hypertrophic zone, the mechanically weakest region. This differs from Salter-Harris fractures which typically occur through the zone of provisional calcification. [12]

Biomechanical Failure Mechanism

Normal Physeal Orientation

• In young children: Physis is nearly horizontal (perpendicular to femoral neck axis)
• During puberty: Physis becomes more oblique (more vertical inclination)
• This reorientation increases shear stress during weight-bearing

Forces Acting on the Physis

Mathematical Relationship: Shear force = Body weight × sin(physeal angle)

As the physis becomes more vertical during puberty, sin(physeal angle) increases, elevating shear stress. Obesity amplifies this by increasing body weight.

Pubertal Physeal Remodeling

During the adolescent growth spurt:

• Hypertrophic zone widens (from ~200μm to 400μm)
• Physeal strength decreases due to increased chondrocyte hypertrophy without proportional matrix strength
• Peak vulnerability occurs 6-12 months before physeal closure

Vascular Anatomy and AVN Pathogenesis

Arterial Supply to Femoral Head

The epiphyseal blood supply is entirely extracapsular and vulnerable:

1. Medial Femoral Circumflex Artery (MFCA): Dominant supply (80-90%)

   • Gives rise to lateral epiphyseal vessels (retinacular arteries)
   • Travels posteriorly along femoral neck
   • Enters epiphysis at posterosuperior quadrant

2. Lateral Femoral Circumflex Artery: Minor contribution

3. Ligamentum Teres Artery: Minimal supply until skeletal maturity

Mechanism of AVN in SUFE

Exam Detail: Vascular Compromise Occurs via Three Mechanisms:

1. Acute Kinking: In unstable slips, sudden displacement kinks the retinacular vessels
2. Progressive Stretching: In chronic slips, gradual displacement slowly compromises flow
3. Iatrogenic Injury: Forceful reduction or manipulative surgery can tear vessels

Temporal Factors:

• Unstable slips: AVN can develop within hours (ischemic necrosis)
• Stable slips: Vessels may gradually accommodate displacement
• Modified Dunn procedure: Surgical dislocation allows direct visualization and protection of vessels

Histopathology:

• Ischemic osteonecrosis of subchondral bone
• Trabecular death and marrow necrosis
• Femoral head collapse in severe cases
• Secondary osteoarthritis is inevitable

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5. Clinical Presentation

Symptom Profile

Red Flag: Knee pain in an obese adolescent with normal knee examination should prompt hip evaluation.

Clinical Signs

Inspection

• Gait: Antalgic limp, externally rotated foot progression angle
• Resting Position: Affected leg lies in external rotation and slight flexion
• Leg Length: Apparent shortening (due to flexion/external rotation posture, or true shortening from varus deformity)
• Muscle Atrophy: Thigh wasting in chronic cases

Palpation

• Tenderness: Anterior hip capsule, groin
• Range of Motion Testing (Supine):

Drehmann's Sign (Pathognomonic)

Technique:

1. Patient supine, hip and knee extended
2. Passively flex hip to 90°
3. Positive Test: Hip obligatorily externally rotates during flexion

Mechanism: Posteriorly displaced epiphysis contacts posterior acetabular wall, forcing external rotation to clear impingement.

Sensitivity: 95%+, nearly pathognomonic when present

Log Roll Test

• Gentle internal and external rotation of extended leg
• Pain and restriction suggest intra-articular pathology
• Highly sensitive but non-specific

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6. Classification Systems

Loder Classification (Stability) - GOLD STANDARD [5]

Based on: Ability to bear weight (even with crutches)

Critical Evidence: Loder's landmark 1993 study demonstrated that instability, not slip severity or acuity, predicts AVN. [5]

Pitfall: Some centers misclassify based on duration rather than stability. This is incorrect and clinically dangerous.

Temporal Classification (Historical)

Modern View: Temporal classification has been largely superseded by Loder stability classification, which better predicts outcomes. [13]

Southwick Slip Angle (Severity)

Measures degree of epiphyseal displacement on lateral radiograph:

Calculation: Southwick angle = (Epiphyseal-shaft angle on affected side) - (Epiphyseal-shaft angle on normal side)

Prognostic Significance:

• Angles 40° correlate with higher likelihood of unsatisfactory functional outcome [4]
• Severe slips (50°) almost inevitably develop femoroacetabular impingement and early osteoarthritis

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7. Differential Diagnosis

Primary Differentials

Must-Not-Miss Diagnoses

1. Septic Arthritis: Differentiate using Kocher criteria, aspirate if suspicious
2. Tumor (Ewing sarcoma, osteosarcoma): Suspect if night pain, systemic symptoms
3. Legg-Calvé-Perthes: Critical age distinction (younger than SUFE)

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8. Investigations

Radiographic Imaging (Essential)

Views Required

For Stable SUFE:

1. Anteroposterior (AP) Pelvis: Both hips for comparison
2. Frog-Leg Lateral: Both hips (most sensitive view for subtle slips)

For Unstable SUFE:

1. AP Pelvis: Both hips
2. Cross-Table Lateral: Avoids painful hip flexion required for frog-leg view

Radiographic Signs

Klein's Line (Trethowan Sign)

Technique:

• On AP radiograph, draw a line along superior border of femoral neck
• Extend line laterally across the epiphysis

Normal: Line intersects lateral portion of epiphyseal ossification center SUFE: Line passes above epiphysis, failing to intersect it (or intersects less than normal side)

Sensitivity: 85-90% on AP view, 95%+ on lateral view

Lateral View Findings

Frog-Leg Lateral (most sensitive):

• Direct visualization of posterior slip
• "Ice cream falling off cone" appearance
• Epiphysis appears to be posterior to femoral neck centerline

Posterior Sloping Angle (PSA):

• Angle between femoral neck axis and epiphyseal plate
• PSA ≥14° on contralateral hip suggests increased slip risk (consider prophylactic pinning) [4]
• PSA 40° correlates with poor functional outcomes [4]

Capener Sign

• Metaphyseal blanch (new bone formation) on chronic slips
• Indicates physeal remodeling attempt

Advanced Imaging

MRI Indications

Exam Detail: Pre-Slip (Prodromal SUFE):

• Obese child with hip pain
• Normal radiographs
• High index of suspicion

MRI Findings in Pre-Slip:

• Physeal widening
• Perichondral edema
• Focal marrow edema
• Allows early intervention before frank slip

Post-Operative:

• Suspected AVN (perform 6-12 weeks post-op if clinical concern)
• Chondrolysis evaluation
• Assessment of femoral head viability before revision surgery

MRI Sensitivity: 100% for physeal abnormalities (can detect pre-radiographic slips)

CT Scan

• Indication: Severe/complex deformity, pre-operative planning for corrective osteotomy
• Information: 3D anatomy, precise slip angles, femoral version, acetabular coverage

Ultrasound

• Limited role: Can detect joint effusion
• Not sensitive for slip diagnosis

Laboratory Investigations

Baseline Blood Tests

For All Patients:

• Full blood count (exclude infection, anemia)
• CRP and ESR (if suspecting septic arthritis)
• Endocrine Screening (if atypical features):
  • Thyroid function tests (TSH, free T4)
  • Growth hormone/IGF-1
  • Gonadotropins (LH, FSH)
  • Serum calcium, phosphate, alkaline phosphatase
  • Renal function (if CKD suspected)

Indications for Endocrine Work-Up:

• Age < 10 years or 16 years
• BMI < 85th percentile (thin patient)
• Bilateral SUFE
• Short stature or delayed puberty
• Family history of endocrinopathy

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9. Management

Immediate Emergency Management

Upon Diagnosis:

1. Make Patient Non-Weight Bearing Immediately

   • Wheelchair or carry to prevent slip progression
   • Even stable slips can convert to unstable with continued weight-bearing

2. Urgent Orthopaedic Referral

   • Unstable SUFE: Emergency same-day surgery
   • Stable SUFE: Urgent surgery within 24-48 hours

3. Analgesia

   • NSAIDs (ibuprofen 10mg/kg TDS)
   • Avoid opiates initially (may mask progression)

4. Do NOT Manipulate Hip

   • No range of motion exercises
   • No attempted reduction
   • Maintain hip in position of comfort

Surgical Management (Definitive Treatment)

In Situ Fixation (Standard of Care)

Principle: Stabilize slip without reduction, accepting current deformity

Technique - Percutaneous Cannulated Screw Fixation:

Exam Detail: Operative Steps:

1. Patient Positioning: Supine on radiolucent table with affected leg in gentle traction
2. Image Intensifier: AP and lateral views
3. Entry Point: Anterior femoral neck, distal to vastus ridge
4. Guidewire Placement:
   • Central-central position (center of head on both AP and lateral views)
   • Perpendicular to physis
   • Avoid penetrating physis excessively (3-5mm threads across physis)
5. Screw Selection: Single 6.5mm or 7.3mm cannulated screw (partially threaded)
6. Final Position:
   • 5mm from subchondral bone on all views
   • Perpendicular to physis
   • Adequate threads (minimum 3) engaging epiphysis

Single vs Multiple Screws:

• Current Evidence: Single screw is sufficient for stable slips [14]
• Multiple screws: No biomechanical advantage, higher complication rate (chondrolysis from joint penetration)
• Two screws: May be considered for severe/unstable slips (controversial)

Pearls:

• "Center-center-center": Center of head in AP, lateral, and safe zone (central third of epiphysis)
• Avoid posterior placement (risks retinacular vessels)
• Remove drill frequently to prevent thermal necrosis

Management of Unstable SUFE (Controversial)

Option 1: Urgent In Situ Fixation (Most Common)

• Fix slip without reduction
• AVN rate: 18-24% [6]
• Lower technical difficulty
• Rationale: Reduction may disrupt remaining vascular supply

Option 2: Gentle Closed Reduction + Fixation

• Controversial, higher AVN rates reported (23-27.6%) [6]
• May be considered if slip occurred < 24 hours ago
• Reduction by positioning only (no forceful manipulation)

Option 3: Modified Dunn Procedure (Surgical Hip Dislocation)

Exam Detail: Technique:

• Open surgical dislocation via Gibson approach
• Trochanteric flip osteotomy (Ganz technique)
• Direct visualization and protection of retinacular vessels
• Complete reduction of epiphysis
• Fixation with Kirschner wires or screws

Advantages:

• Anatomic reduction (prevents FAI in severe slips)
• Direct visualization of vessels (AVN rate 9.9-19.9% in experienced hands) [6,15]

Disadvantages:

• Technically demanding (steep learning curve)
• Longer operative time
• Risk of AVN if vessels damaged during dissection
• Risk of femoral neck fracture

Evidence: Systematic review of 636 hips showed AVN rate of 19.9%, with better anatomic results than in situ pinning for severe slips. [15] Best results in high-volume centers.

Current Indications (Specialized Centers Only):

• Severe unstable slips (50°)
• Acute unstable slips in experienced hands
• Selected chronic severe slips with FAI risk

Contralateral Hip Management

Risk of Contralateral Slip: 20-40% [11]

Indications for Prophylactic Fixation

Strong Indications (Most surgeons agree):

1. Endocrine disorder present
2. Age < 10 years with wide-open triradiate cartilage
3. PSA ≥14° on contralateral side [4]
4. Bilateral physeal abnormalities on imaging
5. Non-compliance/inability to follow-up

Relative Indications (Surgeon-dependent):

1. Obesity (BMI 95th percentile)
2. Developmental delay (unreliable symptom reporting)
3. Parental preference after counseling

Arguments Against Prophylactic Pinning:

• 60-80% of contralateral hips never slip (unnecessary surgery)
• Risk of iatrogenic complications (joint penetration, femoral neck fracture)
• Physeal arrest (short femoral neck)
• Ethical concerns about operating on normal hip

Current Practice: Shared decision-making with family, individualized based on risk factors. [11]

Post-Operative Care

Immediate Post-Op (0-6 weeks)

• Weight-Bearing:
  • "Stable slips: Partial weight-bearing with crutches immediately"
  • "Unstable slips: Non-weight-bearing for 4-6 weeks"
• Radiographs: Immediate post-op (AP and lateral) to confirm position
• Mobilization: Physiotherapy for gait training, crutch walking
• Activity: No sports or running

Intermediate Phase (6 weeks - 3 months)

• Progressive Weight-Bearing: As tolerated
• Radiographs: 6 weeks (assess healing, slip progression, screw position)
• Return to School: After comfortable weight-bearing established
• Physiotherapy: Hip strengthening, ROM exercises

Long-Term Follow-Up

• Radiographs: 3 months, 6 months, annually until skeletal maturity
• Monitor For:
  • Screw penetration (growth may push screw into joint)
  • AVN (develops 3-12 months post-op)
  • Chondrolysis
  • Slip progression (rare with proper fixation)
  • Contralateral slip

Return to Sports

• Non-contact Sports: 3-4 months (swimming, cycling)
• Contact Sports: 6-12 months if healed and pain-free
• Never: If unstable slip with AVN risk

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10. Complications

Early Complications

1. Avascular Necrosis (AVN) - Most Devastating

Incidence by Slip Type:

Pathophysiology:

• Disruption of lateral epiphyseal vessels
• Ischemic necrosis of femoral head
• Subchondral collapse

Clinical Presentation:

• Increasing pain 3-12 months post-op
• Reduced range of motion
• Limp

Radiographic Signs:

• Increased density of femoral head (early)
• Subchondral lucency ("crescent sign")
• Femoral head collapse (late)

MRI Findings:

• Epiphyseal marrow edema
• Absence of enhancement on contrast MRI
• Definitive diagnosis

Management:

• Mild AVN: Observation, protected weight-bearing
• Moderate AVN: Core decompression (controversial)
• Severe AVN with collapse: Salvage procedures (proximal femoral osteotomy, arthrodesis, total hip replacement)

Prognosis: Poor. Most progress to severe osteoarthritis requiring arthroplasty in 3rd-4th decade.

2. Chondrolysis

Definition: Acute destruction of articular cartilage

Incidence: 5-8% (historically higher before modern fixation techniques)

Causes:

• Screw Penetration: Most common (screw tip breaches joint)
• Persistent Pin Placement: Chronic irritation
• Immunologic: Cartilage antigen exposure

Clinical Features:

• Pain and stiffness 3-6 months post-op
• Profound restriction of all hip movements
• Joint space narrowing on radiograph

Radiographic Criteria (Waldenström):

• Joint space < 3mm
• Uniform narrowing

Management:

• Remove hardware if penetrating joint
• NSAIDs, physiotherapy (limited efficacy)
• Protected weight-bearing
• Many progress to arthrodesis or arthroplasty

Prognosis: Variable. Some spontaneously improve; many develop permanent stiffness.

Late Complications

3. Femoroacetabular Impingement (FAI)

Mechanism: Residual "pistol-grip" deformity from healed slip causes abnormal contact between femoral neck and acetabular rim during hip flexion/internal rotation

Types:

• CAM-type: Femoral neck asphericity
• Pincer-type: Acetabular overcoverage (less common in SUFE)
• Combined: Most SUFE patients

Incidence:

• Mild slips (< 30°): 20-30%
• Severe slips (50°): 80-90%

Clinical Presentation:

• Groin pain in early adulthood (20s-30s)
• Positive anterior impingement test (FADIR)
• Activity-related pain

Imaging:

• Alpha angle 55° on lateral radiograph (CAM lesion)
• MRI: Labral tears, cartilage damage

Management:

• Conservative: Activity modification, NSAIDs, physiotherapy
• Surgical: Hip arthroscopy with femoral osteochondroplasty
• Severe Cases: Proximal femoral osteotomy (realignment)

4. Osteoarthritis

Inevitability: Moderate-severe slips have extremely high lifetime risk of OA

Timeline:

• Mild slips: OA in 5th-6th decade (similar to general population)
• Moderate slips: OA in 4th-5th decade
• Severe slips: OA in 3rd-4th decade

Mechanism: Abnormal biomechanics → accelerated cartilage wear

Management:

• Joint preservation strategies (osteotomy) in younger patients
• Total hip arthroplasty when symptomatic and radiographically advanced

Surgical Complications

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11. Prognosis

Short-Term Outcomes (1-2 Years)

Stable Slips:

• 90-95% good to excellent outcomes
• Most return to full activities
• Minimal pain

Unstable Slips:

• 50-60% good outcomes (heavily dependent on AVN development)
• If AVN develops: Poor outcomes in majority

Long-Term Outcomes (10-30 Years)

Functional Outcomes by Slip Severity

Predictors of Poor Outcome

1. Instability at Presentation (Loder unstable) - Strongest predictor [5]
2. AVN Development - Almost always leads to arthroplasty
3. Slip Angle 40° [4]
4. Delayed Diagnosis (6 months of symptoms)
5. Inadequate Fixation (slip progression)

Total Hip Arthroplasty

Incidence:

• Overall: 15-20% of SUFE patients eventually require THA
• Unstable with AVN: 60-70% require THA
• Severe slips: 40-50% require THA

Age at THA: Mean 35-45 years

THA Outcomes in SUFE:

• Functional outcomes similar to primary OA at short-term follow-up [4]
• Revision rates NOT significantly different from primary OA
• Technical challenges: Abnormal anatomy, retained hardware, young patient age

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12. Prevention and Screening

Primary Prevention

Childhood Obesity Reduction:

• Public health interventions targeting obesity
• Most modifiable risk factor
• No direct screening programs for SUFE exist

Secondary Prevention (Early Detection)

High-Risk Populations:

• Obese adolescents with hip/knee/thigh pain → Low threshold for hip radiographs
• Children on growth hormone therapy → Annual clinical hip examination
• Endocrine disorder patients → Hip imaging if any symptoms

Contralateral Hip Surveillance:

• After unilateral SUFE: Clinical exam every 3 months until physeal closure
• Educate families on symptoms (pain, limp)
• Radiographic surveillance: 3-month intervals for first year

Education:

• Primary care physicians: Knee pain = examine the hip
• Parents: Weight-bearing restrictions, symptom recognition

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13. Key Guidelines and Evidence

Landmark Studies

Loder et al., 1993 (Stability Classification) [5]

• Defined stable vs unstable based on weight-bearing ability
• Unstable SUFE: AVN rate 47% vs 0% in stable
• Changed paradigm from temporal to stability classification
• Impact: Now universal standard for prognostication

Navarre, 2020 (New Zealand Literature Review) [4]

• Maori/Pacific Islander populations: Highest SCFE burden worldwide
• PSA ≥14° threshold for prophylactic pinning
• PSA 40° correlates with poor functional outcomes
• Impact: Influenced prophylactic pinning decision-making

Veramuthu et al., 2022 (AVN Meta-Analysis) [6]

• Meta-analysis of 33 studies on AVN rates
• In situ fixation AVN rate: 18.5%
• Modified Dunn procedure: 19.9% (not significantly different)
• Parsch method: 9.9% (but milder slips)
• Impact: Supports modified Dunn in experienced hands for severe slips

Society Guidelines

British Society for Children's Orthopaedic Surgery (BSCOS):

• Single screw fixation recommended
• Prophylactic pinning: Shared decision-making with family
• No consensus on routine prophylactic fixation

American Academy of Orthopaedic Surgeons (AAOS):

• In situ fixation is standard of care
• Insufficient evidence to recommend routine prophylactic fixation
• Modified Dunn procedure: Limited to experienced surgeons in severe slips

Pediatric Orthopaedic Society of North America (POSNA):

• Unstable SUFE = Emergency
• Stable SUFE = Urgent (not emergency)
• Avoid forceful reduction

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14. Examination Focus (Viva/OSCE Scenarios)

Opening Statement

"Slipped Upper Femoral Epiphysis is a Salter-Harris type I fracture through the proximal femoral physis affecting adolescents during the pubertal growth spurt. It is characterized by posterior and inferior displacement of the femoral epiphysis relative to the metaphysis. The Loder classification based on weight-bearing ability is the most important prognostic indicator, with unstable slips carrying up to 47% risk of avascular necrosis compared to less than 10% in stable slips."

Common Viva Questions

Q1: What is Klein's Line and what does it demonstrate?

Model Answer: "Klein's line is drawn along the superior border of the femoral neck on an AP radiograph of the pelvis. Normally, this line should intersect the lateral portion of the femoral epiphyseal ossification center. In SUFE, the epiphysis has slipped posteromedially, so Klein's line passes superior to the epiphysis without intersecting it—this is called Trethowan's sign. This radiographic finding has approximately 85-90% sensitivity on AP views and is one of the cardinal signs of SUFE."

Q2: Explain the vascular anatomy and why AVN occurs in unstable SUFE.

Model Answer: "The blood supply to the femoral epiphysis comes predominantly from the medial femoral circumflex artery, which gives rise to the lateral epiphyseal vessels, also called retinacular arteries. These vessels travel posteriorly along the femoral neck, entering the epiphysis at the posterosuperior quadrant. In unstable SUFE, the sudden displacement causes acute kinking and potential tearing of these vessels. The femoral head has no significant collateral supply from the ligamentum teres until skeletal maturity, making it entirely dependent on these retinacular vessels. This is why unstable slips have such high AVN rates—up to 47% in Loder's original series—compared to stable slips where the vessels may gradually accommodate."

Q3: Why should you never attempt forceful reduction of a chronic slip?

Model Answer: "Chronic slips undergo a process of physeal remodeling where new bone forms along the metaphyseal neck (called the Capener sign). The retinacular vessels become draped over this remodeled anatomy in a new position. If you attempt forceful closed reduction, you risk stretching or tearing these repositioned vessels, precipitating AVN in a slip that might otherwise have low vascular risk. This is why the gold standard for stable chronic slips is in situ fixation—we 'fix it where it lies' and accept the deformity rather than risk catastrophic vascular injury."

Q4: What are the indications for prophylactic fixation of the contralateral hip?

Model Answer: "This is an area of ongoing controversy. The risk of contralateral slip is 20-40%, but this means 60-80% of hips would undergo unnecessary surgery if we pinned all prophylactically. Strong indications where most surgeons agree include: underlying endocrine disorder, age less than 10 years with wide-open triradiate cartilage, posterior sloping angle of 14 degrees or more on the contralateral hip, bilateral physeal abnormalities on imaging, and non-compliance or inability to follow up. Relative indications include severe obesity and developmental delay. The decision should be individualized with shared decision-making involving the family, weighing the risk of future slip against the risks of prophylactic surgery."

Q5: Describe the modified Dunn procedure and when it's indicated.

Model Answer: "The modified Dunn procedure, refined by Ganz, involves surgical hip dislocation to anatomically reduce a severely displaced epiphysis. The technique uses a Gibson approach with a trochanteric flip osteotomy, which preserves the medial femoral circumflex artery attachment. The hip is dislocated anteriorly, allowing direct visualization of the retinacular vessels. The abnormal callus and fibrous tissue are removed, the epiphysis is reduced anatomically, and fixation is achieved with K-wires or screws. The advantage is anatomic restoration, which prevents femoroacetabular impingement in severe slips. The AVN rate is approximately 19.9% in meta-analysis, comparable to in situ fixation for unstable slips. It's indicated for severe unstable slips, particularly in high-volume centers with surgeons experienced in the technique. The main disadvantage is technical complexity and the learning curve associated with surgical hip dislocation."

OSCE Scenario: History and Examination

Scenario: You are in the emergency department. A 13-year-old obese boy presents with right knee pain for 2 weeks, worsening today. Please take a focused history and examine the patient.

Key History Points to Elicit:

• Pain location: Knee, but probe for hip/groin/thigh pain
• Duration: 2 weeks (chronic symptoms)
• Acute worsening: Today (acute-on-chronic?)
• Trauma: Often absent or minor
• Past medical history: Endocrine disorders, medications (growth hormone)
• Family history: SUFE, endocrine disorders

Focused Examination:

1. Gait: Antalgic, externally rotated foot
2. Knee Exam: Normal (referred pain)
3. Hip Exam:
   • Inspection: External rotation resting position
   • Palpation: Groin tenderness
   • Log roll test: Painful
   • Drehmann's sign: Flex hip → obligatory external rotation
   • ROM: Loss of internal rotation (most sensitive)

Management:

• "This child has concerning features for SUFE. I would make him immediately non-weight bearing, provide analgesia, and order urgent AP and frog-leg lateral radiographs of both hips. If SUFE is confirmed, I would urgently refer to pediatric orthopaedics for surgical stabilization within 24-48 hours."

Common Mistakes

❌ Mistake 1: Examining only the knee in an adolescent with knee pain ✅ Correct: Always examine the hip—50% of SUFE presents as knee pain

❌ Mistake 2: Classifying based on duration (acute vs chronic) rather than stability ✅ Correct: Loder classification (stable vs unstable based on weight-bearing) is the gold standard

❌ Mistake 3: Attempting reduction of chronic slips ✅ Correct: In situ fixation without reduction for stable slips

❌ Mistake 4: Allowing continued weight-bearing after diagnosis ✅ Correct: Immediate non-weight bearing for all SUFE to prevent progression

❌ Mistake 5: Missing endocrine work-up in atypical cases ✅ Correct: Screen TSH, GH, gonadotropins in age < 10, thin patients, or bilateral SUFE

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15. Patient and Family Education

What is SUFE?

"Your child has a condition where the 'growth plate'—the area of growing cartilage at the top of the thigh bone—has become unstable and slipped. Think of it like a scoop of ice cream sliding off a cone. The ball of the hip joint (the scoop) has slipped backward off the top of the thigh bone (the cone). This happens during the teenage growth spurt when the growth plate is softer and more vulnerable."

Why did this happen?

"The exact cause isn't fully understood, but we know certain factors increase risk. The growth spurt weakens the growth plate temporarily. Extra body weight increases the force across this growth plate. Sometimes hormonal imbalances can contribute. It's important to know this is not caused by anything you or your child did wrong."

Can you push it back into place?

"No, and this is very important. The blood vessels feeding the ball of the hip are very delicate. If we try to force the bone back into place, we could tear these vessels, causing the bone to die—a complication called avascular necrosis. This would be much worse than the original problem. The safest approach is to stabilize the bone where it currently is using a metal screw. We call this 'in situ fixation,' which means 'fix it in place.'"

What is the operation?

"The surgery is called percutaneous screw fixation. Using X-ray guidance, the surgeon makes a small incision on the thigh and inserts a special screw through the bone to hold the growth plate stable. The screw crosses the growth plate and prevents any further slipping while the bone heals. It's a minimally invasive procedure, usually taking 45-90 minutes."

What about the other hip?

"There is a 20-40% chance (about 1 in 3-4) that the opposite hip will also slip, usually within the next 18 months. Some doctors recommend fixing the other hip at the same time to prevent this, while others prefer to watch it closely. We will discuss the risks and benefits of both approaches. If we choose to watch the other hip, you'll need to bring your child back for regular check-ups and X-rays, and come to the hospital immediately if there's any pain or limping on the other side."

Recovery expectations

• Hospital Stay: 1-3 days typically
• Weight-Bearing: Crutches for 4-6 weeks
• School: Can return after 1-2 weeks (with crutches)
• Sports: 3-4 months for non-contact, 6-12 months for contact sports
• Follow-up: Regular X-rays for at least 1 year to monitor healing

Long-term outlook

"Most children with mild slips do very well with minimal long-term problems. However, there is an increased risk of hip arthritis later in life, particularly if the slip was severe. We will monitor your child until the growth plates have closed (around age 16-18) to watch for complications. It's important to attend all follow-up appointments."

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16. References

1. Peck DM, Voss LM, Voss TT. Slipped Capital Femoral Epiphysis: Diagnosis and Management. Am Fam Physician. 2017;95(12):779-784.

2. Aronsson DD, Loder RT, Breur GJ, Weinstein SL. Slipped capital femoral epiphysis: current concepts. J Am Acad Orthop Surg. 2006;14(12):666-679.

3. Bouchard MD, Vescio BG, Munir M, et al. The Epidemiology of Slipped Capital Femoral Epiphysis in Children and Adolescents: A Systematic Review of Risk Factors and Incidence Across Populations. JBJS Rev. 2025;13(5). doi:10.2106/JBJS.RVW.25.00052

4. Navarre P. Slipped Capital Femoral Epiphysis: A Review of the New Zealand Literature. J Bone Joint Surg Am. 2020;102(Suppl 2):8-14. doi:10.2106/JBJS.20.00066

5. Loder RT, Richards BS, Shapiro PS, Reznick LR, Aronson DD. Acute slipped capital femoral epiphysis: the importance of physeal stability. J Bone Joint Surg Am. 1993;75(8):1134-1140.

6. Veramuthu V, Munajat I, Islam MA, Mohd EF, Sulaiman AR. Prevalence of Avascular Necrosis Following Surgical Treatments in Unstable Slipped Capital Femoral Epiphysis (SCFE): A Systematic Review and Meta-Analysis. Children (Basel). 2022;9(9):1374. doi:10.3390/children9091374

7. Lehmann CL, Arons RR, Loder RT, Vitale MG. The epidemiology of slipped capital femoral epiphysis: an update. J Pediatr Orthop. 2006;26(3):286-290.

8. White CJK, Kodra JD, Bollepalli H, et al. The Seasonal Incidence of Slipped Capital Femoral Epiphysis: A Systematic Review and Meta-Analysis. Children (Basel). 2025;12(6):729. doi:10.3390/children12060729

9. Tokmakova KP, Stanton RP, Mason DE. Factors influencing the development of osteonecrosis in patients treated for slipped capital femoral epiphysis. J Bone Joint Surg Am. 2003;85(5):798-801.

10. Bhatia NN, Pirpiris M, Otsuka NY. Body mass index in patients with slipped capital femoral epiphysis. J Pediatr Orthop. 2006;26(2):197-199.

11. Kocher MS, Bishop JA, Weed B, et al. Delay in diagnosis of slipped capital femoral epiphysis. Pediatrics. 2004;113(4):e322-e325.

12. Pritchett JW, Perdue KD. Mechanical factors in slipped capital femoral epiphysis. J Pediatr Orthop. 1988;8(4):385-388.

13. Fahey JJ, O'Brien ET. Acute slipped capital femoral epiphysis: review of the literature and report of ten cases. J Bone Joint Surg Am. 1965;47:1105-1127.

14. Bompadre V, Liu RW, Heffernan MJ, et al. Single versus double screw fixation for treatment of slipped capital femoral epiphysis: a biomechanical analysis. J Pediatr Orthop. 2013;33(6):620-624.

15. Gorgolini G, Caterini A, Efremov K, et al. Surgical treatment of slipped capital femoral epiphysis (SCFE) by Dunn procedure modified by Ganz: a systematic review. BMC Musculoskelet Disord. 2022;22(Suppl 2):1064. doi:10.1186/s12891-022-05071-9

16. Assi C, Mansour J, Kouyoumdjian P, Yammine K. Valgus slipped capital femoral epiphysis: a systematic review. J Pediatr Orthop B. 2021;30(2):116-122. doi:10.1097/BPB.0000000000000758

17. Ziebarth K, Milosevic M, Lerch TD, et al. High survivorship and little osteoarthritis at 10-year follow-up in SCFE patients treated with a modified Dunn procedure. Clin Orthop Relat Res. 2017;475(4):1212-1228.

18. Nguyen AR, Ling J, Gomes B, et al. Slipped capital femoral epiphysis: rationale for "prophylactic" fixation of the contralateral hip. J Pediatr Orthop. 2013;33(5):e46-e50.

19. Larson AN, Yu EM, Melton LJ, et al. Incidence of slipped capital femoral epiphysis: a population-based study. J Pediatr Orthop B. 2010;19(1):9-12.

20. Kalogrianitis S, Tan CK, Kemp GJ, et al. Does unstable slipped capital femoral epiphysis require urgent stabilization? J Pediatr Orthop B. 2007;16(1):6-9.

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17. Summary Box: SUFE at a Glance

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Last Updated: January 6, 2026 Evidence Level: High (20 citations from systematic reviews, landmark trials, and cohort studies)