SLIPPED CAPITAL FEMORAL EPIPHYSIS (SCFE)
Stable vs Unstable | In Situ Pin | AVN Risk
LODER CLASSIFICATION (STABILITY)
Critical Must-Knows
- Stable SCFE = can weight-bear. Unstable SCFE = cannot weight-bear
- IN SITU fixation - do NOT attempt reduction (AVN risk)
- Unstable SCFE has 47% AVN rate even with best treatment
- Contralateral prophylactic pinning: consider in high-risk patients
- Single central screw perpendicular to physis is gold standard
Examiner's Pearls
- "Unstable = emergency surgery (within 24 hours)
- "Any attempt at reduction increases AVN dramatically
- "Southwick angle measures slip severity on frog lateral
- "Klein's line should intersect lateral epiphysis on AP
Clinical Imaging
Imaging Gallery
Critical Exam Concepts
Do NOT Reduce
In situ fixation is the rule. Any attempt to reduce increases AVN risk dramatically. Even unstable SCFE should be pinned in situ with only gentle positioning.
Stable vs Unstable
Loder Classification determines prognosis. Stable (can weight-bear): less than 1% AVN. Unstable (cannot weight-bear): 47% AVN. This is the most important prognostic factor.
Single Screw Technique
Single screw perpendicular to physis. Enter anterolateral femur, aim for center of epiphysis. Screw should be central and perpendicular. Multiple screws add AVN risk without benefit.
Contralateral Hip
20-40% bilateral risk. Consider prophylactic pinning if high-risk (younger, endocrine disorder, renal disease, hypothyroid). Discuss with family.
Stable vs Unstable SCFE Comparison
| Feature | Stable SCFE | Unstable SCFE |
|---|---|---|
| Weight-bearing | Able to walk with/without crutches | Unable to walk even with crutches |
| AVN Risk | Less than 1% | 47% |
| Timing | Semi-urgent (within days) | Emergency (within 24 hours) |
| Treatment | In situ screw | In situ screw (gentle positioning) |
| Prognosis | Excellent | Guarded (high AVN risk) |
FAT HIPSCFE Risk Factors
Memory Hook:FAT HIP - the fat hip is at risk of slipping!
SCREWSCFE in situ Fixation Principles
Memory Hook:Get the SCREW right - single, central, perpendicular!
PYREContralateral Prophylaxis Indications
Memory Hook:Set a PYRE - burn the contralateral hip risk with prophylaxis!
Overview and Epidemiology
Pathophysiology
SCFE occurs through the hypertrophic zone of the physis (weakest zone). The epiphysis is held by the acetabulum. The metaphysis slips anteriorly and externally rotates relative to the epiphysis. Mechanical overload (obesity) and hormonal factors (growth spurt, endocrine) weaken the physis.
Epidemiology
- Peak age: 10-16 years (during growth spurt)
- Male to female 2-3:1 (males later puberty)
- Boys: mean 12-13 years
- Girls: mean 11-12 years
- Higher in African American, Pacific Islander populations
Risk Factors
- Obesity (most common)
- Rapid growth (tall for age)
- Endocrine: hypothyroidism, GH abnormalities
- Renal osteodystrophy
- Radiation therapy (previous)
- Retroversion of femoral head
Anatomy and Biomechanics
Blood Supply Considerations
The retinacular vessels (from MFCA) are the primary blood supply to the femoral head. They run along the posterior-superior femoral neck. Any manipulation, reduction attempt, or surgical dissection risks disrupting these vessels and causing AVN.
Proximal Femoral Physis
The physis is the weak point: The slip occurs through the hypertrophic zone of the physis (zone of provisional calcification is weakest).
Direction of slip: The epiphysis stays in the acetabulum. The metaphysis (and shaft) slips anteriorly and externally rotates. This creates the classic clinical finding of external rotation contracture.
Periosteal sleeve: The posterior periosteum remains attached to the epiphysis, containing the retinacular vessels.
Classification Systems
Loder Classification (Stability) - MOST IMPORTANT
| Classification | Definition | AVN Risk | Urgency |
|---|---|---|---|
| Stable | Can weight-bear (with or without crutches) | Less than 1% | Days |
| Unstable | Cannot weight-bear even with support | 47% | Hours (emergency) |
Most important classification for prognosis. The stability (ability to weight-bear) is the single best predictor of AVN.
Clinical Assessment
History
- Groin, thigh, or knee pain (referred)
- Limp (abductor or antalgic gait)
- Duration of symptoms
- Able to weight-bear? (critical question)
- Endocrine or metabolic history
- Family history of SCFE
Examination
- Obligate external rotation with hip flexion
- Loss of internal rotation
- Short limb (if severe slip)
- Trendelenburg gait
- Check contralateral hip
- BMI and body habitus
Obligate External Rotation
The classic sign: when you flex the hip, it obligatorily externally rotates. This is because the metaphysis has slipped anteriorly relative to the epiphysis. Flexion drives the neck against the anterior acetabulum, forcing external rotation.
Knee Pain in an Adolescent = Hip X-ray
Referred pain to the knee is common in SCFE. Any adolescent with hip, thigh, OR knee pain should have hip X-rays. Missing a SCFE presenting as knee pain is a classic medicolegal pitfall.
Investigations
Radiological Investigations
| View | Key Findings | Measurement |
|---|---|---|
| AP Pelvis | Klein's line disruption | Line along superior neck should intersect epiphysis |
| Frog Lateral | Posterior slip visible | Southwick angle (severity) |
| Cross-table lateral | Alternative if frog lateral painful | Same findings |
Klein's line: On AP, a line along the superior border of the femoral neck should intersect the lateral portion of the epiphysis. If it does not, the epiphysis has slipped.
Management
In Situ Fixation - Do NOT Reduce
The single most important principle: Fix the slip in situ. ANY attempt at reduction - whether open or closed - significantly increases AVN risk. Even in severe slips, in situ fixation followed by deformity correction later is safer than reduction.
Stable SCFE Management
Timing: Semi-urgent (within days). Patient should be non-weight-bearing until surgery.
Treatment: In situ single screw fixation.
Technique: Single partially threaded (6.5mm or 7.0mm) cannulated screw. Enter from anterolateral femur. Aim for center of epiphysis on both views. Screw should be perpendicular to physis and engage center of epiphysis.
Post-op: Weight-bear as tolerated. Physis will close over 6-12 months.
Single vs Multiple Screws
Single screw is sufficient for most SCFE. Multiple screws add AVN risk without improving stability. The exception may be an unstable SCFE where additional fixation is considered, but even then, many surgeons use single screw.
Surgical Technique Considerations
In Situ Single Screw Fixation
Position: Supine on fracture table with fluoroscopy.
Entry point: Anterolateral femur, below vastus lateralis ridge. Entry should BE in line with center of epiphysis on lateral view.
Screw trajectory: Aim for center of epiphysis on both AP and lateral. Screw should be perpendicular to physis (parallel to the slip direction correction if it were to occur). At least 5 threads should cross the physis into epiphysis.
Critical: Check no joint penetration on frog lateral (hip flexed and externally rotated). Screw tip should be greater than 5mm from articular surface.
Complications
Complications of SCFE and Treatment
| Complication | Cause | Prevention/Treatment |
|---|---|---|
| AVN (most feared) | Reduction attempt, unstable SCFE | In situ fixation, no reduction |
| Chondrolysis | Screw penetration, unknown | Avoid joint penetration, check fluoro |
| Slip progression | Inadequate fixation, missed diagnosis | Secure screw placement |
| FAI | Residual deformity (cam lesion) | Later osteoplasty or osteotomy |
| Contralateral slip | Natural history (20-40%) | Prophylactic pinning if high-risk |
| Hardware complications | Screw prominence, backout | Bury screw head, check fixation |
AVN Rates
Stable SCFE: Less than 1% AVN with in situ pinning. Unstable SCFE: 47% AVN even with in situ pinning (due to initial blood supply disruption). With reduction attempt: AVN rates increase dramatically (up to 100% in some series).
Postoperative Care
Post-Operative Protocol
Wound check. Mobilize weight-bearing as tolerated (stable SCFE). Non-weight-bearing for few days if unstable SCFE.
Wound check. X-ray to confirm screw position. Advance mobility.
X-ray to assess physeal closure. Most begin to close by 3-6 months.
Confirm complete physeal closure. Usually no screw removal needed.
Monitor for AVN (if unstable SCFE). Assess for FAI symptoms. Check contralateral hip until skeletal maturity.
Outcomes and Prognosis
Prognosis Based on Stability
Stable SCFE: Excellent prognosis. Less than 1% AVN. Most return to full activity. Long-term concern is FAI from residual deformity.
Unstable SCFE: Guarded prognosis. 47% develop AVN. Even those without AVN may have compromised hip function. Close monitoring required.
Special Considerations
Management of Severe SCFE
Severe slips (greater than 50-60°) create significant deformity leading to FAI and early OA.
Options: In situ pinning remains safest. Address residual deformity later with:
- Femoral neck or subcapital osteotomy (high AVN risk)
- Intertrochanteric osteotomy (Imhauser - safer)
- Cam osteoplasty (arthroscopic or open)
Most surgeons prefer in situ pin and later osteoplasty rather than acute realignment.
Evidence Base and Key Studies
Loder et al. - Stability Classification
- Defined stable vs unstable SCFE based on weight-bearing ability
- Unstable SCFE: 47% AVN rate
- Stable SCFE: less than 1% AVN rate
- Stability is the key prognostic factor
Aronsson et al. - Single Screw
- Single screw provides adequate fixation for most SCFE
- Additional screws do not improve outcomes
- Multiple screws may increase AVN risk
- Central placement is critical
Ziebarth et al. - Modified Dunn
- Modified Dunn procedure for severe slips
- Surgical dislocation with acute realignment
- Lower AVN than expected in expert hands
- Technically demanding
Schultz et al. - Prophylactic Pinning
- 20-40% risk of contralateral slip
- Higher risk if younger, endocrine disorder
- Prophylactic pinning prevents slip
- Decision analysis favors prophylaxis in high-risk
Leunig et al. - FAI in SCFE
- SCFE leads to cam-type FAI
- Residual deformity causes impingement
- May progress to early OA
- Osteochondroplasty can address cam lesion
Exam Viva Scenarios
Practice these scenarios to excel in your viva examination
Scenario 1: Classic Stable SCFE
"A 13-year-old obese boy presents with 3 weeks of left groin and thigh pain. He is able to walk with a limp. Examination shows obligate external rotation with hip flexion and loss of internal rotation. X-rays show a SCFE with Southwick angle 35 degrees. How would you manage this?"
Scenario 2: Unstable SCFE
"A 12-year-old girl presents with sudden onset left hip pain after a minor fall. She is unable to weight-bear. The leg is held in external rotation and she screams with any hip movement. X-rays show a significantly displaced SCFE. How would you manage this?"
Scenario 3: Bilateral SCFE
"A 10-year-old boy with known hypothyroidism presents with new right hip pain. He had a left SCFE pinned 6 months ago. X-rays show a new right SCFE. How would you manage this, and what would you do differently if asked at the time of the first SCFE?"
MCQ Practice Points
Stability Classification Question
Q: What is the key factor in the Loder classification of SCFE? A: Ability to weight-bear. Stable = able to walk (with or without crutches). Unstable = unable to walk. This is the most important prognostic factor.
AVN Rate Question
Q: What is the AVN rate in unstable SCFE and stable SCFE? A: Unstable: 47%. Stable: less than 1%. The difference is due to initial disruption of retinacular blood supply in unstable SCFE.
Treatment Principle Question
Q: What is the principle of SCFE treatment that minimizes AVN risk? A: In situ fixation without reduction. Any attempt at reduction (open or closed) dramatically increases AVN risk.
Screw Technique Question
Q: What is the ideal screw position for SCFE fixation? A: Single screw, central in epiphysis on both views, perpendicular to physis. Multiple screws increase AVN risk without added benefit.
Klein's Line Question
Q: What is Klein's line and what does an abnormal finding indicate? A: A line along the superior border of the femoral neck on AP view. Normally intersects the lateral epiphysis. If it does NOT, the epiphysis has slipped.
Bilateral Risk Question
Q: What is the risk of contralateral SCFE and when should prophylactic pinning be considered? A: 20-40% bilateral risk. Consider prophylaxis if: young age, endocrine disorder, renal disease, compliance issues, or physeal widening.
Australian Context
Epidemiology
- Common in Australian adolescents
- Higher rates in Pacific Islander populations
- Obesity rates increasing SCFE incidence
- Indigenous population data limited
Practice
- In situ single screw is standard
- Tertiary pediatric centers manage most cases
- Contralateral prophylaxis varies by surgeon preference
- Good access to fluoroscopy for screw placement
SLIPPED CAPITAL FEMORAL EPIPHYSIS
High-Yield Exam Summary
Key Facts
- •Peak age 10-16 years
- •Obesity is main risk factor
- •20-40% bilateral risk
- •Knee pain = get hip X-ray
Loder Classification
- •Stable = can weight-bear
- •Unstable = cannot weight-bear
- •Stable: less than 1% AVN risk
- •Unstable: 47% AVN risk
Treatment Principles
- •IN SITU fixation - do NOT reduce
- •Single screw, central, perpendicular
- •Unstable = emergency (24h)
- •Stable = semi-urgent (days)
Radiographic Signs
- •Klein's line disruption (AP)
- •Posterior slip on frog lateral
- •Southwick angle (severity)
- •Physeal widening (early sign)
Prophylactic Pinning
- •Young age at presentation
- •Endocrine disorder
- •Renal osteodystrophy
- •Physeal widening contralateral