Slipped Capital Femoral Epiphysis (SCFE) - Most Likely X-ray Findings
In a 12-year-old obese male presenting with limp and right knee pain, the most likely X-ray findings are posterior and medial displacement of the femoral head (epiphysis) relative to the femoral neck (metaphysis), best visualized on the lateral view, with possible widening and irregularity of the proximal femoral growth plate. 1, 2, 3
Why SCFE is the Primary Diagnosis
- Obesity is a major risk factor: Severely obese children are significantly more likely to develop SCFE, and they have higher rates of bilateral involvement 1, 3
- Age and presentation are classic: SCFE typically occurs in patients 8-15 years old (peak 10-16 years) who present with limp and pain 2, 3, 4
- Knee pain is a common referral pattern: Hip pathology frequently refers pain to the knee, and SCFE is one of the most commonly missed diagnoses in children because clinicians focus on the knee rather than obtaining hip radiographs 5, 2, 3
Specific Radiographic Findings to Expect
Early/Imminent SCFE
- Widening of the proximal femoral epiphyseal plate 6
- Irregular demarcation of the growth plate 6
- These findings may be subtle on anteroposterior views 6
Established SCFE (Most Likely in This Case)
- Posterior displacement of the femoral head: The epiphysis slips posteriorly and is best visualized on lateral radiographs 4, 6
- Medial displacement: The lateral tangent of the femoral neck creates a smaller secant of the lateral femoral head on lateral views 6
- Klein's line abnormality: On anteroposterior view, a line drawn along the superior femoral neck fails to intersect the femoral epiphysis (normally it should intersect the lateral portion) 3, 7
- Metaphyseal blanch sign: Increased density at the metaphyseal side of the physis 7
Additional Chronic Features
- Duplicate contours of the medial femoral neck 6
- Femoral neck deformities 6
- Metaphyseal remodeling changes 6
Critical Imaging Protocol
Both hips must be imaged in two perpendicular planes 6, 7:
- Anteroposterior pelvis view (includes both hips for comparison) 3, 7
- Frog-leg lateral views bilaterally if the patient can bear weight (stable SCFE) 3, 7
- Cross-table lateral view if the patient cannot bear weight (unstable SCFE) 3
The lateral view is essential because early slips are often invisible on anteroposterior radiographs alone 4, 6.
Common Diagnostic Pitfalls to Avoid
- Imaging only the knee: Since this patient presents with knee pain, the critical error is obtaining knee radiographs without hip imaging 5, 2
- Unilateral hip imaging: Always image both hips, as 20-40% of cases eventually develop bilateral involvement 3
- Relying solely on anteroposterior views: The posterior displacement is much better visualized on lateral projections 4, 6
- Dismissing as a "groin pull": Groin pulls are extremely rare in adolescents; suggestive symptoms mandate hip radiographs to exclude SCFE 7
Alternative Diagnoses (Less Likely Given Obesity)
While other conditions could theoretically present similarly, the combination of obesity, age, and referred knee pain makes SCFE overwhelmingly most likely:
- Osgood-Schlatter disease: Would show tibial tubercle irregularity and fragmentation, but typically presents with anterior knee pain directly over the tibial tuberosity, not referred pain from the hip 8
- Blount disease (tibia vara): Would show tibial bowing on knee radiographs, but presents with leg deformity rather than isolated knee pain 1, 8
- Patellofemoral pain syndrome: Requires normal imaging to diagnose and doesn't explain the limp in an obese adolescent 9
The clinical imperative is to obtain bilateral hip radiographs (AP and lateral views) immediately, not knee radiographs, as SCFE requires urgent surgical stabilization to prevent complications including avascular necrosis and progressive deformity. 3, 4, 7