Slipped Capital Femoral Epiphysis

Courtesy: Sally Hobson, Hull Royal Infirmary, UK

Definition

• Slipped capital femoral epiphysis is a Salter–Harris Type I injury occurring through the hypertrophic zone of the proximal femoral growth plate.

• The femoral head remains within the acetabulum, while the femoral neck and shaft displace superolaterally and externally rotate relative to the epiphysis.

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Epidemiology

• Commonly occurs between 9 and 13 years of age.

• Presentation tends to occur earlier in girls than in boys.

• Bilateral involvement occurs in approximately 30 percent of cases.

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Risk Factors

• Occurs during the pre-pubertal growth spurt.

• Increased shear forces across the physis.

• Obesity, although not present in all cases.

• Endocrine and metabolic disorders, including:

  • Hypothyroidism

  • Cushing syndrome

  • Rickets

• Connective tissue disorders such as Marfan syndrome.

• History of irradiation or chemotherapy.

• Down syndrome.

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Clinical Presentation

• Presentation patterns:

  • Acute on chronic: approximately 50 percent

  • Acute: approximately 20 percent

  • Chronic: approximately 30 percent

• Symptoms include:

  • Pain in the hip, thigh, or knee

  • Irritable hip

• Clinical signs include:

  • Limb shortening and external rotation, more pronounced in severe slips

  • Restricted internal rotation of the hip

  • Obligatory external rotation during hip flexion

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Investigations

Radiography

• Frog-leg lateral view of the hip is the most important radiographic view.

• Findings may include:

  • Widening of the physis

  • Posterior and inferior displacement of the femoral head

Trethowan Sign (Klein Line)

• A line drawn along the superior border of the femoral neck on the anteroposterior view should intersect the femoral head.

• In slipped capital femoral epiphysis, the line passes superior to the femoral head.

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Magnetic Resonance Imaging

• Useful for diagnosing pre-slip or early disease.

• Helps assess the vascularity of the femoral head, particularly in unstable slips.

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Classification

Loder Classification

• Stable slipped capital femoral epiphysis: patient is able to bear weight, with or without crutches.

• Unstable slipped capital femoral epiphysis: patient is unable to bear weight.

• Stability is the most important predictor of avascular necrosis.

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Southwick Angle Classification

• Quantitative assessment of slip severity using lateral radiographs.

• A slip angle greater than 60 degrees is considered severe.

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Treatment Principles

• Strict bed rest until surgical intervention.

• Prompt surgical stabilization is required to prevent further slippage.

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Surgical Management

Gold Standard Treatment

• In situ fixation using a single cannulated screw.

• Key technical considerations:

  • Entry point should be anterior on the femoral neck.

  • Fluoroscopic screening through the full range of hip motion to ensure no joint penetration.

  • The screw is intended to remain permanent.

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Management of Severe Slips

• Options include:

  • In situ pinning

  • Gentle, controlled reduction when deemed safe

  • Open reduction techniques, including:

    • Modified Dunn osteotomy

    • Surgical hip dislocation, when indicated

• These procedures carry a high risk of avascular necrosis.

• National and international guidelines emphasize caution due to this risk.

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Prophylactic Fixation of the Contralateral Hip

• Considered in patients at high risk for bilateral disease.

• Decision is based on:

  • Presence of endocrine or metabolic abnormalities

  • Younger age at presentation

  • Patient compliance

  • Increased posterior sloping angle

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Complications

Chondrolysis

• Often related to:

  • Intra-articular screw penetration

  • Guidewire advancement into the joint

• Prevention requires meticulous intraoperative imaging.

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Avascular Necrosis

• Most commonly occurs in severe and unstable slips.

• Typically leads to significant pain, joint destruction, and poor outcomes.

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Femoroacetabular Impingement

• Cam-type impingement may develop following in situ fixation.

• Results in:

  • Externally rotated gait

  • Limb shortening

  • Progressive hip dysfunction

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Late Screw-Related Complications

• Late screw penetration due to collapse or avascular necrosis.

• Growth of the femoral neck away from the screw in younger patients.