Slipped capital femoral epiphysis (SCFE) usually occurs in early adolescence and preferentially affects boys. Obesity is a significant risk factor. Genetic factors also contribute. SCFE is bilateral in one fifth of patients, and unilateral SCFE becomes bilateral in up to two thirds of patients. The exact cause of SCFE is unknown but probably relates to weakening of the physis (growth plate), which can result from trauma, hormonal changes, inflammation, or increased shearing forces due to obesity.
Onset is usually insidious, and symptoms of slipped capital femoral epiphysis are associated with stage of slippage. The first symptom of SCFE may be hip stiffness that abates with rest; it is followed by a limp, then hip pain that radiates down the anteromedial thigh to the knee. Up to 15% of patients present with knee or thigh pain, and the true problem (hip) may be missed until slippage worsens. Early hip examination may detect neither pain nor limitation of movement.
In more advanced stages, findings may include pain during movement of the affected hip, with limited flexion, abduction, and medial rotation; knee pain without specific knee abnormalities; and a limp or Trendelenburg gait. The affected leg is externally rotated. If blood supply to the area is compromised, avascular necrosis and collapse of the epiphysis may occur.
Because treatment of advanced slippage is difficult, early diagnosis of slipped capital femoral epiphysis is vital. Anteroposterior and frog-leg lateral x-rays of both hips are taken. X-rays show widening of the epiphyseal line or apparent posterior and inferior displacement of the femoral head. To help determine displacement, Klein lines are drawn on the x-ray on the superior border of the femoral neck. The femoral head will be below the Klein line on the affected side, whereas a significant portion of the femoral head will be above the Klein line on the unaffected side.
Ultrasonography and MRI are also useful, especially if x-rays are normal.