Etiology and Epidemiology
Slipped capital femoral epiphysis (SCFE) is a common adolescent hip disorder that is an orthopedic emergency. The incidence is 10.8 per 100,000, and it is slightly higher in males. African-American and Hispanic populations are at higher risk. Approximately 20% of patients with SCFE will have bilateral involvement at presentation, and another 20% to 40% may progress to bilateral involvement. The average age is 10 to 16 years, with a mean of 12 years in boys and 11 years in girls. Additional risk factors for SCFE include obesity, trisomy 21, and endocrine disorders (hypothyroid, pituitary tumor, growth hormone deficiency).
SCFE is classified as stable or unstable. Unstable patients refuse to ambulate. Stable patients have an antalgic gait. SCFE can also be characterized as acute (symptoms less than 3 weeks) or chronic (symptoms over 3 weeks). Acute-on-chronic SCFE is seen when more than 3 weeks of symptoms are accompanied by an acute exacerbation of pain and difficulty/inability to bear weight.
The presentation is variable, based on severity and type of slip. Patients will often report hip or knee pain, limp or inability to ambulate, and decreased hip range of motion. There may or may not be a traumatic event. Any knee pain should trigger an examination of the hip, as hip pathology can cause referred pain to the anterior thigh and knee along the obturator nerve. The patient usually holds the affected extremity in external rotation. As the hip is flexed, it will progressively externally rotate. There is usually a limitation of internal rotation, but there may also be a loss of flexion and abduction. If the patient can bear weight, it is typically an antalgic gait with the affected leg in external rotation. It is important to examine both hips to determine bilateral involvement.
Anteroposterior and frog-leg radiographs are indicated. Patients with known SCFE or with a high index of suspicion should not undergo frog-leg lateral radiographs. Instead, a cross table lateral radiograph reduces the risk of iatrogenic progression. The earliest sign of SCFE is widening of the physis without slippage (preslip condition). Klein’s line is helpful in assessing the anteroposterior radiograph for SCFE. The slippage can be classified radiographically as type I (0-33% displacement), type II (34-50%), or type III (>50%). The likelihood of complications increases with degree of displacement.
Patients with SCFE should be immediately made non-weight bearing and referred to a pediatric orthopedist. The goal is to prevent further slippage, enhance physeal closure, and minimize complications, which is usually accomplished with internal fixation in-situ with a single cannulated screw. More severe cases may require osteotomy or bone graft epiphysiodesis to realign the femur. There is controversy surrounding the prophylactic fixation of the nonaffected side. Assessment for endocrine disorders is important, particularly in children outside the range of 10 to 16 years of age.
The two most serious complications of SCFE are chondrolysis and avascular necrosis. Chondrolysis is destruction of the articular cartilage. It is associated with more severe slips and with intra-articular penetration of operative hardware. This can lead to severe osteoarthritis (OA) and disability. Avascular necrosis occurs when there is a disruption of the blood supply to the capital femoral epiphysis. This usually happens at the time of injury, but may occur during forced manipulation of an unstable slip. Avascular necrosis may occur in up to 50% of unstable SCFEs and may lead to OA.