X-ray showing a slipped capital femoral epiphysis, before and after surgical fixation. https://en.wikipedia.org/wiki/Slipped_capital_femoral_epiphysis
Overview
Slipped capital femoral epiphysis, or SCFE, is one of the most common orthopedic hip disorders affecting adolescents. Specifically, a SCFE is the anterior and superior displacement of the femoral neck metaphysis in relation to the capital epiphysis. This slip occurs through the physis, or growth plate resulting in an unstable and very painful hip.
Etiology
While the precise cause of SCFE remains unclear, it is believed to be multifactorial. Increases in BMI as a result of childhood obesity likely promote a shear stress across a physis that is weakened by the hormonal milieu associated with normal childhood growth spurts. It is believed that testosterone weakens the physis and estrogen acts to strengthen the physis thus explaining the difference in incidence between girls and boys. These disturbances in the normal hormonal balance in the setting of increased mechanical stress present an increased risk of developing a SCFE. In addition, SCFE is also occasionally associated with other endocrine disturbances like hypothyroidism, pituitary disorders, and renal failure. Thus, one can conclude that SCFE most commonly occurs in children with some alteration or disturbance of normal growth. Trauma is only noted to be a cause in 10% of cases.
Epidemiology
The most recent study in 2010 suggests that the incidence of SCFE is approximately 8.3 unilateral cases and 0.5 bilateral cases per 100,000 children. Roughly 19% of patients go on to develop a slip in the contralateral hip at a mean of 166 days after the first slip.
SCFE most often occurs in an obese prepubertal male. Sex and race are important considerations as males are 1.5 times more likely to develop a SCFE than females, African American children are nearly 4 times more likely compared to Caucasians, and Hispanics are 2.5 times more likely compared to Caucasians. The average age of onset is 12.1 + 1.8 years of age. Some cases of SCFE occur in children younger than 10 years of age or older than 16 years of age. These children are atypical in that they are below the 50th percentile in weight and 10th percentile in height.
Symptoms
SCFE can be a difficult diagnosis to make because the symptoms can often be vague and the onset can be insidious. Patients typically present with a limp and either knee, hip, thigh, or back pain or some combination thereof. Pain is a common presenting complaint in SCFE. Pain can often be referred. Patients that never complain of hip pain, but rather knee or groin pain, should still be evaluated for SCFE. In fact, approximately 15% of patients present only with thigh or knee pain. Patients also often present with a limp or refusal to bear weight on the affected leg. The limp is an antalgic gait with a positive Trendelenberg sign. Patients may also report decreased range of motion.
Diagnosis
The diagnosis of SCFE is based on the symptoms at presentation, clinical suspicion, and careful examination of radiographs. A careful physical exam is important. Examination will typically demonstrate an obese body habitus or very tall and slender habitus with a history of recent growth spurt in the case of atypical SCFE.
Gait examination will reveal an antalgic gait with a positive trendelenberg (unilateral SCFE) or waddling gait (bilateral SCFE). Foot is usually turned out. Examination of the hip ROM will reveal decreased internal rotation , flexion, abduction, and obligatory external rotation when the hip is passively flexed to 90 degrees.
In any case where SCFE is suspected, AP radiographs of the pelvis and a frog leg lateral view of the affected hip must be obtained. The frog leg lateral view should be avoided in patients with an acute slip (slip occurs suddenly, with severe pain, child is unable to bear weight on affected limb), as further slipping of the epiphysis is possible. A cross table lateral view is the best alternative in these patients. SCFE can be as subtle as a widening of the epiphysis without apparent slippage (pre-slip). These cases are best evaluated with MRI. On an AP film, a line drawn along the superior femoral neck, Klein’s line, should normally intersect a portion of the femoral head. In a patient with SCFE, the femoral head will drop below this line. In a frog leg lateral view, the slip is generally more obvious, with the femoral head displacing posterior and medial to the femoral neck. Studies have shown that frog leg lateral views detect approximately 15% more cases of SCFE than AP views. Equivocal plain films with a high suspicion for SCFE are best evaluated with MRI.
Treatment
As soon as a SCFE is diagnosed, the patient should be made completely non-weight bearing and an urgent orthopedic consultation is mandatory. The slip can often progress if left untreated. The goals of treatment are to prevent any further slippage and to stimulate early physeal closure, while avoiding any possible complications.
The usual technique for repair of a SCFE is in situ pinning of the epiphysis without reduction with one or two cannulated screws depending on whether the slip is determined to be stable or unstable. Outcome after surgical repair is generally good, but depends on the degree of the slip. The prophylactic pinning of contralateral hips in the patient presenting with a unilateral SCFE remains controversial but is being considered in cases caused by endocrine disease.
Complications
Complications of SCFE include chondrolysis, avascular necrosis (AVN) of the femoral head, and osteoarthritis. Chondrolysis is the dissolution of cartilage on the articular surface causing pain and decreased ROM. Chondrolysis is now a relatively rare complication but has been in a wide range 1.8-55% of cases with incidence increasing in very unstable slips. Its occurrence is decreasing with improved fixation techniques. AVN is caused by compromise of the lateral epiphysial vessels from acute slip or placement of a pin in the posterior-superior quadrant of the capital epiphysis.
It is nearly unheard of in stable slips but can complicate from 3-84% of unstable SCFE cases. Osteoarthritis is another common complication that is more likely to develop in cases of more severe slip or as a post-surgical complication. These complications should be considered in cases of recurrent pain in the post-operative patient or in the patient with prior SCFE. These complications are easily evaluated with plain radiography or MRI in cases of questionable osteonecrosis that has not appeared on plain films.
References
- Kienstra et al. “Slipped Capital Femoral Epiphysis.” www.uptodate.com. Last update June 7, 2011. Accessed March 26, 2012.
- Peck D. Slipped Capital Femoral Epiphysis: Diagnosis and Management. American Family Physician. August 2010.