Slipped capital femoral epiphysis (SCFE) is the most common hip abnormality presenting in adolescence and is a primary cause of early osteoarthritis. SCFE occurs in 10.8 cases per 100,000 children and usually occurs in children 8 to 15 years of age.  It is primarily associated with obesity and growth surges but occasionally can occur in patients with endocrine disorders such as hypothyroidism and hypogonadism. 
Unfortunately, SCFE frequently is misdiagnosed, and it has symptoms that can be misleading.  Early treatment leads to better outcome but is confounded by frequent delays in diagnosis. [4, 5] A study by Schur et al of 481 patients diagnosed with SCFE found that the average time from onset of symptoms to diagnosis was 17 weeks, with a range of zero to 169 weeks.  The pathology is localized to the proximal aspect of the femur, but symptoms may occur in the knee or thigh, thereby leading to misdiagnosis. [2, 7]
(See the image below.)
Classification and grade
SCFE is commonly classified in 2 ways: (1) as acute or chronic, or (2) as stable or unstable. The slip is classificed as acute if present for less than 3 weeks, as as chronic if present for more than 3 weeks. In the second classification, SCFE is considered stable if the patient can bear weight on the extremity without a crutch or walker; if unable to bear weight, the SCFE is considered unstable. [2, 1]
The Wilson or Southwick method can be used to measure the grade of severity of the slip in SCFE. In the Wilson method, a mild slip is epiphysis displacement that is less than one third the width of the metaphysis; a moderate slip, between one third and one half the width; and a severe slip, more than one half the width. The Southwick method uses the epiphyseal shaft angle on the frog-leg lateral radiograph, with the angle calculated by subtracting the epiphyseal shaft angle on the uninvolved side from that on the SCFE side. A mild slip is considered less than 30 degrees; moderate, between 30 and 50 degrees; and severe, more than 50 degrees. 
Radiographs are the easiest images to obtain and provide an excellent screening examination for hip pain in any patient. In patients with SCFE, advanced stages of the disease are easy to identify; however, subtle changes early in the course are more difficult to detect. Before the femoral epiphysis actually has become displaced, only a slight widening of the affected physis may be evident. 
Diagnosis is made using anteroposterior (AP) pelvis and lateral frog-leg radiographs. [8, 9, 2, 1] MRI or CT may be able to detect SCFE in early cases. Computed tomography (CT) scanning is a sensitive method of measuring the degree of tilt and detecting early disease, but it is rarely needed. CT may be performed with low doses, and reconstructions may allow viewing of the relationship of the femoral head to the metaphysis in three planes. Magnetic resonance imaging (MRI) depicts the slippage earliest, and MRI can demonstrate early marrow edema and slippage. MRI may be helpful in follow-up studies of the contralateral hip. [10, 11, 12, 13]
A metaphyseal blanch is an increase in density in the proximal metaphysis. It is presumed that metaphyseal blanch represents an attempt at healing that occurs before there is visible displacement of the epiphysis.
Diagnosis is made using AP pelvis and lateral frog-leg radiographs. Abduction of the femur for the frog-leg view may result in increased slippage and should be performed with caution. Radiologic signs include the Steel sign, which is a double density found at the metaphysis on anteroposterior radiography; widening of the physis compared with the uninvolved sign; and the epiphysis falling below the Klein line (a line drawn along the superior edge of the femoral neck that should cross the epiphysis, but in SCFE, the epiphysis falls below the Klein line). [1, 2, 8, 9, 14]
(See the images below.)
On AP radiographs, close attention should be paid to the physis. Early in SCFE, the physis may widen. Increased opacity in the metaphysis, described as blanching, may occur as an early healing response, and the epiphysis may appear smaller because it is tilted dorsally.
The lateral radiograph demonstrates slippage earliest because the slippage begins with posterior displacement and progresses with medial rotation.
The Southwick method can be used by creating an axis for the femoral neck and determining whether the epiphysis is tilted. (See the image below.) 
An additional method is to draw a line along the lateral aspect of the femoral neck on the AP view; this line, known as the line of Klein, should intersect a portion of the femoral head. 
Degree of confidence in radiographic findings of SCFE is high. When the aforementioned constellation of findings is present, false-positive and false-negative findings do not occur.
Computed tomography (CT) scanning is a sensitive method for measuring the degree of tilt and detecting disease, but it is rarely needed. Usually, CT scanning is performed only at the request of the treating physician for documenting the severity of the tilt.
Magnetic Resonance Imaging
The earliest way to detect SCFE is by using MRI. With MRI, early marrow edema and slippage can be demonstrated. This is demonstrated with increased signal on T2-weighted and water-sensitive images. MRI can be considered in patients for whom the clinical suspicion of SCFE is high and in whom the radiographs appear normal. MRI can be considered for follow-up imaging of the contralateral hip. 
Marrow edema is a nonspecific finding, and while it can indicate early bone changes in SCFE, it has numerous other causes, such as infection or even tumor. Those diagnoses are rarely considered with the proper clinical evaluation.
Ultrasonographic findings are rarely specific, and the sensitivity of sonography is unknown. Hip effusions of blood often have been reported and are suggestive of fracture.
The radionuclide bone scan is sometimes used during workup but prior to diagnosis. Accumulation of the bone scanning agents can be decreased after fixation and in patients with an acute slip and significant displacement. The decrease is usually limited to the epiphysis. The decreased accumulation is associated with increased incidence of chondrolysis.