Chapter 109: Slipped Capital Femoral Epiphysis

• The classic presentation of slipped capital femoral epiphysis (SCFE) is that of an obese adolescent with nonradiating, dull, aching pain in the hip, groin, thigh, or knee without a history of trauma.

• Patients with SCFE may also present with isolated thigh or knee pain.

• The traditional classification of SCFE is based on intensity and duration of symptoms into four patterns of presentation: pre-slip, acute, acute on chronic, and chronic.

• Imaging requires both lateral and AP views of the hip.

• The goals of treatment of SCFE are to prevent further slipping by stabilizing the diseased physis and preventing further growth complications.

SCFE is characterized by a displacement of the capital femoral epiphysis from the femoral neck through the physeal plate. It is one of the most common hip disorders of adolescence, with an overall. There is an overall incidence of 10.8 per 100,000.¹ The average age at the time of diagnosis is 11 to 12 years for girls and 12.5 to 13.5 years for boys.^1–3 SCFE is more common in males than females with a ratio of approximately 1.5 to 1 and is more frequent in African Americans and Hispanics^1,3 Obesity is a significant risk factor in the development of SCFE as approximately one-half of children who acquire a SCFE have weights at or above the 95th percentile.^4,5 About 10% to 20% of children have bilateral slippage at presentation, and another 10% to 20% are diagnosed subsequently with a second slip during adolescence.^6,7

The two most common features of the presentation of SCFE are pain and altered gait. The classic presentation is that of an obese adolescent with a complaint of nonradiating, dull, aching pain in the hip, groin, thigh, or knee without a history of trauma. However, 15% of patients present with isolated thigh or knee pain.⁸ SCFE is more likely to be missed at the initial visit if hip pain is absent or thigh pain is present.

SCFE has traditionally been classified based on intensity and duration of symptoms into four patterns of presentation: pre-slip, acute, acute on chronic, and chronic.

Pre-slips refer to those with pain but without discernable displacement of the epiphysis.

Children with acute slips have symptoms of less than 3 weeks duration. The acute presentation is often associated with trauma. The symptoms are characterized by the onset of severe pain, external rotational deformity and limitation of motion of the hip, shortening, and frequently inability to bear weight. Active motion of the hip is severely limited by muscle spasm, and the patient complains of intense pain with any attempt at passive motion.

The acute on chronic presentation occurs when a patient with an extended history of symptoms, and signs of chronic SCFE presents with an acute increase in pain and loss of motion of the affected hip. Chronic SCFE is the most frequent pattern of presentation and is characterized by vague, intermittent symptoms over a protracted period, generally considered to be longer than 3 weeks.

Patients with chronic SCFE generally have limited any strenuous and sporting activities due to discomfort. They often complain of dull pain often exacerbated by walking or going up stairs and does not resolve quickly with rest. Patients often complain of knee or thigh pain rather than hip pain. On physical examination the patient will usually have altered gait. If a unilateral SCFE is present, the patient will have an antalgic gait (pain on weight bearing of the affected side so that the patient takes a quick, short step on the involved side and a long step on the other side). If bilateral SCFE's are present, the patient will have more of a waddling gait. On inspection, the affected leg is in an externally rotated position and may be shortened. Disuse atrophy of the upper thigh and gluteal muscle may be present. On palpation, there may be tenderness over the hip anteriorly. Despite a complaint of pain to the general area of the knee, there will be no localized tenderness to palpation and the remainder of the knee examination is normal. Range of motion is decreased primarily on internal rotation, abduction, and flexion but may be painful in all directions. The degree of restriction of range of motion is dependent upon the severity of the slip. When the hip is passively flexed from an extended position, the thigh of the affected limb abducts and externally rotates. This finding is very suggestive of SCFE.⁹

SCFE has also been classified based on biomechanical stability as “stable” or “unstable.”¹⁰ A slip is stable if walking and weight-bearing is possible with or without crutches. Unstable slips are those in which the child has such severe pain that walking is not possible even with crutches. Patients with unstable slips may have forewarning symptoms such as vague pain in their hips, thighs, or knees for weeks to even months prior to sustaining an unstable SCFE.¹¹

Lastly, SCFE can be classified by severity and graded as mild, moderate, or severe. A mild slip is one in which the displacement of the epiphysis is less than one-third of the diameter of the femoral neck. A moderate slip is displacement of more than one-third but less than one-half of the diameter of the neck. A severe slip is displacement of more than one-half of the diameter of the neck.

The term SCFE is actually a misnomer because the epiphysis remains in normal position in the acetabulum while the femur distal to the physis (growth plate) displaces, most commonly anterolaterally and superiorly.¹² This displacement of the proximal femoral metaphysis gives the appearance of the epiphysis being displaced posteriorly and inferiorly. The cause of SCFE is the application of stress to the most proximal femur in an amount that exceeds the strength of the capital femoral physis.¹³ The underlying etiology of SCFE remains unknown but likely is secondary to multiple factors that result in a weakened physeal plate that is loaded with higher-than-normal shear stress leading to the slippage. Proposed contributing factors include trauma (especially in acute and acute on chronic slips), obesity, inflammatory changes that weaken the physeal plate, genetic predisposition, and endocrine and metabolic disorders.

The majority of cases of SCFE occur during the adolescent growth phase (a period of significant hormonal change). One should especially consider endocrine disorders when a patient less than 10 years of age or over 15 to 16 years of age presents with SCFE.⁹ The most common endocrinopathy associated with SCFE is hypothyroidism, followed by growth hormone deficiency.¹⁴ Because severe hypothyroidism often may go undiagnosed, some authors recommend a screening T4, TSH, and bone age (hand radiograph) for all newly diagnosed patients with SCFE.¹⁵ Other endocrine and metabolic disorders associated with SCFE include pituitary adenoma, gigantism, craniopharyngioma, hypopituitarism, transient hyperthyroidism, hyperparathyroidism, hypogonadism, Klinefelter's syndrome, renal osteodystrophy, and vitamin D deficiency or dysfunction.⁹

The vast majority of cases of SCFE can be diagnosed with hip radiographs. In as many as 25% of missed cases, radiographs are either misinterpreted or inadequate.¹⁶ The minimum radiographic examination consists of an anteroposterior (AP) view and lateral projections of both hips. Bilateral views are obtained to allow for comparison to identify subtle findings and because of the high incidence of bilateral disease.

On the AP view, there may be mild widening, lucency, and irregularity of the physis.¹⁷ The most reliable sign of an early slip may be blurring of the junction between the metaphysis and the growth plate (Fig. 109-1).¹⁸ The height of the epiphysis may be diminished because the femoral head has rotated posteriorly. With this posterior slippage of the femoral head, the portion of the head that is located behind the metaphysis may be projected as a semicircular area of increased density on the proximal part of the neck called the “blanch sign of Steel” (Fig. 109-2).¹⁹ In the normal AP view, a line drawn along the superior femoral neck intersects the lateral portion of the femoral head (Klein's line).²⁰ In a patient with SCFE, the line passes outside of the epiphysis or just at its superior edge (Fig. 109-3). There may be a smaller portion of the femoral head above the line compared to the contralateral hip (assuming the opposite hip is normal). Green et al.²⁰ recommend a modification of Klein's line to improve sensitivity. Using the modified Klein's line, a physician should consider the diagnosis of SCFE if the epiphyseal width lateral to Klein's line differs by 2 mm or more between hips.

Lateral projections are necessary, as the diagnosis cannot be made on the AP film in approximately 10% to 15% of cases.¹⁸ Lateral films include either the frog-leg lateral or the cross-table lateral radiographic view (true lateral view). The frog-leg lateral often demonstrates the posterior displacement and step-off of the epiphysis on the femoral neck. In cases of acute onset of pain, the lateral view should be done cross-table to avoid displacing the physis while flexing and abducting the femur to obtain a frog-leg lateral view.¹³ This cross-table lateral radiographic view also helps to better define the extent of posterior displacement of the femoral epiphysis than the AP view. However, this view is technically difficult to obtain in the extremely obese patient.

Ultrasonography may aid in the diagnosis, staging, and follow-up management of SCFE.²¹ CT scanning has been used as a tool for standardizing the assessment of slip severity in chronic slips. However, it has not been shown to be superior to plain films.²² MRI has been suggested as a means to detect early, radiographically occult but symptomatic pre-slips and as a tool for screening for bilateral involvement, especially in high-risk patients such as those with endocrinopathies.²³ MRI and bone scan are useful adjuncts in the evaluation of children with SCFE who are at risk for osteonecrosis.

Once the diagnosis of SCFE has been made, no further weight bearing should be allowed. Patients with chronic untreated symptoms for a number of weeks (stable slips) have had catastrophic progression to an unstable slip with a poor outcome.²⁴ The use of crutches or a wheelchair and bed rest is, therefore, recommended to prevent further slipping or falling and converting a stable to an unstable slip. Prompt orthopedic referral is mandatory. Acute or unstable slips should be admitted to the hospital for treatment.

The goals of treatment of SCFE are to prevent further slipping by stabilizing the diseased physis (thereby reducing the incidence and onset of osteoarthritis at the affected hip) and to avoid complications such as osteonecrosis (avascular necrosis) of the femoral head, chondrolysis (narrowing of the joint space and loss of articular cartilage), and femoroacetabular impingement (abnormal connection between the proximal femoral metaphysic and the acetabular rim). Generally, the treatment of SCFE is operative. The gold standard for stabilization, regardless of severity, is the use of the cannulated screw, with one or two screws placed in the center of the epiphysis.²⁴ Closed reduction of an acute slip before pinning is controversial. Decisions regarding timing of surgery and operative technique should be left to the discretion of the orthopedic surgeon.

Osteonecrosis or avascular necrosis occurs with acute slips. It occurs at higher rates with more severe slips.²⁵ An unstable SCFE (i.e., epiphysis is displaced from the metaphysis or the patient is unable to bear weight even with crutches at the time of presentation) has been identified to be the most useful predictor of future avascular necrosis.²⁶ It does not occur in untreated chronic slips but can be a complication of operative pinning. When a patient complains of persistent pain and stiffness of the hip following reduction and pinning of the acute SCFE, avascular necrosis should be suspected.⁹ A bone scan can confirm this diagnosis.

Chondrolysis may occur with an untreated SCFE or may present postoperatively. Clinically it presents with flexion deformity of the hip with restriction of range of hip motion in all planes.⁹ Femoroacetabular impingement is believed to be caused by residual abnormal morphology with prominence of the femoral metaphysis abutting the acetabular rim. It may be symptomatic and can lead to osteoarthritis of the affected hip.^27–29 Even mild slips are at risk for developing femoroacetabular impingement.³⁰ If avascular necrosis, chondrolysis, or femoroacetabular impingement is suspected, the patient should be referred to an orthopedic surgeon for further management.

Approximately 30% to 60% of patients with SCFE have at initial presentation, or later develop, bilateral involvement.^6,7 Patients with underlying endocrinopathies have an even higher risk of bilateral involvement, ranging from 60% to as much as 100% of the time.^14,15 Thus, all patients with unilateral involvement, especially those with endocrinopathies, should be followed closely for the subsequent development of contralateral involvement to prevent delay in diagnosis. A reduction in body mass index in obese patients may reduce the risk of subsequent contralateral SCFE.³¹ The clinician should keep in mind that second slips are often asymptomatic, establishing the need for scheduled return visits for repeat examinations. In almost 90% of the patients who initially had unilateral SCFE's but develop subsequent contralateral slips, the second slip was diagnosed within 18 months after the diagnosis of the first slip.⁹ Thus, careful follow-up in the first 1 to 2 years following initial diagnosis of unilateral SCFE is essential but should continue until the end of growth. Despite the fact that many sequential slips are asymptomatic, patients should also be educated about the vague presenting symptoms and instructed to seek medical attention immediately if such symptoms develop. Baghdadi and colleagues³² found the contralateral slip in the majority of patients to be mild. However, about one-third of the contralateral hips were painful, and one patient had an unstable slip. Prophylactic pinning of the contralateral hip in patients with a unilateral slip remains controversial.^33,34

With increasing severity of the slip, there is a higher incidence of premature degenerative arthritis, chondrolysis, and avascular necrosis.³⁵ The development of femoroacetabular impingement appears to be an exception, as this complication is not related to severity of the slip with even mild slips at risk.³⁰ Overall, mild slips do carry an excellent long-term prognosis.² For this reason, early diagnosis is a critical factor in assuring the best possible prognosis. Avascular necrosis is the most serious complication of SCFE carrying the worst prognosis. The natural history of avascular necrosis after treatment of SCFE is that of gradual degenerative changes for which reconstructive surgery is often required in adolescents and early adulthood.³⁶