Slipped Capital Femoral Epiphysis


Slipped capital femoral epiphysis (SCFE, pronounced “skiffy”) occurs when there is slippage of the femoral metaphysis relative to the epiphysis along the physis (growth plate). SCFE is thus technically a growth plate fracture. Because the femoral head is secured by the acetabulum, the neck and shaft slip relative to the head ( Figures 1 and 2). SCFE is most commonly (but not exclusively) seen in adolescent overweight males. SCFE is usually treated with percutaneous pin fixation, to prevent further slippage.

 
Figure 1: A slipped capital femoral epiphysis of the left hip is shown on the radiograph. (Case courtesy of Prof Frank Gaillard, Radiopaedia.org, rID: 8229)
 

Figure 2: The relationship of the femoral head to the neck after a slip, has been likened to an ice cream scoop falling off its cone.


Structure and Function

SCFE is usually seen during periods of rapid growth: in boys, between the ages of 12 and 16 and in girls, between the ages of 10 and 13. This suggests that some factor related to growth makes the growth plate susceptible. Sometimes SCFE develops gradually over several weeks or months, without overt injury; by analogy, this is a “pathological fracture” of the growth plate, again suggesting an underlying disorder of the tissue.

 

Several studies have revealed various pathologic physeal changes in SCFE, including replacement of the normal growth plate with abnormal cartilage and fibrous tissue. There may be widening of the physis along with hypocellularity and loss of columnar organization. The slip generally occurs through the proliferative and hypertrophic zones of the physis, where chondrocytes and normal components may have been replaced by ground substance. These pathologic findings seem to at least partially revert to more normal structure following fixation and stabilization of the slip.

 

In most cases of SCFE, the femoral neck and shaft slip anteriorly and rotate externally relative to the femoral head. Following this migration, impingement of the anterior femoral metaphysis may occur during hip flexion, leading to cyst formation, damage of the labrum or acetabular cartilage, and other degenerative changes.

 

The etiology of SCFE is unknown in most cases, and is thought to possibly be multifactorial. In general, the slip is caused by an inability of the proximal femoral physis to resist physiologic loads.

 

Endocrinopathies that weaken the physis are thought to be responsible for 5% to 8% of SCFE cases. These include hypothyroidism, panhypopituitarism, growth hormone deficiency, parathyroid derangements, and hypogonadism. The increased prevalence of hypothyroidism in Down syndrome suggests why SCFE is more common in these patients. However, routine screening for endocrinopathies is not recommended for all patients with SCFE. Renal osteodystrophy may also weaken the physis due to the associated secondary hyperparathyroidism.

 

A history of radiation to the hip or pelvis, genetics, and the immune system may have roles in physeal pathology as well, though the exact risks are somewhat unclear.

 

Finally, other anatomic factors that risk physeal failure place patients at risk for SCFE, especially with concomitant obesity. These include reduced femoral anteversion (or retroversion), in which a reduced neck-shaft angle positions the physis more vertically and subjects it to greater shearing forces.



Patient Presentation

The prototypical patient with SCFE is an obese adolescent male. Patients often present with hip or groin pain, limp, and decreased range of motion at the hip, though half of all children with SCFE may not complain of hip pain at all. Pain may be referred to the distal thigh or knee in some patients, since irritation of the obturator nerve at the hip refers pain to the medial aspect of the knee. Others may simply complain of altered gait.

 

Patients sometimes identify an inciting event for their symptoms, though these episodes rarely involve high energy trauma. Symptoms may have persisted for days or weeks prior to the child’s initial presentation. Both hips must be evaluated, as many cases of SCFE, as noted, initially present with bilateral disease.

 

The patient will often present with decreased internal rotation, abduction, and flexion of the affected hip. Increasing slip severity can lead to a propensity towards external rotation as the examiner flexes the hip, a motion termed “obligate external rotation.” The child may have an antalgic gait with progressive external rotation of the foot and knee. In more severe slips, the affected limb may also appear shorter than the contralateral side.

 

SCFE can be classified on presentation according to whether the patient is able to bear weight on the affected side. In a “stable SCFE, the patient is able to walk or bear weight. In an “unstable SCFE,” the patient cannot walk or bear weight. This is usually associated with a more severe slip. This classification is especially informative regarding prognosis, as stable SCFE’s have a lower risk of osteonecrosis and other complications.



Objective Evidence

Anteroposterior (AP) and lateral plain radiographs of both hips should be obtained in cases of suspected SCFE and are typically the only imaging necessary. Cross-table lateral films may be taken instead of a frog-leg lateral in cases of unstable SCFE in order to avoid further displacement or pain to the patient.

 

Frog lateral views are generally the most reliable means for detection of SCFE. As the slip progresses, it becomes evident on the AP view as well. Possible findings include widening of the physis, anterior displacement and external rotation of the femoral neck and shaft relative to the head, decreased height of the capital femoral epiphysis, and increased distance between the metaphysis and acetabular teardrop.

 

In a normal hip, part of the femoral head is intersected by Klein’s line (Figure 3), which is drawn along the lateral border of the femoral neck on a frog lateral. In SCFE, the femoral head sits “below,” or inferomedial to, Klein’s line, though the reliability of this sign has been questioned recently.

 
Figure 3. Frog lateral x-ray of a 12-year-old male with several weeks of right groin pain who was found to have right SCFE. Klein’s line is shown in green bilaterally. This line should normally intercept the lateral part of the superior femoral epiphysis, as shown on the left. If the line fails to contact bone in the epiphysis, as shown on the right, a slipped upper femoral epiphysis can be diagnosed.


The magnitude of the slip is often described in terms of femoral head displacement as a percentage of the femoral neck diameter (mild is less than 33%, moderate is 33% to 50%, and severe is greater than 50%). Alternatively, the slip angle (between the femoral epiphysis and neck) can be measured on the lateral view and described as mild (less than 30 degrees), moderate (30to 60 degrees), or severe (greater than 60 degrees).

 

Though additional imaging is generally unnecessary, magnetic resonance imaging (MRI) can detect distortion of the physis with bone marrow edema before the development of radiographically detectable SCFE. This is termed a “pre-slip” (Figure 4). Computed tomography (CT) is rarely needed, but can allow for evaluation of physeal closure in patients who present very late in the course of SCFE.

 
Figure 4: MRI can detect a slipped epiphysis even without much displacement. (Image courtesy Journal of Children's OrthopaedicsVol. 11, No. 2 https://doi.org/10.1302/1863-2548-11-160276)

 

  

Epidemiology

SCFE has an annual incidence of 2 to 13 per 100,000 and is 1.5 to 2 times more common in males. This condition typically affects boys aged 12 to 15 years and girls aged 10 to 13. It is also more common among those with higher body weights, with about half of SCFE patients at or above the 90th percentile for weight, and about 70% over the 80th percentile. The current literature suggests that more than half of children with SCFE are obese. Twenty percent of SCFE patients present with initial bilateral involvement, and another 10% to 20% develop a contralateral slip an average of 18 months after the initial one.

 

 

Differential Diagnosis

SCFE should be suspected in all children with open physes, a limp, and complaints of hip, groin, thigh, or knee pain until proven otherwise. Other conditions that may be considered include transient synovitis, Legg-Calve-Perthes disease, septic arthritis, osteomyelitis, and fracture. Various metabolic and systemic disorders may also be associated with SCFE, including obesity, endocrinopathies, renal osteodystrophy, and anatomic variation of the hip joint.

 


Red Flags

Any adolescent patient that presents with a limp and complains of pain in the hip, groin, thigh, or knee should be considered to have SCFE until proven otherwise. Specifically, complaints of thigh or knee pain merit examination of the hip, as these may otherwise result in delayed diagnosis, misdiagnosis, and unnecessary imaging or procedures. Additionally, both hips should be examined closely so as not to miss potential bilateral cases. Diagnosis of SCFE in pre- or post-pubertal patients should raise suspicion for underlying metabolic or systemic abnormality. Inability to bear weight on the affected extremity may indicate an unstable SCFE, which requires more urgent intervention.

 


Treatment Options and Outcomes

Both stable and unstable SCFE require surgical management in order to prevent slip progression. In situ fixation is typically performed in most cases. Forceful manipulation is never recommended, as this may increase the risk of osteonecrosis. This is especially true with stable slips, which by definition cannot be easily reduced.

 

In situ fixation is most commonly achieved with the use of one or two cannulated screws under fluoroscopic guidance. One screw is typically sufficient for stable slips (Figure 5), but two are sometimes used for unstable cases in order to provide increased fixation strength. When using a single screw, it should be inserted perpendicular to the physis and in the center of the epiphysis in both the AP and lateral planes. This “center-center” location reduces the risk of penetration through the posterior femoral neck and osteonecrosis while increasing the surgeon’s ability to achieve good screw purchase in the femoral head.

 
Figure 5. Post-operative frog lateral x-ray of the patient in Figure 3 demonstrating in situ fixation of right SCFE.

 

Prophylactic pinning of the contralateral (normal-appearing) hip is controversial. In brief, if the contralateral hip is pinned before it slips, by definition there is no displacement. The presence of displacement is thought to be associated a higher risk of degenerative joint disease, such that this preventative step may be helpful. On the other hand, there are risk of complications from prophylactic surgery in an unaffected hip, and if that surgery is indeed not necessary – something that will never be known—those risks were assumed in vain. Prophylactic fixation is performed more commonly in SCFE patients with significant growth remaining, endocrinopathies, or history of pelvic radiation; that is, in patients with a higher risk of developing a contralateral slip.

 

For severe slips, in situ pinning may result in residual deformity, impingement, and degenerative changes. Additionally, sufficient stabilization of a severe slip with in situ pinning is difficult because it is not always possible to obtain the proper screw trajectory. Accordingly, closed reduction maneuvers have been described for severe, unstable SCFE. These should only be performed by experienced surgeons and never in a forceful manner. The goal of this manipulation is not anatomic alignment, but sufficient reduction to allow more appropriate screw trajectory. While outcomes studies suggest that osteonecrosis is associated with closed reduction maneuvers, it is unclear whether this risk is truly due to the reduction or rather the underlying severe slip itself. Open procedures are technically demanding operations and usually require a trochanteric osteotomy to visualize and correct the deformity. Even in experienced hands, there is a risk of osteonecrosis and other post-operative complications. Thus treatment of these severe, unstable slips remains a matter of debate.

 

Several series have reported good or excellent outcomes in 90% to 95% of patients treated with in situ fixation. In series with less favorable results, outcomes seem to worsen with increasing slip severity and longer follow-up. Osteoarthritis is a common long-term consequence of both treated and untreated SCFE due to the anatomic and biomechanical changes that damage the articular cartilage of the hip joint. More severe slips appear to be at risk for earlier onset and increased severity of osteoarthritis.

 

Two potential complications of in situ fixation are osteonecrosis and chondrolysis. Osteonecrosis may be iatrogenic or the result of an unstable slip itself. While stable slips rarely lead to this complication, osteonecrosis is seen frequently (about 55% of cases) with unstable cases. Chondrolysis can be caused by unrecognized pin penetration. Patients with osteonecrosis or chondrolysis tend to have poor outcomes and early osteoarthritis. Other complications include screw failure or impingement, slip progression, leg length discrepancy, and fracture of the proximal femur.

 


Risk Factors and Prevention

Though the specific cause of SCFE is often unknown, a number of conditions are thought to increase the risk of a slip. These include obesity, endocrinopathies, renal osteodystrophy, radiation, and anatomic variations at the hip joint. Children with Down syndrome are also at elevated risk due to the higher prevalence of hypothyroidism in this population. SCFE is 6 to 8 times more common in patients with an endocrine abnormality as well as those with renal osteodystrophy. An underlying metabolic or systemic disorder should be considered in SCFE patients who are younger than 8 years, older than 15 years, or underweight.

 

 

Miscellany

Exam writers typically describe an acute SCFE case as an obese adolescent who complains of a painful limp following minor trauma or activity (i.e., while playing baseball).

 

Exam writers also expect you to recognize SCFE on the differential diagnosis of knee pain in the case of a “classic SCFE patient.”

 

Some studies of adult total hip arthroplasty patients suggest that 40% of these individuals initially suffered some type of pediatric hip disorder, SCFE chief among them.

 

Slipped capital femoral epiphysis, pediatric hip, osteoarthritis, osteonecrosis

 


Skills

Perform a thorough physical examination of the hip. Identify risk factors for SCFE. Diagnose SCFE on plain radiographs. Identify potential complications (osteonecrosis & chondrolysis)