. Slipped capital femoral epiphysis. Musculoskeletal Medicine for Medical Students. In: OrthopaedicsOne - The Orthopaedic Knowledge Network. Created Feb 19, 2012 13:31. Last modified May 07, 2012 14:54 ver.7. Retrieved 2017-09-19, from http://www.orthopaedicsone.com/x/noG8B.
Slipped capital femoral epiphysis (SCFE) occurs when the femoral head is displaced from the femoral neck and shaft along the physis (growth plate). Since the femoral head is secured by the acetabulum, the neck and shaft slip relative to the head. A SCFE is considered stable if the patient can bear weight on the affected extremity or unstable if the patient is unable to bear weight. The slip can be further categorized as acute, acute-on-chronic, or chronic.
This condition is classically described in obese adolescent patients. Children with metabolic abnormalities can be at increased risk as well. 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. Children who fit this clinical picture should be considered to have SCFE until proven otherwise.
SCFE patients sometimes identify an inciting event for their symptoms, though these episodes rarely involve significant trauma. Symptoms may have persisted for days or weeks prior to the child’s initial presentation. Both hips must be evaluated, as 20% of SCFE cases initially present with bilateral slips that may be missed if the patient’s complaints only seem to point to the more symptomatic slip.
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, termed “obligate external rotation.” The child may have a limping 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.
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.
SCFE has an annual incidence of 2 to 13 per 100,000 and is 1.4 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 51% to 77% 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. Underlying endocrine disorders are thought to be accountable for 5% to 8% of SCFE cases.
Pathology and pathophysiology
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.
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.
SCFE should be suspected in all children with 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.
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, 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.
Radiographic and laboratory findings
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 most reliable 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, 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.
(Image courtesy of radiopaedia.org)
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°), moderate (30° to 60°), or severe (greater than 60°).
Though additional imaging is generally unnecessary, magnetic resonance imaging (MRI) can detect “pre-slips” in patients with strongly suspected SCFE but normal x-rays. MRI is also helpful in early detection of osteonecrosis. 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. Bone scans may aid in assessment of the femoral head in cases of osteonecrosis.
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.
Both stable and unstable SCFE require surgical management in order to prevent slip progression. While closed reduction and spica casting were once discussed as options, in situ fixation is now typically advocated as the treatment of choice. While inadvertent manipulation- such as that which may occur during positioning or transfer of the patient- may not necessarily be detrimental to the child, forceful manipulation has been shown to increase the risk of osteonecrosis and must be avoided.
In situ fixation is most commonly achieved with the use of a cannulated screw under fluoroscopic guidance. The screw 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 pin penetration through the posterior femoral neck and osteonecrosis while increasing the surgeon’s ability to achieve good screw purchase in the femoral head.
Many authors do not believe that any potential biomechanical advantages of multiple-screw constructs outweigh the increased risk of pin penetration and osteonecrosis. Nonetheless, a second screw may provide significant stability in unstable SCFE. A currently controversial topic is prophylactic pinning of the contralateral hip. Many surgeons note the high rate of bilateral SCFE as well as the long-term risk of arthritis in SCFE patients while others point to the potential risks of prophylactic surgery in an unaffected hip. However, prophylactic fixation is performed more commonly in SCFE patients with endocrinopathies or history of pelvic radiation.
Alternatively, bone graft epiphysiodesis, proximal femoral osteotomy, or femoral neck osteoplasty may be considered in select patients.
Several series have reported good or excellent outcomes in 90% to 95% of SCFE patients treated with in situ fixation. In series with less favorable results, outcomes seem to worsen with increasing slip severity. 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, it is seen in up to 58% of 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.
The psychosocial and economic effects of SCFE have not been well examined. Some studies of adult total hip arthroplasty patients suggest that 40% of these individuals initially suffered some type of pediatric hip disorder. Along these lines, SCFE may have functional and financial implications in adulthood.
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).
On plain radiographs, the relationship between the epiphysis and the rest of the proximal femur in SCFE is sometimes described as “ice cream falling off the cone”.
Slipped capital femoral epiphysis, pediatric hip, osteoarthritis, osteonecrosis
Skills and competencies
Perform thorough physical examination of the hip
Identify risk factors for SCFE
Recognize SCFE on plain radiographs
Identify potential complications of SCFE