Slipped Capital Femoral Epiphysis

Functional Classification

The most useful and popular current classification is that of stable and unstable slip, based on the patient’s ability to bear weight. The patient with a “stable” slip is able to bear full or partial weight, with or without crutches. The patient with an unstable slip presents like an acute femoral fracture and is unable to bear any weight on the extremity. If the patient can ambulate without weight bearing using crutches, Loder suggests that this is not to be classified as unstable. The presence of prodromal symptoms is not relevant to the classification.

One must remember that the Loder classification is a clinical classification and may underestimate the actual instability of some SCFE. Evaluating physeal disruption and stability at the time of open surgery, Ziebarth and colleagues found that the Loder classification had a sensitivity of 39% and a specificity of 76%.

Classification Based on Onset of Symptoms

For many years SCFE was classified as acute, chronic, or acute-on-chronic. An acute SCFE has been characterized as one occurring in a patient with prodromal symptoms for 3 weeks or less, and presents as a sudden, fracture-like episode occurring after usually minor trauma. The patient is in severe pain and either cannot ambulate or is able to do so only with great difficulty. Radiographs demonstrate little or no femoral neck remodeling changes typical of chronic SCFE ( Fig. 15.1A ). A traumatic Salter 1 type of fracture separation of the capital epiphysis occurs with much greater trauma and without prodromal symptoms. In these the femoral head may be dislocated out of the hip capsule and the femoral head almost invariably is avascular.

Chronic SCFE is the most frequent form of presentation. Typically, an adolescent presents with a few months’ history of vague groin pain, upper or lower thigh pain, and a limp. In an international study by Loder, 85% of 1630 children with 1993 slipped epiphyses had chronic symptoms, and 15% had acute slipped epiphysis, as defined as the child’s presenting with symptoms beginning less than 3 weeks prior. Radiographs of patients with chronic SCFE show a variable amount of posterior migration of the femoral epiphysis and remodeling of the femoral neck in the same direction (see Fig. 15.1B ). Thus, the upper end of the femur develops a “bending of the neck,” as described by Müller. The clinical symptoms, physical findings, and anteroposterior (AP) radiographic features especially may be sufficiently minor that the unwary physician fails to make the proper diagnosis.

The acute-on-chronic slipped epiphysis is one in which prodromal symptoms have been present for more than 3 weeks with a sudden exacerbation of pain and inability to walk. Radiographs show evidence of both femoral neck remodeling with epiphysis displaced beyond the remodeling point of the femoral neck (see Fig. 15.1C ).

Morphologic Classification

SCFE may also be categorized by the degree of displacement of the capital femoral epiphysis on the femoral neck. Several methods for categorizing slip based on the extent of displacement exist. Southwick recommended measuring the femoral head-shaft angle on AP ( Fig. 15.2A ) or frog-leg lateral views (see Fig. 15.2B ). By this method, mild slips are ones in which the head-shaft angle differs by less than 30 degrees from the normal contralateral side. In moderate slips, the angle difference is between 30 and 60 degrees, and in severe slips the angle differs by more than 60 degrees from the contralateral normal side. When the contralateral hip is affected or not assessed, the femoral head-shaft angle of the affected hip is calculated from normal values for this angle; according to Southwick, these normal values are 145 degrees on the AP view and 10 degrees posterior on the frog-leg lateral view. Guzzanti and Falciglia and others have pointed out that, because of the three-dimensional nature of the deformity of slipped epiphysis and inconsistencies of patient positioning for frog-leg lateral radiographs, measurement of the femoral head-shaft angle on this view is subject to substantial error. Head-shaft or head-neck angles can be obtained either from true lateral radiographs or from specifically positioned, modified lateral radiographs (Billing ^{, , ,} or Dunlap techniques). The head-neck angle can be determined most accurately and reproducibly on CT scans of the head and neck ( Fig. 15.3 ), ^, but this method is not routinely used because most patients do not undergo CT.

Mechanical Factors

A number of features of the adolescent hip in general and of patients with slipped epiphysis in particular make it likely that mechanical causes are at least partly responsible for slipped epiphysis. Three important features of the predisposed hip contribute to or may be the primary cause of slipped epiphysis: (1) thinning of the perichondral ring complex with maturation, altering the mechanical strength of the physis, periosteum, and perichondral ring; (2) relative or absolute retroversion of the femoral neck; and (3) a change in the inclination of the adolescent proximal femoral physis relative to the femoral neck and shaft. ^d

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Endocrine Factors

The stereotype of an obese, hypogonadal male (the so-called adiposogenital syndrome) presenting with chronic bilateral slipped epiphyses has long stimulated the thought that some alteration in the balance of thyroid, growth, and sex hormones was the cause of slipped epiphysis. ^, Evidence of hormonal alteration in most patients, even those fitting this image, is lacking. ^{, , , ,} An “age-weight” test has been described to determine the likelihood of atypical SCFE and the need for further diagnostic investigation. Patients younger than 10 years of age or older than 16 years were found to be four times more likely to have an atypical SCFE. For patients of the same age, those below the 50th percentile for weight were more than eight times more likely to have an atypical SCFE. Some patients do have an endocrine abnormality, the most common being hypothyroidism (slips can occur either before or during replacement therapy), growth hormone deficiency (slips usually occur during or after replacement therapy), and chronic renal failure (due to uncontrolled secondary hyperparathyroidism).

An endocrinologic cause for slipped epiphysis has long been suspected, based on the common association of this condition with obesity and, at least in boys, hypogonadal features (the so-called adiposogenital syndrome), and the fact that the condition most frequently manifests during the adolescent growth spurt. Furthermore, slips are known to occur in patients with known endocrine abnormalities, most commonly hypothyroidism (treated or not), ^e

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abnormalities treated by growth hormone administration, ^f

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and chronic renal failure. ^g

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SCFE has also occurred in patients with prior pelvic irradiation, ^h

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Rubinstein-Taybi syndrome, Klinefelter syndrome, and rarer endocrinopathies, such as primary hyperparathyroidism ^{, ,} and panhypopituitarism associated with intracranial tumors. ^, One study showed that slips developed in hypothyroid patients both before and during replacement therapy, whereas in growth hormone-deficient patients a slipped epiphysis developed during or after growth hormone replacement therapy. Sixty-one percent of the patients with these disorders had or developed bilateral slips. Thus prophylactic pinning of the normal contralateral side must be strongly considered in endocrinopathy-associated slipped epiphysis. Blethen and Rundle found that the risk for development of SCFE in patients receiving growth hormone treatment for idiopathic short stature was approximately the same as that reported in the general population but was significantly higher in patients with growth hormone deficiency, Turner syndrome, or chronic renal insufficiency (91 per 100,000 in this study).

Slipped epiphysis associated with chronic renal insufficiency is thought to be secondary to uncontrolled secondary hyperparathyroidism. Loder and Hensinger noted that 95% of slips associated with chronic renal failure were bilateral, and almost all of these presented simultaneously. Approximately 50% of cases were treated conservatively by medical management of the renal disease, including renal transplantation, whereas the other 50% required surgery for the slip. Because there was a relatively high incidence of slip progression after surgical treatment (12 of 21 hips), monitoring of the hips must continue until skeletal maturity in these patients.

To summarize, most patients with SCFE prove to be normal by current endocrinologic evaluations, however, and screening for abnormalities is not warranted unless clinical suspicion exists based on the presence of signs and symptoms other than obesity. In these patients, who constitute the vast majority of those with slips, it seems plausible that mechanical factors, including femoral retroversion, thinning of the perichondral ring complex with adolescent maturation, obesity, and some as yet unidentified hormonal or biochemical factor that results in weakening of the proximal femoral physis combine to make the proximal femoral physis more susceptible to shearing forces, which in turn cause the actual displacement of the physis.

Stable, Chronic Slipped Capital Femoral Epiphysis

In stable, chronic SCFE, the presenting complaint is usually pain in the region of the groin, which may be referred to the anteromedial aspect of the thigh and knee. In some patients, complaints of pain are exclusively or predominantly localized to the lower thigh or knee; this localization results in the continued problem of a delayed or incorrect diagnosis. ^,

Primary care physicians and orthopaedists must be ever mindful of the prevalence of slipped epiphysis in the adolescent population. A high index of suspicion is critical due to the indolent nature of complaints in patients with stable slips and the propensity for complaints of pain to be localized to the distal thigh or knee. The adage that any child or adolescent who presents with complaints of pain in the knee region must first undergo careful examination of the hip, including radiography if necessary, before examination of the knee, is still true. Vague symptomatology can lead to a delay in diagnosis, which in turn can lead to poor outcomes. Schur and colleagues demonstrated no improvement in the speed of diagnosis over a 10-year period. The average time from the onset of symptoms to the time of diagnosis was 17 weeks. The time from initial evaluation to the time of diagnosis was significantly greater if the child was first evaluated by a primary care provider. Similarly, Hosseinzadeh and colleagues reported an average time of 13.4 weeks from the time of initial evaluation to diagnosis when a child was first seen by a non-orthopaedic provider.

The pain is typically described as dull and vague; it may be intermittent or continuous, and it is exacerbated by physical activity, such as running or sports. The onset of pain may be of several weeks or months in duration. The patient will have an antalgic limp, with the affected side held in a position of increased external rotation. The examining physician should not ask the patient to perform strenuous examination maneuvers, such as running, hopping on either foot, or squatting, because these maneuvers could theoretically induce acute displacement of a stable slip. Thigh atrophy may be apparent in unilateral cases; the often associated obesity may make this finding difficult to discern. Local tenderness may be elicited anteriorly over the hip joint. Examination of the arc of motion of the affected hip reveals a restriction of internal rotation, abduction, and flexion. Commonly, the examiner notes that as the affected hip is flexed, the thigh tends to rotate into progressively more external rotation, and that flexion is limited ( Fig. 15.5 ). The loss of internal rotation on examination, with complaints of pain at the limit of internal rotation, is a key finding in stable SCFE. The limitation of hip motion actually represents a change in location of a relatively preserved arc of motion rather than a loss of motion. Increased hip extension, external rotation, and adduction are usually present, with decreased flexion, internal rotation, and abduction, depending on the severity of the slip. The presence of hip flexion contracture should alert the physician to the possibility of chondrolysis. There may be shortening of the affected extremity by 1 to 2 cm. The stereotypical patient with chronic slipped epiphysis is male, obese, and hypogonadal. Other patients have a normal habitus. ^{, ,}

Unstable Acute or Acute-on-Chronic Slipped Capital Femoral Epiphysis

Patients presenting with unstable acute or acute-on-chronic slipped epiphysis characteristically report the sudden onset of severe, fracture-like pain in the affected hip region, usually as the result of a relatively minor fall or twisting injury. The severity of the symptoms makes the patient unable to bear weight and likely to seek prompt medical attention. Occasionally, presentation to the physician is delayed for some unfortunate reason, and the patient may have resumed weight bearing. The patient usually lies with the affected limb in external rotation and refuses to move the hip. Moderate shortening of the limb is apparent to the examiner. Severe pain results from any movement of the limb.

Chondrolysis Complicating Slipped Capital Femoral Epiphysis

Patients presenting with chondrolysis complicating slipped epiphysis tend to have a history of more continuous pain and greater interference with daily activities because of the loss of hip joint range of motion. On examination, the affected hip is held in an externally rotated position at rest, with flexion contracture and global restriction of hip motion. The patient usually complains of pain throughout the arc of motion rather than just at its extremes.

Plain Radiography

Plain radiography in AP and lateral views is the primary and often the only imaging modality needed to evaluate slipped epiphysis. The earliest radiographic sign is widening and irregularity of the physis with rarefaction in its juxtaepiphyseal portion. This early stage has been termed preslip by some authors, ⁱ

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because actual displacement may not be evident on the radiographs. In the earliest phase of mild slips with typical posterior displacement, the AP radiographic findings may be subtle. In the normal hip, a line drawn tangential to the superior femoral neck (Klein line) on the AP view intersects a small portion of the lateral capital epiphysis. When typical posterior displacement of the capital epiphysis has occurred, this line intersects a smaller portion of the epiphysis or not at all (Trethowan sign; Fig. 15.6 ). The “metaphyseal blanch sign,” a crescent-shaped area of increased density overlying the metaphysis adjacent to the physis, may be seen on the AP radiograph ( Fig. 15.7 ). This increased density is due to the overlapping of the femoral neck and the posteriorly displaced capital epiphysis. In the normal adolescent hip, a portion of the diaphysis of the neck inferomedially is intraarticular and overlies the posterior wall of the acetabulum, creating a dense triangular appearance. In most patients with slipped epiphysis, this dense triangle is lost as that portion of the neck becomes located lateral to the acetabulum ( Fig. 15.8 ).

Whenever slipped epiphysis is suspected based on the patient’s history, the physical examination findings, or the presence of any subtle findings on the AP radiograph, it is essential to obtain lateral radiographs of the hip as well. The frog-leg lateral view is customarily obtained. This view has several advantages: it is easily obtained by having the patient flex and abduct the hips; soft tissue obscuring of the bony image is minimized; and both hips can be visualized on one film. This view is adequate to confirm the diagnosis of most cases of slipped epiphysis. However, variations in positioning make it an imprecise method of assessing the severity of slip. This view also is not usually adequate for assessing the possibility of penetration of the hip joint by a metallic implant. Alternative lateral radiographic views include a true lateral radiograph; the modified Dunlap lateral radiograph ; and the modified Billing lateral radiograph. ^, To obtain the modified Billing view, an AP view of the hip is obtained with the limb resting on a wedge in a position of 90 degrees of flexion, approximately 65 degrees of abduction, and neutral rotation.

When the slip is acute, little or no remodeling of the femoral neck is apparent on radiographs; only the displacement of the capital epiphysis on the femoral neck through the physis is seen. When the slip has been present for some time, allowing for some remodeling of the femoral neck, this remodeling appears as a bending of the femoral neck in the direction of the “slipping” capital epiphysis. Appositional new bone is present on the inferomedial surface of the neck, and the anterosuperior neck resorbs, producing a rounding or “hump” appearance. In patients with a component of acute progression after an initial period of slow displacement of the capital epiphysis with femoral neck remodeling, both radiographic features are present; that is, the femoral neck is remodeled to some extent, and the capital epiphysis is displaced beyond the margin of the femoral neck remodeling (see Fig. 15.1A and C ).

Computed Tomography

Computed tomography of the upper femur has been useful in documenting the presence of decreased upper femoral neck anteversion or true retroversion, and it is also believed to be more accurate in the measurement of the head-neck angle (similar to the head-shaft angle of Southwick as described for plain radiographs, but the angle measured is the tangent to the base of the epiphysis and the axis of the femoral neck; see Fig. 15.3 ). However, CT of the hip is not usually necessary to document or treat slipped epiphysis.

CT, however, can be useful in the management of slips. First, CT of the hip can be very helpful in demonstrating whether penetration of the hip joint by fixation devices has occurred ( Fig. 15.9 ). Pin penetration can be difficult to recognize on plain radiographs because hip stiffness due to either AVN or chondrolysis can make patient positioning difficult, or patient obesity may make visualization of the margins of the femoral head difficult. Another indication for CT is to confirm closure of the proximal femoral physis. Documentation of closure can be difficult with plain radiography but may be important in the investigation of continued or recurrent pain in a hip previously treated for slipped epiphysis. Finally, three-dimensional reconstructed CT images can be used to assess the severity of residual deformity of the upper femur, especially when reconstructive osteotomy is being considered.

Technetium-99 Bone Scan

Bone imaging with technetium-99 shows increased uptake in the capital femoral physis of an involved hip, decreased uptake in the presence of AVN, and increased uptake in the joint space in the presence of chondrolysis. With respect to the detection of involvement of the hip with slipped epiphysis, however, clinical examination and careful assessment of AP and good lateral radiographs usually suffice to make the proper diagnosis. If further assessment is required because of equivocal involvement after clinical assessment and plain radiography, either ultrasonography or CT is more sensitive and specific in confirming the presence of an early mild slip, or so-called preslip. Abnormally decreased uptake in the epiphysis is highly specific for the diagnosis of AVN. When chondrolysis is present, there is increased uptake of isotope on both sides of the joint on bone scintigraphy.

Ultrasonography

Ultrasonography has been used in the assessment of slipped epiphysis. ^{, ,} Several authors have found that ultrasonography is useful in the detection of early slips by demonstrating joint effusion and a “step” between the femoral neck and the epiphysis created by slipping. ^{, ,}

Magnetic Resonance Imaging

Although early detection of SCFE has been recorded using magnetic resonance imaging (MRI), ^{, ,} plain radiography, CT, or ultrasonography can usually achieve this goal more cheaply and expediently. If the results of the radiographs are negative, but the patient has symptoms, a body habitus, and a physical examination consistent with SCFE, MRI may detect physeal widening and irregularity, which are the earliest signs of SCFE. MRI is a sophisticated imaging technique highly specific for the detection of AVN. However, the presence of a stainless steel implant can seriously degrade the quality of the image and prevent an accurate diagnosis.

Initial Management

Patients with suspected stable SCFE should be escorted to the radiology suite, preferably in a wheelchair or on a stretcher. Patients with an unstable slip should be immobilized on a stretcher with light skin traction applied to the affected limb to minimize pain with transportation and should be provided with appropriate analgesics as soon as a plan for definitive management has been formulated. Patients with stable slips may be adequately evaluated with good AP and frog-leg lateral views of both hips. Cross-table lateral radiographs may be more accurate for assessing the presence and severity of slips but are not recommended because they are difficult to obtain if the patient is obese or in severe pain and they expose the patient’s gonads to a higher dose of radiation as compared to a frog lateral. Frog-leg lateral views are not needed and should not be attempted in patients with unstable slips. Additional manipulation of the leg results in unnecessary pain and further risk to the femoral epiphysis blood supply.

Once the diagnosis has been confirmed and an open capital femoral physis noted, the patient should be admitted to the hospital and placed on bed rest until prompt, definitive management of the SCFE is undertaken. Acute displacement of the epiphysis after diagnosis of mild chronic slip has been documented repeatedly. ^, This event can dramatically alter the patient’s prognosis. ^{, , , ,}