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 of the most significant complications of an unstable slipped epiphysis (and its treatment) is the development of AVN of the femoral capital epiphysis. ^‡ The reported incidence of AVN in unstable slips may be as high as 47%. ^§

Classification Based on Onset of Symptoms

‡ References .

§ References .

Radiographic appearance of slipped capital femoral epiphysis (SCFE) on presentation. A, Appearance of acute SCFE on a frog-leg lateral view. The displacement of the epiphysis is suggestive of a Salter-Harris type I fracture of the upper femoral physis. There are no secondary adaptive changes noted in the femoral neck. B, Frog-leg lateral radiographs in a patient with many months of thigh discomfort and a chronic slipped epiphysis. Adaptive changes in the femoral neck predominate, and the epiphysis is centered on the adapted femoral neck. C, Frog-leg lateral radiographs of a patient with acute-on-chronic SCFE. The patient had several months of vague thigh pain, with sudden, severe exacerbation of that pain. The acute displacement of the epiphysis is evident. Unlike in acute SCFE (see A ), secondary adaptive remodeling changes are also present in the femoral neck, beyond which the epiphysis has acutely displaced.

‖ References .

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 ( Fig. 18-1, C ).

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. 18-2, A ) or frog-leg lateral views ( Fig. 18-2, B ). 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. 18-3 ), but this method is not routinely used because most patients do not undergo CT.

Southwick method of measuring the head-shaft angle to assess the severity of slipped capital femoral epiphysis. A, Lines are drawn corresponding to the axis of the femoral shaft and the base of the capital femoral epiphysis. The head-shaft angle is the angle between the axis of the femoral shaft and is perpendicular to the base of the epiphysis. Normally this angle is 145 degrees. B, Similar lines may be drawn on the frog-leg lateral radiographs. Mild slips have less than 30 degrees of displacement, moderate slips have 30 to 60 degrees of displacement, and severe slips have more than 60 degrees of displacement compared with the contralateral normal side.

Measurement of the head-neck angle on computed tomography (CT) scan. Although this is the most accurate way to measure the head-neck angle, CT is not necessary in the routine management of patients with slipped capital femoral epiphysis.

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. ^¶

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), ^# abnormalities treated by growth hormone administration, * ^a and chronic renal failure. SCFE has also occurred in patients with prior pelvic irradiation, 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).

# References .

References .

The search for metabolic abnormalities in “normal” patients has not produced consistent findings. A study of iliac crest biopsy specimens found no abnormalities in patients with slips. A study of height, weight, body proportions, and skeletal and sexual maturation prospectively in 23 patients with slips found that boys in the study tended to be obese; both boys and girls had relatively longer legs, and growth and maturation were not different from those in normal children. The time of occurrence of slipped epiphysis was most closely related to the patient’s bone age and growth spurt peak, and no endocrine abnormality was found. Normal levels of thyroid hormone, growth hormone, and the growth hormone action mediators insulin-like growth factor 1 (IGF-1) and its binding protein 3 (IGFBP-3) ²⁰⁰ have been found in otherwise healthy patients with slipped epiphyses.

Other studies have noted endocrine abnormalities. One such study found 71% of patients had weights above the 80th percentile and that levels of active thyroid hormone (triiodothyronine) were significantly low in 25% of patients. Furthermore, testosterone and growth hormone levels were low in 76% and 87% of patients tested, respectively. These authors concluded that a “delicate hormonal imbalance” was the basis of slipped epiphysis. Another study noted parathyroid hormone and 1,25-dihydroxyvitamin D abnormalities in 13 patients with slips. They found a transient decrease in the serum levels of the midportion of the parathyroid hormone peptide and of 1,25-hydroxyvitamin D. They were uncertain whether these transient deficiencies during the growth spurt were the cause or the result of slipped epiphysis.

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, 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. 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. 18-5 ). 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.

Clinical examination of a patient with a stable slipped capital femoral epiphysis. Hip flexion and external rotation are limited. With flexion of the affected hip, the limb rotates externally.

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, 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. 18-6 ). 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. 18-7 ). 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. 18-8 ).

Anteroposterior radiographic appearance of a normal hip and a hip with mild chronic slipped capital femoral epiphysis. A, Normal hip. A line drawn parallel to the superior femoral neck (Klein line) will intersect the lateral-most portion of the capital femoral epiphysis. B, Hip with mild chronic slip. Klein line does not intersect the capital epiphysis (Trethowan sign). Lateral radiographs will confirm the diagnosis.

Metaphyseal blanch sign of Steel in slipped capital femoral epiphysis. A crescent-shaped area of increased density lies over the metaphysis of the femoral neck adjacent to the physis. This density is produced by overlapping of the femoral neck and the posteriorly displaced capital epiphysis on the anteroposterior view of the hip.

(Courtesy Howard H Steel, MD, Shriner’s Hospital for Children, Philadelphia.)

Scham sign of slipped capital femoral epiphysis. A, In the normal hip, the inferomedial femoral neck overlaps the posterior wall of the acetabulum, producing a triangular radiographic density on the anteroposterior view. B, With displacement of the capital epiphysis, this dense triangle is lost because this portion of the femoral neck is located lateral to the acetabulum.

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. 18-1, A 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. 18-3 ). 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. 18-9 ). 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.

Computed tomography (CT) evaluation of implant penetration into the femoral head. Plain radiographs show no early evidence of chondrolysis or penetration of the hip joint by the screw on anteroposterior ( A ) or frog-leg lateral ( B ) projections. CT scan ( C ) showing that implant penetration of the joint has nearly occurred and that penetration of the joint by a drill probably has occurred. Changes in the articular surface due to chondrolysis are present.

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 are more accurate for assessing the presence and severity of slips but may be difficult to obtain if the patient is obese or in severe pain. Frog-leg lateral views should not be attempted in patients with unstable slips because of the unnecessary pain the imaging position will induce.

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.

Definitive Treatment

The primary purpose of definitive treatment for SCFE is to stabilize the capital femoral epiphysis to the femoral neck to prevent further slipping. Other goals may include closure of the capital femoral physis and reduction of the epiphyseal displacement. Definitive treatment alternatives for the management of SCFE include in situ internal fixation or pinning; bone graft epiphysiodesis; primary osteotomy through the apex or base of the femoral neck or intertrochanteric area, with or without fixation of the epiphysis to the femoral neck; and application of a spica cast. The choice of treatment depends on the type of slip and its severity, and individual preferences and prejudices.

Stable Slipped Capital Femoral Epiphysis

In Situ Pinning

The treatment of choice for a stable slipped epiphysis is screw fixation between the capital epiphysis and the neck of the femur. A single cannulated screw provides stable fixation in most grades of slip. The goal of pinning is stability rather that epiphyseal closure, which may or may not occur. Excellent radiographic control, either with AP and frog-lateral fluoroscopy, or with true lateral views on a fracture table, enables placement of enough screw threads across the physis to block further slipping. The screw should be in the center of the femoral head and the tip of the screw should not be close to the articular surface. Older practice attempted to achieve “subchondral” pin placement, which often resulted in intraarticular pins, which caused chondrolysis of the hip. With unstable slips, two screws may be used for additional stability and rotational control. A great many alternative techniques have been used. ^†a

Percutaneous In Situ Fixation With a Fracture Table

Operative Technique.

†a References .

The technique of percutaneous in situ fixation of SCFE is diagrammed in Plate 18-1 (see also Video 18-1 ). This technique is specifically indicated for unstable slips and is also appropriate for stable slips, at the surgeon’s discretion. Several excellent, partially threaded, 6.5- to 7.3-mm stainless steel or titanium cannulated screw systems are available. The type selected is at the surgeon’s discretion. The surgeon should be familiar with the guidewire, drill, tap, and measuring instrumentation of the system chosen and confirm that they are in good working order with an appropriate range of implants available before commencing the procedure. The patient is placed on a suitable fracture table with the affected leg held in extension and neutral to slight internal rotation (see “ Unstable Slipped Capital Femoral Epiphysis ”) and the contralateral limb positioned either in wide abduction and extension in traction or supported in flexion and abduction, to permit fluoroscopic imaging of the affected hip in the lateral position. Excessive internal rotation of the affected limb should be avoided. The surgeon should confirm that the C -arm fluoroscope is working well and that the femoral epiphysis is clearly visible on both AP and true lateral projections. The limb is then prepared and draped using either a “shower curtain” barrier draping technique or U -draping of the torso and lower leg out of the surgical field and covering the C -arm with a sterile drape.

The desired trajectory of the screw as seen on fluoroscopy is identified by placing a guidewire on the surface of the limb and marking the skin with an indelible marker in both the AP and lateral projections. It is very important for the surgeon to realize that in a typical SCFE, the femoral neck is relatively retroverted, and displacement of the capital epiphysis is essentially posterior. The ideal placement of a single cannulated screw is as close to the center of the capital epiphysis and as perpendicular to the physis as possible. Thus the entry point of the screw must be at the base of the femoral neck, and the screw is directed posteriorly into the center of the capital epiphysis. With increasing severity of the slip, the entry point will be found progressively more superior on the femoral neck. Only in the mildest of slips with minimal relative femoral retroversion will an insertion point on the lateral femoral cortex allow adequate fixation of the capital epiphysis in SCFE. In very severe slips, if the screw is not placed very anteriorly on the femoral neck it may exit the femoral neck posteriorly and reenter the capital epiphysis. This placement should be avoided, because it will allow continued displacement due to inadequate fixation, loss of fixation, or implant breakage due to continued movement between the bone fragments. In addition, a screw exiting the posterior femoral neck may disrupt the blood supply to the epiphysis.

A guidewire is inserted percutaneously at the intersection of the lines drawn on the skin and advanced to the base of the femoral neck. The location and orientation of the guidewire should be confirmed fluoroscopically. The guidewire is advanced into the epiphysis, aiming at the exact center of the femoral head on both fluoroscopic views without encroaching on the joint space. The guidewire is measured and a screw of appropriate length is selected. The bone is then drilled and tapped with cannulated instruments. Several fluoroscopic checks are made during drilling and tapping so that the guidewire is neither advanced into the joint nor withdrawn from its channel. The screw is inserted over the guidewire. After satisfactory placement of the screw has been confirmed, the guidewire is removed and the stab incision closed. The limb should be released from traction and the hip placed through a range of motion while the surgeon evaluates the relationship of the screw to the hip joint fluoroscopically to be certain that the screw has not penetrated the joint space.

Specific advantages of this technique include more secure draping of the limb, a percutaneous technique with minimal visible scarring, and elimination of the need to manipulate or support the limb during surgery. Disadvantages include the inability to move the limb freely to confirm no pin encroachment of the hip joint before the end of the procedure; potentially greater difficulty visualizing the femoral epiphysis in the true lateral position; and awkward positioning and draping procedures (usually staged) with bilateral slips. If difficult patient positioning or extreme obesity makes visualization of the femoral head and hip joint inadequate in the true lateral projection, intraoperative arthrography of the hip can be a great help ( Fig. 18-10 ).

If difficulty is encountered in visualizing the outline of the capital epiphysis on fluoroscopy during pinning of a slip, an intraoperative arthrogram can be helpful. The radiopaque dye is injected into the hip capsule, allowing better visualization of the femoral head.

Postoperative Management.

We allow protected partial weight bearing with crutches as soon as the patient is comfortable, usually within 24 hours of surgery; patients with unstable slips may be slower to walk. The patient uses crutches for 6 weeks, during which time the pain should resolve completely. Athletic activities are allowed after 3 months. The patient is monitored for the development of complications or contralateral slip by clinical examination and radiography every 3 to 6 months until skeletal maturity.

Percutaneous In Situ Fixation Using a Radiolucent Tabletop.

This technique may be used instead of the fracture table technique at the surgeon’s discretion, but only if the slip is stable. The technique is detailed in Figure 18-11 . The main advantages of this technique include simpler setup and draping; the ability to put the hip through a wider range of motion when assessing for possible joint encroachment by the pin, without breaking the sterile field or having to remove the patient’s limb from traction; better lateral visualization of the upper femur in the flexed, abducted position because of a smaller amount of soft tissue overlying the hip; and much simpler positioning and draping for bilateral slips. Disadvantages include the occasional need for a small incision through the fascia lata to prevent this tissue from bending the guidewire when flexing and abducting the hip. The use of a stout guide pin and larger diameter screw usually prevents bending of the pin. The ability to move the hip through a full range of motion allows fluoroscopic visualization of the entire femoral head. This technique is usually not used in the management of unstable slips because hip movement may displace the femoral head and compromise its vascularity.

Technique of pinning a stable slipped capital femoral epiphysis on a radiolucent tabletop. This technique of cannulated screw fixation is indicated only for stable slips, at the surgeon’s preference. A, The patient is positioned on a radiolucent tabletop and the fluoroscope is positioned over the patient. The affected extremity is prepared and draped free. In cases of bilateral slips, both lower extremities may be draped into the surgical field. B, Top, A fluoroscopic projection; bottom, a frog-leg lateral projection. The trajectory of the guidewire is marked on the skin, as described for the percutaneous technique (see Plate 18-1 ). A 1-cm incision is made at this point and carried through the fascia lata. C, The guidewire is advanced through the fascia lata incision and onto the base of the femoral neck, as in the percutaneous technique. D, To obtain the lateral radiograph, the hip is flexed to 90 degrees and then abducted maximally. The surgeon must insert a finger into the wound to prevent the anterior edge of the fascia lata from bending the guidewire on flexion of the hip. After satisfactory guidewire placement has been achieved, the length of screw needed is measured, and drilling, tapping, and screw insertion are performed as in the percutaneous technique. After removal of the guidewire, the hip is placed through full range of motion while the surgeon assesses the position of the screw in the epiphysis fluoroscopically. The wound is closed in routine fashion.

The patient must first be assessed before surgery both clinically and radiographically to determine that the slip is stable and to establish whether there is slip on the contralateral side. After induction of anesthesia, the patient is positioned on a radiolucent tabletop. The C -arm fluoroscope should come from the opposite side of the table to be unobtrusive to the surgical team, and adequate visualization of the capital epiphysis is confirmed in both the AP and flexed/abducted lateral positions. The patient’s affected extremity (or both extremities, in the case of bilateral slips) is draped free. The intended trajectory of the guidewire can be marked on the skin as for the percutaneous technique. This will facilitate limiting the incision required. The lateral projection of the capital epiphysis is obtained by flexing the hip 90 degrees, then abducting it maximally in a position of neutral rotation. Because the hip rarely abducts 90 degrees, this does not represent a true lateral projection. With the patient lying in this position and the patient’s upper thighs supported on the radiolucent tabletop, placing the guidewire along the posterolateral thigh to determine the trajectory of the guidewire in this position may be awkward. A 1- to 2-cm incision is made at the intersection of the lines drawn on the skin, and sharp dissection is carried through the fascia lata.

After the guidewire has been placed through the incision in the fascia lata, it is positioned on the base of the femoral neck under fluoroscopic control. After initial advancement of the guidewire into the proximal femur, the hip is flexed and abducted for the lateral projection. The surgeon may use the cannulated screwdriver over the guide pin to prevent bending of the guide pin by the fascia lata as the hip is flexed. The position of the guidewire is confirmed in this lateral position. The limb is returned to the neutral position. If the first guidewire is not adequately positioned, a second is placed, using the first as a guide to making the appropriate changes in the trajectory of the guidewire.

Once satisfactory positioning of the trajectory has been confirmed, the guidewire is advanced into the center of the epiphysis under fluoroscopic control. Drilling, tapping, screw insertion, and confirmation of adequate placement of the screw without encroachment on the joint are then performed as in the percutaneous technique. Advancement of the screw such that three or four threads have crossed into the epiphysis should be confirmed in the lateral projection. With severe slips, advancement will not appear to be adequate on the AP view. The hip is then taken through as full a range of motion as possible while the surgeon assesses the position of the screw within the epiphysis, viewing multiple positions under fluoroscopy. The wound is irrigated and closed. Postoperative management is the same as noted for the fracture table technique.

Cannulated Screw, Design and Positioning.

A number of well-designed, partially threaded cannulated screw systems are available, and the selection is at the surgeon’s discretion. Essential features include a large core diameter and thread (at least 6.5-mm thread diameter with a 4.5-mm core diameter or larger), reverse cutting threads with an adequate effective extraction system should the screw have to be repositioned or removed, and a stout guidewire to avoid bending and jamming problems during screw insertion. The length of the threaded portion is at the surgeon’s discretion; we prefer the longer partial thread or fully threaded designs to facilitate placing of the threads across the physis, and for more secure fixation in the metaphysis. Some surgeons report that stainless steel implants are easier to remove than titanium devices.

Reviews of the results of cannulated screws in the management of SCFE with the fewest complications have demonstrated that single screws should be placed either directly in the center of the capital epiphysis or at a position slightly inferior and posterior to this ideal position. The more eccentric the screw placement from this central position, the greater the risk of inadequate fixation and further migration of the capital epiphysis, inadvertent protrusion of the end of the screw into the hip joint, or both. Because of the typical posterior-inferior migration of the capital epiphysis, the screw must be inserted in a similar direction beginning at the anterior base of the femoral neck or superior to this point, depending on the severity of the slip.

Clinical studies have repeatedly demonstrated that single-screw fixation yields satisfactory results and is perhaps superior to multiple-pin or multiple-screw fixation for both stable and unstable slips. ^‡a Double-screw fixation is frequently recommended for unstable slips, and a biomechanical study found double-screw constructs to be 66% stiffer and stronger than single-screw fixation in a hip model. The biomechanical benefit should be weighed against the increased risk of screw-related complications. For example one study found that pin-related complications increased from 4.6% with one pin or screw to 20% with two and 36% with three.

‡a References .

The location of the single cannulated screw does influence the result of in situ fixation. A relatively inferior position, avoiding the superior and anterior quadrant of the epiphysis, has been suggested to result in the fewest complications.

Screw-Related Complications.

Complications directly related to the use of screws include perforation into the joint space by the screw or guidewire, either transiently during insertion or persistently afterward; failure of physeal fusion, with growth of the epiphysis off the end of the screw or progression of the slip; loss of fixation either in the femoral neck or in the epiphysis; implant failure (fracture) secondary to failure-producing stress concentration at the physis or posterior neck in cases in which the device exits the neck and reenters the epiphysis; fracture of the femoral neck or intertrochanteric area at the site of screw insertion secondary to stress concentration; and difficult or failed efforts at screw extraction. By far the most important of these complications is implant protrusion into the hip joint.

Walters and Simon were the first to carefully identify the potential for joint space violation by metallic implants (despite apparently “safe” placement on radiographs) and to clearly recognize the association of metallic pin encroachment on the joint and chondrolysis. They noted in an in vitro study that pin penetration may go unrecognized on AP, true lateral, and especially frog-leg lateral radiographs because these views may not be tangential to the articular surface where the pin or screw has protruded, and up to 2 cm of intrusion into the joint could be missed. The best position for avoidance of penetration was with the pin placed in the center of the head on both views. Examining the hip with fluoroscopy through a full range of motion, and avoiding subchondral pin placement remain the best ways to avoid joint penetration. Walters and Simon showed a direct relationship between pins or screws placed into the joint and chondrolysis.

Currently chondrolysis is rare and may occur in patients in whom pin penetration of the joint has never occurred. After surgery, if there is any question of screw protrusion, CT of the hip should be undertaken.

Fractures of the femoral neck and the subtrochanteric area after in situ pin fixation have been reported. Of the four patients reported to incur femoral neck fracture, AVN developed in two and nonunion of the fracture site in one. This is a serious but apparently very rare complication of in situ fixation. Subtrochanteric fractures have been reported through unused drill holes, emphasizing the importance of careful surgical technique with a minimum number of perforations of the femoral cortex.

Undue prominence of the implant at the entry site anteriorly has led to loss of fixation due to a “windshield wiper” effect in which the overlying soft tissues caused toggling of the implant within the femoral neck and, in one case, due to the development of a false aneurysm. Exit of the implant from the posterior femoral neck led to implant fracture in one series but to no problems in another.

Routine Removal of Screws.

In the past, fixation devices were routinely removed after physeal fusion in patients with SCFE. Reasons for removal included concerns regarding the potential long-term toxic complications of a retained implant; the possible induction of local malignancy; difficult to impossible extraction at a later date, making revision surgery likewise more difficult or impossible; and the risk of fracture at the entry site of the implant. As a practical matter, the usual reason for removing Steinmann pins was the fact that they were most commonly left protruding from the lateral femoral cortex or anterior femoral neck and caused symptoms from soft tissue impingement. Routine removal of screws remains controversial. ^§a The design of some screws makes them difficult to remove, especially the early varieties without reverse-cutting threads or, in the case of titanium implants, without satisfactory extraction instrumentation. Today’s devices generally pose little problem with extraction.

Summary of In Situ Pinning.

§a References .

We believe that in situ pinning with a single cannulated screw inserted either percutaneously or through a limited exposure is the procedure of choice for stable SCFE, regardless of severity. The screw should be placed as close to the center of the capital epiphysis as possible. Although one such screw may suffice for unstable slips, we insert two guidewires, followed by one or two cannulated screws. We prefer to position the threads across the physis without attempting to achieve compression between the head of the screw and the threads, although we believe that attempting to achieve this is a reasonable alternative technique. We consider open bone graft epiphysiodesis for SCFE when the severity of the slip is such that insertion of the screw without exiting the posterior femoral neck and reentering the capital epiphysis appears impossible, or when osteopenia or some other factor has resulted in inadequate fixation and continued progression of the slip. We do not advocate routine removal of cannulated screws but do so after closure of the physis if symptomatic, if deep wound infection or joint encroachment is considered possible, or to respect parental concerns about retention of an implant.

Bone Graft Epiphysiodesis

“Open bone peg epiphysiodesis,” or simply “open epiphysiodesis” of the capital femoral physis, and its results have been described by many authors. ^‖a In this procedure, a portion of the residual physis is removed by drilling and curettage, and a dowel or “peg” of autologous bone graft (usually harvested from the ipsilateral iliac crest) is inserted across the femoral neck into the epiphysis through a drill hole fashioned to receive the graft. This procedure may be combined with open reduction of the epiphysis and may be used to treat either stable or unstable slips. In unstable slips, supplementary internal fixation, postoperative traction, or spica cast immobilization for 3 to 8 weeks until early stabilization has occurred have all been recommended.

Operative Technique.

‖a References .

The technique of open bone graft epiphysiodesis is summarized in Plate 18-2 . The patient is placed on a radiolucent tabletop or fracture table with fluoroscopy available, and the affected hip is prepared and draped. Either a Smith-Peterson anterior or a Watson-Jones anterolateral surgical approach can be used. The latter approach is recommended by Weiner and colleagues because it is more familiar to most surgeons and the incision can be incorporated into subsequent revision surgery or total joint arthroplasty. The joint is opened through an H – or T -shaped incision into the capsule. Soft tissue retractors are placed within the capsule, with care taken not to violate the posterior periosteum of the femoral neck where the residual blood supply to the femoral head courses. A guidewire is driven through the anterior femoral neck across the physis into the epiphysis under fluoroscopic control. The femoral neck is perforated over the guidewire with a cannulated drill bit or large hollow-mill drill ( / ₁₆ inch in diameter), and the drill is advanced into the epiphysis over the guidewire. If a hollow-mill drill is used, the cylindrical core of bone, containing the portions of capital epiphysis, physis, and metaphysis, is removed. A curet is used to enlarge the cylindrical tunnel and to curet additional portions of the physis. Strips or a cylinder of corticocancellous bone are harvested from the iliac crest and driven into the tunnel from the femoral neck across the physis into the capital epiphysis. If a cortical window has been removed from the femoral neck, it is replaced, and the wound is closed in the usual fashion.

Postoperative Management.

Patients with a stable slip may be allowed out of bed with protected weight bearing using crutches or a walker until radiographic evidence of physeal closure has occurred. Patients with unstable slips should either be placed in a spica cast for 3 to 6 weeks or maintained in split Russell traction until comfortable, and then allowed protected weight bearing as for stable slips.

Results.

Reports of the results of bone peg epiphysiodesis have been contradictory. Although some authors have reported satisfactory outcomes, others have reported frequent complications, including AVN, chondrolysis, and heterotopic ossification. The excellent results reported by Weiner and colleagues of 185 cases noted only a 4% loss of fixation and less than 1% avascular necrosis rate in chronic slips, with 4% avascular necrosis in the acute slips. ³⁰¹ On the other hand Ward and others found that almost 50% of the grafts resorbed, moved, or fractured.

Summary

Most authors who have compared the techniques of in situ pinning and open epiphysiodesis have concluded that the former is a simpler procedure, with less intraoperative blood loss, fewer postoperative complications, and comparable postoperative results. The technique of bone graft epiphysiodesis should not be abandoned altogether, however. Bone graft epiphysiodesis is probably best indicated in the management of chronic slips of such severity that the treating surgeon is uncomfortable with the feasibility of pinning in situ, or for slips that have progressed despite apparently adequate pinning (especially if there is evidence of loss of fixation due to osteopenia).

Spica Cast

Although immobilization in a hip spica cast is most commonly used as an adjunct to closed reduction, pinning, bone graft epiphysiodesis, or osteotomy of the upper femur, it has also been described for the definitive management of slipped epiphysis.

There is little indication for this modality in modern management. Because affected patients frequently are obese, nursing management becomes a monumental task. We believe that spica casting as definitive management for chronic SCFE should be reserved for the occasional desperate situation in which other treatment options are not feasible or have failed, and in which no other reasonable treatment alternative exists. Spica casting may occasionally be an option in very young patients or those with chronic renal failure whose medical management may improve their associated hyperparathyroidism promptly and in whom surgery is considered inadvisable.

Residual Deformity After Primary Treatment

When there is residual displacement of the capital epiphysis following primary treatment, the offset of the femoral head and neck decreases, and the proximal metaphysis is prominent and may enter the joint with hip flexion. This metaphyseal prominence may produce femoroacetabular impingement, and labral and articular damage, with subsequent hip pain and degenerative arthritis.

The need for correction of residual deformity after closure of the physis is the subject of some debate. Evidence that corrective osteotomy favorably influences the long-term prognosis for the development of osteoarthrosis is uncertain, with some series showing benefit whereas others report no improvement in prognosis. Some patients with residual deformity, especially excessive external rotation and decreased hip flexion, will seek treatment to improve their arc of motion.

Proximal Femoral Osteotomy

Proximal femoral osteotomy has been performed to correct residual deformity after stabilization of the slipped epiphysis. ^#a Surgical procedures include reduction at the physis with osteotomy through the fracture callus, * ^b known as the Dunn procedure (also cuneiform osteotomy of the femoral neck) as previously described. Others include a closing wedge osteotomy at the base of the neck, either intra­capsular or extracapsular (Barmada and colleagues ); or intertrochanteric osteotomy (Imhauser and Southwick). ^†b The rate of complications noted in earlier reports, especially AVN, has been related to the proximity to the capital epiphysis, being highest for osteotomies at superior neck and lowest for those at the intertrochanteric level. Conversely, the greater the distance between the corrective osteotomy and the apex of deformity, the more severe the secondary compensating deformity will be, and the greater the difficulty of total joint arthroplasty. Opinions as to the indications for these procedures vary from performance of intracapsular osteotomy for as little as 20 degrees of head-shaft deformity to performing these procedures rarely or never, regardless of the severity of the deformity. The locations of the osteotomies described in this section are diagrammed in Figure 18-12 .

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