JBJS | Slipped Capital Femoral Epiphysis*†

The Journal of Bone & Joint Surgery, Volume 82, Issue 8

Instructional Course Lecture | August 01, 2000

Slipped Capital Femoral Epiphysis*†

Randall T. Loder, M.D.‡; David D. Aronsson, M.D.§; Matthew B. Dobbs, M.D.#; Stuart L. Weinstein, M.D.#

An Instructional Course Lecture, American Academy of Orthopaedic Surgeons
*No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. No funds were received in support of this study.
†Printed with permission of the American Academy of Orthopaedic Surgeons. This article, as well as other lectures presented at the Academy's Annual Meeting, will be available in March 2001 in Instructional Course Lectures, Volume 50. The complete volume can be ordered online at www.aaos.org, or by calling 800-626-6726 (8 a.m.-5 p.m., Central time).
‡Shriners Hospital for Children, 2025 East River Parkway, Minneapolis, Minnesota 55414. E-mail address: rloder@shrinenet.org.
§University of Vermont, Robert T. Stafford Hall, Room 434B, Burlington, Vermont 05405-0084. E-mail address: daronsso@zoo.uvm.edu.
#University of Iowa Hospitals and Clinics, 200 Hawkins Drive, Suite 01026 JPP, Iowa City, Iowa 52242. E-mail address for S. L. Weinstein: stuart-weinstein@uiowa.edu.

The Journal of Bone & Joint Surgery. 2000; 82:1170-1170

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Introduction

Slipped capital femoral epiphysis is a well known disorder of the hip in adolescents that is characterized by displacement of the capital femoral epiphysis from the metaphysis through the physis. The term slipped capital femoral epiphysis is a misnomer because the epiphysis is held in the acetabulum by the ligamentum teres, and thus it is actually the metaphysis that moves upward and outward while the epiphysis remains in the acetabulum. In most patients, there is an apparent varus relationship between the head and the neck, but occasionally the slip is into a valgus position, with the epiphysis displaced superiorly in relation to the neck^106,109. In the vast majority of cases, the etiology is unknown. Although the condition may be associated with a known endocrine disorder^71,77,129, with renal failure osteodystrophy⁷⁴, or with previous radiation therapy^75,77, this Instructional Course Lecture deals only with idiopathic slipped capital femoral epiphysis.

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Fig. 1:: Anteroposterior radiographs showing the metaphyseal blanch sign and Klein's line. The metaphyseal blanch sign is a radiographic double density seen at the level of the metaphysis (arrow); this double density reflects the posterior cortical lip of the epiphysis as it is beginning to slip posteriorly and is radiographically superimposed on the metaphyseal density. Klein's line is drawn along the anterior or superior aspect of the femoral neck; the epiphysis should normally intersect this line (left). In an early slipped capital femoral epiphysis, the epiphysis is flush with or even below this line (right).

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Fig. 2:: Radiograph showing a pin (open arrow) exiting the posterior part of the femoral neck and entering the posterior aspect of the epiphysis. The pin also penetrates the femoral head and protrudes into the hip joint (solid arrow).

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Fig. 3:: Drawing showing the blood supply to the femoral head. The most important contribution to this blood supply is from the posterosuperior epiphyseal vessels that originate from the medial femoral circumflex artery.

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Fig. 4:: Drawing showing the technique used for positioning the skin incision. The line X-Y represents a line overlying the center of the femoral head and perpendicular to the physis on the anteroposterior fluoroscopic image. The line Y-Z represents a line overlying the center of the femoral head and perpendicular to the physis on the lateral fluoroscopic image. The skin incision is made at the intersection of these lines.

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Fig. 5-A:: Figs. 5-A through 5-D: A ten-year-old boy with a stable (chronic) mild slipped capital femoral epiphysis involving the left hip.
Fig. 5-A: Preoperative anteroposterior pelvic radiograph.

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Fig. 5-B:: Preoperative frog-leg lateral pelvic radiograph.

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Fig. 5-C:: Postoperative anteroposterior (Fig. 5-C) and frog-leg lateral (Fig. 5-D) pelvic radiographs showing placement of the screw perpendicular to the physis.

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Fig. 5-D:: Postoperative anteroposterior (Fig. 5-C) and frog-leg lateral (Fig. 5-D) pelvic radiographs showing placement of the screw perpendicular to the physis.

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Fig. 6:: Illustration showing the technique for performing an open epiphyseodesis. A rectangular window of bone is removed from the anterior aspect of the femoral neck, and a cylindrical tunnel is created across the physis. Multiple strips of corticocancellous bone from the iliac crest are then driven into the tunnel as bone pegs across the physis.

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Fig. 7:: Illustration showing the location of the anterior-based trapezoid wedge of bone that is removed from the metaphysis of the femoral neck during the cuneiform osteotomy. The epiphysis is then gently reduced and internally fixed with three pins.

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Fig. 8:: Illustration showing the location of the anterosuperior-based wedge of bone that is removed during the compensating base-of-neck osteotomy. The osteotomy site is internally fixed with multiple pins.

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Fig. 9:: Illustration showing the location of the anterolateral-based wedge of bone that is removed during the intertrochanteric osteotomy. This osteotomy includes flexion, abduction, and internal rotation of the distal fragment. The osteotomy site is internally fixed with a compression hip screw.

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Fig. 10:: Radiographs of the left hip of a fourteen-year-old boy who had immediate severe hip pain following acute trauma, without prior hip symptoms. The radiograph on the left was made at presentation. Those in the middle and on the right were made during a one-year follow-up period and show the rapid development of avascular necrosis and severe degenerative changes.

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Fig. 11:: Graph showing the worsening mean scores on the Iowa hip-rating scale for a group of 124 patients (155 hips) with a slipped capital femoral epiphysis¹⁹ (SCFE). Deterioration over time is most marked with increasing severity of the slip.

Etiology

Multiple theories have been proposed for the etiology of idiopathic slipped capital femoral epiphysis, and it is likely a result of both biomechanical and biochemical factors¹²⁸. The combination of these factors results in a weakened physis with subsequent failure.

Mechanical factors⁹⁵ associated with the disorder are obesity^62,72, increased femoral retroversion^36,37,95, and increased physeal obliquity⁸³. The vast majority of children with a slipped capital femoral epiphysis are obese, which increases the shear stress across the physis. Obesity is also associated with femoral retroversion, with anteversion averaging 10.6 degrees in adolescents with normal weight but only 0.40 degree in obese adolescents³⁶. This femoral retroversion increases the stress across the physis⁹⁵. Children with a slipped capital femoral epiphysis also have a more vertical proximal femoral physis (an increase of 8 to 11 degrees compared with that in children without the disorder) even in the contralateral, normal hip. The combination of mechanical forces resulting from femoral retroversion and increased physeal slope is enough to cause a slipped capital femoral epiphysis⁹⁵. The mean shear load to failure of the proximal femoral physis in adolescents of normal weight is 4.0 times body weight; the mean shear load to failure in adolescents who are running, who are obese, or who have neutral version (or 10 degrees of relative retroversion) is 5.1 times body weight. Finally, recent data⁶⁴ have shown that children with the disorder have deeper acetabula (a mean center-edge angle of Wiberg¹³⁰ of 37 degrees compared with a mean of 33 degrees in control subjects). Greater coverage of the femoral head yields more shear stress across the physis.

Biochemical factors are also likely involved. Slipped capital femoral epiphysis is a disease of puberty³¹, when many hormonal changes occur⁸⁵; this raises the possibility of an association between the disorder and endocrine function. The increased prevalence of slipped capital femoral epiphysis in children who have hypothyroidism, who are receiving growth hormone supplementation, or who have hypogonadism also suggests an association between the disorder and endocrine dysfunction. Rapid longitudinal growth occurs during puberty in response to growth hormone. This is due to the increased physiological activity of the physis and is associated with widening of the physis. Decreased physeal strength occurs at puberty⁸⁵; the cause is not clear, but it may be due to the increased cartilage width of the zones of hypertrophy and to provisional calcification¹¹⁴.

The effects of the gonadotropins on the physis may explain the male predominance of slipped capital femoral epiphysis; estrogen reduces physeal width and increases physeal strength⁴⁴, whereas testosterone reduces physeal strength⁸⁵. This probably also accounts for the fact that the disorder is extremely rare in girls after menarche¹¹¹. Although most children with a slipped capital femoral epiphysis do not have a demonstrable endocrine disorder^{16,30,80,98,131}, a subtle but as yet undiagnosable endocrinopathy may be present. In some children, there is a delay in bone age compared with chronological age^85,111, which further supports this concept.

Slipped capital femoral epiphysis does not appear to be a heritable disorder. Rennie⁹⁹ discovered that the risk of a slipped capital femoral epiphysis in a second family member was 7.1 percent and that 14.5 percent of patients with a slipped capital femoral epiphysis had a close relative who also had the disorder. A few families with the disorder may have an autosomal dominant inheritance with incomplete penetrance⁹⁹. The findings of HLA-typing in children with a slipped capital femoral epiphysis have varied^10,40.

Routine histological evaluation and electron microscopy studies of slipped capital femoral epiphysis demonstrate a deficiency and abnormality in the supporting collagenous and proteoglycan framework of the physis. Both the hypertrophic and the proliferative zones are abnormal. Whether these abnormalities represent the cause or the effect of the slipped capital femoral epiphysis is not known. Chondrocyte clustering and disarray occur in a thickened hypertrophic zone^2,94, and ultrastructural studies have demonstrated defective collagen fibrils and defects in collagen banding in this zone³. The proliferative zone demonstrates changes in proteoglycan and glycoprotein concentrations, with increased glycoprotein staining in the territorial matrix and increased proteoglycan staining in the extraterritorial matrix.

Epidemiology and Demographics

The prevalence of slipped capital femoral epiphysis is not completely known. The prevalence has been reported as 0.2 per 100,000 in eastern Japan⁸⁷, as 2.13 per 100,000 in the southwestern United States, and as high as 10.08 per 100,000 in the northeastern United States⁶¹. Most series have demonstrated a male predominance. Early in the twentieth century, 90 percent of the children with the disorder were boys, but more recently male predominance has decreased to 60 percent⁴³. The mean duration of symptoms before the diagnosis of chronic slipped capital femoral epiphysis is five months, with no difference noted with respect to gender. The mean age at diagnosis is 13.5 years for boys and 12.0 years for girls, with a typical age-range of nine to sixteen years⁷². The majority of the children are obese; at least 50 percent of the children with the disorder are over the ninety-fifth percentile for weight according to age^62,72. The age at onset decreases with increasing obesity⁷². The mean age at onset for children over the ninety-fifth percentile for weight according to age is 12.4 years; the mean age for children under the tenth percentile for weight according to age is 14.3 years. Although the chronological age at the onset of slipped capital femoral epiphysis varies, the physiological age-range appears to be smaller, with a "narrow window" of time during which it can occur⁶⁹. In latitudes north of 40 degrees, the onset of slipped capital femoral epiphysis occurs more frequently in the summer and autumn months^{4,33,41,73,85}.

The reported prevalence of bilaterality varies and depends on the study, the method of radiographic measurement, race, and possibly the type of treatment. In most series, a prevalence of 18 to 50 percent has been reported⁷²; however, recent studies with follow-up into adulthood have demonstrated a prevalence of bilaterality as high as 63 percent^41,50,51. The percentage of bilaterality has been found to be higher in black children (34 percent) than in Hispanic children (17 percent), white children (17 percent), and Asian children (18 percent), according to a study of 1630 children⁷². Treatment may affect the prevalence of bilaterality. In one study⁴⁷, the prevalence was 36 percent in 169 patients treated with in situ pinning and 7 percent in thirty treated with a spica cast. Therefore, it is mandatory that close attention be paid to the contralateral, normal hip in children who have a unilateral slipped capital femoral epiphysis treated with in situ pinning.

Between 50 and 60 percent of patients with bilateral involvement have it when they are first seen⁷². Eighty-two percent of second cases of slipped capital femoral epiphysis that develop in patients who initially presented with unilateral involvement are seen within eighteen months after the first presentation^{28,41,68,72,111,132}. In addition, children who are seen first with unilateral involvement and in whom bilateral slipped capital femoral epiphysis later develops have a younger age at presentation than children in whom the disorder does not develop bilaterally^{28,68,72,108,116}. This difference is seen in both the chronological age (twelve compared with thirteen years) and the pelvic bone age. Of those with unilateral involvement, 60 percent have a slipped capital femoral epiphysis in the left hip⁷².

The predilection for slipped capital femoral epiphysis varies by race. The relative racial frequency of slipped capital femoral epiphysis is 1.0 for whites, 4.5 for Pacific Islanders, 2.2 for blacks, 1.05 for Amerindian peoples (Native Americans and Hispanics), 0.5 for Indonesian-Malay peoples (Chinese, Japanese, Thai, Vietnamese, and so on), and 0.1 for Indo-Mediterranean peoples (those of Near East, North African, or Indian subcontinent ancestry)⁷². There are at least two possible explanations for these racial differences. One is that they reflect the mean body weight for each racial group, which further supports the theory that obesity is a major factor in the cause of the disorder⁷². The second explanation is that there is a racial variability in acetabular depth and femoral head coverage; the acetabula in adolescent black children are deeper than those in white children⁶⁴.

Classification

Slipped capital femoral epiphysis is classified according to both the clinical nature and the magnitude of the disorder. The traditional clinical categories are pre-slip, acute, chronic, and acute-on-chronic^{1,5,15,32,126}. Classification into these four categories depends on the patient's history, physical examination, and radiographs.

In the pre-slip stage, patients usually complain of weakness in the leg, limping, or pain in the groin or the knee on exertion. Prolonged standing or walking may produce these symptoms. On physical examination, the most consistent positive finding is lack of internal rotation. On radiographs, there may be generalized osteopenia of the hemipelvis and the proximal part of the femur in patients who limp or who have limited their activity. There may be widening and irregularity of the physis⁹³.

An acute slipped capital femoral epiphysis is an abrupt displacement through the proximal physis in which there was a preexisting epiphysiolysis³². Ten to 15 percent of slipped capital femoral epiphyses have been acute in most large series^15,68. The clinical criteria for an acute slipped capital femoral epiphysis include a duration of symptoms of less than three weeks and demonstration of an external rotation deformity, shortening, and marked limitation of motion secondary to pain on physical examination. In general, the greater the amount of slip, the more the motion is restricted. However, 67 percent of patients with an acute slipped capital femoral epiphysis have a one to three-month history of mild prodromal symptoms before the acute episode, indicating that there was a pre-slip or a mildly slipped capital femoral epiphysis prior to the acute episode^{1,15,21,32,106}. The traumatic episode may be as trivial as turning over in bed. The pain is usually severe enough to prevent weight-bearing.

Chronic slipped capital femoral epiphyses are by far the most common and account for 85 percent of all slips⁶⁸. Patients with a chronic slipped capital femoral epiphysis present with pain in the groin, thigh, and knee that varies in duration, often ranging from months to years. They may have a history of exacerbations and remissions of the pain and limp. Physical examination demonstrates an antalgic gait, with loss of internal rotation, abduction, and flexion of the hip⁹⁶. In more severe cases, patients have a limb-length discrepancy and a natural positioning of the lower extremity in external rotation. As the hip is flexed, the lower extremity spontaneously moves into a position of increased external rotation. Importantly, 46 percent of the patients have pain in the knee or the distal part of the thigh as the initial symptom, emphasizing the importance of a hip examination in a child who complains of knee pain^19,49.

An acute-on-chronic slipped capital femoral epiphysis is one associated with chronic symptoms initially and with subsequent development of acute symptoms as well as a sudden increase in the degree of slip.

The traditional classification depends on the memory of the child or parent, or both, and may be inaccurate; it also does not give a prognosis with regard to the potential for avascular necrosis. Two newer and more clinically useful classifications, one clinical and one radiographic, depend on physeal stability. The clinical classification depends on the ability of the child to walk⁷⁰. The slipped capital femoral epiphysis is considered stable when the child is able to walk with or without crutches, and it is considered unstable when the child cannot walk with or without crutches. The radiographic classification depends on the presence or absence of a hip effusion on ultrasonography^58,59. If the ultrasound demonstrates the absence of metaphyseal remodeling and the presence of an effusion, an acute event is likely to have occurred and the slipped capital femoral epiphysis is considered unstable. If the ultrasound demonstrates metaphyseal remodeling and the absence of an effusion, an acute event has not occurred and the slipped capital femoral epiphysis is considered stable.

This classification is important because it is predictive of the prognosis. The traditional classification of slips as acute or chronic is misleading because it does not consider the stability of the hip, which is highly predictive of the development of avascular necrosis. Unstable slipped capital femoral epiphyses have a much higher prevalence of avascular necrosis (up to 50 percent in some series) compared with stable slipped capital femoral epiphyses (nearly 0 percent)⁷⁰. The high rates of complications with unstable slips are most likely secondary to vascular injury caused at the time of the initial displacement^8,70. The development of avascular necrosis is associated with the findings on bone scans made before treatment. A cold bone scan (demonstrating an absence of vascularity) essentially is seen only in unstable cases. When a patient has such a bone scan, the risk of subsequent development of avascular necrosis is 80 to 100 percent¹⁰¹. The symptoms of a child with an unstable slipped capital femoral epiphysis mimic those of a child with a hip fracture, and indeed the slipped capital femoral epiphysis may be considered a type of Salter-Harris type-I fracture¹⁰³. The child has severe pain and resists any passive or active attempt to move the lower extremity. The extremity is held in a flexed and externally rotated position.

Radiographs demonstrate an inferior and posterior slip of the proximal femoral epiphysis relative to the metaphysis. In a gradual slip, there are radiographic signs of superior and anterior remodeling on the femoral metaphysis and of periosteal new bone formation at the epiphyseal-metaphyseal junction posteriorly and inferiorly. In an early slip, the changes can be subtle and both anteroposterior and lateral radiographs must be made. The epiphysis typically slips posteriorly⁹⁶ and as such is often seen only on a lateral radiograph in the earlier stages. Other helpful radiographic signs are the metaphyseal blanch sign of Steel¹¹⁷ and Klein's line⁶⁵ (Fig. 1). The metaphyseal blanch sign of Steel is a double density seen at the level of the metaphysis on an anteroposterior radiograph; the double density reflects the posterior cortical lip of the epiphysis as it is beginning to slip posteriorly and is radiographically superimposed on the metaphyseal density. Klein's line is drawn on a radiograph along the anterior or superior aspect of the femoral neck; the epiphysis should normally intersect this line. In an early slipped capital femoral epiphysis, the epiphysis is flush with or even below this line.

Other imaging methods may be needed in the evaluation of a child with a slipped capital femoral epiphysis. A bone scan¹⁰¹ and a magnetic resonance imaging scan allow earlier diagnosis of avascular necrosis and chondrolysis. Advances in ultrasonography have allowed visualization of an effusion in the hip (a sign of an unstable slipped capital femoral epiphysis) and remodeling of the femoral neck (a sign of a stable slipped capital femoral epiphysis). Computerized tomography scanning provides three-dimensional imaging of a slipped capital femoral epiphysis, creating an awareness that the epiphysis remains in the acetabulum while the femoral neck displaces anteriorly. This process results in a retroversion deformity of the proximal part of the femur.

The severity of a slipped capital femoral epiphysis is commonly assessed by two different methods. The first is evaluation of the amount of displacement of the epiphysis on the metaphysis. The disorder is considered mild when the epiphyseal-metaphyseal displacement is less than one-third of the width of the femoral neck, moderate when the displacement is one-third to one-half of the width of the femoral neck, and severe when the displacement is greater than one-half of the width of the femoral neck⁴⁹. However, because of the remodeling associated with a gradual slip⁷⁶, this method is less accurate than the angular measurement method, which typically involves measurement of the epiphyseal-shaft angle on the frog-leg lateral radiograph as described by Southwick¹¹². The angle of slip can also be categorized into groups. Slip angles of less than 30 degrees are considered mild; those of 30 to 50 degrees, moderate; and those of more than 50 degrees, severe¹⁵. This classification is probably most important with regard to long-term prognosis. Mild and moderate slips have an excellent long-term prognosis with regard to the Iowa hip score when treated with in situ pinning, whereas severe slips are associated with a more rapid decline in Iowa hip scores over time^19,20.

Treatment

The most important priority in the management of a patient with a slipped capital femoral epiphysis is primum non nocere (first, do no harm)⁷. Most investigators agree that once a slipped capital femoral epiphysis has been diagnosed, treatment is indicated to prevent progression of the slip. The goal of treatment is to prevent additional slippage while avoiding the complications of avascular necrosis and chondrolysis. Chondrolysis is defined as narrowing of the joint space to at least one-half of that in the contralateral hip in unilateral cases and as narrowing of the joint space to less than three millimeters in bilateral cases^49,81,124. There are several treatment methods, and each has its own advantages and disadvantages.

The treatment of a patient with a slipped capital femoral epiphysis has changed because of improved imaging techniques. Twenty-five years ago, radiographs were the only imaging technique used to evaluate a patient with the disorder. Patients were often treated with in situ fixation with multiple pins, and intraoperative spot radiographs were used to control pin placement. Pin placement was not always ideal with this technique, and malpositioned pins were associated with complications, including additional slippage, chondrolysis, and avascular necrosis in 20 to 40 percent of patients^7,125. The high rate of complications associated with in situ fixation with multiple pins led others to try treatment with a hip-spica cast, open epiphyseodesis, or femoral osteotomy. The development of intraoperative fluoroscopy to assist in the placement of internal fixation devices has markedly lowered the complication rate associated with internal fixation.

Stable Slipped Capital Femoral Epiphysis

The current treatment methods for a patient with a stable (chronic) slipped capital femoral epiphysis include: (1) immobilization in a hip-spica cast¹², (2) in situ stabilization with single or multiple pins or screws^5,7,120,126, (3) open epiphyseodesis with iliac crest^97,127 or allogeneic¹⁰⁷ bone graft, (4) open reduction with a corrective osteotomy through the physis and internal fixation with use of multiple pins^25,123, (5) compensating base-of-neck osteotomy with in situ stabilization of the slipped capital femoral epiphysis with use of multiple-pin fixation^9,67, and (6) intertrochanteric osteotomy with internal fixation¹¹². The advantages and disadvantages of each method are discussed below.

Hip-Spica Cast

Immobilization in a bilateral hip-spica cast avoids the complications associated with an operative procedure. The prevalence of bilateral slipped capital femoral epiphysis is approximately 20 to 40 percent^41,50,51,72, and a hip-spica cast also provides prophylactic treatment of the contralateral hip. Hurley et al.⁴⁷ compared the results of in situ pinning in 169 patients with those of immobilization in a hip-spica cast in thirty patients. After a mean duration of follow-up of 2.8 years, slipped capital femoral epiphysis had developed in the contralateral hip of sixty-one patients (36 percent) treated with in situ pinning. After a mean duration of follow-up of 3.6 years, slipped capital femoral epiphysis had developed in the contralateral hip of two patients (7 percent) treated with a hip-spica cast. Betz et al.¹² evaluated thirty-two patients (thirty-seven hips) treated with a hip-spica cast. A reduction was not attempted, and the cast was worn until the metaphyseal lucency adjacent to the physis was no longer visible on radiographs. The duration of immobilization in the cast averaged twelve weeks. Avascular necrosis did not develop in any hip, but the slip progressed in two hips (5 percent) and chondrolysis developed in seven (19 percent). Meier et al.⁸² evaluated thirteen patients (seventeen hips) who were treated with a hip-spica cast for a mean duration of twelve weeks. The slip progressed in three hips, chondrolysis developed in nine, and full-thickness cast-pressure sores developed in two. In total, complications occurred in fourteen of the seventeen hips, which led those authors to abandon the hip-spica cast as a treatment for slipped capital femoral epiphysis. In addition to the high rate of complications, the hip-spica cast is awkward and cumbersome for the family, particularly if the patient is obese. The hip-spica cast does not stabilize the slipped capital femoral epiphysis, and most investigators have reported progression of the slip in 5 to 10 percent of patients, despite immobilization in the cast^12,82. For all of these reasons, we do not recommend a hip-spica cast for treatment of slipped capital femoral epiphysis.

In Situ Stabilization with Use of Single or Multiple Pins or Screws

Since O'Brien and Fahey⁸⁸ reported on the remodeling potential of the proximal part of the femur in patients with a slipped capital femoral epiphysis, in situ fixation with multiple pins has been the most popular treatment method. Long-term follow-up studies of in situ fixation have shown that postoperative remodeling occurs and that the loss of internal rotation of the hip in most patients is not clinically relevant^11,52. In the past, the three-dimensional anatomy of slipped capital femoral epiphysis was not well understood and reliable intraoperative imaging techniques were not available. As a result, insertion of the pins often was started on the lateral aspect of the femoral shaft, a technique similar to that used in treating a hip fracture in an adult. Since the proximal part of the femur is retroverted in a patient with a slipped capital femoral epiphysis, the pins were often placed in the anterosuperior aspect of the epiphysis, achieving suboptimal fixation. To improve fixation, clinicians angled the pins more posteriorly. The pins often exited the posterior aspect of the femoral neck and entered the epiphysis in the posterosuperior quadrant, which jeopardized the blood supply to the femoral head (Fig. 2).

The most important contribution to the blood supply to the femoral head is from the lateral epiphyseal vessels²². Brodetti¹⁷ demonstrated that the lateral epiphyseal vessels enter the femoral head in the posterosuperior quadrant and anastomose with the vessels from the round ligament at the junction of the medial and central thirds of the femoral head (Fig. 3). The ideal position for a screw, therefore, is in the central area or neutral zone of the femoral head. If a pin is placed in the posterosuperior quadrant, the risk of damage to the epiphyseal blood supply is increased. This risk is minimized by placement of a single screw in the center of the epiphysis, perpendicular to the physis⁵. A comparison of single-screw fixation and double-screw fixation in a calf model demonstrated only a slight increase in stiffness with two screws, which does not justify the increased risk of complications associated with the use of two screws⁶⁰.

Another reason to use as few pins or screws as possible is that, even with the use of anteroposterior and true lateral radiographs, there is an area (the "blind spot") that cannot be visualized¹²⁵. This blind spot is often the site of unrecognized pin protrusion. Pin protrusion can be associated with the development of chondrolysis and subchondral bone changes. With multiple pins, the possibility that one or more will protrude into the joint is increased; this risk is lowered when a single screw is used^14,84,126. The advantages of single-screw fixation in a patient with a stable slipped capital femoral epiphysis include a high rate of success and a low prevalence of additional slippage and of complications^5,39,118. It is presently the most common treatment for slipped capital femoral epiphysis in North America.

Operative technique: The technique for percutaneous insertion of a single screw has been previously described^5,84. The patient is positioned on a fracture table or radiolucent table in the supine position to allow simultaneous biplane anteroposterior and lateral fluoroscopic imaging. It is important to emphasize that the technique is image-dependent, so excellent visualization of the femoral head and neck is required before the procedure is begun. Since the procedure is performed percutaneously through a small skin incision with use of a cannulated screw, it is important to locate the proper starting position for the guide-pin. To determine the starting point, a guide-pin is placed on the skin overlying the proximal part of the femur and, under anteroposterior fluoroscopic guidance, the pin is positioned such that it projects over the center of the femoral neck and head, crossing the physis in a perpendicular fashion. Once this pin position has been obtained, a marking pen is used to draw a line on the skin reflecting the pin position on the anteroposterior image. The same procedure is used for the lateral fluoroscopic image, and a one-centimeter skin incision is made at the intersection of the two lines (Fig. 4). The guide-pin is advanced freehand through the soft tissues to engage the anterolateral femoral cortex. The position and angulation of the guide-pin are adjusted, with fluoroscopic guidance, to obtain the proper alignment before the guide-pin is drilled into the bone. It is ideal to advance the guide-pin into the center of the femoral head, perpendicular to the physis, as seen on both the anteroposterior and the lateral fluoroscopic images on the first attempt, since multiple drill-holes can weaken the bone, causing a fracture through an unused hole¹⁸. After the appropriate screw length has been determined, a 7.3-millimeter stainless-steel cannulated screw is placed over the guide-pin and is advanced until five threads engage the epiphysis (Fig. 5-A, Fig. 5-B, Fig. 5-C, and Fig. 5-D). The screw should not be left protruding beyond the lateral aspect of the femoral shaft, where it can be toggled by the soft tissues, leading to screw loosening⁷⁸. After surgery, the patient begins partial weight-bearing with use of crutches and gradually advances to full weight-bearing as tolerated. Most patients can walk without crutches within two to four days.

The results of single-screw fixation in patients with slipped capital femoral epiphysis have been gratifying. Aronson and Carlson⁵ reported excellent or good results in thirty-six (95 percent) of thirty-eight mild slips, ten of eleven moderate slips, and eight of nine severe slips. Avascular necrosis developed in only one patient (2 percent), with an unstable slipped capital femoral epiphysis, and chondrolysis developed in none. Ward et al.¹²⁶ reported on forty-two patients (fifty-three hips) with a slipped capital femoral epiphysis treated with single-screw fixation. After a mean duration of follow-up of thirty-two months, 92 percent of the patients demonstrated physeal fusion and were able to participate in full activities. Neither chondrolysis nor avascular necrosis developed in any patient. Samuelson and Olney¹⁰⁴, using a similar percutaneous technique, reported excellent results in seven patients treated with two Knowles pins and in seventeen patients treated with a single Knowles pin.

Open Epiphyseodesis with Iliac Crest or Allogeneic Bone Graft

Open epiphyseodesis with iliac crest bone graft to stabilize the slipped capital femoral epiphysis was first reported by Ferguson and Howorth³³, in 1931. This procedure avoids the complications associated with internal fixation, including unrecognized pin protrusion, damage to the lateral epiphyseal vessels, and hardware failure. The surgical technique involves an anterior iliofemoral exposure of the hip joint. A rectangular window of bone is removed from the anterior aspect of the femoral neck. A hollow mill is used to create a cylindrical tunnel across the physis, and multiple corticocancellous strips of iliac crest bone graft are driven into the tunnel as bone pegs across the proximal femoral physis (Fig. 6). Weiner et al.¹²⁷ reported on their thirty-year experience with this technique, which they used to treat 159 patients (185 hips) who had a slipped capital femoral epiphysis. Additional slipping developed in four hips (2 percent); avascular necrosis, in one (1 percent); and chondrolysis, in none.

An advantage of open epiphyseodesis with iliac crest bone graft is that the graft is inserted at the correct angle in the center of the femoral head, minimizing the risk of damage to the blood supply of the femoral head. The graft is not inserted as deeply as is recommended for internal fixation, so there is less risk of graft protrusion into the hip joint. However, the fixation provided by the iliac crest bone graft is not as secure as that achieved by internal fixation. Rao et al.⁹⁷ evaluated forty-three patients (sixty-four hips) treated by open bone-peg epiphyseodesis. At the time of healing, twenty-seven hips (42 percent) had had additional slipping. Avascular necrosis developed in four hips (6 percent); chondrolysis, in three (5 percent); and additional complications, in fourteen (22 percent). Other disadvantages of open bone-peg epiphyseodesis include increased blood loss, a longer duration of anesthesia, and a larger scar. As a result of these complications, Rao et al. stated that they no longer recommend open bone-peg epiphyseodesis as the initial treatment for slipped capital femoral epiphysis.

Schmidt et al.¹⁰⁷ developed a technique to percutaneously place a freeze-dried, irradiated cortical strut allograft across the physis. The technique is similar to that used for the percutaneous insertion of a single screw but, instead of a screw, a ten-millimeter cannulated reamer is placed over the guide-pin to ream a channel to within two millimeters of the subchondral bone. A cortical strut allograft then is passed into the channel and is advanced until at least one centimeter is across the physis. Schmidt et al. evaluated thirty-one patients (thirty-eight hips) who had a mean duration of follow-up of three years and six months and reported that the Harris hip rating was excellent for thirty-five hips, good for one, and fair for two. Six patients (19 percent) had a major complication, including avascular necrosis, chondrolysis, femoral neck fracture, subtrochanteric hip fracture, bilateral coxa vara deformity, and unilateral coxa vara deformity in one patient each. Despite these complications, those authors still recommended this technique, particularly for a patient with a severe slipped capital femoral epiphysis.

Open Reduction with Corrective Osteotomy Through the Physis and Internal Fixation with Use of Multiple Pins

A cuneiform osteotomy through the physis is the ideal method with which to correct the retroversion deformity of the femoral neck, but is it safe? The surgical technique involves an anterior Smith-Petersen²⁵ or anterolateral¹²³ exposure of the hip. A wedge of bone is removed from the metaphysis of the femoral neck. This allows the epiphysis to be anatomically repositioned on the metaphysis without creating tension on the epiphyseal vasculature (Fig. 7). The osteotomy is created with use of osteotomes, rongeurs, curets, and a Kerrison punch (Codman, Raynham, Massachusetts). After the femoral neck is sufficiently shortened, the epiphysis is reduced and internally fixed with use of three pins. Fish³⁴ performed the cuneiform osteotomy in sixty-one patients (sixty-six hips) and reported that fifty-five hips (83 percent) had an excellent result; six (9 percent), a good result; two (3 percent), a fair result; and three (5 percent), a poor result. DeRosa et al.²⁵ evaluated twenty-three patients (twenty-seven hips) with a severe slipped capital femoral epiphysis treated by cuneiform osteotomy. After a mean duration of follow-up of eight years and five months, no hip had an excellent result; nineteen hips (70 percent) had a good result; four (15 percent), a fair result; and four, a poor result. Avascular necrosis developed in four hips (15 percent) and chondrolysis, in eight (30 percent). In addition, two patients (7 percent) lost fixation and required additional surgery, a skin erosion developed over one of the pins and required pin removal, and a buttock pressure sore developed in another patient. Despite the 15 percent rate of avascular necrosis in their study, DeRosa et al. stated that they would still recommend the cuneiform osteotomy for patients with a severe slipped capital femoral epiphysis.

Velasco et al.¹²³ evaluated sixty-five patients (sixty-six hips) treated with open reduction of a slipped capital femoral epiphysis. In sixty hips, the open reduction of the slip was combined with a cuneiform subcapital wedge resection of the femoral neck according to the technique described by Dunn and Angel²⁹. At a mean of sixteen years, chondrolysis had developed in eight hips (12 percent) and avascular necrosis, in seven (11 percent). Of the forty-eight hips that had been followed for a minimum of ten years (mean, 20.6 years), twenty-two (46 percent) had a good result; sixteen (33 percent), a moderate result; and ten (21 percent), a poor result. Degenerative arthritis was seen in nineteen (40 percent) of the forty-eight hips. Because of the high risk of avascular necrosis and subsequent poor results in most series, we do not recommend a physeal cuneiform osteotomy as the initial treatment of slipped capital femoral epiphysis.

Compensating Base-of-Neck Osteotomy with in Situ Stabilization of the Slipped Capital Femoral Epiphysis with Use of Multiple-Pin Fixation

Kramer et al.⁶⁷ described an anterosuperior-based wedge osteotomy of the femoral neck. They stabilized both the osteotomy site and the slipped capital femoral epiphysis with multiple pins (Fig. 8). They reported on fifty-five patients (fifty-six hips) who all had had a positive preoperative Trendelenburg test and had walked with a lurching gait. After the osteotomy, forty-eight patients (87 percent) had a negative Trendelenburg test. Nine hips (16 percent) had a poor result because of pain, a limp, or a decreased range of motion. Avascular necrosis developed in two patients (4 percent) and chondrolysis, in one (2 percent). Barmada et al.⁹ described an extracapsular basilar neck osteotomy that was performed in an attempt to repair slipped capital femoral epiphysis while avoiding the risk of avascular necrosis. The prevalence of avascular necrosis associated with basilar neck osteotomy is less than that associated with cuneiform osteotomy. However, only 35 to 55 degrees of correction is possible with this technique²⁴. One benefit of the basilar neck osteotomy is improvement in hip motion. A disadvantage is that it shortens the femoral neck, which may result in impingement of the greater trochanter against the lateral aspect of the acetabulum during hip abduction. If there is premature closure of the proximal femoral physis, as is often seen in patients with a slipped capital femoral epiphysis, shortening of the femoral neck may aggravate a limb-length discrepancy.

Intertrochanteric Osteotomy with Internal Fixation

Southwick¹¹² described an intertrochanteric osteotomy through the lesser trochanter. This osteotomy improves hip motion and is not associated with avascular necrosis. The technique advocated by Crawford²³ involves an intertrochanteric osteotomy with flexion, abduction, and internal rotation of the distal fragment (Fig. 9). The osteotomy site is fixed with a compression hip screw, and the slipped capital femoral epiphysis, if it is unstable, is fixed with a percutaneous cannulated screw. The intertrochanteric osteotomy is also a compensating osteotomy with correction limited to 45 degrees on the anteroposterior radiograph and to 60 degrees on the lateral radiograph as measured by the Southwick method¹¹³. An anterolateral wedge of bone is removed, so this osteotomy is also a shortening procedure. There is a risk that a limb-length discrepancy will be created if considerable correction is achieved. Schai et al.¹⁰⁵ evaluated fifty-one patients who had a slipped capital femoral epiphysis of 30 to 60 degrees that was treated with an intertrochanteric osteotomy and followed for a mean duration of twenty-four years. Moderate osteoarthritis developed in fourteen patients (27 percent) and severe osteoarthritis, in nine (18 percent). Thirty-five patients (69 percent) had a shorter limb on the affected side, and two patients (4 percent) had a limb-length equalization procedure. Avascular necrosis developed in only one patient (2 percent). A summation of the results of these series indicates that intertrochanteric osteotomy with use of the Southwick technique is not the ideal initial treatment for a slipped capital femoral epiphysis because the outcome of the procedure is relatively poor compared with that of current techniques of in situ single-screw fixation.

Jerre et al.⁵³ evaluated the results of different realignment procedures in thirty-six patients (thirty-seven hips) after a mean duration of follow-up of 33.8 years (range, twenty-six to forty-two years). Serious short-term complications developed in seven (32 percent) of the twenty-two hips treated with subcapital osteotomy, three of the eleven hips treated with intertrochanteric osteotomy, and three of the four hips treated with manipulative reduction. Jerre et al. reported that 41 percent of the hips treated with subcapital osteotomy, four of those treated with intertrochanteric osteotomy, and none of those treated with manipulative reduction had an excellent or good result.

Unstable Slipped Capital Femoral Epiphysis

The treatment of an unstable slipped capital femoral epiphysis (acute or acute-on-chronic) is similar to that of a stable slipped capital femoral epiphysis but is considerably more controversial. The role of immediate reduction compared with delayed reduction is controversial, as is the role of preoperative traction. Loder et al.⁷⁰ compared the results of treatment in twenty-five hips (twenty-four patients) that had a stable slipped capital femoral epiphysis with those in thirty hips (thirty patients) that had an unstable slipped capital femoral epiphysis. The result was satisfactory in 96 percent of the twenty-five hips that had a stable slipped capital femoral epiphysis and in 47 percent of the thirty hips that had an unstable slipped capital femoral epiphysis. Avascular necrosis developed in none of the hips in the former group and in fourteen hips (47 percent) in the latter group. De Sanctis et al.²⁶ evaluated seventy patients (eighty-one hips) who had an unstable slipped capital femoral epiphysis (acute or acute-on-chronic) that was treated with a gentle closed reduction and fixation with use of one or two screws or pins. A complication developed in eight hips: three (4 percent) had chondrolysis, three had a wound infection, and two (2 percent) had avascular necrosis. De Sanctis et al. concluded that a gentle reduction with percutaneous single-screw fixation is a stable, safe, and reliable method for treating patients who have an unstable slipped capital femoral epiphysis.

Herman et al.⁴⁵ evaluated the cases of twenty-one patients (twenty-one hips) with a severe slipped capital femoral epiphysis (a displacement of more than 50 percent) after a mean duration of follow-up of 2.8 years. Fifteen patients had an unstable slipped capital femoral epiphysis; nine of them were treated with a gentle closed reduction and internal fixation with use of either one or two screws. Five of the nine hips had a complete reduction of the slipped capital femoral epiphysis, and avascular necrosis developed in three of them. Four hips had an incomplete reduction, and none had avascular necrosis. The authors hypothesized that injury to the epiphyseal vasculature occurs at the time of the acute slipped capital femoral epiphysis.

Peterson et al.⁹² evaluated ninety-one patients (ninety-one hips) with an unstable slipped capital femoral epiphysis after a mean of forty-four months. Forty-two hips had a closed reduction performed less than twenty-four hours after presentation, and avascular necrosis developed in three (7 percent). Forty-nine hips had a closed reduction performed more than twenty-four hours after presentation, and avascular necrosis developed in ten (20 percent). The authors hypothesized that the acute displacement of the femoral head may kink the posterior blood vessels, compromising the blood flow to the epiphysis. In this situation, a timely reduction of the slipped capital femoral epiphysis may restore blood flow to the epiphysis. In contrast, Loder et al.⁷⁰ assigned patients who had an acute slip into two groups on the basis of the time-interval between the onset of symptoms and the operative stabilization. Avascular necrosis developed in seven of eight hips that had operative stabilization less than forty-eight hours after the onset of symptoms and in seven (32 percent) of twenty-two hips that had operative stabilization more than forty-eight hours after the onset of symptoms. However, the present data cannot be used to develop guidelines with regard to the exact timing of operative stabilization, since the cause-and-effect relationship between the timing of operative stabilization and the development of avascular necrosis cannot be determined. We do not know whether a hip with a more severe unstable slipped capital femoral epiphysis, which would likely be associated with a higher risk of avascular necrosis, was stabilized sooner in an effort to reduce the child's discomfort as quickly as possible, or whether a hip with a less severe unstable slipped capital femoral epiphysis, which theoretically might be associated with a lower risk of avascular necrosis, was stabilized later since the child may have been more comfortable.

Complications

Avascular Necrosis

Avascular necrosis is the most devastating complication of slipped capital femoral epiphysis (Fig. 10). The factors responsible for the development of avascular necrosis are an acute unstable slipped capital femoral epiphysis, overreduction of an acute slipped capital femoral epiphysis, attempts at reduction of the chronic component of an acute-on-chronic slipped capital femoral epiphysis, placement of pins in the superolateral quadrant of the femoral head, and femoral neck osteotomy^{17,19,22,27,66,70}. The frequency of avascular necrosis is increased if a cuneiform or basilar neck osteotomy is performed prior to physeal closure. The complication of avascular necrosis is rare in patients with a stable slipped capital femoral epiphysis, but it occurs frequently in patients with an unstable slipped capital femoral epiphysis⁷⁰. A patient with avascular necrosis typically complains of pain in the groin or knee. On physical examination, there is a loss of motion of the hip, particularly internal rotation, and the hip is irritable on passive internal and external rotation. Plain radiographs are unremarkable early in the course of the disorder, but changes diagnostic of avascular necrosis (collapse of the femoral head with cyst formation and sclerosis) develop after a few months. All cases of avascular necrosis after slipped capital femoral epiphysis are radiographically apparent within one year. An early bone scan¹¹⁹ or magnetic resonance image often shows asymmetry between the femoral heads, predicting the eventual development of avascular necrosis.

The treatment of avascular necrosis is not particularly rewarding for the patient or the clinician. Non-weight-bearing walking with crutches, range-of-motion exercises, and anti-inflammatory medication may help to minimize symptoms and epiphyseal collapse. An internal fixation device that protrudes into the hip joint should be backed out of the joint or removed, if the physis is closed, to reduce additional damage to the hip. In severe cases, a hip arthrodesis or joint arthroplasty may be needed.

Chondrolysis

The etiology of chondrolysis in slipped capital femoral epiphysis is unknown. The possible role of an autoimmune phenomenon or some factor interfering with cartilage nutrition is yet to be defined. Risk factors leading to chondrolysis include immobilization in a cast, unrecognized permanent pin penetration, severe slipped capital femoral epiphysis, and prolonged symptoms before treatment.

The prevalence of chondrolysis in patients with a slipped capital femoral epiphysis is 5 to 7 percent^48,79. A patient typically complains of pain in the groin or knee, and physical examination demonstrates a loss of hip motion, particularly internal rotation. The diagnosis is confirmed by radiographs that demonstrate a decrease in the width of the joint space of greater than 50 percent compared with the uninvolved side or, in patients who have bilateral involvement, a joint space of less than three millimeters. Hips that demonstrate increased uptake with premature closure of the greater trochanter on an early bone scan have been associated with an increased risk for the development of chondrolysis⁷⁹. The prevalance of chondrolysis increases with the increasing severity of the slipped capital femoral epiphysis, but it is not increased in the black population^6,13,63,115 as previously reported^48,91,122. The frequency of chondrolysis can be reduced with use of single-screw fixation rather than fixation with multiple screws or pins. With multiple pins or screws, the possibility that one or more may protrude into the joint is increased, and pin protrusion has been associated with an increased risk of chondrolysis³⁸. The frequency of chondrolysis can also be reduced by not using a hip-spica cast⁸² and by waiting until physeal closure prior to performing a subtrochanteric osteotomy³⁵.

As is the case with avascular necrosis, the treatment of chondrolysis is not particularly rewarding for the patient or the clinician. Non-weight-bearing walking with crutches, range-of-motion exercises, and anti-inflammatory medication may help to alleviate the symptoms. If there is pin protrusion, backing the pin out of the joint or removing it, if the physis is closed, helps to minimize damage to the hip. Some have recommended lengthening of the contracted muscle or muscles if a hip contracture develops. Arthrodesis may also be necessary in severe cases.

Internal Fixation Devices

The frequency of problems related to internal fixation devices (slip progression, pin breakage, and joint penetration by the pins) is decreasing with the use of fluoroscopic guidance and cannulated single-screw fixation. The risk of fracture through an unused pinhole can be avoided with use of fluoroscopy to position the guide-pin correctly on the first attempt and by entering the bone proximal to the lesser trochanter.

Natural History without Treatment

Two major issues arise when slipped capital femoral epiphysis is untreated: the risk of additional progression and the risk of degenerative joint disease in adult life. Unfortunately, there are few long-term studies of patients with a slipped capital femoral epiphysis and even fewer that have included untreated patients^{15,19,20,42,89,93,102}.

Risk of Progression

The natural history of slipped capital femoral epiphysis is unpredictable, and the risk of additional progression is difficult to ascertain. Ordeberg et al.⁹⁰ studied a series of patients twenty to sixty years after diagnosis of slipped capital femoral epiphysis without primary treatment. Few patients had restrictions in working capacity or social life. However, there was a risk of slip progression as long as the physis remained open⁵⁴. Carney et al.¹⁹ reported on thirty-six cases of slipped capital femoral epiphysis that were initially observed. Additional displacement occurred in six hips (17 percent) after the initial diagnosis; the slipped capital femoral epiphysis became severe in five of them. Of these six hips, two were untreated and the other four were stabilized surgically. Eleven of the original thirty-six patients had an acute episode superimposed on the chronic slipped capital femoral epiphysis. All eleven slips progressed to severe displacement and required surgical stabilization.

Risk of Degenerative Joint Disease

Little is known about the risk of degenerative joint disease. Howorth⁴⁶ stated that slipped capital femoral epiphysis is likely the most frequent cause of degenerative joint disease of the hip in middle-aged patients, and it is a common source of pain and disability. However, this theory is not necessarily supported by other studies. In reviews of a large series of patients with degenerative joint disease, the numbers of patients who were known to have a slipped capital femoral epiphysis have been small, averaging approximately 5 percent^57,86,110. Murray⁸⁶, however, reported an association with slipped capital femoral epiphysis in 40 percent of his 200 patients who were thought to have primary degenerative joint disease. He described a tilt deformity caused by bone resorption laterally with new bone formation medially, which he thought was compatible with an old slipped capital femoral epiphysis. Stulberg et al.¹²¹ described a similar deformity, the pistol-grip deformity, in 40 percent of patients without known prior hip disease who had total hip arthroplasty. This deformity was also thought to be compatible with an old slipped capital femoral epiphysis. Resnick¹⁰⁰, however, refuted this theory in a pathological study of forty-eight femoral heads from patients with evidence of a tilt deformity on radiographs. The specimens suggested that the deformity was solely related to the remodeling changes of osteoarthritis. In summary, whether subclinical forms of slipped capital femoral epiphysis lead to early osteoarthritis remains uncertain because of the controversy over the prevalence of the disorder.

What is known is that the severity of the untreated slipped capital femoral epiphysis correlates with the long-term prognosis with regard to degenerative joint disease^{19,20,55,56,89,105}. Oram⁸⁹ reported on twenty-two hips with an untreated slipped capital femoral epiphysis, eleven of which were observed for more than fifteen years. The hips with a moderate slipped capital femoral epiphysis retained good function for years, whereas degenerative joint disease with resultant poor function developed within fifteen years in the hips with a severe slipped capital femoral epiphysis. Jerre^55,56 and Ross et al.¹⁰² reported increasingly poor results with longer follow-up. In those studies, many patients did well early on, but symptoms increased and function decreased with increasing age. Carney and Weinstein²⁰ also studied the natural history of untreated, chronic slipped capital femoral epiphysis. They evaluated thirty-one hips in twenty-eight patients who had a mean age of fifty-four years and had been followed for a mean of forty-one years. The mean Iowa hip-rating score was 89 points for the entire group, 92 points for the seventeen hips in which the slipped capital femoral epiphysis was mild, 87 points for the eleven hips in which it was moderate, and 75 points for the three hips in which it was severe. There were four complications: displacement to a severe degree in two hips, and chondrolysis and avascular necrosis in one hip each. The chondrolysis developed in a hip in which the slipped capital femoral epiphysis was mild and the avascular necrosis, in a hip in which it was severe. Although patients with a mild slipped capital femoral epiphysis appear to have a favorable prognosis, patients in whom the disorder is moderate or severe have a high prevalence of degenerative joint disease. At a mean of forty-one years after the diagnosis, all hips with a mild slipped capital femoral epiphysis had an Iowa hip-rating score of more than 80 points, whereas only 64 percent of the hips with a moderate or severe disorder had similar ratings. Thirty-six percent of the hips in which the disorder was mild had no degenerative changes; however, all of the hips in which the slipped capital femoral epiphysis was moderate or severe had evidence of degenerative joint disease. Poor results, however, can occasionally be seen even with a minimally slipped capital femoral epiphysis^15,19,20,102. In summary, the natural history of chronic (stable) slipped capital femoral epiphysis is favorable provided that displacement is mild and remains so.

Little data are available on the natural history of untreated acute slipped capital femoral epiphysis. The acute episode is followed by a two to three-week period of intolerance to weight-bearing. As the pain and spasm subside, some motion returns, although the hip remains moderately painful in a position of external rotation. Degenerative changes (joint-space narrowing, subchondral bone cysts, and epiphyseal collapse) develop within a few months, and the patient is left with residual flexion, adduction, and external rotation contractures⁹³ (Fig. 10).

Long-Term Results of Treatment

Wilson et al.¹³² reviewed the results in 300 hips in 240 patients treated between 1936 and 1960; 187 were treated with in situ pinning, with good clinical results in 81 percent and good radiographic results in 77 percent. Seventy-six hips in which correction of the deformity had been attempted had poorer results (60 percent had good clinical results, and 55 percent had good radiographic results). Hall⁴², in a study of 138 patients, reported that the best results were obtained with the use of multiple pins; sixteen (80 percent) of twenty patients had an excellent result. The worst results were seen after realignment had been attempted with manipulation or osteotomy. Osteotomy of the femoral neck led to a poor result in 36 percent of the hips and to avascular necrosis in 38 percent.

Patients with a slipped capital femoral epiphysis in southern Sweden were followed for more than thirty years⁴³. Symptomatic treatment or in situ pinning resulted in high clinical ratings and few radiographic changes, with a secondary reconstructive procedure needed in only 2 percent of the hips. When closed reduction and a spica cast were used, the combined rate of avascular necrosis and chondrolysis was 16 percent and a reconstructive procedure was needed in 35 percent of the hips. When femoral neck osteotomy was performed, the combined rate of avascular necrosis and chondrolysis was 30 percent and a reconstructive procedure was necessary in 15 percent of thirty-three hips.

Carney et al.¹⁹ reported on 155 hips in 124 patients who were followed for a mean of forty-one years and were assessed with use of the Iowa hip-rating system and a radiographic classification of degenerative joint disease, with grade 0 indicating no degenerative disease and grade 3 indicating severe degenerative disease. The slipped capital femoral epiphysis was classified as acute, chronic, or acute-on-chronic. According to the head-shaft angle¹¹², the degree of the slip was mild in 42 percent, moderate in 32 percent, and severe in 26 percent. Twenty-five percent of the hips that had a chronic slipped capital femoral epiphysis received symptomatic treatment only; 30 percent were managed with a spica cast; 24 percent, with in situ pinning; and 20 percent, with osteotomy. The results worsened as the severity of the slip increased and when realignment had been performed (Fig. 11). Avascular necrosis, which developed in 12 percent of the hips, and chondrolysis, which developed in 16 percent, were more common with increasing severity of the slip. Reduction was performed in thirty-nine hips and realignment, in sixty-five hips. For the 116 hips that had not been reduced, the mean Iowa hip rating was 85 points and the mean radiographic grade was 1.7. Avascular necrosis developed in seven (6 percent) of those hips and chondrolysis, in fourteen (12 percent). For the thirty-nine hips with a slipped capital femoral epiphysis that had been reduced, the mean Iowa hip rating was 72 points and the mean radiographic grade was 2.4. Avascular necrosis developed in twelve of those hips (31 percent) and chondrolysis, in eleven (28 percent). Twenty-seven hips with a chronic slipped capital femoral epiphysis that had in situ pinning demonstrated a mean Iowa hip rating of 90 points and a mean radiographic grade of 1.5. Avascular necrosis developed in one of those hips and chondrolysis, in none. The long-term results of that study support the use of in situ pinning as the treatment of choice for slipped capital femoral epiphysis. Realignment was associated with appreciable complications and had an adverse effect on the outcome. Regardless of the severity of the slip, in situ pinning provided the best long-term function and the longest delay of degenerative arthritis with the lowest risk of complications. Although limb-length discrepancy and motion in abduction and internal rotation were affected by the severity of the slip, function was not significantly impaired.

In conclusion, these series demonstrate that, regardless of the severity of the slip, in situ pinning provides the best long-term function, the lowest risk of complications, and the most effective delay of degenerative arthritis. Many patients with a slipped capital femoral epiphysis respond well to this treatment, as seen at the time of long-term follow-up, if the slipped capital femoral epiphysis is mild or moderate in severity, good congruity is maintained between the femoral head and the acetabulum, and avascular necrosis and chondrolysis do not develop. Hips with a severe slipped capital femoral epiphysis and those with avascular necrosis or chondrolysis undergo more rapid deterioration with degenerative changes. Slipped capital femoral epiphysis differs from other pediatric disorders of the hip, such as Legg-Calvç¬erthes disease and developmental hip dysplasia, in that slipped capital femoral epiphysis occurs at an age when the majority of acetabular development is completed and acetabular adaptation to a deformity of the femoral head cannot occur.

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