Slipped Capital Femoral Epiphysis (SCFE)

Introduction and Definitions

Slipped capital femoral epiphysis (SCFE) is a disorder of the adolescent hip in which the proximal femoral physis fails mechanically, allowing the metaphysis to translate and rotate relative to the epiphysis. Although the displacement is conventionally described as the epiphysis “slipping” off the metaphysis, the actual mechanical event is the reverse: the epiphysis stays in the acetabulum while the femoral neck and shaft displace anteriorly and externally rotate beneath it, producing the characteristic posterior and medial position of the femoral head relative to the metaphysis. The condition is one of the most important diagnoses in adolescent orthopedics, since delayed diagnosis is common, the consequences of missed or delayed diagnosis include severe deformity and avascular necrosis with lifelong disability, and the surgical treatment is among the most consequential decisions in pediatric orthopedic practice. This chapter synthesizes content from Tachdjian’s Pediatric Orthopaedics, Apley & Solomon’s, Miller’s Review, and Operative Hip Arthroscopy.

Epidemiology

The incidence of SCFE is approximately 10-11 per 100,000 in the United States, with substantial variation by sex, ethnicity, and geographic region. Boys are affected approximately 1.5 to 2 times more often than girls. The peak age of onset is 13 years in boys and 11 years in girls, reflecting the timing of pubertal growth and physeal maturation. Bilateral SCFE occurs in 20-40% of cases overall, with the contralateral slip typically developing within 18-24 months of the initial slip. The condition is significantly more common in African American, Hispanic, and Polynesian populations than in white European-descended populations. The classical risk factor profile is the obese adolescent male in late puberty (so-called “Andy Gump” body habitus of relative short stature for weight, with delayed sexual maturation).

Etiology and Pathogenesis

The fundamental defect in SCFE is mechanical failure of the proximal femoral physis under physiological load. Several factors contribute to the increased risk during the adolescent growth spurt: (1) the physis is most active during pubertal growth, and the rapid metaphyseal expansion produces a thicker but mechanically weaker physeal cartilage; (2) the orientation of the physis becomes more vertical during the adolescent growth spurt, increasing the shear forces across it; (3) excess body weight in the obese patient increases the loading; (4) hormonal factors — particularly the imbalance between sex steroids and growth hormone — affect the strength of the physeal cartilage. The classical hormonal associations include the condition’s predilection for the period of late puberty (when the growth plate is most vulnerable) and its strong association with endocrine disorders. The endocrine risk factors deserve specific mention because they have important clinical implications. SCFE is associated with hypothyroidism, growth hormone deficiency, panhypopituitarism, hypogonadism, renal osteodystrophy (where the SCFE is bilateral and often associated with severe deformity), and radiation exposure of the pelvis. The classical

teaching is that any patient with SCFE outside the typical age range (younger than 10 or older than 16) should undergo endocrine evaluation; many practitioners now recommend endocrine screening (TSH, growth factors, electrolytes including calcium and phosphate, renal function) for any SCFE patient given the prevalence of subclinical endocrine disease.

Classification

Temporal Classification The classical temporal classification recognizes three types based on the duration of symptoms: Acute SCFE: Symptoms present for less than 3 weeks. The patient typically presents with sudden onset of severe hip or knee pain, often with a precipitating event (a fall, a trip, a sporting injury) and is unable to bear weight. The physeal injury is recent and the physis is still potentially capable of healing in a corrected position. Chronic SCFE: Symptoms present for more than 3 weeks. The patient typically reports a gradual onset of hip or knee pain over weeks to months, sometimes with antalgic gait and external rotation of the affected limb. The physis has been progressively displacing over time and may have begun to remodel. Acute-on-chronic SCFE: A history of chronic symptoms of weeks to months, with a sudden worsening associated with acute mechanical event. This combination is particularly common and represents the chronic remodeling of the physis with superimposed acute additional displacement. Stability Classification (Loder) The Loder classification (1993), based on ability to weight-bear, has become the most important practical classification because it predicts the risk of avascular necrosis: Stable SCFE: The patient can bear weight on the affected limb, with or without crutches. The risk of avascular necrosis (AVN) is approximately 5%. Unstable SCFE: The patient cannot bear weight on the affected limb even with crutches. The risk of avascular necrosis is approximately 50% — a tenfold increase over the stable form, and the most consequential single clinical finding for prognosis. Radiographic Severity Classification The Southwick classification (modified) grades the severity of the slip on the lateral radiograph by the head-shaft angle: Mild: Head-shaft angle less than 30° greater than the contralateral side. Moderate: Head-shaft angle 30-50° greater than the contralateral side. Severe: Head-shaft angle greater than 50° greater than the contralateral side.

The Wilson classification provides a similar grading based on the percentage of displacement of the epiphysis relative to the metaphysis: mild (<33%), moderate (33- 50%), severe (>50%).

Clinical Features

The classical presentation is of an obese adolescent with a limp and pain in the hip, groin, anterior thigh, or — characteristically — the knee. The phenomenon of referred knee pain from a hip lesion is one of the great teaching points of pediatric orthopedics: the obturator nerve innervates both the hip joint capsule and the medial knee, and pathology of the hip can produce isolated knee pain that completely conceals the underlying hip diagnosis. The orthopedic teaching is therefore: “in any adolescent with knee pain, examine the hip; in any adolescent with hip pain, examine the knee.” Failure to examine the hip in an adolescent with knee pain has been the cause of countless missed and delayed SCFE diagnoses, with the consequences of more severe slip, increased difficulty of treatment, and worse outcomes. The acute unstable SCFE presents with severe pain, inability to bear weight, and the limb held in obvious external rotation with shortening. The chronic stable SCFE presents with gradual onset of mild to moderate hip or knee pain, antalgic limp, decreased internal rotation of the hip, and the limb in slight external rotation at rest. Physical examination reveals: decreased internal rotation of the hip (the most consistent and reliable finding); the classical Drehmann sign (when the affected hip is flexed, it goes into obligatory external rotation rather than the normal slight internal rotation); the limb in mild to severe external rotation at rest; apparent shortening of the limb; antalgic gait or, in unstable disease, inability to bear weight. The contralateral hip should be examined carefully, since bilateral involvement is common and contralateral SCFE may be present even when asymptomatic.

Imaging

Plain radiographs are the standard initial imaging study, and the indispensable views are the AP pelvis and the frog-lateral (or true lateral) view of both hips. The AP pelvis alone is insufficient because the typical posterior slip of the epiphysis is best seen on the lateral view; many missed SCFEs reflect inadequate imaging rather than misinterpretation. The classical AP-pelvis findings are subtle in early SCFE: a widened, irregular, “fuzzy” appearance of the proximal femoral physis; the Klein line (a line drawn along the superior border of the femoral neck) failing to intersect the lateral aspect of the epiphysis (which it should normally cross); the “metaphyseal blanch sign” of Steel (a crescent-shaped area of increased density at the metaphyseal-physeal junction); and a relatively short or “atrophic” appearance of the femoral head as it slips posteriorly. The frog-lateral or true lateral view reveals the posterior slip of the epiphysis as a clear discontinuity between the femoral neck and the epiphysis, with the epiphysis tilted posteriorly. The Southwick angle (head-shaft angle, the angle between the long axis of the femoral neck and a line perpendicular to the line connecting the anterior and posterior

aspects of the proximal femoral physis) is measured on this view and quantifies the severity of slip. MRI may be useful in two specific situations: early “pre-slip” SCFE, in which the physis shows widening and inflammatory changes but no obvious displacement on plain radiographs; and the unstable SCFE in which assessment of vascular compromise to the femoral head is required. CT may be used for surgical planning in severe deformity but is rarely required for initial diagnosis.

Treatment

Principles The treatment of SCFE has several core principles: (1) immediate cessation of weight- bearing once SCFE is suspected, even before radiographs are obtained, to prevent further displacement; (2) prompt surgical fixation in all but the most minor cases, because non- surgical management has uniformly poor outcomes (spica casting is no longer routinely used because it does not reliably prevent further slippage and is associated with chondrolysis); (3) the goal of fixation is to stabilize the epiphysis in its currently displaced position with minimal additional manipulation, since aggressive reduction maneuvers risk avascular necrosis; (4) recognition that bilateral involvement is common, with consideration of prophylactic contralateral fixation in selected high-risk patients. In Situ Fixation In situ fixation with a single percutaneous cannulated screw is the standard treatment for stable SCFE of any severity. The principle is to fix the epiphysis to the metaphysis through the physis, achieving physeal closure and preventing further slip. The procedure is performed on a fracture table under image intensification: a guidewire is inserted from the anterolateral aspect of the proximal femur (often through a stab incision in the lateral thigh), advanced across the physis along an axis perpendicular to the displaced physis, and a cannulated screw is placed over the guidewire. The screw should engage at least 4-5 mm of the epiphyseal bone but should not penetrate the joint surface (because of the risk of chondrolysis from intra-articular hardware). A single screw is the standard for most cases; some authors advocate two screws for severe slips or unstable disease, but single-screw fixation has the advantage of reduced complications and is well-supported by the literature.

Reduction of Unstable SCFE The unstable SCFE presents a particular dilemma. Gentle positional reduction occurs spontaneously when the patient is positioned on the fracture table and the limb is internally rotated; this gentle reduction is generally accepted and does not significantly increase AVN risk. Aggressive reduction maneuvers — forceful internal rotation, adduction, or extension to “reduce” the slip — are associated with high rates of avascular necrosis and are generally avoided. The current consensus is that whatever reduction is achieved by positioning is accepted, and fixation is performed in that position; further reduction is not pursued.

A subset of authors favors urgent open reduction of unstable SCFE through a modified Dunn procedure (a posterior approach with anatomical reduction of the epiphysis on the metaphysis under direct vision, preserving the medial femoral circumflex artery), with reported lower rates of AVN in their series than conventional in situ fixation. The procedure is technically demanding and is currently used principally in specialist centers; the routine adoption awaits further validation by larger series.

Prophylactic Contralateral Fixation The decision to fix the contralateral asymptomatic hip prophylactically remains debated. Arguments in favor include the 20-40% rate of bilateral involvement (often within 18-24 months), the risk of missing a developing contralateral slip in asymptomatic patients, and the morbidity of a future second operation. Arguments against include the unnecessary surgery in the majority of patients who will not develop a contralateral slip, the small but real complication rate of the prophylactic procedure, and the potential interference with later imaging. The current consensus is that prophylactic fixation should be considered in patients at high risk of contralateral slip: patients with endocrine disorders, patients younger than typical (in whom more residual growth means more time for contralateral slip), patients with previous evidence of contralateral physeal change on imaging, and patients in whom compliance with follow-up is uncertain. The Loder modified Oxford skeletal maturity score is one tool used to predict the residual risk. Severe Deformity Correction Severe chronic SCFE with established deformity may require corrective osteotomy to address the persistent deformity. Three principal levels of osteotomy have been described, each with different risk-benefit profiles: Subcapital osteotomy (Dunn osteotomy, modified Dunn / Ganz approach): Osteotomy at the level of the slip, providing the most complete deformity correction but with the highest risk of avascular necrosis. The procedure is now performed principally through the surgical hip dislocation approach (Ganz approach) with preservation of the medial femoral circumflex artery, which has substantially reduced but not eliminated the AVN risk. Femoral neck base osteotomy (Kramer or Barmada osteotomy): Osteotomy at the base of the femoral neck, with intermediate correction and intermediate AVN risk. Intertrochanteric osteotomy (Imhauser, Southwick, or biplanar osteotomies): Osteotomy in the intertrochanteric region, providing extra-articular correction without disturbing the femoral neck vascularity. The AVN risk is lowest of the osteotomy options, but the correction is incomplete and the patient is left with persistent intra-articular deformity that contributes to ongoing femoroacetabular impingement. The choice between these osteotomies depends on the severity of deformity, the patient’s symptoms, the surgeon’s experience, and the assessment of risk-benefit for the individual patient.

Complications

Avascular Necrosis (AVN) Avascular necrosis is the most consequential complication of SCFE, with overall rates of approximately 5-10%. The risk is substantially higher in unstable SCFE (approximately 50%), with aggressive reduction attempts, with subcapital osteotomy, and with delayed treatment. The pathogenesis is disruption of the medial femoral circumflex artery supply to the femoral head, either by the original slip event (in unstable disease) or by surgical manipulation. AVN presents within 6-24 months of the index event with progressive hip pain, decreased range of motion, and characteristic radiographic changes of femoral head sclerosis, fragmentation, and collapse. Treatment options range from conservative management for mild disease to total hip arthroplasty for established collapse.

Chondrolysis Chondrolysis — destruction of the articular cartilage of the hip with severe stiffness and pain — was historically a major complication of SCFE, with rates as high as 30% in some series. The pathogenesis is uncertain but is thought to involve a combination of mechanical factors (intra-articular screw penetration, persistent intra-articular deformity), autoimmune factors, and possibly racial factors (chondrolysis was historically more common in African American patients). Modern attention to avoiding intra-articular screw penetration and the abandonment of spica casting have markedly reduced chondrolysis rates to approximately 1-7% in current series. Femoroacetabular Impingement Femoroacetabular impingement (FAI) is now recognized as a near-universal late consequence of SCFE, even in adequately fixed disease. The displaced femoral head produces cam-type impingement against the acetabular rim with hip flexion and internal rotation, producing pain, decreased range of motion, and progressive labral and cartilage damage. Treatment options include arthroscopic or open femoral osteochondroplasty (Ganz surgical hip dislocation with femoral neck recontouring), which has become increasingly common in the management of post-SCFE FAI. Other Complications Other recognized complications include progressive slip after fixation (rare with adequate single-screw fixation), nonunion of the physis (uncommon), implant-related problems, leg- length discrepancy, and post-SCFE arthritis in adulthood. The long-term outcome of SCFE is one of progressive risk of degenerative arthritis, with approximately 10-30% of patients requiring total hip arthroplasty by middle age, the rate depending on severity of original slip and complications.

Summary and Take-Home Points

Slipped capital femoral epiphysis is one of the most important diagnoses in adolescent orthopedics, with the typical patient being an obese adolescent male in late puberty

presenting with hip or knee pain. The diagnosis is established by clinical examination (with the cardinal finding of decreased internal rotation and the Drehmann sign) and by plain radiographs (AP pelvis and frog-lateral, with attention to the Klein line, the metaphyseal blanch sign, and the lateral-view discontinuity). The Loder classification of stable versus unstable SCFE, based on the ability to weight-bear, is the most important prognostic indicator: stable disease has approximately 5% AVN risk; unstable disease, 50% AVN risk. Treatment is urgent surgical fixation with a single percutaneous cannulated screw in situ for the great majority of cases; gentle positional reduction is acceptable for unstable SCFE, while aggressive reduction maneuvers are avoided. Severe deformity may require corrective osteotomy (modified Dunn / Ganz, base of neck, or intertrochanteric), each with different risk profiles. The cardinal teaching points are: examine the hip in any adolescent with knee pain; image both hips with AP and lateral views; do not delay diagnosis or surgical fixation; consider endocrine workup in atypical presentations; recognize and manage the late complications of AVN, chondrolysis, and femoroacetabular impingement. The single greatest improvement in SCFE care has been the recognition that prompt diagnosis and stabilization is the principal determinant of long-term outcome.