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John M. Roberts, MD
Retired Chief of Staff, Pediatric Orthopedics
Springfield Shriners Hospital
Springfield, Massachusetts

Pretest

Discussion

Slipped Capital Femoral Epiphysis: (SCFE) is the posterior displacement of the femoral capital epiphysis on the femoral neck through sudden or gradual deformation of the subcapital growth plate. Body habitus and structural changes occurring in the upper femur during early adolescence are predisposing factors. Unimpeded progression of deformity may lead to severe pain and loss of motion of the hip joint because of proximal displacement of the femoral neck to impinge on the anterior rim of the acetabulum. Timely treatment of slipped upper femoral epiphysis can prevent severe displacement. Feared sequela are avascular necrosis of the femoral head, chondrolysis, and degenerative osteoarthrosis.

The acute onset and inability to walk after falling characterize an acute, unstable slip. Fixation is required but manipulation may potentiate the high risk of avascular necrosis of the femoral head. Open reduction with careful repositioning of the femoral head under direction vision is undertaken by some, but should not be delayed. If osteotomy is to be considered at all, realignment would best obtained by careful excision of the proximal portion of the femoral neck, excision of growth plate, and internal fixation of the repositioned femoral head on neck.

Demography

Typically, SCFE occurs between 11 and 13 years of age in females and 13 to 16 years of age in males. Sixty percent of patients are above the 90th percentile for weight. It occurs bilaterally in 20% to 40%, even more commonly in juvenile SCFE (less than the average age of 12 years for girls and 14 years for boys). If bilateral, the contralateral slip occurs within 18 months in over 80% of cases. The overall relative incidence is 1-3/100,000. Compared to white patients, it occurs more than twice as often in African-American patients and more than four times as often in Polynesian cases.

Etiology

During the adolescent growth spurt, changes in the configuration and composition of the upper femur predisposing to a slipped epiphysis include: a more vertical orientation of the subcapital physis; elongation of the neck of the femur; disorganized physeal matrix; and femoral retroversion. Experimental computations support the hypothesis that SCFE can occur with normal activities in an obese adolescent.

A genetic factor is supported by the increased incidence in first and second degree relatives. SCFE has also been noted to occur in identical twins.

SCFE patients <9 years of age who are short in stature may have hypothyroidism. Other metabolic disorders that may present with SCFE include renal osteodystrophy, growth hormone deficiency, and multiple endocrine neoplasia 2-B.

Clinical Presentation

The onset of pain and limp may be insidious (chronic slip) or sudden (acute slip). When a patient is unable to continue walking on an acute slip, it is termed unstable; risk of avascular necrosis is >40% in an unstable slip. An acute-on-chronic slip occurs when an acute slip is superimposed on a chronic slip.

Whereas the direction of the slippage is posterior, the femur tends to roll into lateral rotation. The patient stands and lies with the involved extremity held in lateral rotation. Lateral rotation increases as the hip is flexed. Range of rotation of the hip in extension is best tested with the patient prone and the knees flexed; the involved hip may fail to rotate medially to neutral position.

Analysis

The degree of slip is measured either on a cross-table lateral radiograph or a lateral projection of the upper femur obtained with an anteroposterior beam aimed at a hip flexed to 90° and held to maximum abduction. A computed tomography scan can be used to gauge posterior displacement of the epiphysis, but the "cuts" should be carefully aligned with the longitudinal axis of the femoral neck.

A slip can be graded as grade 1 (0%-33% slip), grade 2 (33%-50% slip), or grade 3 (>50% slip). The severity of slip has been measured by the head-shaft angle on the frog-leg radiogram: a mild slip is <30°, moderate 30° - 60°, and severe >60°.

A chronic slip is characterized by new bone formation in the step off between the posterior rim of the femoral head and the posterior border of the femoral neck. Late radiographic changes include narrowing of the "joint space" to <3 mm, indicating chondrolysis; increased relative density and segmental collapse of the femoral head indicating avascular necrosis; and exostosis, marginal cysts, and lateral subluxation, signs of osteoarthritis.

Treatment

The primary goal of treatment is prevention of further slip. This can usually be accomplished expeditiously by percutaneous in situ fixation with a cannulated screw placed over a guide pin. Accurate placement of the guide pin and screw are possible with biplane images obtained with a C-arm. A single screw inserted anteriorly through the cortex at the base of the neck and directed proximally, medially, and posteriorly so that it passes into the center of the femoral head perpendicular to the proximal surface and stops 0.5 cm short of subchondral bone will avoid avascular necrosis and/or chondrolysis in most cases.

Reduction of an acute SCFE by intended manipulation is avoided, but improvement of the position of the epiphysis sometimes occurs as a patient is positioned on the operating table. If open reduction in a severe acute slip is considered, this should be done promptly to decompress the associated increased intra-articular pressure. Prophylactic in situ fixation of the contralateral hip may be considered when there is increased expectation of bilateral involvement such as in a child with hypothyroidism or a juvenile slip. One year after initial treatment of SCFE, a derotational osteotomy of the femur may be indicated if there is enough limitation of internal rotation to cause dysfunction. A closing wedge intertrochanteric osteotomy to increase flexion as well as abduction of the femoral neck will compensate for the posterior displacement of the femoral head. If long-term supportive and symptomatic treatment for avascular necrosis fails, upper femoral osteotomy to bring uninvolved joint surface into the superior weightbearing area may be accomplished. Arthrodesis for a stiff, painful hip in a bad position from either avascular necrosis or chondrolysis may be indicated, but should be performed so that it can be converted to a total hip arthroplasty later in life if back pain, contralateral hip pain, or ipsilateral knee pain ensue.