Slipped capital femoral epiphysis (SCFE) is an adolescent hip disorder defined as a posterior and inferior slip of the proximal femoral epiphysis relative to the metaphysis. However, the relationship of the epiphysis and its articular surface relative to the acetabulum is not altered, and the movement is better defined as an anterior and superior slip of the proximal femoral metaphysis (neck) relative to the epiphysis. The technique of internal fixation is much easier to comprehend when this is understood.

The vast majority (>95%) of SCFEs are stable.¹ A child with a stable SCFE is able to walk, with or without crutches; a child with an unstable SCFE is unable to walk, with or without crutches. The prognosis for a child with a stable SCFE is very good, with an incidence of osteonecrosis approaching zero. The prognosis for a child with an unstable SCFE is guarded due to the increased risk of osteonecrosis, which may be up to 50%.

A child with a stable SCFE has a history of intermittent limp for several weeks to months. It may or may not be associated with thigh, knee, or groin pain. Hip pain is variably present, often resulting in diagnostic delay. Physical examination demonstrates a loss of internal rotation and spontaneous external rotation with hip flexion. Abduction and flexion are usually decreased, especially in more severe cases (>50°). In the long-standing case, shortening of the lower extremity with varying degrees of thigh atrophy is noted; the parents will also describe a gradually increasing external rotation gait and limb-length discrepancy.

Any child with a stable SCFE and open physes needs treatment. Without stabilization, progression is highly likely. The goals of treatment are to (1) prevent further slipping until physeal closure; (2) avoid complications, primarily osteonecrosis and chondrolysis; and (3) maintain adequate hip function. Four main treatments have been described: (1) internal fixation, (2) epiphysiodesis, (3) proximal femoral osteotomy, and (4) spica cast immobilization. Today, most authors advocate an in situ fixation with a single screw for any mild or moderate stable SCFE. The initial treatment of severe SCFE is more controversial. Primary osteotomy has been advocated by some to improve joint mechanics, motion, and hip function. However, the incidence of complications is higher with osteotomy than in situ fixation, so most surgeons recommend in situ fixation as the primary treatment for severe SCFE. In situ fixation allows the synovitis to subside, which will in itself result in improved motion. After complete physeal closure (usually 1 or 2 years later), the child’s functional limitations, gait pattern, and pain can be more leisurely assessed. A decision regarding the need for osteotomy can then be made after a thorough discussion of the risks and benefits with the child and parents.

Circumstances for bilateral pinning (ie, prophylactic fixation of the opposite hip) include patients with underlying endocrinopathies (hypothyroidism, renal insufficiency, growth hormone supplementation) and the very young child (open triradiate cartilage and/or age younger than 9 years in girls or 11 years in boys).

In a stable SCFE, the diagnosis is confirmed with AP and lateral pelvis radiographs (Figure 1); both views are needed because an early SCFE is often seen only on the lateral view. Both hips should always be visualized, as the incidence of simultaneous bilateral SCFE may approach 20%. Either frog-lateral or cross-table lateral radiographs may be used. Proponents of the cross-table lateral view argue that the variability in positioning for the frog-lateral view due to the limitation of hip motion inaccurately represents the SCFE. The frog-lateral view can also theoretically convert a stable SCFE to an unstable SCFE. Proponents of the frog-lateral view argue that the lateral epiphyseal-shaft angle, commonly used to assess slip magnitude, is measured on the frog-lateral view. It is also the view on which many of the preoperative osteotomy plans are dependent. Comparisons between literature series are also possible with this view due to its common use.

Slip magnitude is best measured using the epiphyseal-shaft angle.² This angle is measured on the frog-lateral pelvis radiograph (Figure 2). A line is drawn between the anterior and posterior tips of the epiphysis at the physeal level; a line is then drawn perpendicular to this epiphyseal
line. A line is next drawn along the midaxis of the femoral shaft. The epiphyseal-shaft angle is the angle formed by the intersection of the perpendicular line and the femoral shaft line. It is measured for both hips, and the magnitude of slip displacement is the angle of the involved hip minus the angle of the contralateral normal hip. Using this angle, SCFEs can be classified as mild (<30°), moderate (30° to 50°), or severe (>50°). In the case of bilateral SCFEs, 10° to 12° is used as the normal hip angle.