Slipped Capital Femoral Epiphysis

Slipped capital femoral epiphysis is a disorder of the adolescent hip. The proximal femoral epiphysis is displaced relative to the femoral neck through the physis (growth plate), most commonly during the adolescent growth spurt.

It has a well established association with obesity, because increased body mass loads a relatively weakened, actively growing physis.

It is an orthopaedic emergency once identified, because the slip can progress to complete displacement and carries a serious risk of avascular necrosis of the femoral head if not promptly recognised and stabilised.

The critical priority is immediate weight-bearing restriction and urgent orthopaedic referral once the diagnosis is suspected or confirmed.

Pathophysiology and risk factors

• The proximal femoral physis is relatively weakened during the rapid growth phase of adolescence, owing to changes in the orientation and mechanical properties of the growth plate.
• Physeal vulnerability combined with increased shear forces across the hip (particularly with increased body weight) causes progressive displacement of the epiphysis relative to the femoral neck.
• The epiphysis remains in its normal position within the acetabulum, while the femoral neck displaces anteriorly and rotates externally relative to it. This produces the characteristic radiographic and clinical findings.
• Obesity is the single most important, well established risk factor. Increased body mass raises the shear forces transmitted across the vulnerable, growing physis.
• The condition is somewhat more common in boys than girls. It typically presents slightly later in boys, reflecting the later pubertal growth spurt.
• Endocrine conditions are important, though less common, underlying or contributing causes: hypothyroidism, growth hormone deficiency or excess, and renal osteodystrophy.
• Consider an endocrine cause in atypical presentations: younger age, presentation outside the typical adolescent age range, or bilateral disease. Bilateral involvement is substantially more frequent with an underlying endocrine abnormality than in typical, idiopathic disease.
• Bilateral involvement occurs in a substantial minority of affected adolescents. It may be simultaneous but more commonly is sequential, with the second hip involved after initial unilateral presentation. Carefully and continuously monitor the contralateral hip after diagnosis and treatment of the first side.

• The characteristic presentation is hip, groin, thigh or, because of referred pain, knee pain, together with a limp.
• Presentation is classified as stable or unstable. In a stable slip the adolescent can bear weight, with or without crutches. In an unstable slip the adolescent cannot bear weight even with support.
• An unstable slip is more acute and severe, with a substantially higher risk of avascular necrosis. The distinction directly affects urgency of treatment and prognosis.
• Onset may be acute (after a relatively minor trauma or exertional event, though the trauma does not cause the underlying physeal abnormality), chronic (insidious, developing over weeks to months), or acute-on-chronic (acute worsening of pre-existing chronic symptoms).
• The temporal pattern carries some relevance to the presumed mechanism and severity.
• On examination, the affected hip has limited internal rotation and obligate external rotation on attempted hip flexion. This reflects the altered relationship between the femoral neck and the displaced epiphysis, and is a useful, relatively specific sign.
• Consider the diagnosis in any adolescent with hip, groin, thigh or knee pain and a limp, particularly with risk factors such as obesity. Prompt clinical and radiographic evaluation is time-critical.

• Plain radiography of the pelvis is the essential, standard diagnostic investigation. Obtain both anteroposterior and frog-leg lateral views.
• The lateral view frequently shows the slip more clearly than the anteroposterior view and, in some subtle or early cases, is the only view on which the abnormality is clearly apparent.
• Compare both hips carefully to identify subtle asymmetry that might otherwise be overlooked.
• The characteristic finding is displacement of the femoral epiphysis relative to the femoral neck.
• Klein line is drawn along the superior border of the femoral neck on the anteroposterior radiograph. It should normally intersect a portion of the epiphysis. In a slip it fails to intersect an adequate portion, which is a useful standard technique, particularly for subtle slips.
• Keep a low threshold for imaging in any adolescent with a compatible clinical picture.
• The frog-leg lateral view can precipitate further displacement in an already unstable slip. Use careful clinical judgement about the views obtained in a clinically unstable child (complete inability to bear weight). Some protocols recommend avoiding the frog-leg lateral view in this higher-risk presentation because of this theoretical risk.
• Magnetic resonance imaging may be used in diagnostic uncertainty, or to assess early, subtle physeal changes ("pre-slip") not yet clear on plain radiography. Plain radiography remains the standard primary investigation for the great majority of presentations.

• Immediate, strict weight-bearing restriction is the essential first step once the diagnosis is suspected or confirmed, because continued weight-bearing risks further slip progression and complications.
• Implement the restriction immediately on clinical suspicion. Do not wait for confirmatory imaging or specialist assessment where this would cause any meaningful delay.
• Refer urgently to orthopaedics. Surgical treatment is generally undertaken as soon as reasonably practicable once the diagnosis is confirmed, because delay increases the risk of progression and complications.
• An unstable slip carries a substantially higher risk of avascular necrosis and is generally treated as an urgent, same-day surgical emergency.
• In situ percutaneous screw fixation is the standard surgical treatment for the great majority of presentations. It stabilises the epiphysis in its current position without attempting to reduce or correct the slip, because attempted reduction adds substantial risk of avascular necrosis, particularly for chronic, established slips.
• The aim is to prevent further slip progression and allow the physis to fuse in its stabilised position.
• Prophylactic contralateral fixation stabilises the unaffected hip at the same time as the presenting hip, even without symptoms or radiographic abnormality on that side. It is considered in selected cases, particularly with an underlying endocrine abnormality that substantially increases the risk of bilateral involvement, or other specific risk factors for contralateral slip.
• This remains an area of clinical debate, and practice varies with the individual risk profile.
• Avascular necrosis of the femoral head is the most serious complication, particularly with unstable slips and any delay in diagnosis and treatment. It can cause substantial long-term hip dysfunction and premature osteoarthritis. Prompt diagnosis, immediate weight-bearing restriction and urgent surgical stabilisation minimise this risk.
• Provide structured, long-term orthopaedic follow up. This includes surveillance of the contralateral hip for subsequent slip, monitoring for avascular necrosis and other longer-term complications, and discussion of weight management where obesity is a contributing risk factor.