Slipped Capital Femoral Epiphysis
On this page
Direct answer
Slipped capital femoral epiphysis is displacement of the femoral head through the physis, usually posteriorly and medially, during adolescence. It classically affects obese boys aged about 10 to 16 years and presents with hip or referred knee pain, with the leg held externally rotated. Urgent in situ pinning fixes the physis and prevents further slip, and forced reduction is avoided because it raises the risk of avascular necrosis.
What you must remember
- Mechanism: the femoral head slips through the hypertrophic zone of the physis, usually posteriorly and medially relative to the neck.
- Typical patient: obese adolescent boys during the growth spurt, the commonest group affected.
- Associations: obesity, hypothyroidism and growth hormone abnormalities are recognised risk factors.
- Presentation: hip pain, limp or referred knee pain, with restricted internal rotation of the flexed hip.
- Trethowan sign: Klein's line drawn along the superior femoral neck fails to intersect the epiphysis; its diagnostic value is limited.
- Southwick angle: the slip angle measured on the lateral view, where a larger angle indicates a more severe slip.
- Stability: a stable slip allows weight bearing, while an unstable slip cannot bear weight and carries a higher risk of avascular necrosis.
- Complications: avascular necrosis, chondrolysis and progression of the slip after treatment.
A stepwise approach from suspicion to fixation
Recognition depends on thinking of the hip in any obese adolescent with knee pain. Examination and imaging then confirm the slip and guide urgent surgery.
- Recognise the hip: consider SCFE in any obese adolescent with hip or knee pain, and check internal rotation with the hip flexed, which is typically restricted.
- Image both views: take an anteroposterior pelvis and a frog-leg lateral radiograph, and measure the Southwick angle on the lateral film.
- Classify stability: label the slip as stable or unstable according to whether the child can bear weight, since an unstable slip needs emergency management.
- Stabilise surgically: perform in situ pinning promptly with one or more cannulated screws across the physis, without reducing the displacement.
- Protect the other hip: consider prophylactic pinning of the contralateral hip, because a slip on the other side can develop later.
- Monitor: follow the child for avascular necrosis and chondrolysis, the main complications, and for slip progression.
Where the exam tries to catch you
Questions on this topic usually test recognition, the reason against reduction, and the contralateral hip.
- Trap: manipulating the hip to reduce the slip Correct: forced reduction increases the risk of avascular necrosis, so the physis is stabilised in situ.
- Trap: treating knee pain in an obese adolescent as a knee problem Correct: referred pain from the hip is common, so the hip must be examined and imaged.
- Trap: delaying an unstable slip for elective surgery Correct: an unstable slip needs emergency pinning because it carries a high risk of avascular necrosis.
- Trap: ignoring endocrine causes in a slim adolescent with a slip Correct: hypothyroidism and growth hormone abnormalities are recognised causes, so endocrine review is considered.
Frequently asked questions
Which radiograph best shows a slipped capital femoral epiphysis?
The frog-leg lateral radiograph best shows a slipped capital femoral epiphysis because it displays the posterior displacement of the femoral head. An anteroposterior pelvis film is taken alongside it, and the Southwick angle is measured on the lateral view.
What is the Trethowan sign in slipped capital femoral epiphysis?
The Trethowan sign is a radiographic finding in which Klein's line, drawn along the superior femoral neck, fails to intersect the epiphysis. Its diagnostic value is limited, so it is interpreted alongside the clinical picture and both hip radiographs rather than in isolation.
Why is in situ pinning used for slipped capital femoral epiphysis?
In situ pinning is used for slipped capital femoral epiphysis to fix the physis in its displaced position and prevent further slip. Forced reduction is avoided because manipulation raises the risk of avascular necrosis of the femoral head, a major complication.
Why is the contralateral hip considered in slipped capital femoral epiphysis?
The contralateral hip is considered in slipped capital femoral epiphysis because a significant proportion of children later develop a slip on the other side. Prophylactic pinning of the unaffected hip is therefore discussed, particularly in younger or higher-risk patients.