Title: Picture quiz: Chronic knee pain in an adolescent
A 13 year old girl presented to her GP with right knee pain lasting several weeks. There was
no apparent precipitating cause, and the pain was exacerbated by sporting activities. Knee
examination was normal. Hip examination revealed marked limitation of internal rotation.
The patient was investigated with pelvic radiographs which are presented below:
1. What is the diagnosis?
2. What is the radiograph view on the right called and why is it used?
3. What are the potential complications of this condition?
4. How do you manage this condition?
Slipped capital femoral epiphysis. (SCFE) Adolescent knee pain in the presence of a normal
knee exam should be Slipped Capital Femoral Epiphysis (SCFE) until proven otherwise.
Differentials of knee pain in adolescents include:
- Referred hip pain (Slipped Capital Femoral Epiphysis, late-onset Perthe’s disease)
- Knee Pathologies: Apophysitis (e.g. Osgood-Schlatter disease), Osteochondritis
dessicans, patellar subluxation, patellar tendinopathy, , ligamentous injury, meniscal
- Rheumatological conditions such as Juvenile Idiopathic arthritis
- Local benign tumours eg osteochondroma
- Rare malignant tumours and childhood leukaemia
SCFE, also called Slipped Upper Femoral Epiphysis (SUFE), is a hip condition affecting
rapidly growing adolescents and has an incidence of 10/100,000 0-14 year olds per year.
There is anterior displacement of the femoral metaphysis relative to the epiphysis resulting
from an insufficiency fracture through the hypertrophic zone of the physis (growth plate)
This can potentially disrupt the blood supply to the femoral head. Around ¼ of children have
bilateral SCFE, so examination of the contralateral hip is mandatory.
There are two types of SCFE:
The first, accounting for 80% of all SCFEs, is referred to as a stable slip and has a minimal
risk of avascular necrosis as the epiphysis slips slowly and incrementally. Early diagnosis and
fixation is therefore essential to prevent the development of complications. ‘Stable’ slips
usually present with an insidious onset of hip/ groin pain, or simply isolated distal thigh and
knee pain. The non-specific symptoms may mean that the disease is overlooked and
consequently stable slips may progress to more serious slips with greater complication rates.
Clinicians must be alert to the diagnosis in children in the 10-14 age group presenting with
any pain in the hip/ thigh or knee.
In the other type where the child will be unable to weightbear - an unstable slip- there is a
much worse prognosis. The epiphysis suddenly slips off the metaphysis and the patient
presents with acute pain as though they had sustained a femoral neck fracture. The sudden
movement tears the tenuous blood supply to the epiphysis.
2. Frog-lateral radiograph
In ‘stable’ slips, the plain AP pelvic radiograph may be unremarkable, with the frog-lateral
view being more sensitive. Klein’s line may be drawn on the AP radiograph to help identify
SCFE (Radiograph below). This is a line drawn along the femoral neck and should normally
pass through the epiphysis (right hip: normal). In a SCFE, the line remains superior to the
head instead of passing through it (left hip: abnormal - Trethowan’s sign).
An AP pelvic radiograph with Klein’s line drawn is now presented:
With stable slips, prognosis is very good. However, unstable slips can potentially lead to
avascular necrosis, coxa vara and secondary osteoarthritis
Diagnostic delay worsens the outcome of stable SCFE as the femoral head progressively
deforms1 or occasionally an acute-on-chronic slip may occur. Whereas prompt recognition of
a SCFE results in an AVN rate close to 0%, the AVN rate following an acute slip approaches
50% AVN. Thus, acute unstable slips often result in permanent long-term disability with
significant limitation of occupational capacity and mobility as there is no satisfactory
orthopaedic treatment for AVN. Multiple studies have drawn attention to this problem, but
misdiagnosed SCFE remains a common cause of medico-legal claims, often in excess of
In this case of a chronic SCFE, urgent paediatric orthopaedic referral and prompt screw
fixation is required to prevent further displacement and avoid the transition from a relatively
benign and treatable condition to one with significant complications.
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DC Perry, CE Bruce. Evaluating the child who presents with an acute limp. BMJ
Lowndes S, Khanna A, Emery D, Sim J, Maffulli N. Management of unstable slipped upper
femoral epiphysis: a meta-analysis. Br Med Bull 2009;90:133-46.
Maclean J. A crippling slip. Summons 2008;Spring:16-17