Endgames Picture Quiz

A child with knee pain

BMJ 2012; 344 doi: https://doi.org/10.1136/bmj.e250 (Published 19 January 2012) Cite this as: BMJ 2012;344:e250
  1. John Adu, foundation year 2, orthopaedics,
  2. Matthew Nixon, specialist registrar, orthopaedics,
  3. Alfie Bass, consultant paediatric orthopaedic surgeon
  1. 1Alder Hey Hospital, Liverpool L12 2AP, UK
  1. Correspondence to: J Adu john.adu{at}doctors.org.uk

A 13 year old boy presented to the accident and emergency department because he was unable to bear weight on his left leg and had a history of pain in the left knee. The pain began 10 days before, after a fall, at which time he had a dull pain in his knee but was still able to bear weight. Three days before his attendance he tripped again, and after this injury, the pain had become more severe and he was unable to bear weight.

He was otherwise healthy, with no history of joint problems. He was not particularly active or sporty and had a body mass index of 25.6.

On examination, he was in moderate pain and was unable to bear weight. Both knees were normal, but his left leg was shortened and externally rotated, with no evidence of bruising or injury. Examination of his left hip showed limitation of flexion, abduction, and, in particular, internal rotation because of pain. All other joint examinations were unremarkable. He underwent radiography (fig 1).


  • 1 What type of radiograph is this and what does it show?

  • 2 How is this condition classified?

  • 3 How else might this condition present?

  • 4 What complications are associated with this condition?

  • 5 How would you manage this condition?


1 What type of radiograph is this and what does it show?

Short answer

Figure 1 is a “frog lateral” radiograph and it shows a widened physis and malalignment of the epiphysis and proximal femoral metaphysis (fig 2), confirming the diagnosis of a left slipped upper femoral epiphysis.


Fig 2 Frog lateral radiograph showing a widened physis and malalignment of the epiphysis and proximal femoral metaphysis on the left side

Long answer

Slipped upper femoral epiphysis is the transphyseal displacement of the upper femoral epiphysis from the metaphysis.1 Frog lateral (while the patient is supine with both knees flexed, soles of feet together, and the thighs maximally abducted) and anteroposterior radiographs are part of the standard diagnostic work-up. Acutely, radiographs typically show an inferoposterior slip (fig 2),1 which is best seen on a lateral radiograph in the early stages.2 Billing’s lateral view is a more standardised view in which the patient is supine with the knee flexed to 90° and the hip resting on a 25° wedge. This has been shown to be the most sensitive method of detection.3 4 5 Magnetic resonance imaging is sometimes useful in early slips and may exclude other causes, such as infection and Legg-Calvé-Perthes disease.

Mild slips can easily be missed on anteroposterior views. Trethowan’s sign is shown on the anteroposterior view when Klein’s line (drawn along the superior border of the femoral neck) fails to intersect with the femoral head (fig 3).3 6 Trethowan’s sign must be compared with the normal contralateral side, but in bilateral disease the sign will need to be interpreted in the diseased side in isolation, along with studying lateral views.


Fig 3 Anteroposterior radiograph showing Trethowan’s sign. Klein’s line bisects less of the femoral head in the left hip compared with the normal right. Widening of the physis is also seen

Other signs on the anteroposterior view include widening and irregularity of the physis and the metaphyseal blanch sign,7 in which the posteriorly subluxed epiphysis creates a shadow on the metaphysis, or a broken Shenton’s line, especially in severe slips, which denotes shortening of the ipsilateral leg.

2 How is this condition classified?

Short answer

Slipped upper femoral epiphysis may be classified according to the ability to bear weight (stable or unstable); chronologically in relation to the time of onset of symptoms; or radiographically, depending on the degree of displacement. Classification based on stability is the most useful in clinical practice and is also predictive of prognosis.

Long answer

Slipped upper femoral epiphysis is traditionally classified as pre-slip, acute, chronic, or acute on chronic. Acute and chronic slips are differentiated by symptoms lasting more or less than three weeks. An acute on chronic slip describes an acute deterioration in longstanding symptoms, whereas a pre-slip is seen in an at risk child who has pain. However, this system may be inaccurate and is not useful for prognosis.8 9 10

Loder’s classification is based on the stability of the physis.11 Children with a stable slipped upper femoral epiphysis can weight bear, with or without crutches, whereas those with an unstable slip cannot weight bear at all. This classification is more useful in clinical practice, for treatment and prognosis.

The severity of slipped upper femoral epiphysis can be classified radiographically according to the extent of displacement of the epiphysis on the metaphysis into mild (0 to a third), moderate (a third to a half), and severe slips (more than a half). The angle of the epiphyseal shaft (angle of Southwick) on the frog lateral view can also be measured to classify slips as mild (<30°), moderate (30-60°), or severe (>60°).

3 How else might this condition present?

Short answer

This rare condition can present with a limp or pain in the groin, thigh, or knee. The duration of symptoms can vary from days to months, or even years, depending on the stability of the slip.

Long answer

The incidence of slipped upper femoral epiphysis in the United Kingdom is one to seven cases per 100?000 children (0-16 years old) per year.12 The mean age at diagnosis is 13.5 years in boys and 12 years in girls, with boys being more commonly affected.13 Risk factors include obesity, endocrine diseases, and renal osteodystrophy,14 15 16 17 and these may lead to earlier presentation.

Stable slips are more common, forming 85-90% of cases.11 Symptoms are usually seen in the groin or thigh, but knee pain is the initial symptom in about 46% of patients and should be considered to originate from the hip until proved otherwise.18 19 20 Symptoms may vary in duration from months to years.1 Unstable slips are rare and may present to the accident and emergency department as an acute “fracture,” with a short history of severe pain and an inability to bear weight.

On examination the leg is often flexed and externally rotated, with reduced range of movement of the affected hip, particularly internal rotation.1 2 Furthermore, the affected leg may be forced out into external rotation when the hip is passively flexed as a result of reduced internal rotation. Asymmetrical internal rotation may be more easily detected by examining the patient prone.

4 What complications are associated with this condition?

Short answer

The development of avascular necrosis and degenerative joint disease. Management aims to prevent these two complications.

Long answer

The most serious early complication is avascular necrosis, and the risk of developing this complication is related to the stability of the slip and the timing and choice of surgical intervention.11 21 22 23 24 25 Later complications include degenerative joint disease; this complication has several causes, including chondrolysis and malunion of the proximal femur, which lead to femoral acetabular impingement. Hip arthroscopy may be needed to manage such problems.

Contralateral disease is common and prophylactic fixation is controversial. In our unit all patients are followed up until skeletal maturity, and patients are educated to present urgently if symptoms develop.11 Our criteria for prophylactic fixation are development of contralateral hip pain or stiffness, presence of a metabolic abnormality, and young age (under 10 years). In some centres prophylactic fixation is also recommended if parents are unreliable or if the surgeon is worried that the parents may not understand the complexities of diagnosis and seriousness if left untreated.

5 How would you manage this condition?

Short answer

Stable slips are best treated with fixation in situ at the time of presentation. This patient had an unstable slip and was therefore at risk of avascular necrosis. Surgery should be performed either within 24 hours or after one week of the onset of symptoms.

Long answer

Knee pain is often the only presenting symptom, but clinicians must also consider hip pathology when assessing children with a painful knee. Missed slips of the upper femoral epiphysis and the development of complications are common causes for litigation. The risk of avascular necrosis in stable slips is 0%,11 so these are best treated with fixation in situ.11 21 22 Various techniques have been used in the past, but single cannulated screw fixation has become the gold standard (fig 4).11 21 22 One of the consequences of a displaced slipped upper femoral epiphysis is malalignment of the proximal femur and altered biomechanics of the hip joint. Corrective osteotomies can be performed later to restore the range of movement. Proximal intracapsular osteotomies are closer to the deformity and so are better at restoring anatomy, but they carry a greater risk of causing iatrogenic avascular necrosis.23 24 Alternatively, extracapsular osteotomies are less able to restore true anatomical alignment, but carry a lower risk of avascular necrosis.


Fig 4 This left sided slipped upper femoral epiphysis was fixed using a single cannulated screw

Unstable slips carry a 47% risk of avascular necrosis and need urgent fixation,11 21 although the timing of management is highly controversial. Some centres (such as ours) advocate either immediate fixation within 24 hours or delaying surgery for one week to allow oedema to settle and granulation tissue to form before adding further surgical trauma.1 21 The argument against delay is that the slip must be stabilised as soon as possible to reduce vascular insult.

Children presenting with a slipped upper femoral epiphysis should be screened for underlying medical conditions (such as renal failure, hypothyroidism, hyperthyroidism, and sex hormone problems) and referred to the appropriate specialist if necessary.

Patient consent

The patient was managed using a single cannulated screw to fix the slipped epiphysis within 24 hours of presentation.


Cite this as: BMJ 2012;344:e250


  • Competing interests: All authors have completed the ICMJE uniform disclosure form at www.icmje.org/coi_disclosure.pdf (available on request from the corresponding author) and declare: no support from any organisation for the submitted work; no financial relationships with any organisations that might have an interest in the submitted work in the previous three years; no other relationships or activities that could appear to have influenced the submitted work.

  • Provenance and peer review: Not commissioned; externally peer reviewed.

  • Patient consent obtained.


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