Slipped upper femoral epiphysis (SUFE), also known as a slipped capital femoral epiphysis (SCFE), (plural: epiphyses) is a relatively common condition affecting the physis of the proximal femur in adolescents. It is one of the commonest hip abnormalities in adolescence and is bilateral in 20-40% of cases 10.
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Epidemiology
Slipped upper femoral epiphysis is more common in boys than girls and more common in African Caribbean patients than Caucasian patients. The age of presentation is somewhat dependent on gender with boys presenting later (10-17 years) than girls (8-15 years) 2.
Risk factors
Conditions that may predispose to SUFE include:
obesity: significant risk factor 6
Clinical presentation
Patients may present in different ways depending on the epiphysis stability and the duration of the onset of the symptoms.
Patients with an unstable slip present similarly to those with an acute femoral fracture and are unable to bear weight on the affected limb. A patient with a stable slip can tolerate weight bearing. It's important to understand that this refers to clinical presentation, but even the patient initially able to bear weight is at risk of evolving to an acute displacement if bed rest is not established 10.
Regarding the onset of symptoms, SCFE is usually classified into three groups 10:
acute: severe hip pain and inability to bear weight, usually after a minor trauma, with prodromal symptoms such as vague groin or thigh pain for up to 3 weeks before the acute presentation
chronic: represents the most common presentation. Vague groin and thigh pain for more than 3 weeks, may progress to a limp
acute-on-chronic: the prodromal symptoms have been present for more than 3 weeks, but there is a sudden worsening of the symptoms, including becoming unable to bear weight when previously able to
Pathology
Slipped upper femoral epiphysis is a type I Salter-Harris growth plate injury due to repeated trauma on a background of mechanical and probably hormonal predisposing factors.
During growth, there is a widening of the physeal plate which is particularly pronounced during a growth spurt. Also, the axis of the physis alters during growth and moves from being horizontal to being oblique. As the physis becomes more oblique, shear forces across the growth plate increase and result in an increased risk of fracture and resultant slippage.
Radiographic features
In all situations, especially when imaging children, the fewest number of radiographs, with the smallest exposed area is performed. Gonad protection is usually used in pelvic x-rays of children. However, there should always be one radiograph without lead protection so that the entire pelvis is visualised.
Plain radiograph
The radiographic series used to investigate varies depending on institution:
AP and frog-leg: two view assessment is common ref
AP only: a perceived concern about a risk of a worsening slip means that a frog-leg lateral is only performed if the orthopaedic surgeon or radiologist agrees ref
frog-leg only: to reduce the dose, only frog-leg lateral is performed because it is this view that is most sensitive and the AP rarely adds diagnostic information ref
In the pre-slip phase, there is a widening of the growth plate with irregularity and blurring of the physeal edges and demineralisation of the metaphysis. This is followed by the acute slip, which is posteromedial. In a chronic slip, the physis becomes sclerotic and the metaphysis widens (coxa magna).
The slip that occurs is posterior and, to a lesser extent, medial. It is therefore is more easily seen on the frog-leg lateral view rather than the AP hip view. Because the epiphysis moves posteriorly, it appears smaller because of projectional factors.
On the AP, a line drawn up the lateral edge of the femoral neck (line of Klein) fails to intersect the epiphysis during the acute phase (Trethowan sign).
The metaphysis is displaced laterally and therefore may not overlap the posterior lip of the acetabulum as it should normally (loss of triangular sign of Capener) 5.
The metaphyseal blanch sign, a sign seen on AP views, involves increases in the density of the proximal metaphysis. It represents the superposition of the femoral neck and the posteriorly displaced capital epiphysis.
Alignment of the epiphysis with respect to the femoral metaphysis can be used to grade the degree of slippage: see SUFE grading.
Ultrasound
Ultrasound may be performed in the assessment of hip pain. However, it should not be used as a replacement for a pelvic radiograph. Findings are nonspecific and may include hip joint effusion. In some cases, malalignment of the femoral epiphysis and metaphysis may be seen.
CT
CT is a sensitive and accurate method of measuring the degree of upper femoral epiphyseal tilt and detecting the disease in its early stage. Multi-plane reconstruction allows assessment of the relationship of the femoral head to the metaphysis in three planes. However, the dose required for the examination means that it should not be used unless absolutely necessary.
MRI
In the acute stage, marrow oedema results in an increased signal on T2-weighted sequences, e.g. STIR. Marrow oedema is non-specific, and while it may indicate early bone changes in SUFE, there are numerous other causes, e.g. infection or a tumour.
MRI can be used to examine the contralateral hip which is important because of the high incidence of bilateral slip.
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STIR
high signal in epiphysis and metaphysis
joint effusion
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T1
low signal in oedematous regions
metaphyseal displacement
Treatment and prognosis
Treatment of unstable slipped upper femoral epiphysis has progressively shifted exclusively towards surgical pinning. Conservative management (e.g. limitation of activity and casting) is no longer recommended.
Treatment of the contralateral hip is more controversial. Bilateral SUFE is relatively common (~20%) and stabilisation of the unstable side can, in fact, precipitate slip on the contralateral side. As such prophylactic pinning is recommended by some 3.
If a significant deformity is present, then osteotomies and even joint replacement may be required.
Complications
long term degenerative osteoarthritis: ~90%
osteonecrosis of the femoral head (10-15%): increased incidence with the number of attempted reductions and with multiple screws for pinning 3
chondrolysis (7-10%): acute cartilage necrosis
deformity
femoroacetabular impingement: occurs in some patients who have a residual hip deformity post-correction characterised by relative posterior and medial displacement of the capital femoral epiphysis which then leads to an anterolateral prominence of the metaphysis which abuts the acetabular rim 9
Differential diagnosis
When the slip is evident, and no secondary degenerative changes are present, then the diagnosis is usually readily made. Ideally, however, the diagnosis is made early in which case the differential is that of a painful hip and includes:
developmental dysplasia (late presentation)
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