Description of the condition
Although a rare condition, slipped upper femoral epiphysis (SUFE) is one of the most common types of paediatric and adolescent hip disorder. SUFE involves instability of the growth plate (often called the physis) at the junction between the head and neck of the thigh bone (femur) resulting in the head of the femur staying in the acetabulum and the neck slipping forward and outward. Although, the cause is poorly understood, several anatomical features and medical conditions have been implicated. The following features lead to an increase in the shear forces across the physis and can lead to SUFE (Herring 2008):
increased weight (> 80th centile);
femoral retroversion (> 10º);
increased physis height due to widened hypertrophic zone;
more vertical slope of the physis; and
Medical conditions associated with SUFE include endocrine disorders, renal failure osteodystrophy and previous radiation therapy (Loder 2000). About 30% of SUFE patients subsequently develop bilateral SUFE with the other hip slipping as well.
The incidence of SUFE varies with sex, age, and racial group, with an overall incidence of 10 per 100,000 children. This may be an under-estimate, as mild cases may not be diagnosed until arthritis supervenes many years later. SUFE is more common in boys (75% of cases) with the peak incidence occurring at 12 to 15 years compared to 10 to 13 years in girls. Thus, boys tend to have their slip two years older than girls (Montgomery 2009). SUFE is rarely reported after the age of 20 years (Kelsey 1970). The classical presentation is an overweight child presenting with groin, thigh or knee pain or both (referred pain, obturator nerve) and limping. There may be a history of minor trauma. The child may be able to ambulate (stable slip) or may not be able to do so even with crutches (unstable slip). If the participant can walk, and there is an external rotation of the involved limb and it is not possible to sit comfortably without keeping the leg straight (as the hip cannot bend). There is usually restriction in the range of movement of the affected hip. With increasing severity, SUFE is associated with increasing pain and disability.
Several classifications have been proposed for SUFE.
Functionally, SUFE may be classified according to weight-bearing status (Loder 1993) as:
stable: patient is able to ambulate and bear their weight; or
unstable: patient is unable to ambulate with or without crutches.
In a case series of 55 SUFEs, Loder showed that avascular necrosis (AVN) developed in 47% of unstable slips compared to none in patients with stable slips (Loder 1993). Anatomical reduction of SUFE occurred in 26 unstable slips (out of 30) and in only two of the stable slips (out of 25). Loder was not able to demonstrate an association between early reduction and the development of AVN. Table 1 provides a glossary of terms associated with slipped upper femoral epiphysis.
|AVN||Avascular necrosis; the death of the bone secondary to the loss of blood supply|
|Chondrolysis||The gradual thinning and subsequent loss of the articular cartilage|
|Prodromal symptom||Prodrome is an early symptom (or set of symptoms) that might indicate the start of a disease before more specific symptoms occur|
|Retroversion||Pointing backward relative to the front of the body. Normally, the femoral neck is pointing 15º forward|
|SUFE or SCFE||These are the two most common abbreviations for the slipped upper (or capital) femoral epiphysis|
SUFE has been classified chronologically; relating to the onset of symptoms.
Preslip: patient has symptoms with no anatomical displacement of the femoral head. There may be useful radiological evidence such as widening of the physis, osteopenia of the pelvis.
Acute: there is an abrupt displacement through the proximal physis with symptoms and signs developing over a short period of time (< 3 weeks).
Chronic: patients with a chronic slipped capital femoral epiphysis present with pain in the groin, thigh, and knee that varies in duration, often ranging from months to years.
Acute on chronic: initially, patient has chronic symptoms, but develops acute symptoms as well following a sudden increase in the degree of slip.
Radiographical classification is based on the degree of displacement either by proportion of slip, or by the angular displacement of slip. Wilson 1965 classified slips as:
mild slip (grade I) where the displacement of the physis as a proportion of neck width is less than one third;
moderate slip (grade II), displacement is between one third and one half of neck width; or
severe slip (grade III) has displacement of greater than one half of neck width.
Angular displacement is measured by the Southwick angle of the slip (Southwick 1967). The angle is measured on the lateral view of the both hips. It is measured by drawing a line perpendicular to a line connecting the posterior and anterior tips of the epiphysis at the physis. The angle between the perpendicular line and the femoral shaft line is the angle. The angle is measured bilaterally. The slipped side is then subtracted from the normal side. The number calculated determines the severity which is classified as:
mild slip (Grade I) < 30°;
moderate slip (Grade II) is 30° to 50°; or
severe slip (Grade III) is > 50°.
In practice, most clinicians tend to use a combination of the Loder classification and one of the radiographic classifications. There is some crossover between the classifications but severe slips are more likely to be unstable (Montgomery 2009).
Most investigators agree that once a SUFE has been diagnosed, surgical treatment is indicated to prevent progression of the slip. The goal of treatment has always been to prevent additional slippage while avoiding the complications of avascular necrosis (AVN) and chondrolysis (Loder 2000). Recently, the importance of reducing the slip has been emphasised in preventing femoro-acetabular impingement (FAI) and premature osteoarthritis (OA) (Dodds 2009; Ganz 2003).
Description of the intervention
There is almost a universal consensus about the treatment of Grade I and (to a lesser extent) grade II SUFE: placing a single screw across the growth plate through a very small incision on the thigh to prevent further slip until growth plate closure. This procedure is commonly referred to as a percutaneous pinning or pinning in situ (PIS). Sometimes, more than a single screw is required to prevent further progression depending on the initial stability, severity and bone quality. Some advocate multiple smooth pins in very young affected children (less than 8 years old) to allow for growth (Staheli 2008). The screw must not be removed prior to physeal closure, otherwise progression of the slip may resume. The appropriateness of removal after physeal closure is contended. If the slip is more severe, a more involved procedure or corrective surgery may be necessary. Pinning in situ may not be physically possible without reducing the slip, hence the need for reduction. Forceful closed reduction of a slipped epiphysis is contraindicated due to high risk of AVN. Some advocate pinning in situ with a re-alignment procedure performed at a later date. Others recommend immediate open reduction and fixation. There are several techniques used to achieve open reduction and fixation including Dunn's osteotomy, Fish osteotomy and surgical dislocation. However, the relative effectiveness of these techniques is contested.
The timing of operation is controversial. Given the rarity of the condition, most studies that looked at the timing of surgery and outcome were underpowered. In a meta-analysis of five studies (130 unstable SUFEs where 56 were treated within 24 hours and 74 were treated after 24 hours of symptom onset), Lowndes 2009 found that the odds for developing AVN if treatment occurs within 24 hours might be halved for developing AVN when compared to later treatment, although the difference was not statistically significant (P = 0.44). Peterson 1997 showed early stabilization within 24 hours was associated with less AVN (3/42 = 7%) in comparison with those stabilized after 24 hours (10/49 = 20%). Kalogrianitis 2007 showed that AVN developed in 50% (8/16) of unstable SUFE. All but one of these SUFE were treated between 24 and 72 hours after symptom onset. Kalogrianitis 2007 recommended immediate stabilization of unstable slips presenting within 24 hours, or if not possible, delaying the operation for at least one week. However, consistent with lack of power to inform the issue of timing, Loder 1993 noted more AVN in patients treated within 48 hours compared to those treated after 48 hours (7/8 versus 7/21).
Prophylactic pinning of the normal contra-lateral side is also controversial. The quoted risk of contralateral slip varies from 18 to 60%. Prophylactic PIS is not free of risk which should be weighed against the benefit. Both proponents and opponents have some evidence to support their views (Jerre 1994; Herring 2008). Stasikelis 1996 performed a retrospective review of 50 children who presented with unilateral SUFE to determine parameters that predict the later development of a contralateral slip. They found the modified Oxford bone age (a measure of physiological maturity) strongly correlated with the risk of development of a contralateral slip; contralateral slip developed in 85% of patients with a score of 16, in 11% of patients with a score of 21, and in no patients with a score of 22 or more. The modified Oxford bone age is based on appearance and fusion of the iliac apophysis, femoral capital physis, and greater and lesser trochanters.
We adopted a pragmatic approach for contralateral pinning where the following factors play a role in decision making:
age of the child (< 10 years is associated with a higher risk of bilaterality);
the aetiology of the slip (renal osteodystrophy and endocrine disorders have a high incidence of bilaterality);
the compliance of the child and family; and
the nature of current slip (Severe slip occurred over a very short period of time with no prodromal symptoms may justify pinning the other side).
How the intervention might work
The goal of treatment is to prevent additional slippage by providing mechanical stability using screws or pins while avoiding the complications of avascular necrosis (AVN) and chondrolysis. AVN and chondrolysis are the most important and robust outcomes of SUFE treatment. They are readily identifiable and their development is a good indicator for a bad outcome. However, the opposite is not true.
The potential for further slip continues until physeal closure (ossification of the growth plate). After physeal healing, there may be a residual displacement which impair function and quality of life, whilst the patient is still young. A realignment procedure (such as trochanteric, subtrochanteric or femoral neck osteotomy) may improve function in these patients. In older patients with established degenerative changes, total hip replacement may be indicated. Reducing the slip provides extra stability, improved function and may prevent or reduce long term complications; provided short term complications such as AVN and chondrolysis do not occur.
Why it is important to do this review
The management of SUFE is controversial and still evolving with advancing knowledge, surgical skills and expertise. The infrequency of cases, the various classifications in use, the various treatment options, and lack of robust evidence for outcomes, has resulted in the lack of clear, evidence-based recommendations for treatment (Montgomery 2009). This has led to significant variations in clinical practice threatening possible optimum care for this group of patients. There have been a few published attempts (Loder 2000; Lowndes 2009; Wright 2009) to produce recommendations to treat SUFE (Loder 2000; Lowndes 2009; Wright 2009). However, these attempts lacked a rigorous and structured approach of critically appraising the available evidence, which is the purpose of this review.