Study Guide

SCFE (Slipped Capital Femoral Epiphysis)

Key Points:

Typical SCFE involves posterior and medial slippage of the proximal femoral epiphysis relative to the metaphysis (anterior and lateral slippage of the metaphysis relative to the epiphysis).
Valgus SCFE is rare, resulting in the opposite deformity.
Most commonly seen in obese, adolescent males.
May present with hip, thigh or knee pain, commonly with a limp, out-toeing and increased hip external rotation on the affected side
Radiographic findings include physeal widening and malalignment of the epiphysis in relation to the metaphysis. Surgical stabilization of the epiphysis is the initial goal of treatment.
Residual deformity may result in pain, impingement and early arthritis, potentially requiring additional surgical management.

Description:

Traditionally slipped capital femoral epiphysis (SCFE) has been described as posterior and medial slippage of the capital femoral epiphysis with respect to the metaphysis. However, the epiphysis is held in the acetabulum by the ligamentum teres; thus, the metaphysis actually moves laterally and anteriorly in relation to the epiphysis.

In most patients, SCFE results in varus alignment. Valgus slips are uncommon and may be associated with underlying endocrinopathies (Shank 2010).

Epidemiology:

The prevalence of SCFE in the U.S. ranges from 2 to 11 per 100,000 (Loder, 1996). African Americans, males, and obese children are more frequently affected. The typical age groups are 12-15 years in boys and 11-14 years in girls. Juvenile onset (age less than 10 years) should raise the suspicion of an underlying endocrinopathy.

Atypical slips may be seen in patients with endocrine abnormalities (hypothyroidism, hypopituitarism, acromegaly as well as growth hormone supplementation, hyperparathyroidism), kidney disease and those who have received radiation treatment (Loder, 2001).

Mechanical factors implicated in the development of SCFE include relative retroversion of the femur, deep set acetabulae, increased physeal slope and obesity (Pritchett, 1988; Mirkopulos, 1988).

Roughly one third (18-50%) of cases may show bilateral involvement either at presentation or within the next 18-24 months (Loder, 1993). Various factors have been used to predict the risk of contralateral slip (Riad, 2007; Zide, 2011).

Clinical Findings:

Hip, thigh or knee pain and limp are common presenting symptoms. Progressive external foot progression may be noted. A history of radiation, renal disease, thyroid or other endocrine disorders including growth hormone treatment may be present in the setting of non-idiopathic slip.

On exam, in a typical varus SCFE, there is increased hip external rotation and limited flexion, abduction, internal rotation. In some instances there is obligate external rotation with flexion of the affected side (Drehmann sign). The affected extremity may be shorter in a unilateral slip, and a Trendelenberg sign may be present. Clinically, a slip is deemed stable if the patient is able to bear weight on the affected side, even with assistive devices (Loder, 1993). This is of prognostic significance as the rate of avascular necrosis (AVN) is higher (20-60%) in the unstable slips, and negligible in stable hips.

Imaging Studies:

Radiographs:

Order pelvic views (not hip), both AP and frog lateral view, so the contralateral hip can be used for measurement of the Southwick slip angle and to evaluate for a “silent” SCFE.
- For suspected unstable SCFE order a cross table lateral view of the hip instead of the frog leg lateral view so the unstable hip is not manipulated (Southwick angle will not be measurable on this view, but the SCFE should be obvious)
There may be evidence of acetabular retroversion or a deep acetabulum.
Radiographic signs of SCFE include:
- Widening and irregularity of the physis
- Metaphyseal blanch sign of Steele
- Abnormal Klein’s line: a line along the superior border of the neck normally intersects approximately 15-20% of the epiphysis
- Coxa vara is seen in more advanced slips
On the lateral view:
- Posterior slippage of the epiphysis is noted
- The Southwick (lateral epiphyseal-shaft) slip angle:
  - Measured on the frog leg lateral view
  - Calculated by measuring the abnormal side and subtracting the measurement on the unaffected side (or subtracting the average normal of 12 degrees in the case of bilateral SCFE) (Southwick 1967).
  - This can be used to classify the severity of slips as mild (less than 30 degrees), moderate (30-60 degrees) or severe (more than 60 degrees).

Bone scan: May be used to assess vascularity of the head

CT scan: Not typically indicated in diagnosis of SCFE, but may be useful in preoperative planning for complex reconstruction, such as prior to multi-planar Southwick osteotomy

MRI:

In very early slips, without obvious radiographic findings, MRI may demonstrate periphyseal edema and/or a small joint effusion.
Newer protocols allow for assessment of femoral head vascularity
Evaluation for post-SCFE impingement, detection of labral tears and chondral damage.
3D printing of the proximal femoral anatomy based on CT or MR imaging may be of additional utility in planning complex reconstructions

Treatment:

The gold standard treatment of SCFE remains in situ screw fixation (especially for mild to moderate slips), although some centers have adopted more aggressive approaches (closed manipulation or mini-open reduction before fixation or the modified Dunn procedure) that improve capital alignment so as to minimize potential damage to the articular cartilage and labrum due to a non-concentric joint.

Stable Slip

In situ screw fixation is the recommended treatment for a stable slip, and is performed percutaneously under fluoroscopic guidance. Attempting to reduce or manipulate a stable slip may result in physeal or vascular damage and increase the risk of AVN. The patient is positioned on a fracture table with the affected hip in neutral position, with patella forward. There is no attempt at intentional reduction. The unaffected limb is flexed and abducted out of the way. Fluoroscopy is brought in prior to draping to ensure appropriate positioning of the image intensifier. Many surgeons prefer a double fluoroscopy machine technique to avoid moving the fluoroscopy machine between the AP and lateral imaging positions. Pinning on a flat Jackson table is an alternate technique, but results in more difficult imaging and the potential for bending the guide wire as the affected limb must be moved in and out of the frog lateral position. The starting point of the screw is usually anterolateral on the neck and should be proximal to the lesser trochanter (to minimize risk of fracture) and distal to the intertrochanteric line (to avoid iatrogenic screw head impingement). The screw should preferably be perpendicular to the physis on AP and lateral views and should be directed towards the center of the epiphysis to minimize risk of inadvertent joint penetration. The screw tip should be left 5 mm short of the sub-chondral bone. Five threads should cross the physis (Carney 2003).

Unstable Slip

For an unstable slip, inadvertent reduction with patient positioning may occur, or a mini-open reduction may be accomplished using an anterior approach with digital reduction (to the point of correction of the acute deformity) and fixation with K wires (Parsch, 2009) or screws. Fixation with 2 screws it typical in the treatment of unstable slips to avoid spinning the epiphysis as the screw is inserted. Decompression of the capsule to minimize the risk of AVN in unstable slip is a consideration (Schrader 2016). This may be performed with a Cobb elevator directed up the femoral neck to disrupt the capsule, or through direct approach to the hip. The modified Dunn procedure via a surgical hip dislocation approach (Slongo, 2010) is another option for an unstable slip, but is recommended with caution as there are significant complications associated with the procedure including hardware failure (15%) and AVN (26%) (Sankar, 2013). The modified Dunn should be limited to acute, unstable, severe slips (greater than 50-degree slip angle), done within 24 hours by an experienced surgeon (Upasani, 2014).

Prophylactic Pinning

There is a 10-30% risk of a subsequent contralateral slip in patients presenting with a unilateral slip. Most of the subsequent slips are mild. The risk varies by age, skeletal maturity (modified Oxford score), and underlying disorders. Subsequent contralateral slip is highest in untreated renal disease, endocrinopathies, and patients with a history of radiation. Prophylactic pinning is recommended in these situations. Prophylactic pinning may also be considered in patients suspected to be non-compliant with follow up, as well as younger patients (girls less than 10 years, boys less than 12 years, modified oxford score of 16 or less), and those with posterior sloping angle (PSA) more than 15-18 degrees on the unaffected side. (Barrios, 2005; Phillips, 2013)

Complications:

Avascular necrosis (AVN): one of the most feared complications of SCFE and is seen almost exclusively in unstable slips (Tokmakova, 2003). The percentage of AVN varies from 10-80% with most large series reporting approximately 25% AVN for unstable slips. Factors associated with AVN include unstable slips, forcible closed reduction, young age, and Down Syndrome.
Chondrolysis (0-2%): This may be seen in both treated as well as untreated slips. Inadvertent joint penetration by the screw is one of the postulated etiologic factors in the development of chondrolysis.
Limb length discrepancy: May be due to loss of epiphyseal height due to physeal position, AVN, or growth arrest in patients treated with screw fixation.
Slip progression: This is an uncommon complication after screw fixation. Insufficient number of threads crossing the physis (less than 5) has been shown to increase the risk of progression (Carney 2003).
Pistol grip deformity and femoroacetabular impingement (FAI): The loss of head neck offset as a result of the slip results in the “pistol grip” deformity of the proximal femur. This results in cam-type femoroacetabular impingement and damage to the labrum and articular cartilage. This can be addressed by a variety of proximal femoral osteotomies (subcapital, intertrochanteric, subtrochanteric) with additional osteochondroplasty of the femoral head neck junction and labral/cartilage repair vs debridement as needed.

References:

Barrios C, Blasco MA, Blasco MC, Gascó J. Posterior sloping angle of the capital femoral physis: a predictor of bilaterality in slipped capital femoral epiphysis. J Pediatr Orthop. 2005; 25(4):445-9.
Carney BT, Birnbaum P, Minter C. Slip progression after in situ single screw fixation for stable slipped capital femoral epiphysis. J Pediatr Orthop. 2003; 23(5):584-9.
Loder RT, Richards BS, Shapiro PS, et al. Acute slipped capital femoral epiphysis: the importance of physeal stability. J Bone Joint Surg Am. 1993;75(8):1134-40.
Loder RT, Aronson DD, Greenfield ML. The epidemiology of bilateral slipped capital femoral epiphysis. A study of children in Michigan. J Bone Joint Surg Am. 1993; 75(8):1141-7.
Loder RT. The demographics of slipped capital femoral epiphysis. An international multicenter study. Clin Orthop. 1996; 322:8-27.
Loder RT, Greenfield ML. Clinical characteristics of children with atypical and idiopathic slipped capital femoral epiphysis: description of the age-weight test and implications for further diagnostic investigation. J Pediatr Orthop. 2001; 21(4):481-7.
Mirkopulos N, Weiner DS, Askew M. The evolving slope of the proximal femoral growth plate relationship to slipped capital femoral epiphysis. J Pediatr Orthop. 1988; 8(3):268-73.
Parsch K, Weller S, Parsch D. Open reduction and smooth Kirschner wire fixation for unstable slipped capital femoral epiphysis. J Pediatr Orthop. 2009; 29(1):1-8.
Phillips PM, Phadnis J, Willoughby R, Hunt L. Posterior sloping angle as a predictor of contralateral slip in slipped capital femoral epiphysis. J Bone Joint Surg Am. 2013; 95(2):146-50.
Pritchett JW, Perdue KD. Mechanical factors in slipped capital femoral epiphysis. J Pediatr Orthop. 1988; 8(4):385-8.
Riad J, Bajelidze G, Gabos PG. Bilateral slipped capital femoral epiphysis: predictive factors for contralateral slip. J Pediatr Orthop. 2007; 27(4):411-4.
Sankar WN, Vanderhave KL, Matheney T, Herrera-Soto JA, Karlen JW. The modified Dunn procedure for unstable slipped capital femoral epiphysis: a multicenter perspective. J Bone Joint Surg Am. 2013; 95(7):585-91.
Schrader T, Jones CR, Kaufman AM, Herzog MM. Intraoperative Monitoring of Epiphyseal Perfusion in Slipped Capital Femoral Epiphysis. J Bone Joint Surg Am. 2016; 98(12):1030-40.
Shank CF, Thiel EJ, Klingele KE. Valgus slipped capital femoral epiphysis: prevalence, presentation, and treatment options. J Pediatr Orthop. 2010; 30(2):140-6.
Slongo T, Kakaty D, Krause F, Ziebarth K. Treatment of slipped capital femoral epiphysis with a modified Dunn procedure. J Bone Joint Surg Am. 2010; 92(18):2898-908.
Southwick WO. Osteotomy through the lesser trochanter for slipped capital femoral epiphysis. J Bone Joint Surg Am. 1967; 49(5):807-35.
Tokmakova KP, Stanton RP, Mason DE.Factors influencing the development of osteonecrosis in patients treated for slipped capital femoral epiphysis. J Bone Joint Surg Am. 2003; 85-A(5):798-801.
Upasani VV, Matheney TH, Spencer SA, Kim YJ, Millis MB, Kasser JR. Complications after modified Dunn osteotomy for the treatment of adolescent slipped capital femoral epiphysis. J Pediatr Orthop. 2014; 34(7):661-7.
Zide JR, Popejoy D, Birch JG. Revised Modified Oxford Bone Score: A Simpler Systemfor Prediction of Contralateral Involvement inSlipped Capital Femoral Epiphysis. J Pediatr Orthop. 2011; 31(2):159-64.

Top Contributors:

Mihir Thacker, MD