Slipped Femoral Capital Epiphysis

Slipped femoral capital epiphysis is the disorder of the proximal femoral physis that leads to slippage of the epiphysis relative to the femoral neck. It is one of commonest hip abnormalities in adolescence. It affects both the hips in about 20% cases.

The incidence for slipped capital femoral epiphysis is about 10 cases per 100,000 children.

Boys presenting in the age group 10-17 years and girls in 8-15 years.

Obesity is a significant risk factor because it places more shear forces around the proximal growth plate in the hip at risk.

Males have 2.4 times the risk compared with females.  The left hip is affected more commonly than the right.

Rate of familial involvement is 5-7%.

In patients younger than 10 years, Slipped femoral capital epiphysis is associated with endocrine disorders. Bilaterality is more common in these younger patients.

Pathophysiology of Slipped Femoral Capital Epiphysis

Risk factors associated with the disorder are

• Obese children (single greatest risk factor)
• males
• Certain races
  • African Americans
  • Pacific islanders
• Period of rapid growth associated with puberty
• Femoral retroversion

The slip occurs due to mechanical forces acting on a susceptible physis. Physis is the growth plate that contributes to growth of the bone. This slip is through the hypertrophic zone of the physis. It is caused by weakness of the perichondral ring.

Cartilage in the hypertrophic zone acts as a weak spot. It must be noted that, epiphysis itself remains  in the acetabulum while the neck displaces anteriorly and externally rotates  making epiphysis posterior.

In patients with slipped femoral capital epiphysis , the epiphyseal growth plate is unusually widened, primarily due to expansion of the zone of hypertrophy. There is abnormal cartilage maturation, endochondral ossification, and perichondral ring instability.

Read normal cartilage structure.

This leads to less organization of the normal cartilaginous columnar architecture. Slippage occurs through this weakened area.

The position of the proximal physis normally changes from horizontal to oblique during preadolescence and adolescence. This makes the complressive hip forces shearing nand contribute to fast development of slipped femoral capital epiphysis in susceptible cases.

Femoral neck retroversion and a reduced neck-shaft angle can increase the shear forces across the hip, leading to the condition. 

Associated Endocrine Disorders

• Hypothyroidism
• Low growth hormone level
• Pituitary tumors
• Craniopharyngioma
• Down syndrome
• Renal osteodystrophy
• Adiposogenital syndrome

Classification of Slipped capital Femoral Epiphysis

Stable vs. Unstable Classification

This is based on patient’s ability to bear weight wihtout external aid like crutches.

Stable

• Able to bear weight with or without crutches
• Minimal risk of osteonecrosis (<10%)

Unstable

• Unable to ambulate (not even with crutches)
• Associated with high risk of osteonecrosis (~47%)

Southwick Classification

Measurement of the difference between both hips in the femoral head-shaft angle on the frog lateral radiograph.

Difference between these two angles obtained on the affected and unaffected sides determines the degree of slip and resulting abnormal alignment

Mild

<30°

Moderate

30-50°

Severe

>50°

Grading System for Slipped Capital Femoral Epiphysis

Grade I

0-33% of slippage

Grade II

34-50% of slippage

Grade III

50% of slippage

Acute and Chronic

If a patient reports symptoms of greater than 3 weeks’ duration but presents with an acute exacerbation then slipped capital femoral epiphysis is termed as  acute on chronic.

Clinical Presentation

Most common presentation is groin and thigh pain but about one fifth of patients can also present as knee pain.

During its early stages the condition is associated with considerable pain, but the time the patient is seen, the disease is usually well developed and the painful acute stage is passed.

Patient walks with a Trendelenberg gait, the body swaying over to the affected side. The pelvis on the sound side tends to drop when weight is born on the affected extremity.

Patient prefers to sit in a chair with affected leg crossed over the other.

The symptoms are usually present for weeks to several months before diagnosis is made

On examination, the patient walks with antalgic [painful], keeps affected limb externally rotated.

The movements of the hip are reduced especially internal rotation, abduction and flexion. On flexion, the hip is found to rotate externally.

The thigh may show atrophy

On palpation of the groin, a hard mass can often be felt, which moves with the femur; it is the thickened head and neck.

Measurement shows the trochanter to be higher than on the unaffected side.

Movement on the affected side is limited. With the patient recumbent on his back, the position of the leg is one of lateral rotation  slight abduction.

In a recent complete separation, the signs resemble those of recent fracture of the neck of the femur, with great pain, external rotation of the limb being restricted by muscular spasm.

Differential Diagnoses

• Femoral Head Avascular Necrosis
• Femoral Neck Fracture including stress fractures
• Groin Injury
• Osteitis Pubis
• Tuberculosis of the hip
• Perthes’ disease
• Congenital dislocation of hip

Laboratory Studies

Routine hormonal screening of children with slipped capital femoral epiphysis  is not indicated.

Patient may be investigated for endocrinopathies and medical disorders especially in atyoical presentation [child is < 10 years old or >16 years,  weight of the child is < 50th percentile]

Imaging Studies

X-rays

Obtain anteroposterior and frog-lateral radiographs of the pelvis or bilateral hips.

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.

frog-leg lateral view shows the slightest backwards displacement better in the anteroposterior view.

This is followed by the acute slip which is posteromedial.

The head of the femur lies in the acetabulum but  slightly displaced in relation to the neck, its border projecting as a beak-like process.

Margin of the head is thinned out and separated by a short distance from the prominence made by the upper angle of the metaphysis.

The femoral neck upper border is lengthened and roughly convex upwards, while its lower border is shortened and to be more sharply curved upwards than normally. The lower border appears to be shortened as it is buried in the concave cervical surface of the epiphysis, and.

In the angle between the lower border of the neck and the underhanging head, new bone is formed.

In a chronic slip, the physis becomes sclerotic and the metaphysis widens (coxa magna).

The femoral head is atrophic and the articular surface  is directed medially, backwards and downwards.

The neck and short and neck-shaft angle appears to be decreased to about 90 degree.

In cases where displacement has been severe, the head is often complete separated from the neck, and lies loose in the acetabulum.

On the AP, a line drawn up the lateral edge of the femoral neck (line of Klein) fails to intersect the epiphysis. (Trethowan’s Sign).

The metaphysis is displaced laterally, and therefore may not overlap posterior lip of the acetabulum as it should normally (loss of triangular sign of Capener) .

It  normally pass through a portion of the femoral head. If not, slipped capital femoral epiphysis is diagnosed.

Alignment of the epiphysis with respect to the femoral metaphysis can be used to grade the degree of slippage.

In frog leg radiograph, a  straight line through the center of the femoral neck proximally should be at the center of the epiphysis. If not, and the line is anterior in the epiphysis, it is likely an slipped capital femoral epiphysis.

Radiographs should be assessed for underlying medical disorders ( rickets, renal osteodystrophy, etc).

Bone scanning/CT

Not required in routine.

Could be used for confirmation of diagnosis

MRI

Measure the degree of displacement

• Measure  epiphyseal perfusion.
• Can quantify the slip better
• Can help diagnose a preslip condition when radiographs are negative
  • Shows growth plate widening and increased signal of the metaphysis

Treatment of Slipped Capital Femoral Epiphysis

Treatment of slipped capital femoral epiphysis  is emergent regardless the severity of the slip. The treatment is surgical.  There is no role for observation or attempts at closed reduction.

Each case needs to be assessed individually for the benefits and risks.

Before treatment determine –

• Acute/chronic
• Stable/unstable
• Radiological grading

The diagnosis should be done as early as possible. Delayed diagnosis may lead to progression of the slip, slip may become unstable and increase the risk of complications like avascular necrosis.

Some authors also advocate prophylactic fixation of the contralateral hip especially in patients younger than 10 years or having endocrinopathies as  these individuals have higher relative risks for bilateral involvement.

Prophylactic treatment should also be considered in a patient or family that is unreliable.

If only affected hip is operated, the other hip should be closely followed up as well and early operative intervention should be done if the other hip becomes symptomatic

Types of Surgical Intervention

Percutaneous in situ fixation  with cannulated screw

It is used to stabilize the epiphysis from further slippage and promote closure of the proximal femoral physis. It is used in both stable and unstable slips. Usually one screw is used.  2 screw constructs have greater biomechanically stability but are advocated when there is greater violation of the physis.

Fixation allows early stabilization of the slippage, enhancement of physeal closure, prevention of further slippage, and decrease in symptoms.  Unstable or grade III slips may require gentle repositioning to improve alignment. Revision of the screw fixation may be needed if the child outgrows the screw.

Open reduction with capital realignment

This is achieved by

• Surgical dislocation with epiphyseal reorientation
• Modified Dunn procedure with formation of a epiphyseal vascular flap

Proximal femoral osteotomy

Osteotomy of the proximal femur may be needed as a secondary procedure for repositioning of the femoral head to improve functional range of motion, or as a primary procedure for patients with severe morphologic displacement.

It can be performed at the subcapital, femoral neck, intertrochanteric and subtrochanteric regions.

Subcapital and femoral neck osteotomies provide the most correction but are associated with the highest risks of osteonecrosis and should be avoided

Typical correction consists of flexion, valgus and derotation

Complications of Slipped Femoral Capital Epiphysis and Surgical Procedures

• Osteonecrosis of femoral head (4-6%)
• Epiphyseal slip of opposite hip (20-80%)
  • risk factors – male, obesity, young age of initial slip, endocrine disorders

• Chondrolysis (0-2%)
  •  Associated with unrecognized implant penetration of the articular surface
  • Spica cast immobilization
  • With increased fluoroscopic use, the prevalence has decreased.

• Residual deformity/ Limb length discrepancy
  • Can be corrected with intertrochanteric/ subtrochanteric osteotomy/Cuneiform osteotomy

• Slip progression
• Other complications
  • Infection (0-2%)
  • Chronic pain (5-10%)
  • Degenerative arthritis
  • Pin associated proximal femur fracture
  • Labral tearing and degeneration

Follow-up

Following fixation,  the patient is put on protected weight bearing for 6-8 weeks. Physical therapy for strengthening, proprioception, balance, and endurance training is initiated may be helpful.

Most children can then return to full activity once they are pain free with full strength. However, some literature advocates for not allowing a return to contact sports until the physis has closed.

Radiographic follow-up is continued until physeal closure is achieved.

References

• Katz DA. Slipped capital femoral epiphysis: the importance of early diagnosis. Pediatr Ann. 2006 Feb. 35(2):102-11.
• Georgiadis AG, Zaltz I. Slipped capital femoral epiphysis: how to evaluate with a review and update of treatment. Pediatr Clin North Am. 2014 Dec. 61 (6):1119-35.
• Peterson MD, Weiner DS, Green NE, Terry CL. Acute slipped capital femoral epiphysis: the value and safety of urgent manipulative reduction. J Pediatr Orthop. 1997 Sep-Oct. 17(5):648-54.
• Loder RT, Richards BS, Shapiro PS, Reznick LR, Aronson DD. Acute slipped capital femoral epiphysis: the importance of physeal stability. J Bone Joint Surg Am. 1993 Aug. 75(8):1134-40.
• Klein A, Joplin RJ, Reidy JA, Hanelin J. Roentgenographic features of slipped capital femoral epiphysis. Am J Roentgenol Radium Ther Nucl Med. 1951 Sep. 66(3):361-74.
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• Azzopardi T, Sharma S, Bennet GC. Slipped capital femoral epiphysis in children aged less than 10 years. J Pediatr Orthop B. 2010 Jan. 19(1):13-8.
• Zupanc O, Krizancic M, Daniel M, et al. Shear stress in epiphyseal growth plate is a risk factor for slipped capital femoral epiphysis. J Pediatr Orthop. 2008 Jun. 28(4):444-51.
• Aronson DD, Carlson WE. Slipped capital femoral epiphysis. A prospective study of fixation with a single screw. J Bone Joint Surg Am. 1992 Jul. 74(6):810-9.
• Kohno Y, Nakashima Y, Kitano T, Irie T, Kita A, Nakamura T, et al. Is the timing of surgery associated with avascular necrosis after unstable slipped capital femoral epiphysis? A multicenter study. J Orthop Sci. 2016 Sep 11.
• Weiner DS, Weiner S, Melby A, Hoyt WA Jr. A 30-year experience with bone graft epiphysiodesis in the treatment of slipped capital femoral epiphysis. J Pediatr Orthop. 1984 Mar. 4(2):145-52.
• Castaneda P, Macias C, Rocha A, Harfush A, Cassis N. Functional outcome of stable grade III slipped capital femoral epiphysis treated with in situ pinning. J Pediatr Orthop. 2009 Jul-Aug.