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Introduction
  • Definition
    • disorder of the proximal femoral physis that leads to slippage of the metaphysis anteriorly and superiorly relative to the epiphysis, which remains anatomically positioned in the acetabulum
  • Epidemiology
    • incidence
      • most common disorder affecting adolescent hips
      • found in 10 per 100,000
    • demographics
      • more common in
        • obese children
        • males (male to female ratio is 2:1.4)
        • specific ethnicities - African Americans, Pacific islanders, Latinos
        • during period of rapid growth (10-16 years of age)
      • average age is
        • 13.4 for boys
        • 12.2 for girls
        • associated with puberty
    • location
      • left hip is more common
      • bilateral in 17% to 50% (~25%)
    • risk factors
      • obesity
        • single greatest risk factor
        • recent data shows trend towards younger age and increased frequency of bilaterality at presentation, possibly related to increased rates of childhood obesity
      • acetabular retroversion and femoral retroversion
        • increased mechanical shearing forces at the physis
      • history of previous radiation therapy to the femoral head region
  • Pathophysiology
    • mechanism
      • due mechanical forces acting on a susceptible physis
    • pathoanatomy
      • slippage occurs though the hypertrophic zone of the physis 
      • in adolescence
        • perichondrial ring thins and weakens
        • undulating mammillary processes in physis unlock, further destabilizing the physis
        • physis is still quite vertical (160° at birth to 125° at skeletal maturity), resulting in increased shearing forces
        • epiphyseal tubercle can provide a rotational pivot point
          • anatomic structure in the posterior superior epiphysis that shrinks with skeletal maturity
      • cartilage in the hypertrophic zone acts as a weak spot 
    • angulation
      • metaphysis translates anterior and externally rotates
      • epiphysis remains in the acetabulum, lies posterior to the translated metaphysis  
    • similar to Salter-Harris type I fracture, but may differ by
      • antecedent epiphysiolysis
      • slower displacement
      • periosteum remains intact (chronic SCFE)
        • in acute SCFE, periosteum is can be partially torn anteriorly over the prominent metaphysis
  • Associated conditions
    • endocrine disorders
      • conditions to look for  
        • hypothyroidism 
          • most common etiology of nonidiopathic SCFE
          • labs: elevated TSH
        • renal osteodystrophy
          • labs: elevated BUN and creatinine
        • growth hormone deficiency
        • panhypopituitarism
      • indications for endocrine workup
        • child is < 10 years old
        • weight is < 50th percentile
    • down syndrome 
Classification
 
Loder Classification -- based on ability to bear weight
Stable Able to bear weight with or without crutches
Minimal risk of osteonecrosis (<10%)
Unstable Unable to ambulate (not even with crutches)
High risk of osteonecrosis (originally ~47%, recent data ~24%)
  • Provides prognostic information for complication of femoral head osteonecrosis
 
Temporal Classification -- based on duration of symptoms; rarely used; no prognostic information
Acute Symptoms that persist for less than 3 weeks
Chronic Symptoms that persist for more than 3 weeks
Acute on Chronic Acute exacerbation of long-standing symptoms
 
Southwick Slip Angle Classification   -- based on femoral epipyseal-diaphyseal angle difference
Mild < 30°
Moderate 30-50°
Severe > 50°
  • Epiphyseal-diaphyseal angle can be measured on both AP and frog lateral pelvis radiographs 
  • Slip angle classification is based on the degree of difference between the affected and unaffected hip
  • If bilateral hips are involved, use 145° as "unaffected" hip reference for AP and 10° as "unaffected" hip reference for lateral  
 
 Grading System -- based on percentage of slippage
Grade I 0-33% of slippage
Grade II 34-50% of slippage
Grade III >50% of slippage
 
Presentation
  • Symptoms
    • groin and thigh pain 
      • most common presentation
    • limp
      • antalgic gait
      • externally rotated foot progression angle
    • knee pain
      • can frequently present as knee pain (15-50%)   
        • due to pain activation of the medial obturator nerve
        • can lead to missed diagnosis
    • motion
      • patients prefer to sit in a chair with affected leg crossed over the other
    • duration
      • symptoms are usually present for weeks to several months before diagnosis is made
  • Physical exam
    • abnormal gait / limp
      • antalgic, waddling, externally rotated gait or Trendelenburg gait
    • decreased hip motion
      • obligatory external rotation during passive flexion of hip (Drehmann sign) 
        • due to a combination of synovitis and impingement of the displaced anterior-lateral femoral metaphysis on the acetabular rim 
      • loss of hip internal rotation, abduction, and flexion
    • abnormal leg alignment
      • externally rotated foot progression angle
    • weakness
      • thigh atrophy
Imaging
  • Radiographs
    • recommended views  
      • AP & frog-leg lateral of right and left hip 
        • lateral radiograph is best way to identify a subtle slip
    • findings on AP of pelvis
      • Klein's line 
        • line drawn along superior border femoral neck 
          • will intersect less of the femoral head or not at all in a child with SCFE 
            • intersects lateral femoral head in a normal hip due to natural lateral overhang of the epiphysis 
          • evaluate for asymmetry between sides
      • epiphysiolysis (growth plate widening or lucency) 
        • an early radiographic finding
      • blurring of proximal femoral metaphysis (metaphyseal blanch sign of Steel)
        • seen on AP due to overlapping of the metaphysis and posteriorly displaced epiphysis
  • MRI 
    • indications
      • can help diagnose a preslip condition when radiographs are negative
    • findings
      • growth plate widening
      • edema in metaphysis 
        • decreased signal on T1, increased signal on T2
Treatment
  • Operative
    • percutaneous in situ fixation    
      • indications
        • both stable and unstable slips
      • technique
        • one vs. two cannulated screws is controversial
          • 2 screw constructs have greater biomechanically stable than the single screw constructs 
          • benefit of 2 screws needs to be considered in the face of greater risk of screw related complications
            • articular surface penetration
        • intentional physeal arrest serves to stabilize the epiphysis and prevent further slippage; however, avoiding physeal arrest may improve remodeling after stabilization
      • anterior capsulotomy is controversial
        • decreases intra-capsular pressure
        • intracapsular pressure in unstable SCFE is double that of control hips, while pressure in stable SCFE is roughly equal to control hips
        • may mitigate intracapsular tamponade, though no clear evidence that this reduces AVN rates
    • contralateral hip prophylactic fixation (bilateral in situ fixation)  
      • indications   
        • remains controversial
        • current indications are high risk patients (contralateral slip ~ 40-80%)
          • initial slip at young age (< 10 years-old)
          • open triradiate cartilage
          • obese males
          • endocrine disorders (e.g. hypothyroidism)
          • modified oxford bone age score </= 18
          • stage 0-3 calcaneus apophysis ossification
    • open epiphyseal reduction and fixation
      • indications
        • remains controversial
        • unstable and severe slips
      • technique
        • capital realignment via the modified Dunn procedure
    • osteochondroplasty
      • indications
        • symptomatic femoroacetabular impingement (FAI) of true cam lesion from metaphyseal bump
        • mild to moderate SCFE deformity (slip angle < 30°)
      • technique
        • arthroscopic
        • limited anterior arthrotomy
        • surgical hip dislocation
    • proximal femoral osteotomy
      • indications
        • painful or function-limiting proximal femoral deformity
        • severe SCFE deformity (slip angle >30- 45°)
        • absence of severe hip osteoarthritis and osteonecrosis
      • technique
        • femoral neck osteotomy
          • cuneiform osteotomy
          • can provide greatest correction of deformity
          • use is controversial due to high rates of AVN (37%) and osteoarthritis (37%)
        • intertrochanteric (Imhauser) osteotomy 
          • most commonly used 
        • subtrochanteric (Southwick) osteotomy
Techniques
  • Percutaneous in situ fixation 
    • goal
      • to stabilize the epiphysis from further slippage and promote closure of the proximal femoral physis 
    • technique
      • reduction
        • forceful reduction is not indicated and increases risk of osteonecrosis
        • "serendipitous reduction" is often obtained with positioning on OR table
      • number of screws 
        • single cannulated screw sufficient and decreases risk of osteonecrosis (compared to multiple pins) in unstable SCFE   
      • screw insertion
        • perpendicular to physis
          • screw must start on the anterior surface of the proximal femur in order to cross perpendicular to the physis and enter into the central portion of the femoral head on both the AP and lateral views (center-center), which has slipped posteriorly 
          • starting point should not be medial to intertrochanteric line - will result in impingement between the head of the screw and acetabulum with hip flexion
        • oblique to physis
          • in severe slips, a relatively oblique insertion starting at the intertrochanteric region may be required, rather than perpendicular, to avoid impingement from head of the screw
      • screw position
        • advance until 5 threads cross physis
          • < 5 threads engaged in epiphysis increases risk of progression of slip >10° (<5 threads 41% progressed, >/= 5 threads 0% progressed)
        • screws should be at least 5mm from subchondral bone in all views
      • imaging
        • use fracture table to obtain good radiographic visualization
        • to confirm that pin is not penetrating the hip joint
        • approach-withdraw technique
          • rotate hip from maximal internal rotation or maximal external rotation under live fluoroscopy
          • the screw tip appears to approach the subchondral bone, then withdraw from it
          • the moment of change from approach to withdraw is the true position of the screw
          • in that view, insert the screw to appropriate position  
    • postoperative
      • stable slips are able to bear weight after fixation
      • unstable slips are kept touch-down weight bearing for 6 weeks
    • outcomes
      • does not treat deformity at head-neck junction
      • unsatisfactory outcomes in 10-20% have resulted in advocacy of other techniques to correct the deformity and mitigate long-term risk of chondral damage
  • Surgical hip dislocation, open capital realignment and fixation (Modified Dunn procedure) 
    • goal
      • to correct the acute proximal femoral deformity, protect femoral head blood supply and stabilize the epiphysis
    • technique
      • surgical hip dislocation via Gibson approach (Ganz technique)
        • lateral decubitus position
        • straight lateral skin incision centered over greater trochanter
        • interval: gluteus maximus (inferior gluteal n.) / gluteus medius (superior gluteal n.)
        • trochanteric flip osteotomy
        • Z-shaped anterior capsulotomy
          • visualize slip with prominent metaphysis 
        • temporarily pin epiphysis with K-wires prior to dislocation
        • bone hook around femoral neck for traction
        • ligamentum teres cut
        • hip is dislocated
      • develop retinacular soft tissue flaps
        • incise periosteum along femoral neck
        • extend incision distally to level of lesser trochanter, to reduce tension on retinacular vessels
        • bluntly develop periosteal flaps anteriorly and posteriorly using periosteal elevator
      • mobilize epiphysis 
        • starting anterior, use chisel to free epiphysis entirely from metaphysis
        • epiphysis will remain attached to posterior retinacular flap (blood supply) 
      • debride metaphysis
        • there will be prominent reactive callus along the posterior metaphysis, which needs to be removed to permit proper epiphyseal reduction and avoid kinking of retinacular vessels  
      • reduce epiphysis to metaphysis
      • fixation 
        • 2-3 3.0mm K-wires
        • one antegrade starting from fovea across epiphysis
        • one to two retrograde across epiphysis
    • possible benefit of reducing intracapsular hip pressure in unstable SCFE
      • intracapsular pressure in unstable SCFE is double that of control hips, while pressure in stable SCFE is roughly equal to control hips
      • may mitigate intracapsular tamponade, though no clear evidence that this reduces AVN rates
    • postoperative
      • touch-down weight bearing for 6 weeks
    • outcomes
      • complication rate 37%
      • AVN rates approaching 26% (comparable to 24% AVN rate for unstable SCFE treated in situ pinning)
      • steep learning curve 
  • Osteochondroplasty
    • goal
      • to address pain and loss of motion related to hip impingement from prominent metaphyseal bump in mild to moderate chronic SCFE deformity 
    • technique
      • arthroscopy
        • reserved for mild SCFE deformity 
        • remove metaphyseal bump with arthroscopic burr
          • difficult to fully resect superior and lateral portions of the bump
      • limited anterior arthrotomy
        • useful when metaphyseal bump cannot be fully removed arthroscopically
        • modified Smith-Peterson approach
      • surgical hip dislocation
        • moderate SCFE deformity 
        • trochanteric flip osteotomy
        • hip dislocated anteriorly
        • curved osteotome to remove bump
        • burr to recreate normal contour of head-neck junction
    • outcomes
      • no long term data
      • improvement in pain and function
      • no osteonecrosis
      • poor outcomes associated with preexisting cartilage damage
  • Flexion intertrochanteric (Imhauser) femoral osteotomy 
    • goal
      • to correct symptomatic proximal femoral deformity in moderate to severe chronic SCFE deformity
    • technique 
      • lateral approach
        • supine position
        • straight lateral skin incision from greater trochanter distal down the femoral shaft
        • reflect vastus lateralis to expose lateral femur
      • transverse osteotomy just proximal to lesser trochanter
      • correction
        • flexion through the osteotomy
        • internal rotation of distal shaft
        • mild valgus correction
    • postoperative
      • touch-down weight bearing for 3 months
    • outcomes
      • good to excellent functional results
      • 2-7% AVN
      • useful to prevent arthrosis
Complications 
  • Osteonecrosis of femoral head (4-6%)    
    • may occur as the result of
      • initial trauma
        • increased risk with unstable slips (~24-47%), most common predictor
      • operative complication (4-6%)
        • hardware placement in posteriosuperior femoral neck has the greatest risk of disrupting the vascular supply 
  • Contralateral hip SCFE
    • most common complication after unilateral surgical fixation (20-80%) 
      • risk factors for contralateral slip include 
        • male, obesity, young age of initial slip (< 10 years old, open triradiate cartilage), endocrine disorders
    • weight loss programs
      • decreased BMI reduces rates of subsequent contralateral SCFE
  • Chondrolysis (0-2%)
    • present with
      • narrowed joint space, pain, decreased motion
    • associated with
      • unrecognized implant penetration of the articular surface (0-2%)
        • pin placement into the anterior superior quadrant of the femoralhead has the highest rate of joint penetration
        • intra-articular hardware penetration best assessed by CT scan
      • spica cast immobilization
    • decreased prevalence with modern fluoroscopy
  • Residual proximal femoral deformity & limb length discrepancy
    • increased α-angle associated with symptomatic impingement
    • caused by failure of proximal femur to remodel
      • pistol-grip deformity 
    • treatment
      • intertrochanteric osteotomy (Imhauser) 
        • produces flexion, internal rotation and valgus
      • subtrochanteric osteotomy (Southwick)
      • femoral neck cuneiform osteotomy (controversial due to high rate of osteonecrosis and arthritis)
  • Slip progression
    • occurs in 1-2% of cases following single screw fixation
  • Delayed diagnosis
    • predictors
      • knee pain
      • Medicaid insurance coverage
      • stable slip
    • 88% of patients with presented with an unstable SCFE had unappreciated antecedent symptoms for ~42 days prior to diagnosis
  • Infection (0-2%)
  • Chronic pain (5-10%)
  • Degenerative arthritis 
  • Pin associated proximal femur fracture
  • Labral tearing and degeneration
    • seen with high anterior and medial 2nd screw in-situ fixation 
      • if screw lies medial to intertrochanteric line on AP radiograph, has increased risk of impingement on acetabulum and labrum with hip flexion
 

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