Introduction
  • Progressive, pathologic genu varum centered at tibia
  • Blount's disease is best divided into two distinct disease entities
    • Infantile Blount's  
      • pathologic genu varum in children 0-3 years of age
      • more common
      • deformity rarely from femur
      • typically affects both lower extremities
    • Adolescent Blount's (this topic)
      • pathologic genu varum in children > 10 years of age
      • more likely to have femoral deformity 
      • less common
      • less severe
      • more likely to be unilateral
  • Etiology
    • Blount's is thought to be caused by a dyschondrosis of medial physis of proximal tibia
    • likely multifactorial but related to mechanical overload in genetically susceptible individuals
  • Risk factors
    • obesity
    • African-American descent
  Infantile Blounts Adolescent Blounts
Age 2-5yrs >10yrs
Bilaterality 50% bilateral Usually unilateral
Risks

Early walking, large stature, obesity

 Obesity
Classification Langenskiold No radiographic classification
Severity More severe physeal/epiphyseal disturbance  Less severe physeal/epiphyseal disturbance 
Location Physeal/epiphyseal Metaphyseal
Bone Involvement Proximal medial tibia physis, producing genu varus, flexion, internal rotation, AND may have compensatory distal femoral VALGUS Proximal tibia physis, AND may have distal femoral VARUS and distal tibia valgus
Natural History Self-limited - stage II and IV can exhibit spontaneous resolution Progressive, never resolves spontaneously (thus bracing unlikely to work)
Treatment Options

Bracing and surgery

 Surgery only
 
Presentation
  • Physical exam
    • hallmark is genu varum deformity
    • obesity
    • usually unilateral (compared to bilateral in infantile Blount's)
    • limb-length discrepancy secondary to deformity
    • mild to moderate laxity of medial collateral ligament
Imaging
  • Radiographs  
    • views
      • standing long-cassette AP radiograph of both lower extremities
      • ensure patellas are facing forward (commonly associated with internal tibial torsion)
    • findings suggestive of adolescent Blount's disease
      • narrowing of the tibial epiphysis   
      • widening of the medial tibial growth plate
      • occasional widening of the lateral distal femoral physis
    • metaphyseal beaking less commonly seen with adolescent Blount's
    • measurements
      • metaphyseal-diaphyseal angle (Drennan)  
        • angle between line connecting metaphyseal beaks and a line perpendicular to the longitudinal axis of the tibia
        • >16 degrees is considered abnormal
      • tibiofemoral angle 
        • angle between the longitudinal axis of the femur and tibia
Treatment
  • Nonoperative
    • observation or bracing is unlikely to be successful - treatment is always surgical
      • indications
        • mild cases only
      • outcomes
        • poor outcomes - will progresse and cause medial joint pain and altered kinematics
        • early onset arthritis is common in untreated cases
  • Operative
    • lateral tibia and fibular epiphysiodesis 
      • indications
        • mild to moderate deformity with growth remaining
      • outcomes
        • up to 25% may require formal osteotomy due to residual deformity
    • proximal tibia/fibula osteotomy 
      • indications
        • more severe cases in the skeletally mature 
      • outcomes
        • multiplanar external fixation following osteotomy allows gradual angle and length correction and decreases risk on neurovascular structures
    • distal femoral osteotomy or epiphysiodesis
      • indications
        •  for distal femoral varus deformity of 8 degrees or greater
Surgical Techniques
  • Lateral tibia and fibular epiphysiodesis
    • transient hemiepiphysiodesis
      • technique
        • tether physis with 8-plates or staple
        • may remove implant once correction is achieved
      • pros
        • simple
        • allows for gradual correction is children with adequate growth remaining
        • implants may be removed
      • cons
        • requires significant growth remaining
        • close observation is necessary following operation as growth plate may stop functioning or have a rebound period of accelerated growth
    • permanent hemiepiphysiodesis
      • technique
        • obliteration of physis through small, lateral incision
      • pros
        • limited surgery
        • overcorrection is uncommon
        • does not limit ability to perform corrective osteotomy in future
      • cons
        • cannot correct rotational deformity
        • up to 25% may require formal corrective osteotomy
  • Proximal tibia/fibula osteotomy
    • goals of correction
      • overcorrection to valgus not indicated (as is the case in infantile Blount's)
      • strive for neutral mechanical axis
    • high tibial osteotomy with rigid internal fixation  
      • technique
        • variety of techniques, including closing wedge, opening wedge, dome, serrated and inclined osteotomies
        • variety of fixation devices including cast, pins and wires, screws, plates and screws
      • post-op
        • limited weight bearing with use of crutches for 6-8 weeks
      • pros
        • immediate correction
      • cons
        • potential for neurologic injury due to acute lengthening
        • potential for compartment syndrome
          • consider prophylactic fasciotomies
    •  osteotomy with external fixation and gradual correction
      • technique
        • perform osteotomy, and connect frame that allows for gradual correction
        • Taylor Spatial Frame or Ilizarov ring external fixator  
      • post-op
        • usually 12-18 weeks of treatment are needed
      • pros
        • gradual correction limits neurovascular compromise and risk for compartment syndrome
        • allows for correction of deformity in all planes
      • cons
        • pin site infection
        • duration of treatment
        • bulk of construct