Blount's Disease

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Original Editors - Rachael Lowe

Top Contributors - Leana Louw, Admin, Kim Jackson, Daphne Jackson, Evan Thomas and WikiSysop

Description

Blount's disease, also known as tibia vara, is a developmental growth disorder of the tibia that causes the lower leg to angle outwards, causing bowing of the leg. It is characterised by progressive multiplanar deformities of the leg caused by disordered endochondral ossification of the proximal medial tibial physis.

The cause of Blount's disease is assumed to be multifactoral, mostly mechanically due to childhood obesity. This can be described by the effects of increased weight on the growth plates. The medial proximal tibia fails to develop normally, resulting in genu varum.  Unlike bowlegs, which tend to straighten as the child develops, Blount's disease is progressively worsening. It can cause severe bowing and can affect one or both legs.

Pathogenesis

Looking at the Heuter-Volkmann principle, the pathogenesis of Blount's disease can be described as growth inhibition caused by excessive compressive forces. This pressure on the medial proximal tibia causes structure and function alterations on the cartilage of the epiphysis, further causing chondrocytes and delaying in epiphysis ossification. The increase in medial load with obesity usually lead to genu varum.

Etiology / Epidemiology

The following are known predisposing factors of Blount's disease:

• This condition is more common among children of African and Scandanavian ancestry.
• It is associated with obesity, short stature, and early walking.
• There does not appear to be an obvious genetic factor.

genetic, humoral, biomechanical, and environmental factors control physeal growth and influence the development of normal lower-limb alignment. control physeal growth and influence the development of normal lower-limb alignment. T

Classification

Blount's disease is mostly catagorised into early-onset if it develops in children under 4 years old, and late-onset, when it develops after the age of 4. The late-onset type can further be classified into juvenile (age 4 - 10) and adolescent (after the age of 10) Blount's disease.

t. Also, there are comparable histologic findings at the proximal tibial growth plate9-11

Clinical Presentation

• Unilateral or bilateral (mostly with early onset) presentation
• Multiplanar progressive deformities of the lower leg includes:
  • Tibial varus
  • Procurvatum
  • Internal torsion
  • Limb shortening (due to altered growth)
  • Distal femoral varus (in late-onset)

• Gait abnormalities:
  • Increased knee abduction
  • Increased medial load to the knee
• Early onset knee osteoarthritis as result of deformities

Diagnostic Procedures

Diagnosis are normally made by a clinical assessment and the use of X-rays (full length, AP and lateral). X-rays are use to determine and measure the extent of the deformities. In late-onset Blount's disease, advanced imaging are not routinely done. Other additional investigations include:

• Scanogram: To determine leg length discrepancy
• Arthrogram (intra-operative): Assessment of articular surface postion
• CT scan: 3D surgical planning (early-onset disease with recurrent deformities)
• MRI: Determine
  • Determine intra-articular changes to tibial plateau (e.g. posteromedial depression)
  • Look for medial meniscus hypertrophy in early-onset disease
  • Assess physeal bar formation and changes to growth plates

Langenskiöld classification

This classification system are used to describe the radiographic changes and are divided into 6 progressive type in early onset Blount's disease, describing changes with aging.

• Stage 1: Age 2-3
  • Metaphyseal irregularities in ossification zone
  • Slow development of epiphysis in medial aspect of tibia
  • Medial and/or distal beaking of medial epiphysis
• Stage 2: Age 2.5-4
  • Medial physeal line depresses sharply
  • Beaking medially
  • Wegde-shaping and underdevelopment of medial epiphysis
• Stage 3: Age 4-6
  • Metaphyseal beak depression deepens
  • Metaphysis "step"
  • Medial part of epiphysis more wedge-shaped and underdeveloped
• Stage 4: Age 5-10
  • Narrowing of physis
  • Enlargement of epiphysis
  • Metaphysis "step" deepens
  • Depression in medial metaphysis ocupied by epiphysis
• Stage 5: Age 9-11
  • Clearly separated epiphysis in two parts
  • Epiphysial plate partially double
  • Articular surface medially sloping
• Stage 6: Age 10-13
  • Ossification of medial physis with cessation of growth
  • Normal lateral tibial growth

Outcome Measures

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Medical management

Conservative management

Children who develop severe bowing before the age of 3 may be treated with bracing. However, bracing may fail, or bowing may not be detected until the child is older.

Surgical management

• Realignment tibial osteotomy: To be done before the age of 4 to decrease the risk of recurrent lower extremity deformity and to restore leg length where needed.
• Distraction osteogenesis: For late-onset disease:
  • Aim to achieve multiplanar correction
• The growth of just the outer half of the tibia can be surgically restricted to allow the child’s natural growth to reverse the bowing process. This much smaller surgery is most effective in children with less severe bowing and significant growth remaining.

Differential Diagnosis

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Resources

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Case Studies

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References

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