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Blount's Disease

Blount's disease is an acquired growth disturbance of the medial aspect of the proximal tibial physis, causing varus angulation of the tibia in the metaphyseal region

Walter Putnam Blount (1937)

Aetiology

  • Enchondral ossification is abnormal
  • Possibly, a parallel disorder to coxa vara as triangular shaped bony fragment often present
  • Exact aetiology is unknown, following factors have been proposed :
    • Obesity
    • Walking too early
    • Genetic predisposition
  • Weight bearing is required for development of Blount's disease, as the condition is not seen in non ambulatory patients
  • Adolescent variety is caused by physeal growth arrest, as there is often a history of trauma or infection

Classification

Based on the time of presentation

  • Infantile
    • Onset at 5 y/o or less
    • Occurs predominantly in black race 
    • Male : Female 2:1
    • 50 - 75% bilateral
    • Patients are usually over weight
  • Juvenile
    • Onset between 6 and 9 years
  • Adolescent
    • Usually presents between 8 - 13 years
  • Varus usually does not exceed 20°
  • There are two types of adolescent Blount's disease:
    •  Partial closure of the physis
      • Usually due to trauma or infection
      • Unilateral in 90% of cases
    • "late-onset" tibia vara
      • Idiopathic
      • Most often occurs in obese African-American males
        • less than 50% have bilateral involvement

Clinically

  • The usual age at presentation is 2 y/o or more, as opposed to physiologic bowing which should be improving by 2 y/o
  • Pain is frequently the presenting symptom
  • Pain and tenderness often present over the medial prominence of the proximal tibia
  • Deformity is slight but slowly progressive*,* as opposed to physiologic bowing which resolves with time
  • Leg length discrepancy averages 2 cm
  • Deformity varies from 10o to 45o (average 20o)
  • Lateral thrust and internal tibial torsion are suggestive of Blounts

Classification

Langenskiold classified the condition based on the degree of depression of the medial plateau

  • Stage I
    • Age 2 - 3 years
    • Irregularity of entire metaphysis
    • Medial metaphyseal beaking
  • Stage II
    • Age 2.5 - 4 years
    • Sharp antero-medial depression evident
    • There is a propensity for healing at this stage
  • Stage III
    • Age 4 - 6 years
    • Deepening of the depression makes a step
  • Stage IV
    • Age 5 - 10 years
    • Developed step is filled in by the epiphysis
    • Growth plate is irreversibly damaged at this stage
  • Stage V
    • Age 9 - 11 years
    • A triangular fragment separates
  • Stage VI
    • Age 10 - 13 years
    • Medial growth plate ossification
    • Growth continues in the normal lateral part

X-Ray

  • Infantile Blounts
    • Varus angualtion
    • Medial metaphysical beaking
    • Medial metaphysical depression
    • Medial metaphyseal triangular bone fragment
    • Bony bridge may be seen
  • Adolescent Blounts
    • Thinning of the growth plate
    • The epiphysis is normal in shape 
    • There is no step
  • The metaphyseal- diaphyseal (MD) angle (aka Drennan Angle)
    • Angle between a line drawn through the most distal point of the medial and lateral beaks of the tibial metaphysis and the line perpendicular to axis of the tibia 
    • An angle less than 11 degrees is normal and an angle greater than 16 degrees suggests Blounts
    • A similar angle can be drawn for the femur. The ratio of the femoral MD angle to the tibial MD angle is typically less than 1.
      • In physiological bow leg, average metaphyseal-diaphyseal angle was 9° ± 4°
      • In Blounts, average metaphyseal-diaphyseal angle was 19° ± 5.7°
      • The difference was significant to p less than 0.0000001


Fig 1. Marked varus with medial tibial deformity

Fig 2. Depression of the medial tibial plateau. Partial closure of the medial aspect of the proximal tibial physes.



  • Case Example 1:

    Fig 3. Eight year old female with Blount's disease

    Fig 4. Standing AP radiograph of 8 year old female with Blount's disease

    Fig 5. AP and lateral tiba radiographs of 8 year old female with Blount's disease

     

Pathology

  • Postero-medial portion of proximal tibial physis fails to grow normally
  • Marked changes on the medial side of the physis
    • The zone of proliferation is thin 
    • Cartilage columns are stunted and irregular
    • Matrix calcification is normal
    • The primary trabeculae are oriented horizontally
  • It is not clear whether these changes are primary or secondary to the eccentric compressive forces
  • A bony bridge may be evident (especially if secondary to trauma)

Treatment

Based on the age of the patient and the Langenskiold staging

  • Stage 1 + 2
    • Long leg bracing (KAFO)
      • Try night bracing first, as it does not disable the child 
      • If still no improvement, proceed to day bracing
      • Resolution to normal axis may take up to 1 year
    • Deformity is often reversible at this stage
  • Stage 3 + 4
    • If the deformity persists or increases to these stages, osteotomy is indicated
    • Osteotomise prior to age 4, if possible
    • The deformity is recurrent in stages IV or higher and patient needs to undergo multiple osteotomies until tall enough to do epiphysiodesis
  • Stage 5 + 6
    • If tomograms show a bony physeal bridge, can either excise the bridge or perform an osteotomy, esp. if significant growth remaining
    • Premature medial growth plate closure : epiphyseodesis of the lateral plate plus tibial osteotomy
    • Osteotomy indicated if there is :
      • Severe deformity
      • Severe joint depression
    • In osteotomy aim to correct to 10° valgus
    • Use of an opening wedge may obviate the need for operative correction of LLD
    • Need to warn parents of risk of recurrence post surgery

Prognosis

  • Infantile Form
    • The first 4 years is the main period for progression, after which the deformity remains the same or progresses slowly
    • Deformity may range from 10° - 60°
    • From 9 years to skeletal maturity, there is usually a gradual increase in deformity
  • Adolescent Form
    • Varus deformity increases incidence of early-onset degenerative joint disease

References

  • Feldman D.S. Lower Limb Disorders. In Spivak JM, Di Cesare PE, Feldman DS : Orthopedics; A Study Guide; 1999
  • Milbrandt T.A., Sucato D.J : Pediatric Orthoprdics. In Mark D. Miller : Review of Orthopedics; 2008
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