Blount's Disease

Original Editors - Leana Louw

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

Description

Blount's disease, also known as infantile 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.

Normal genu varum in children has the following characteristics:

• Normal in children under 2 years of age
• Corrects to neutral around 14 months
• Peak genu valgum around 3 years of age
• Corrects to normal physiological valgus around 7 years of age

Etiology / Epidemiology

Blount's disease are said to have a multifactoral etiology, taking genetic and mechanical factors into consideration that leas to increased medial pressure of the proximal medial tibial physis. 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 (8-12 months or even earlier).
• Low vitamin D levels.
• There does not appear to be an obvious genetic factor.
• Early-onset disease: Male > female.

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.

Clinical Presentation

• Unilateral or bilateral (mostly with early onset) presentation:
  • 80% of early-onset and 50% of late-onset cases are bilateral
• 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:
  • Langenskiöld classification (see below)
  • Proximal tibial varus
  • Deformity (severe)
  • Bowing (asymmetrical)
  • Posteriomedial sloping of proximal tibial epiphysis
  • Deformity:
    • Progressive
    • Sharp angular: Abnormal if more than 16° (then has 95% chance of progression)
    • Metaphyseal beaking

• In late-onset Blount's disease, advanced imaging are not routinely done.
• Palpation: The deformity of the proximal medial tibial metaphysis is palpatable as a non-tender bony protuberance.
• Gait: Lateral thrust

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

• Radiographic measurements of metaphyseal-diaphyseal angle and anatomical femoral-tibial angle
• AAOS Pediatrics-Parent/Child Outcome Instrument
• Gait and biomechanical assessment using 3D video analysis
• 6 minute walk test
• Gait and Lower Limb Observation of Paediatrics - (GALLOP)

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.

Approximately 2 years of bracing are done with hip-knee-ankle-foot-othrosis or knee-ankle-foot-othrosis in children with stage I and II on the Langenskiöld classification. Good results are seen with unilateral Blount's disease, but it is less effective in the treatment of bilateral disease and in obese children. The success of bracing is normally seen with improvements within a year, and if successful changes is noted, it is normally worn for 18-24 months.

Surgical management

• Realignment tibial osteotomy: To be done before the age of 4 to decrease the risk of recurrence and to restore leg length where needed.
  • Indicated when bracing fails and with metaphyseal-diaphyseal angles of more than 20 degrees

• Distraction osteogenesis: For late-onset disease:

• • Aim to achieve multiplanar correction
• Growth modualtion: 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 consisting of tension band plate and screws is most effective in children with less severe bowing and significant growth remaining.
• Physeal bar resection: To be done together with osteotomy
• Hemiplateau elevation: May be done together with osteotomy

Differential Diagnosis

The differential diagnosis considers conditions that may lead to pathological genu varum:

• Physiologic bowing (persistent)
• Congenital bowing
• Rickets
• Ollier disease
• Trauma-related deformities to proximal tibia
• Radiation or infection leading to deformities of proximal tibia
• Osteomyelitis
• Metaphyseal chondrodysplasia
• Osteogenesis imperfecta
• Focal fibrocartilaginous defect
• Thrombocytopenia absent radius

Physiotherapy Management

Conservative management

Assessment

• Skin inspection if patient is wearing orthotics
• Assessment for mobility assistive devices
• Gait analysis including alignment and pattern.

Management

Physiotherapy plays a big role in the management of Blount's disease. Strengthening and range of motion eases functional activities and can aid in the progression of secondary compensatory deformities.

• Teaching child and carer how on the use of the orthotics - including skin care and inspection
• Gait re-education with assistive devices
• Maintenance and improvement of range of motion
• Strengthening and stretching to address gait and muscle imbalances
• Hip and core strengthening to aid in position of leg
  • Focus on endurance, as weak hip and core muscle can lead to knee deformities
• Balance and coordination exercises incorporated into play and functional activities
• Exercise for weight loss (in combination with the dietitian) where obesity is known as the cause of the disease
  • Limit strain on the joints by choosing activities with less weight bearing (e.g. cycling, swimming)

Rehabilitation after surgery

The aim of post-operative rehabilitation is to return the patient to their normal activities as soon as possible, and prevent secondary compensatory problems to the legs and back. Rehabilitation normally works well and quick to regain range of motion and strength. Precautions will be determined by the surgeons, and differ widely based on the type of surgery, severity of deformity and radiographic evidence of bone healing.

Physiotherapy management include:

• Management of post-operative pain:
  • Use of ice, heat and ultrasound
• Gait re-education with mobility assistive devices with focus on weight bearing restrictions as per surgeon
• Regain strength to address gait and muscle imbalances and maintain newly-gained alignment
  • Focus on knee, hip and core
• Regain range of motion (with focus on the knee)
  • Stretches
  • Exercises
  • Manual techniques to muscles and joints
• Encourage posture and alignment that was surgically corrected
• Coordination, proprioception and balance - to be commenced when weaned off mobility assistive device, upon clearance of surgeon
  • Encourage one-leg standing, line walking, toe walking
  • Progress to jumps and agility

References

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