Blount's Disease

Synonyms: tibia vara

What is Blount's Disease?^[1]

Blount disease is an asymmetrical disorder of proximal tibial growth that produces a three-dimensional deformity. Tibia vara (also known as genu varus and bow-leggedness) is the main component of the deformity.

Blount disease exists as two clinical variants, early-onset, and late-onset. Late-onset Blount's disease can be divided into juvenile tibia vara (ages 4-10), and adolescent tibia vara (ages 11 and older).^[2]

Blount's disease is caused by disorder of the tibial growth plate (usually the medial aspect) leading to changes in the angle at the knee. This results in bowing of the leg (usually the lower leg). However, unlike bow legs it is pathological and progressively worsens.

Clinically it is difficult to distinguish between simple bowlegs and Blount's disease. However, bow legs are normal in children aged under 2 years.^[3]

Early-onset Blount's disease^[3]

Epidemiology

Presents at age 2-4 years.

Risk factors

Repetitive trauma to a knee with an already varus abnormality.

Presentation

• Usually bilateral.
• Bony prominence over the medial tibial condyle (nontender).^[5]
• Feet held in pronation.
• Shortening of the involved leg.
• Medial angulation and internal rotation of the proximal tibia.
• Gait - painless varus thrust seen.

Investigations

Plain radiographs show increased angulation between the metaphysis and the longitudinal axis of the tibia.

Differential diagnosis^[5]

• Physiological bow legs.
• Rickets.
• Osteomyelitis.
• Trauma.
• Ollier's disease.
• Metaphyseal chondrodysplasia.
• Focal fibrocartilaginous dysplasia.

Late-onset Blount's disease^[6]

Risk factors

• Bow legs.
• Females.
• Afro-Caribbean ethnicity.
• Obesity.
• Walking at an early age.
• Possible family preponderance.

Presentation

• Commonly unilateral.
• Varus deformity.
• Shortening of the involved leg by up to 3-4 cm.
• Pain at the medial prominence of the proximal tibia.
• Medial tibial torsion may also be present.

Investigations

Plain radiographs, as for infantile Blount's disease.

Management^[2]

Surgical options depend on the patient's age, weight, extent of physeal involvement, severity, and number of deformities.

Before 4 years of age, progressive Blount disease should be corrected, preferably by a simple osteotomy. Once medial tibial epiphysiodesis has developed, both a complementary epiphysiodesis and gradual external fixator correction of the other alignment abnormalities, rotational deformity, and limb length are required.^[1]

Otherwise options include growth modulation procedures such as guided growth for gradual correction with hemi-epiphysiodesis and physeal closure to prevent recurrence and equalise limb lengths, physeal bar resection, physeal distraction, osteotomies with acute correction and stabilisation, gradual correction with multi-planar dynamic external fixation, and various combinations of all modalities.

The goals of surgery are to restore normal joint and limb alignment, equalise limb lengths at skeletal maturity, and prevent recurrence.

Prognosis^[1]

Untreated Blount disease is associated with a poor prognosis, especially in young children due to the growth spurt and the early fusion of the growth plate occurring from the ages of 6 to 8.^[7]

Early-onset Blount's disease progresses to more severe deformities, including depression of the medial tibial plateau. Additional deformities in both groups include proximal tibial procurvatum, internal tibial torsion, and limb length discrepancy. Compensatory deformities in the distal femur and distal tibia may occur.^[2]

Untreated Blount disease in adults is rarely encountered. A more common occurrence is the presence of residual abnormalities at skeletal maturity in patients treated for Blount disease in childhood.

Premature osteoarthritis may develop.