Blount’s Disease

Courtesy: Sean Tabaei, MD, Paediatric Orthopaedic Surgeon, Assistant Professor, George Washington University School of Medicine & Health Sciences, Washington DC, USA

BACKGROUND

• In 1937, Blount described a progressive varus deformity of the proximal tibia in otherwise healthy children and adolescents.

• He originally termed the condition osteochondrosis deformans tibiae.

• The condition is now universally known as Blount disease.

• Two distinct radiographic forms are recognized:

  • Infantile Blount disease

  • Adolescent Blount disease

• A third intermediate form, referred to as juvenile Blount disease, has been described by some authors.

• If untreated, Blount disease may progress to:

  • Severe tibial varus

  • Distal femoral and tibial deformities

  • Limb length inequality

  • Articular surface distortion

  • Premature osteoarthritis of the knee

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INFANTILE BLOUNT DISEASE

Characteristics

• Varus deformity of the proximal tibia in an otherwise healthy child

• Typically presents between 2 and 5 years of age

• More common in boys

• Approximately 50 percent bilateral, often asymmetric

• Spontaneous correction may occur in early stages

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Etiology

• Growth deceleration at the posteromedial proximal tibial physis

• Results in:

  • Varus deformity

  • Flexion deformity

  • Internal rotation deformity

  • Medial and posterior sloping of the proximal tibial epiphysis

• Proposed predisposing factors:

  • Early walking

  • Large body size

  • Obesity

• Among these, obesity has the strongest association, though etiology remains multifactorial and incompletely understood

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Clinical Features

• Variable varus deformity of the proximal tibia

• Increased internal tibial torsion

• Palpable medial metaphyseal and epiphyseal beaking

• Limb length inequality in unilateral cases

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LANGENSKIÖLD CLASSIFICATION

• Six radiographic stages (Types 1 to 6)

• Progressive medial physeal and epiphyseal changes

• Spontaneous restoration may occur in Types 2 and 4

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DIFFERENTIAL DIAGNOSIS

• Physiologic bowing

• Focal fibrocartilaginous dysplasia

• Renal osteodystrophy

• Rickets

• Metaphyseal chondrodysplasias

• Post-traumatic or post-infective growth arrest

• Short stature syndromes such as achondroplasia

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LATE-ONSET (ADOLESCENT) BLOUNT DISEASE

Characteristics

• Presents at an older age compared to infantile form

• Patients are more frequently obese

• Radiographic appearance differs from infantile type

• Requires different treatment strategies

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Etiology

• Likely due to mechanical overload of the medial proximal tibial physis

• Excessive body weight, with or without pre-existing varus

• Strong clinical and biomechanical evidence links obesity to adolescent Blount disease

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Heuter–Volkmann Principle

• Compressive forces across the growth plate inhibit growth

• Removal of compression or application of tension accelerates physeal growth

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Clinical and Radiographic Features

• May be unilateral, bilateral, or asymmetric

• Radiographic findings include:

  • Proximal tibial varus

  • Widened medial physeal lucency

  • Zone of physeal injury

• Key radiographic difference:

  • Intra-articular involvement is typical of infantile Blount disease

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Gait Pattern

• Characteristic waddling or lateral thrust gait

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NORMAL LIMB ALIGNMENT AND JOINT ORIENTATION

Limb Alignment

• Refers to colinearity of the hip, knee, and ankle

Joint Orientation

• Describes orientation of articular surfaces relative to:

  • Anatomic axis

  • Mechanical axis

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Axes

• Anatomic axis:

  • Mid-diaphyseal line of the bone

• Mechanical axis:

  • Straight line connecting joint centers

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FRONTAL PLANE MALALIGNMENT

Four possible contributors:

1. Femoral deformity

2. Tibial deformity

3. Joint laxity

4. Condylar deficiency

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MALALIGNMENT ANALYSIS (FRONTAL PLANE)

Stepwise Evaluation

1. Draw mechanical axis deviation

2. Measure mechanical lateral distal femoral angle (normal approximately 100 degrees)

3. Measure medial proximal tibial angle (normal approximately 87 degrees)

4. Measure joint line convergence angle

5. Rule out joint subluxation (joint centers within 3 millimeters)

6. Rule out condylar deficiency

7. Assess hip and ankle orientation

Example Conclusion

• Femoral varus: 12 degrees

• Tibial varus: 12 degrees

• Soft tissue contribution: 8 degrees

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TREATMENT PRINCIPLES

Step 1

• Recognize normal physiologic variants

Step 2

• Observation and parental reassurance when appropriate

Step 3

• If abnormal, treat underlying cause:

  • Medical management (for metabolic disorders)

  • Bracing

  • Surgical intervention

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TREATMENT OPTIONS

• Bracing

• Guided growth or hemiepiphysiodesis

• Internal fixation

• External fixation

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GUIDED GROWTH (HEMIEPIPHYSIODESIS)

Indications

• Varus deformity less than 15 degrees

• At least 2 years of growth remaining

• Limb length discrepancy less than 1 centimeter

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ACUTE VERSUS GRADUAL CORRECTION

Factors Influencing Choice

• Complexity of deformity

• Uni-planar or multi-planar deformity

• Rotational and axial deviation

• Neurovascular structures at risk

• Skin condition and previous scars

• Location of osteotomy

• Soft tissue constraints

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ACUTE CORRECTION (INTERNAL FIXATION)

Advantages

• Faster correction

• Technically simpler

• Immediate correction

Complications

• Neurovascular injury (3.3 to 18 percent)

• Peroneal nerve palsy (up to 15 percent)

• Compartment syndrome (approximately 6 percent)

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GRADUAL CORRECTION (EXTERNAL FIXATION)

Advantages

• Reduced risk of:

  • Peroneal nerve palsy

  • Compartment syndrome

  • Residual deformity

  • Limb length inequality

• Allows progressive and controlled correction

• Deformity analysis can be modified during treatment

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Advantages of Circular External Fixation

• Multiplanar correction:

  • Angulation

  • Rotation

  • Translation

  • Axial deformity

• Highly stable

• Versatile application

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Disadvantages

• Technically demanding

• Bulky frame

• Longer treatment duration

• Increased cost

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HEXAPOD RING FIXATORS

• Allow correction of simultaneous multi-planar deformities

• Use a virtual hinge concept

• High accuracy and stability

• Software-assisted deformity analysis

• Patient-friendly adjustment protocols

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KEY POINTS

• Early diagnosis prevents joint degeneration

• Infantile and adolescent Blount disease are distinct entities

• Obesity plays a major role in late-onset disease

• Guided growth is effective in selected patients

• Gradual correction provides superior accuracy in complex deformities

• Long-term follow-up is essential to detect recurrence