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Introduction |
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Blount's disease is progressive pathologic genu varum centered at the tibia
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Best divided into two distinct disease entities
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Infantile Blount's (this topic)
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pathologic genu varum in children 0-3 years of age
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more common
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typically affects both lower extremities
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Adolescent Blount's
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pathologic genu varum in children > 10 years of age
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less common
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less severe
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more likely to be unilateral
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Etiology
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likely multifactorial but related to mechanical overload in genetically succeptible individuals including
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excessive medial pressure produces an osteochondrosis of the medial proximal tibial physis and epiphysis
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osteochondrosis can progress to a physeal bar
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Risk factors
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overweight children that are early walkers (less than one year)
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Prognosis
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best outcomes are associated with early diagnosis and unloading of the medial joint with either bracing or an osteotomy
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Differential diagnosis
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the following conditions can also lead to pathologic genu varum
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osteogenesis imperfecta
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osteochondromas
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trauma
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various dysplasia
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Anatomy |
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Genu varum is a normal physiologic process in children
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physiologic genu varum
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genu varum (bowed legs) is normal in children less than 2 years
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genu varum migrates to a neutral at ~ 14 months
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continues on to a peak genu valgum (knocked knees) at ~ 3 years of age
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genu valgum then migrates back to normal physiologic valgus at ~ 7 years of age
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Classification |
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Langenskiold Classification
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type I thru IV consist of increasing medial metaphyseal beaking and sloping
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type V and VI have an epiphyseal-metaphyseal bony bridge (congenital bar across physis)
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provides prognostic guidelines
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Presentation |
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Physical exam
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genu varum deformity
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usually bilateral in infants
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may exhibit positive 'cover-up test'
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often associated with internal tibial torsion
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Imaging |
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Radiographs
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views
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ensure that patella are facing forwards for evaluation (commonly associated with interal tibial torsion)
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findings suggestive of Blounts disease
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varus focused at proximal tibia
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severe deformity
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asymmetric bowing
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progressing deformity
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sharp angular deformity
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lateral thrust during gait
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metaphyseal beaking
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different than physiologic bowing which shows a symmetric flaring of the tibia and femur
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measurements
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metaphyseal-diaphyseal angle (Drennan)
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angle between line connecting metaphyseal beaks and a line perpendicular to the longitudinal axis of the tibia
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>16 ° is considered abnormal and has a 95% chance of progression
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<10 ° has a 95% chance of natural resolution of the bowing
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tibiofemoral angle
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angle between the longitudinal axis of the femur and tibia
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Treatment |
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Nonoperative
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brace treatment with KAFO
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indications
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Stage I and II in children < 3 years
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technique
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bracing must continue for approximately 2 years for resolution of bony changes
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outcomes
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improved outcomes if unilateral
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poor results associated with obesity and bilaterality
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if successful, improvement should occur within 1 year
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Operative
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proximal tibia/fibula valgus osteotomy
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indications
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Stage I and II in children > 3 years
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Stage III, IV, V, VI in children < 3
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failure of brace treatment
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technique
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staged procedures may be required for Stage IV, V, VI
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epiphsiolysis required in stage V and VI
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outcomes
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risk of recurrence is significantly lessened if performed before 4 years of age
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Surgical Techniques |
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Proximal tibia/fibula valgus osteotomy
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goals of correction
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overcorrect into 10-15° of valgus because medial physeal growth abnormalities persist
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distal segment is fixed in valgus, external rotation and lateral translation
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technique
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staples and plates function by increasing compression forces across the physis which slows longitudinal growth (Heuter-Volkman principle)
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temporary lateral physeal growth arrest with staples or plates can be used
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increasing use for correction in younger patients
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include a bar resection (epiphysiolysis) when a physeal bar is present (Langenskiold V and VI)
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consider hemiepiphysiodesis if bar > 50%
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medial tibial plateau elevation is required at time of osteotomy if significant depression is present
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consider prophylactic anterior compartment fasciotomy
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