Blount's Disease - Infantile
- Disorder that affects the proximal posteromedial tibial growth plate.
- Etiology unknown; potentially related to increased body weight
- Infantile form has its onset in children less than 3 years of age
- Differential diagnoses include internal tibial torsion and physiologic genu varum.
- Surgery is recommended at or prior to 4 years of age and Langenskiold Stage IV or earlier to minimize risk of recurrence.
Blount disease is a disorder of the proximal (posteromedial) tibial growth plate, which results in progressive bowing of the tibia. This can lead to significant deformity and limb length discrepancy.
Though initially described by Ehrlacher in 1922, this disorder was popularized by Walter Putnam Blount in 1937 (Blount, 1937).
Onset is in children less than 3 years of age. Patients with infantile (early onset) Blount disease were found to be more likely to be bilateral (4.3 times more so) than those with late onset Blount disease. They were also found to be less likely to be African American and male compared to those with late onset Blount disease (Rivero, 2015).
The presenting feature is tibial bowing and internal tibial torsion. The bowing in infantile Blount disease is seen more in the proximal tibia compared to the bowing of tibial torsion that is seen mostly in the mid to distal diaphysis of the tibia (Cover up test- Davids, 2000). These children have internal tibial torsion and may have lateral collateral ligament laxity in the knee. This may manifest as a lateral thrust in stance phase of gait. In cases with unilateral involvement, the affected side may be shorter than the contralateral side.
It is important to differentiate tibial torsion from infantile tibia vara as early intervention with non-operative treatment has the best chances of success in tibia vara. Levine and Drennan, in their landmark paper, reported that 29/30 patients with metaphyseodiaphyseal (M-D) angle of more than 11 degrees went on to develop changes of tibia vara, whereas only 3/58 patients with the M-D angle of less than 11 degrees went on to develop changes of tibia vara (Levine, 1982).
Radiographs of children with infantile Blount disease may show metaphyseal beaking, increased posteromedial slope of both the metaphysis and epiphysis. Advanced stages of the disease may be associated with physeal bar formation. Langenskiold has described these stages (Langenskiold, 1952)
Stage I: Medial metaphyseal beaking.
Stage II: Saucer shaped defect of medial metaphysis.
Stage III: Saucer deepens into a step.
Stage IV: Epiphysis bent down over medial beak.
Stage V: Double epiphysis, severe posteromedial depression
Stage VI: Development of medial physeal bony bar.
The Langenskiold classification is not strictly speaking a severity classification. It describes the stages that a patient with untreated Blount disease may go through. Natural history studies have shown that patients in radiographic stages I-III may undergo spontaneous resolution. (Shinohara, 2002)
Children with infantile tibia vara usually have a normal distal femur, compared to those with adolescent tibia vara in whom distal femoral varus is frequently seen (Gordon, 2006).
MR imaging in patients with infantile Blount disease has shown medial meniscal abnormalities, posteromedial depression of the medial tibial plateau, as well as increased thickness of the medial tibial cartilage (Ho-Fung, 2013; Sabharwal, 2012).
The etiology is not clearly defined. There is some suggestion that obesity and early weight bearing may have a role. Children with Blount disease have higher BMI (Scott, 2007) and advanced bone age compared to their peers (Sabharwal, 2013). A Nigerian study demonstrated decreased zinc and increased alkaline phsophatase levels in the patients with Blount disease (Giwa, 2004).
Bracing in Blount disease:
Bracing in patients with early onset Blount disease has been shown to have good results (Zionts,1998). Best results are seen if bracing is initiated in children less than 3 years of age and Langenskiold stages I and II. The risk factors for failure include bilateral pathology, (Richards, 1998) instability, obesity, and delayed bracing (Raney, 1998).
There has been increasing interest in using guided growth with proximal lateral tibial hemi-epiphysiodesis to correct the proximal tibial deformities. (Scott, 2012). This is a simple procedure. However, it carries the risk of recurrent varus once the hardware is removed and also does not correct the internal tibial torsion that is an integral part of the multiplane deformity. There have also been reports of implant failure when titanium plates and cannulated titanium screws are used in this patient population (Schroerlucke S, 2009). Also, larger patients with a greater degree of deformity have been shown to be at greater risk for failure with this technique (McIntosh AL, 2009).
There are many techniques of proximal tibial osteotomy: opening wedge, closing wedge, spherical dome or oblique plane osteotomy, which can be used for correction in Blount disease.
The proximal tibial varus and internal tibial torsion deformities can be corrected acutely with an oblique plane osteotomy as described by Rab (Rab, 1988). The osteotomy is best performed prior to age 4 years and in Langenskiold stage II and III to decrease the risk of recurrent deformity (Chotigavanichaya, 2002). Compartment syndrome and neurovascular injury are potential risks associated with acute correction, particularly in patients with more significant deformity (Ferriter P, 1987).
Gradual correction of all the components of the deformity (varus, procurvatum, internal torsion and shortening) can be performed using an external fixator. Overcorrection into valgus is recommended given the possibility of recurrent varus deformity.
MR imaging in patients with infantile Blount disease has shown medial meniscal abnormalities as well as posteromedial depression of the medial tibial plateau (Ho-Fung, 2013). If there is intra-articular instability with medial plateau depression with the slope more than 30 degrees, hemi-plateau elevation may be useful. (Schoenecker, 1992) However, there is evidence that radiographs over-estimate the amount of medial plateau elevation and that a portion of the medial tibial plateau is unossified in severe Blount disease (Sabharwal S, 2012; Stanitski DF, 1999). Therefore, if hemi-plateau elevation is being considered, careful evaluation of either a preoperative MRI or arthrogram is critical so that the severity of medial plateau depression can be quantified to determine the amount of correction that will be needed.
Double elevating osteotomy:
This is performed in cases of medial plateau depression as well as uncorrected tibial varus and internal torsion (Gregosiewicz, 1998). The addition of proximal lateral tibial epiphysiodesis to minimize the risk of recurrent varus has also been described (Van Huyssteen, 2005). This may be done with an external fixator.
Physeal bar excision:
Patients with physeal bars (Langenskiold Stage V and VI) who are younger than 7 years of age and with the bar smaller than 30% of the physis, may benefit from a medial proximal tibial physeal bar resection along with a concomitant osteotomy of the tibia to correct the varus deformity (Andrade, 2006).
Complications seen in Blount disease are due to either undercorrection or recurrence of the deformity leading to persistent varus. Long-term studies have suggested that genu varum increases the risk of knee arthritis in adulthood. Other complications are specific to the type of surgery that is performed, but include neurovascular injury, compartment syndrome, nonunion, implant failure, wound healing complication, pin site infection or need for further surgical intervention.
Figures and Tables:
Fig 1:Standing anteroposterior view of the lower extremities reveals Langenskiold's Stage II changes with downsloping and saucer shape defect of the tibial metaphysis. (Contributed by Vinitha Shenava, Texas Children’s Hospital)
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Mihir Thacker MD