Introduction
Background
Erlacher reported the first case of tibia vara in 1922.1 In 1937, Blount reported 13 more cases and reviewed all of the 15 cases that were reported in the literature up to that time. Blount suggested the term tibia vara; however, the eponym drawn from his name remains in common use.2
A brief overview of normal age-related angulation changes in the knee joint helps improve understanding of the disease process:
- A pronounced varus angulation is seen in newborns and in children younger than 1 year. Varus angulation is believed to be secondary to in utero molding of the lower extremities, and this gradually resolves after children start walking.
- Varus angulation usually corrects by the time children reach approximately 18-24 months of age or after they have been walking for approximately 6 months.
- During the ages of 2 and 3 years, pronounced valgus angulation changes occur. The valgus position then partially corrects over the following few years, reaching the adult pattern of mild valgus by 6-7 years of age.
- Any varus angulation at the knee joint seen in individuals older than 2 years is therefore considered abnormal, and such a finding is the basis for the diagnosis of tibia vara, or Blount disease.
Pathophysiology
The common denominator in tibia vara cases is abnormal stress placed on the posteromedial proximal tibial epiphysis that leads to growth suppression. Predisposing factors for the development of the condition include obesity, early walking, and black ancestry. Black children have been noted to have excessive ligamentous laxity, and they begin to walk at an earlier age. Both of these factors predispose them to Blount disease. Obesity and early walking exaggerate the impact of physiologic bowing and increase the stress placed on the physis of the proximal tibia.3,4
Altered mechanical forces in the proximal tibia lead to abnormal axial loading, which results in a change in direction of the weight-bearing forces from the perpendicular to the oblique. The oblique angle tends to displace the tibial epiphysis in a lateral direction, overloading the posteromedial segment and inhibiting its growth (see Image 7). A cycle of further longitudinal growth is established, and this results in progressive varus deformity. Unless the disease is diagnosed and treated early, the condition progressively worsens.
Histologic evaluation confirms the physeal changes. A disordered columnar arrangement of the cartilage cells and suppression of normal endochondral growth are noted, especially on the medial side of the proximal growth plate.
Three major types of tibia vara have been recognized: infantile, late-onset juvenile, and late-onset adolescent. Infantile tibia vara is the most common type. The late-onset types may represent unrecognized or untreated forms of the infantile type or may occur after a neutral mechanical axis has been established.
Frequency
United States
The incidence of Blount disease in the United States is unknown.
International
The worldwide incidence of Blount disease is unknown.
Mortality/Morbidity
Increased mortality is not associated with Blount disease; however, patients with severe untreated tibia vara can have increased morbidity in the form of early onset of osteoarthritis in the third decade of life.
Race
Tibia vara occurs more commonly in blacks than in whites.
Sex
The infantile type of Blount disease demonstrates a female predominance, whereas the late-onset types demonstrate a male predominance.
Age
There are 3 age peaks in persons with tibia vara:
- The infantile type occurs in patients aged 1-3 years.
- Late-onset juvenile type occurs in persons aged 4-10 years.
- Late-onset adolescent type occurs in persons aged 11-14 years.
Presentation
Clinical presentation
Clinically, children with infantile tibia vara present with bowing and length discrepancy in the lower limbs. A nontender bony protuberance can be palpated along the medial aspect of the proximal tibia, representing the deformed medial tibial metaphysis. Pain is not evident. In late-onset tibia vara, leg shortening may be associated with pain and tenderness over the medial prominence of the proximal tibia.
Obesity and bowing are usually obvious on physical examination.4 Bowing may be unilateral or bilateral. Approximately 80% of infantile cases and 50% of late-onset cases are bilateral. On observing the standing child from behind, the bowing is centered below the knee without involvement of the femur. Uncorrected internal tibial torsion is a common associated finding. On walking, a lateral thrust of the knee or sudden lateral knee movement with weight bearing may be noticeable as evidence of progressive tibia vara.
Other problems to consider
The differential diagnosis of Blount disease includes physiologic bowing, congenital bowing, rickets, Ollier disease, trauma, osteomyelitis, and metaphyseal chondrodysplasia. [See also the eMedicine articles Rickets, Osteomyelitis, Acute Pyogenic, and Osteomyelitis, Chronic, as well as Blount's Disease, on Medscape.)
Difficulty may be encountered in differentiating infantile tibia vara from physiologic bowing of the legs. However, the proximal tibial angulation is acute in Blount disease, occurring immediately below the medial metaphyseal beak. This feature results in a metaphyseal-diaphyseal angle greater than 11 º. In physiologic bowing, angular deformity results from a gradual curve involving both the tibia and the femur.
Congenital bowing must be considered. The angulation may occur in the middle portion of the tibia, with a normal-appearing distal femur and proximal tibia.
Mild or healing rickets with residual bowing may be difficult to differentiate from stage 2 infantile tibia vara. However, rickets affects the skeleton in a generalized and symmetric fashion, with loss of the zone of provisional calcification in the physis. In addition, the typical biochemical abnormalities of rickets help differentiate the conditions.
Ollier disease may result in tibial bowing but can be differentiated easily on radiographs by the presence of enchondromas.5
Regarding trauma, growth-plate injuries of the proximal tibia may result in a deformity resembling tibia vara.
Osteomyelitis may be another mimic. Growth plate disturbance secondary to infection may result in an appearance similar to Blount disease.
In patients with metaphyseal chondrodysplasia, multiple metaphyseal deformities are seen, as is a short stature. Radiologically, the changes in this condition mimic those of rickets, but no abnormal serum biochemical results are noted.
Preferred Examination
Radiographic changes found in Blount disease are usually diagnostic. Radiographs provide the most information in this disease because they can be obtained with the patient in an erect position and they provide broad coverage of the area of interest.
Magnetic resonance imaging (MRI) can have limited usefulness in the differential diagnosis of difficult cases. Such cases include those in patients with early growth-plate and marrow changes that are not specific enough to be diagnosed as Blount disease by radiographic findings.
Limitations of Techniques
In patients with early changes, it is difficult to differentiate physiologic bowing from other conditions by radiography. Changes in the growth plate are not easy to detect on radiographs.
MRI cannot be performed with the patient in the erect position, and it does not provide coverage broad enough to diagnose Blount disease. In addition, MRI is more expensive than radiography, particularly because many patients must undergo repeat imaging to evaluate the changes due to Blount disease.
Differential Diagnoses
Osteomyelitis, Chronic
Rickets
Tibial Plateau Fractures
Other Problems to Be Considered
Physiologic bowing
Congenital bowing
Ollier disease
Trauma
Osteomyelitis
Metaphyseal chondrodysplasia
More on Blount Disease |
 Overview: Blount Disease |
| Imaging: Blount Disease |
| Follow-up: Blount Disease |
| Multimedia: Blount Disease |
| References |
| Next Page » |
References
Erlacher, P. Deformierende Prozesse der Epiphysengegend bei Kindern. Archiv für orthopädische und Unfall-Chirurgie, München. 1922;20:81-96.
Blount WP. Tibia vara: osteochondrosis deformans tibiae. J Bone Joint Surg. 1937;19:1-29.
Harcke HT. In: Morrissy RT, Weinstein SL, eds. Lovell and Winter's Pediatric Orthopaedics. Vol 2. 4th ed. Philadelphia: Lippincott-Raven;1996:1055-7.
Sabharwal S, Zhao C, McClemens E. Correlation of body mass index and radiographic deformities in children with Blount disease. J Bone Joint Surg Am. Jun 2007;89(6):1275-83. [Medline].
Silve C, Jüppner H. Ollier disease. Orphanet J Rare Dis. 2006;1:37. [Medline].
Langenskiold A. Tibia vara. A critical review. Clin Orthop. Sep 1989;(246):195-207. [Medline].
Langenskiold A. Tibia vara: osteochondrosis deformans tibiae. Blount's disease. Clin Orthop. Jul-Aug 1981;(158):77-82. [Medline].
Langenskiold A. Tibia vara. Acta Chir Scand. 1952;103:9.
Ducou le Pointe H, Mousselard H, Rudelli A, et al. Blount''s disease: magnetic resonance imaging. Pediatr Radiol. 1995;25(1):12-4. [Medline].
Iwasawa T, Inaba Y, Nishimura G, et al. MR findings of bowlegs in toddlers. Pediatr Radiol. Nov 1999;29(11):826-34. [Medline].
Synder M, Vera J, Harcke HT, Bowen JR. Magnetic resonance imaging of the growth plate in late-onset tibia vara. Int Orthop. 2003;27(4):217-22. [Medline].
Mukai S, Suzuki S, Seto Y, et al. Early characteristic findings in bowleg deformities: evaluation using magnetic resonance imaging. J Pediatr Orthop. Sep-Oct 2000;20(5):611-5. [Medline].
Harcke HT, Mandell GA. Scintigraphic evaluation of the growth plate. Semin Nucl Med. Oct 1993;23(4):266-73. [Medline].
Andrade N, Johnston CE. Medial epiphysiolysis in severe infantile tibia vara. J Pediatr Orthop. Sep-Oct 2006;26(5):652-8. [Medline].
Feldman DS, Madan SS, Ruchelsman DE, Sala DA, Lehman WB. Accuracy of correction of tibia vara: acute versus gradual correction. J Pediatr Orthop. Nov-Dec 2006;26(6):794-8. [Medline].
Gordon JE, Heidenreich FP, Carpenter CJ, Kelly-Hahn J, Schoenecker PL. Comprehensive treatment of late-onset tibia vara. J Bone Joint Surg Am. Jul 2005;87(7):1561-70. [Medline].
Sabharwal S, Lee J Jr, Zhao C. Multiplanar deformity analysis of untreated Blount disease. J Pediatr Orthop. Apr-May 2007;27(3):260-5. [Medline].
Salenius P, Vankka E. The development of the tibiofemoral angle in children. J Bone Joint Surg Am. Mar 1975;57(2):259-61. [Medline].
Further Reading
Keywords
tibia vara, congenital tibia vara, infantile tibia vara, juvenile tibia vara, adolescent tibia vara, infantile Blount disease, juvenile Blount disease, adolescent Blount disease
