You are in: eMedicine Specialties > Radiology > PEDIATRICS Blount DiseaseArticle Last Updated: Nov 29, 2007AUTHOR AND EDITOR INFORMATIONSection 1 of 12
  Author: Jugesh Cheema, MD, Consulting Staff, Department of Radiology, Brigham and Women's Hospital Jugesh Cheema is a member of the following medical societies: American College of Radiology, American Medical Association, American Roentgen Ray Society, Massachusetts Medical Society, and Radiological Society of North America Coauthor(s): H Theodore Harcke, MD, Chief of Imaging Research, Department of Medical Imaging, Alfred I DuPont Hospital for Children; Professor, Departments of Radiology and Pediatrics, Jefferson Medical College Editors: Fredric A Hoffer, MD, FAAP, FSIR, Professor of Radiology, University of Washington; Section Chief of Interventional Radiology, Department of Radiology, Seattle Children's Hospital and Regional Medical Center; Bernard D Coombs, MB, ChB, PhD, Consulting Staff, Department of Specialist Rehabilitation Services, Hutt Valley District Health Board, New Zealand; Marta Hernanz-Schulman, MD, FAAP, Professor, Radiology, Radiological Sciences, and Pediatrics, Director, Department of Pediatric Radiology, Radiologist-in-Chief, Director, Department of Diagnostic Imaging, Vanderbilt University Medical Center, Vanderbilt Children's Hospital; Robert M Krasny, MD, Consulting Staff, Department of Radiology, The Angeles Clinic and Research Institute; Felix S Chew, MD, MBA, EdM, Professor, Department of Radiology, Vice Chairman for Radiology Informatics, Section Head of Musculoskeletal Radiology, University of Washington Author and Editor Disclosure Synonyms and related keywords: tibia vara, congenital tibia vara, infantile tibia vara, juvenile tibia vara, adolescent tibia vara, infantile Blount disease, juvenile Blount disease, adolescent Blount disease INTRODUCTIONSection 2 of 12
  BackgroundErlacher 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:
PathophysiologyThe 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. FrequencyUnited StatesThe incidence of Blount disease in the United States is unknown. InternationalThe worldwide incidence of Blount disease is unknown. Mortality/MorbidityIncreased 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. RaceTibia vara occurs more commonly in blacks than in whites. SexThe infantile type of Blount disease demonstrates a female predominance, whereas the late-onset types demonstrate a male predominance. AgeThere are 3 age peaks in persons with tibia vara:
Clinical DetailsClinical 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 11º. 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 ExaminationRadiographic 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 TechniquesIn 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. DIFFERENTIALSSection 3 of 12
Osteomyelitis, Chronic Rickets Tibial Plateau Fractures Other Problems to Be ConsideredPhysiologic bowing
RADIOGRAPHSection 4 of 12
FindingsRadiography is the primary modality used to diagnose tibia vara. Radiographic findings primarily involve the posteromedial parts of the proximal tibial epiphysis, growth plate, and metaphysis. A standing anteroposterior radiograph of both legs is used to demonstrate bowing and abnormality at the medial aspect of the proximal tibia. In more advanced cases, bowing is seen at both ends of the tibia. On lateral knee radiographs, a posteriorly directed projection at the proximal tibial metaphyseal level is seen. Different radiologic measurements have been used in an attempt to confirm the presence of Blount disease. The femoral-tibial angle helps confirm the varus position of the leg, but it can be misleading secondary to the rotation of the leg, which may be positional or due to a coexisting rotational abnormality. The metaphyseal-diaphyseal angle has been suggested to provide more precise indications of Blount disease than the femoral-tibial angle (see Image 2). The metaphyseal-diaphyseal angle is obtained by measuring the angle formed between a line drawn parallel to the top of the proximal tibial metaphysis and another line drawn perpendicular to the long axis of the shaft of the tibia. Overlap may be found in measurements between patients with and without tibia vara. Angle measurements are 9º ± 3.9º in cases of physiologic bowing and 19º ± 5.7º in patients with Blount disease. Reportedly, angles greater than 20º confirm true tibia vara in children, whereas angles of 15-20º may or may not indicate tibia vara. Another angle used is the tibial metaphyseal-metaphyseal angle. This angle is larger than the metaphyseal-diaphyseal angle in children with the most marked bowing and indicates distal tibial bowing in severe cases. In 1952, Langenskiold first proposed a 6-stage classification of radiographic changes. This remains the most commonly used system (see Image 1).6, 7, 8 This classification was not intended for use in determining the prognosis or the most desirable type of treatment, and the author cautioned against such use. However, the fact remains that surgical treatment commonly is needed for any child with stage 3-6 changes (see Image 6). Degree of ConfidenceIn the most severe cases, the diagnosis can be made with a high degree of confidence in the presence of a tibial metaphyseal-diaphyseal angle measurement of 20º or more. However, in less-severe cases, measurements may not be confirmatory, and differentiating tibia vara from physiologic bowing is difficult. In such patients, 6 months of follow-up observation is recommended (see Image 2). False Positives/NegativesExtreme physiologic bowing may cause false-positive results. Early or less-severe Blount disease may be misdiagnosed as physiologic bowing of the legs when measurements and medial tibial changes are not confirmatory. Some authors have suggested that children with a metaphyseal-diaphyseal angle greater than 11º eventually develop tibia vara, whereas those with measurements less than 11º have physiologic bowing. Other authors have found standard deviations of ± 2.6º and ± 4.6º. Still others have recommended 6 months of follow-up observation to better differentiate the 2 conditions. CT SCANSection 5 of 12
FindingsComputed tomography (CT) has no defined role in the evaluation of Blount disease. MRISection 6 of 12
FindingsAlthough radiographic findings in Blount disease usually are diagnostic, MRI has the advantage of direct depiction of the epiphysis and the growth plate. How MRI can aid in evaluation and treatment of patients with Blount disease is debatable. MRI has a distinct advantage in a subset of patients with advanced or recurrent tibia vara. In these patients, MRI can demonstrate the extent of the physeal bar to quantify the percentage of physeal involvement. On a T2-weighted image, an open physis is bright and the physeal bar appears black. Early physeal fusion of the medial proximal tibial and, less frequently, medial distal femoral physis can occur from the injury of chronic weight bearing. This injury can lead to progressive genu varus from medial tethering of the growth plates. Removal of the physis medially may help restore normal growth.9, 10, 11 An article about MRI changes in bowleg deformities of early infancy suggested a possible role for MRI in differentiating physiologic bowing from Blount disease.12 Children who eventually had Blount disease were found to have a depression of the medial physis and abnormal signal intensity in the metaphysis in addition to the lesion in the epiphysis. In comparison, children with physiologic bowing were found to have high signal intensity only in the epiphyseal cartilage. However, most patients with combined changes did not develop Blount disease (see Image 5). Degree of ConfidenceMRI does not yet have a well-established role in the evaluation of Blount disease. MRI can be useful to the orthopedist who wishes to know which portion of the medial knee (epiphysis, physis, metaphysis) is injured and what corrective steps must be undertaken. MRI is also useful in the assessment of possible development of a physeal bar. ULTRASOUNDSection 7 of 12
FindingsUltrasonography has no known role in the evaluation of Blount disease. NUCLEAR MEDICINESection 8 of 12
FindingsMultiphase bone scintigraphy is sensitive in assessing normal and abnormal growth plate functions in the growing skeleton.13 Mechanical loading and stress factors influence scintigraphic uptake at the growth plate. When immobilization is prolonged and when closure begins, growth-plate activity decreases. In patients with angular deformities of the legs, the half of the growth plate with greater mechanical loading becomes more active than the other half. In patients with Blount disease, increased uptake occurs medially in the tibial plate, and scintigraphic changes may also be seen in the distal femur. Scintigraphy is not used for diagnosis, but it can be useful in making treatment decisions (see Image 4). ANGIOGRAPHYSection 9 of 12
FindingsAngiography has no role in the evaluation of Blount disease. INTERVENTIONSection 10 of 12
No radiologic interventions are used to treat Blount disease. MULTIMEDIASection 11 of 12
REFERENCESSection 12 of 12
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