Infantile Tibia Vara (Blount's Disease) and Childhood Obesity: Current Concepts Review

Dan Irlbeck, Orthotics Resident
Scheck and Siress O & P
February 2005

ABSTRACT

Infantile tibia vara (Blount's disease) is the most common cause of pathological genu varum in childhood.^75,115 Despite almost 100 years of research and a general appreciation of the pathophysiology, clinical characteristics, radiographic features, and natural history of tibia vara, the etiology of the disease is obscure, and efficacy of early treatment remains a subject of controversy. The traditional and prevailing methods of early orthotic management continue to offer debatable reports of efficacy. Orthotic research has produced only anecdotal evidence of effectiveness of particular orthoses.

During the past two decades, the prevalence of obesity in children has risen greatly⁴¹; pediatric obesity now represents one of the most pressing nutritional problems facing children in the United States today.¹¹⁹ Childhood obesity and the associated skeletal disorder of tibia vara suggest Blount's disease as a consequence of obesity.²⁵ Current data clearly emphasizes that the course of the two diseases is closely related.³⁴ This review primarily discusses the pathology, theories of etiology, natural history, affects of childhood obesity, and current trends in early Blount's disease management.

INTRODUCTION

Infantile tibia vara, also known as Blount's disease, is an uncommon developmental disorder that is defined by a varus and internal rotation deformity of the proximal tibia, secondary to growth disturbance of the metaphysis, physial cartilage, and epiphysis. It is an entity distinct from other known rotational or angular deformities of the lower extremity and is not simply a variant of these other problems.^{13,61,73,73,76} The condition was first reported in 1922 by Erlacher (44) but has carried the eponym Blount disease since Blount's classic description and review¹¹ in 1937.

Two other terms (tibia vara and osteochondrosis deformans tibiae) have been used to describe the deformity of Blount's disease. Blount suggested the anatomic term tibia vara, which is the generally accepted term. However, the term does not identify the location of the abnormality, nor does it suggest the etiology of the disease. The term osteochondrosis deformans tibiae is not accurate because it describes a disorder in which the primary or secondary centers of ossification undergo avascular necrosis. Avascular necrosis has never been found in either form of Blount disease.¹²¹ Blount's disease and tibia vara are the most commonly accepted terms for the disease.

EPIDEMIOLOGICAL FEATURES

Children with infantile tibia vara have no apparent abnormality at birth; they are generally healthy, and early growth of the legs is within normal limits.^8,9 Infantile tibia vara is found frequently in black populations with a higher prevalence (one to three) among female obese children who start walking at an early age.^{8,9,16,61,78,81,82,101,122} Infantile tibia vara is asymmetric in presentation, either bilateral (50-75% of cases) or unilateral in most cases.^69,21

The condition is more common in Africa, the West Indies, and Finland, for reasons that are not clear^{5,7-9,11,107,121}, and in 60% of cases the condition affects both legs.²⁸ Langenskiöld and Riska⁷⁹ noted that < 500 cases were reported in the world literature up to 1964. An exact incidence of the disease is not cited in any published report; however, one author found only 37 of 5,000 cases of bowlegs, for an incidence of < 1%.¹⁰⁷ The estimated prevalence of infantile Blount's disease in the population of young children with significant bowlegs in the United States is 0.007, or less than 1%, and unknown internationally. The exact frequency in persons of all ethnicities is unknown and most likely is less than 1%³⁰ and increased if other family members have been diagnosed as having ITV^{33,101, 102}.

CLASSIFICATION SYSTEMS

Some describe the physical features of Blount's disease as genu varus or "bowlegs." There are, however, characteristics that differentiate Blount's from the physiologic bowleg. Blount's disease can occur in growing children of any age and is classified into 2 commonly recognized groups: (1) early onset, termed the infantile form, with onset prior to age three years, and (2) late onset, which includes the juvenile form (children aged 4-10 y.o.a. ) and adolescent form (aged 11 years and older) of the disease. The most common form is infantile. Late onset forms may represent an unrecognized or untreated form of the infantile type or may occur after a neutral mechanical axis has been established. It is now generally accepted that although the two have some similar anatomic and epidemiologic features, adolescent tibia vara should be considered a different disorder from that of infantile tibia vara^11,78 and will not be discussed in this review.

ETIOLOGY

The cause is the most controversial issue concerning Blount's disease. Early authors suggested various causes for the infantile form, including a possible late form of rickets, inflammatory conditions, trauma, infection, or vascular deficiency.^5,11,45 Over the years these causes have been generally rejected. Presently, the incidence of the deformity is most likely secondary to a combination of hereditary and developmental factors.³³

Biomechanical overload of the proximal tibial physis due to static varus alignment and excessive body weight have been implicated in the etiology of infantile tibia vara. The association of early walking, black race, female gender, and obesity in these children supports that explanation. The age at which a child begins walking is another proposed factor in the disease. Because the tibio-femoral angle normally increases from varus at birth to valgus by 18 mos. to 3yrs⁹⁹ it has been hypothesized that walking at an early age produces abnormal stresses on the medial tibial plateau secondary to the physiologic varus. Kessel⁷² and Golding and McNeil-Smith⁵⁴ have regarded this as a major etiologic factor, however other authors refute this association.⁹ Although nearly all children have genu varum at birth, the vast majority does not develop Blount's disease. If a child begins walking at an early age, when the knees are still aligned in marked varus, then weightbearing compressive forces will be greater on the medial aspect of the physis.²⁶ Black and female children walk at an earlier age than white and male children^{9, 8,16,79,81,82,101}, and this factor may account for the greater number of black children and girls with infantile tibia vara.^{13,7-9,81,101}

Patients with Blount's disease are frequently obese.^{5,11,13,45,78} Dietz et al.³⁴ noted that obesity (>120% of ideal body weight) was present in 12 of 18 patients studied, and this percentage was comparable to that noted in patients with slipped capital femoral epiphysis. The incidence of the latter in the general population is approximately three per 100,000 per year.³⁴ Obesity also increases compression at the physis. These clinical observations were supported by a study that used finite element analysis. In this study, Cook and associates²⁶ calculated that 20 degrees of genu varum in a 2-year-old child of normal weight retards growth from the medial aspect of the proximal tibial physis. Obesity and increased height, as seen in an older child, decreased the degree of genu varum necessary to cause abnormal compression on the medial side of the proximal tibial physis.

In addition to race and body weight, the frequency is increased if other family members have been diagnosed as having Blount's disease.^{11,13,26,34,45,52,79,81,101,102,105} Nine percent to 43% of patients have been reported to have an affected parent or sibling,^9,101, but the spectrum of infantile tibia vara within the family is usually consistent with a multifactorial rather than a genetic pattern of inheritance. Considering that roentgenographic changes typical for infantile tibia vara have never been seen before the age of one year and seldom before the age of two, the condition is developmental rather than congenital.⁷⁸

The mechanism of Blount's disease has not been established.^26,107 The cause is probably a combination of many factors, as suggested by Bathfield and Beighton (9), among genetic predisposition, environmental factors and the mechanics of the knee during childhood.

DIFFERENTIAL DIAGNOSES

Bowing of the lower extremities is common and is frequent cause of orthopedic referral¹¹⁷ The parents of children with bowlegs often want to know if the legs are abnormal. The role of the physician is to determine if the bowing is physiologic or pathologic. The clinical and radiographic characteristics of various common and uncommon causes of lower-extremity bowing in children include the following differential diagnoses of lower-extremity bowing: (1) developmental ("physiologic") bowing, (2) congenital bowing,(3) infantile tibia vara (Blount's disease), (4) hypophosphatemic rickets, (5) neurofibromatosis, (6) osteogenesis imperfecta, (7) achondroplasia, and (8) camptomelic dysplasia.²¹

Developmental ("physiologic") Bowing

Developmental (physiologic) bowing is a common condition that causes exaggeration of normal age-related angulation changes at the knee joint. Neonates and infants normally have varus angulation of lower extremities that is believed to be secondary to in-utero molding. Gradual correction of this angulation begins as a child starts walking. The bowing is corrected within 6 months of walking or by 18-24 months of age. After this age, there is normally a change to valgus angulation during the 2nd and 3rd years of life that reverts to the adult pattern by age 6 or 7 years. Thus, any varus angulation at the knee joint after the age of 2 years is abnormal²¹. Exaggerated varus angulation during the 2nd year of life is deemed to be developmental bowing. This condition is typically seen in children who begin walking at an early age and is more common in heavier children as well as in African-American children.^95,117 Developmental bowing does not require treatment, but follow-up is needed to ensure that the bowing resolves and that tibia vara does not develop.

Congenital Bowing

Congenital bowing of the tibia is an unusual condition that is believed to result from an abnormal intrauterine position, although localized skeletal dysplasia or fetal vascular insufficiency may also play a role in some cases. This type of tibial bowing is usually convex posteriorly and medially; less commonly, it is convex laterally. The fibula is also bowed. The foot shows marked dorsiflexion at birth. There is a good prognosis for remodeling during growth, but protective bracing may be necessary in some cases as well as surgical correction.²¹

Neurofibromatosis

Neurofibromatosis is a common genetic disorder. In addition to cutaneous, nervous system, and ocular abnormalities, osseous lesions are seen in neurofibromatosis type 1. There may be Anterolateral bowing of the tibia with or without a hypoplastic fibula, and there is often focal narrowing and intramedullary sclerosis or cystic change at the apex of the angulation, a finding that is consistent with hamartomatous fibrous tissue. The tibia is typically involved at the junction of the middle and distal thirds. The underlying mechanism is mesodermal dysplasia. Pathologic fracture with nonunion may result in pseudoarthrosis of the tibia and sometimes of the fibula, with pencil pointing of the bone fragments. When dysplasia without fracture is diagnosed, prophylactic bracing may be used to prevent development of pseudoarthrosis. The precise mechanism for defective healing and pseudoarthrosis is not known.²¹

Osteogenesis Imperfecta

Osteogenesis imperfecta is one of the more common heritable disorders of the connective tissue. Traditionally, four major types of OI have been described, each with a different mode of inheritance depending on the basis of the specific collagen defect. In all four types of osteogenesis imperfecta, bowing of the long bones results from softening caused by osteoporosis and multiple fractures. Bowing typically involves all the long bones^1,21, and osteotomies and pinning are commonly performed for bowing.

Rickets

Rickets results from deficient mineralization of normal osteoid and interruption of the normal orderly development and mineralization n of growth plates. Vitamin D-resistant (hypophosphatemic) and nutritional rickets are the most common types, with hypophosphatemic rickets being the most common type of rickets in the United States. The bones are soft, with consequent bowing of long ones on weight bearing. Cupping, fraying, and splaying of metaphysis occurs with growth and continued weight bearing. Radiologic changes in rickets occur prominently at sites of rapid growth, including the proximal humerus, distal radius, and distal femur and both ends of the tibia. Treatment is dietary and medical unless the bowing is severe, in which case valgus osteotomies may be performed. The height at the initial diagnosis is usually less than the 10th percentile.⁵⁷ Abnormal genu varum is observed in 95% of patients who have hypophosphatemic rickets.⁵⁷

Camptomelic Dysplasia

Camptomelic dysplasia is a rare inherited disorder that is often fatal in infancy. In newborns, it leads to a large head, a short trunk, and short, bowed limbs. There is angular anterolateral bowing of the limbs that is most marked in the legs, as well as involvement of both femurs and tibias. Camptomelic dysplasia is classified as a bent-bone dysplasia. Treatment is usually supportive.²¹

Achondroplasia

Achondroplasia is the most common form of short-limbed dwarfism. It is the most often autosomal dominant in transmission but with a high rate of spontaneous mutation. Achondroplasia is characterized by shortening and thickening of the long bones with metaphyseal flaring and cupping. The lower extremities are bowed, and treatment of severe bowing requires valgus osteotomies.²¹

PATHOPHYSIOLOGY OF DEFORMITY

The pathophysiology of infantile tibia vara involves retarded growth of the posteromedial aspect of the proximal tibia, resulting in a bowleg deformity at the level of the proximal tibial physis.¹¹² The compressive forces at the medial aspect of the knee appear to cause growth suppression from that area or increased growth from the proximal aspect of the fibula and the lateral aspect of the proximal part of the tibia, or both.⁹³

Histologic changes observed in the medial portion of the tibial physis are consistent with increased compression and reduced growth in these areas. These histologic changes include: (1) islands of densely packed cartilage cells showing more hypertrophy than normal, (2) islands of almost acellular fibrous cartilage, and (3) abnormal groups of capillary vessels.^54,78

The result of continued compression is limited growth of both the physis and epiphysis. The medial aspect of the epiphysis becomes narrowed, and longitudinal growth from the medial aspect of the metaphysis is inhibited. Persistent internal tibial torsion also occurs, the etiology of which is uncertain, but may be related to a relative overgrowth of the fibula that blocks normal development of external tibial torsion (94). Eventually, changes in the growth plate become irreversible and premature bridging of the medial proximal tibial physis occurs. When patients are not treated, severe degenerative joint disease develops during early adulthood⁶⁵.

Weightbearing must be necessary, since the disease does not occur in nonambulatory patients.²⁶ Cook et al²⁶ correlated the epidemiologic and histologic evidence in a biomechanical model that provided evidence for the role of biomechanical overload in the pathogenesis of infantile tibia vara. They analyzed static single-limb stance in children and determined that 10deg and 20deg varus deformities, in children aged 2 years and 5 years. Respectively, could generate compressive forces adequate to retard growth of the medial tibial physis.

Infantile tibia vara is most likely due to a combination of mechanical and biologic factors that impact the disease to varying extents. Furthermore, excessive physiologic bowing often is found in individuals with the infantile form of the disease. It is known that epiphyseal compression inhibits physeal growth (the Heuter-Volkmann law) and distraction stimulates growth.⁴ Delpech demonstrated this stimulation by showing that a release of abnormal pressure from a physis causes increased vertical growth (4). The result of these compressive forces is a relative inhibition of growth of medial compared with the lateral portions of the proximal tibial physis.

In addition, it is also know that damaged cartilage is ossified more slowly.⁷⁸ Histologic sections of the cartilage in the infantile form have exhibited damaged cartilage. If the cartilage on the medial aspect of the plateau is damaged, ossification is delayed on the medial side of the tibia compared to the lateral side. The result is a progressive varus angulation below the knee with a resultant increase in the compressive forces on the physis. The resultant effect is a change of direction of the weightbearing forces on the upper tibial epiphysis from perpendicular to oblique. The obliquity of this force tends to displace the tibial epiphysis laterally. The trabecular pattern of the metaphyseal region in the tibia curves medially to align itself to the deviation of the stress.¹¹⁵

EXAMINATION

Clinical Characteristics

Clinically, it has been difficult to differentiate early infantile Blount's from physiologic bowleg. These children are brought to a physician at 14 to 36 months of age for evaluation of bowlegs. A typical history is that the genu varum has gotten worse since walking began.

The clinical diagnosis of ITV is based upon history, physical examination, and plain radiographs. The history focuses upon risk factors such as racial background, family history of bowlegs, age at ambulation, body weight, and familial predisposition of the bowing deformity.^{9,13,31,54,71,75} The physical exam is limited in its ability to distinguish between physiologic and pathologic bowing. Pain, limb length discrepancy, and limping are rarely seen in ITV. Some investigators have found palpation of a prominent beak of the proximal medial tibia to be helpful.13,54,106,115 Others have described posteromedial instability of the affected knee on stress.106 Finally, others have noted the presence of a stance phase varus thrust to be a positive predictor of pathologic bowing.^13,75 Unfortunately, none of these clinical observations have been evaluated in a systemic fashion. In addition, these tests may be subtle and are difficult to perform, often requiring a high level of sophistication on the part of the examiner.

Obesity and bowing are usually obvious on physical exam, those with tibia vara are often obese, exceeding the 95th percentile for weight.11,34 Bowing may be asymmetric presentation; either bilateral or unilateral, approximately 50-80% of infantile cases and 50% of late-onset cases are bilateral.22,69

The next decision in the evaluation process is whether radiographs of the knees are warranted. One author (56) suggests radiographs are warranted only if the following criteria have been met: (1) genu varum that is relatively sever for the child's age (2) genu varum that, according to the patient's history, has not improved or has gotten worse over the previous three to four months; (3) excessive internal tibial torsion; (4) a height less than the 25th percentile; (5) a positive family history for genu varum; and (6) marked asymmetry of limb alignment. These factors are said to reveal some condition other than physiologic genu varum.⁵⁶ Until there are definite X-ray changes in the physis, it can't be certain whether the patient has Blount's. By repeated clinical and radiographic examinations, however, the diagnosis can be made. Usually by age 2, physiologic bowleg will have shown spontaneous improvement, while the deformity of Blount's disease will have increased and radiographic changes in the proximal tibia will be well developed.²⁸

Several methods have been defined for measurement of the Tibio-Femoral angle (TFA) in growing children. Roentgenographic technique was used upon recognition of the pathology.^81,99,104 Recently, authors have concluded that the great majority of these children have physiologic bowing and routine radiographic screening and referral are not cost effective and expose children to unnecessary radiation. Additionally, limb malrotation when the radiograph is taken may affect the measurement of the TFA significantly¹¹⁰. Recently, clinical examination has become popular because the clinical method is both easily applicable, reproducible^23,63 and an important part of a routine physical examination. Arazi et al.³ reported on TFA changes and intercondylar (IC) or intermalleolar (IM) distance in normal children from the beginning of walking age to the end of the adolescent period. The IC and IM distances were measured with a linear tape measure.⁶³

There is controversy about which measurement is more accurate and easier for routine physical examination to evaluate the TFA or IC/IM distance in children. Cheng et al.²³ noted the IC/IM distance measurement is easier to apply clinically and is as reliable. Conversely, Cahuzac et al.¹⁵ reported that the TFA measurement is more accurate than distance measurement because the standard deviation of IC/IM distance is greater than the mean value. There are also some difficulties observed with regard to the positioning of the subjects, when the distance measurement was performed. In the study by Arazi et al³, there was a fair degree of correlation between weight and the TFA. The largest IM distances were obtained in overweight children. Cahuzac et al.¹⁵ observed this and noted that this finding could result from soft-tissue thickeness over the knees.

A Novel Clinical Exam Technique

A simple clinical examination technique, the "cover up" test, developed by Davids et al³¹ identifies young children with bowlegs who are at high risk for having infantile tibia vara (ITV). This test qualitatively assesses the alignment of the proximal portion of the tibia relative to the thigh or upper leg. Obvious valgus alignment is considered a negative test and is indicative of physiologic bowing. Neutral or varus alignment is considered a positive test and suggests that the child is at greater risk for having infantile tibia vara.

In the study conducted by Davids et al, eighteen children with ITV, evaluated initially prior to 3 years of age, and followed to the time of surgical correction, were compared with 50 children with physiologic bowing, also evaluated initially prior to 3 years of age and followed to resolution (mean follow-up 3 years and 10 months). All of the children with ITV had a positive "cover up" test (sensitivity = 1.00). Eighteen of 25 children with a positive "cover up" test actually had or developed ITV (positive predictive value = 0.72). Forty-three of 50 children with physiologic bowing had a negative "cover up" test (specificity = 0.86). All of the children with a negative "cover up" test actually had physiologic bowing (negative predictive value = 1.00). The authors concluded that children with a negative "cover up" test do not require radiographic evaluation and should be followed clinically for resolution of the bowing. Children with a positive "cover up" test should have radiographic evaluation of the lower extremities or be referred to a specialist for further evaluation and treatment.³¹

Normal Growth

The cycle of growth in the lower limb is very predictable. There is rapid increase in growth during the first 5 years of age, followed by a steady but slower growth from 5 years of age to the onset of the puberty.³⁸ The femur grows more than the tibia with a constant relationship between the femur and the tibia throughout growth. Their proportions are set as early as age 5 years. Tibial length is 80% of femoral length. Fibular length is 98% of tibial length.

Growth around the knee is the largest growth site of all. The knee accounts for about two thirds of growth in the lower limb, 37% for the distal femoral physis and 28% for the tibia.^2,37,38 The lower limbs double in length at age 2 years, and there remains 50% of growth in the lower limbs at the age of 4 years.³⁶

Two studies have charted normal development of the femoral-tibial angle and are helpful in the determination of whether a child's genu varum is a matter for concern. Salenius and Vankka⁹⁹ used radiographs to measure the tibial-femoral angle in a relatively homogeneous Finnish population. Engel and Staheli⁴³ derived measurement from clinical photographs of a more heterogeneous population of children in Seattle, Washington. Both studies observed that normal knee alignment progresses from 10-15 degrees of varus at birth to a maximum or peak valgus angulation of 10 to 15 degrees at the age of 3 to 3.5 years. The studies differed in terms of the age at which neutral tibial-femoral alignment was reached. Engel and Staheli observed neutral tibial-femoral alignment when their patients were an average of 12-14 months old, but Salenius and Vankka noted neutral alignment when their patients were an average of 20-22 months old. In a more recent study by Arazi et al³, they noted a significantly higher degree of valgus angle than in previous reports. The maximal mean valgus angle was 9.6º at 7 years for boys and 9.8º at 6 years for girls. Children aged between 3 and 17 years, exhibited =11º physiologic valgus. A measurable varus angle or a valgus higher than 11º during this period was considered abnormal.

Radiographic Evaluation

Many systems of radiographic evaluation exist. The roentgenographic changes of Blount's disease were first documented by Langenskiold in 1952; described as six stages of progressive change to the medial tibial epiphysis and metaphysis. The severity of bowleg deformity was determined by comparing the tibial-femoral angle (TFA) of affected patients against the normal angle.⁹⁹ The TFA can quantify the amount of bowleg deformity, but some authors argue the usefulness for differentiating physiologic bowlegs from Blount's disease.⁸¹ In 1982, Levine and Drennan introduced the method of measuring the tibial metaphyseal-diaphyseal angle (TMDA) in order to differentiate between severe physiological bowing and tibia vara.

Considered to be one of the best radiographic signs of impending Blount's disease is an increased TMDA, which measures the varus tilt of the proximal tibial metaphysis.^46,81 This angle is formed between a line drawn across the two proximal tibial metaphyseal "beaks" and a line drawn perpendicular to the lateral cortex of the tibial shaft. Bowlegged children over age 18 months with a TMDA = 9º have a 95% chance of having physiologic genu varum. A TMDA = 16º denotes a 95% probability of developing progressive deformity of infantile Blount's disease.⁴⁶ Measurements from 10-15º require close observation. The TMDA, however, can be helpful in the differentiation of these two conditions. In the study by Levine and Drennan⁸¹, physiologic bowlegs was the ultimate diagnosis in 49 of 52 children who had a TMDA of 12º or more. Subsequent studies have shown that measurement of the TMDA to be reproducible between observers.^50,64

Despite the widespread use and acceptance of the tibial metaphyseal-diaphyseal angle, subsequent studies have questioned the predictive value of this measurement.^46,60 Screening studies in the literature⁸¹ were technically flawed because they included radiographic examinations that were not standardized for weight bearing or rotational alignment of the lower extremity.^{30,46,50,81,88,94,101} In addition, these studies include children who already show Langenskiold changes on their radiographs, obviating the need for a predictive radiographic measure of whether the child is at risk for development of Blount disease.^46,60,81 Inclusion of these children may also bias the magnitude of the TMDA measured in these studies.

A study conducted by Davids et al.³⁰ Reexamined the issue of early radiographic evaluation of bowed legs in children between 1 and 3 years of age, using standardized radiographic techniques and stricter, more appropriate clinical inclusion criteria. The authors set out to find that there are no radiographic measures made before the presence of Langenskiöld changes that adequately screen for the subsequent development of Blount's disease. Thirteen children with Blount disease, evaluated before 3 years of age, with initial radiographs showing no sign of Langenskiöld changes, were compared with 50 children with physiologic bowing, also evaluated before 3 years of age with similar radiographic studies. Screening test accuracy was determined retrospectively for measurement of the mechanical axis, the tibial metaphyseal-diaphyseal angle (TMDA), and the epiphyseal-metaphyseal angle (EMA). A radiographic screening method combining the TMDA and the EMA, using cutoff values of 10º and 20º respectively, exhibited the best combination of sensitivity, specificity, and positive predictive value, correctly identifying all cases of Blount's disease and 40 of 50 cases of physiologic bowing. The authors' data suggest those children between 1 and 3 years of age with TMDA < 10º, or TMDA ≥10º and EMA ≤20º, are at less risk for development of Blount's disease. Children with TMDA ≥10º and EMA >20º are at greater risk for development of Blount's disease and should be followed closely³⁰.

Other angles have been reported in the literature that have yet to be validated; 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.²¹

Imaging Techniques

Magnetic Resonance Imaging and Bone Scintigraphy

MRI can have limited usefulness in the differential diagnosis of difficult cases. Magnetic resonance imaging has been performed to evaluate the growth plate in Blount's disease and may be useful in surgical planning.^27,114 It may also be used to predict development of Blount's disease in patients with severe physiologic bowing.⁶⁸ MRI does not yet have a well-established role in the evaluation of Blount's 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. CAT/CT scans have no defined role in the evaluation of Blount's disease.

Multiphase bone scintigraphy (bone scan) is sensitive in assessing normal and abnormal growth plate functions in the growing skeleton. Mechanical loading and stress factors influence scintigraphic uptake at the growth plate. 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's 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.⁶²

Prognostic Factors

In 1952, Langenskiold described 6 radiographic stages related to age and severity of the condition. Stage I (2-3 years old), is characterized by irregular metaphyseal ossification combined with medial and distal protrusion giving a beak-like appearance to the metaphysis. A stage II (3-4 years old), there is a medial sloping of the metaphysis with increased prominence of the beak deformity. Spontaneous regression to normal may occur at this stage. Stage III (4-6 years old), there is a step-off of the medial metaphysis with adjacent irregular epiphyseal ossification, which is irreversible. Stage IV (5-10 years old), the epiphysis begins to occupy the depression created by the step-off of the metaphysis. Stage V (9-11 years old), a step-off deformity of both the epiphysis and the metaphysis is evident. With increased medial sloping of the tibia, the knee joint is stressed and ligamentous laxity develops. Stage VI (>10 years old), there is asymmetric closure of the physis medially.

Langenskiold's classification has been widely discussed and reproduced in different textbooks, but it is now recognized that this classification has a somewhat limited clinical application. Langenskiold himself has subsequently noted that the radiographic stages do not necessarily coincide with prognosis and results of treatment.

Smith's four-grade classification published in 1982¹⁰⁷ is more useful, but its parameters include the degree of measured varus angulation of the lower extremity, which is subject to intraobserver errors.¹¹¹ Catonne's classification is helpful for treatment indications, but his stage 3 is purely descriptive, and the treatment proposed is exactly the same for stages.^1,2,3,17,18 Laville et al⁸⁰, suggested an easier 3-stage classification system for treatment options aimed at obtaining a one-step correction of all deformities.

OUTCOME AND PROGNOSIS

Early diagnosis of ITV is important, because treatment outcomes are clearly superior in younger children, presumably because the biomechanical overload can be corrected prior to irreversible damage having been done to the proximal tibial growth mechanism.^{13,26,40,47,65,82,101,107} The result of continued compression is limited growth of both the physis and epiphysis. The medial aspect of the epiphysis becomes narrow, and longitudinal growth from the medial aspect of the metaphysis is inhibited. Persistent internal tibial torsion also occurs with uncertain etiology.⁹⁴ Eventually, changes in the growth plate become irreversible and premature bridging of the medial proximal tibial physis occurs.

In long-term follow-up of ITV, Doyle et al⁴⁰ found that the outcome depends on the patient's age and severity of deformity at the time of intervention.⁴⁰ The prognosis of the infantile form must be considered separately form the adolescent form of Blount disease. Untreated infantile tibia vara is speculated to be progressive. The literature has demonstrated that partial or complete regression may occur in stages I-IV; however, stages V-VI do not demonstrate a regression.⁴⁰ Long term follow-up of patients with Blount's disease is limited^40,65,101, and it is still unclear if limb abnormality predisposes these patients to development of arthrosis, severe degenerative joint disease, irreversible incongruity and knee instability during early adulthood. Although this has been discussed⁶⁵, few studies support this possibility.^{28,65,71,79,121}

TREATMENT

Nonoperative

The Natural history of bowleg deformity in children is not clear. Most children with so-called physiological bowing will have spontaneous resolutions and will require no treatment. A small number remain in varus and have slow progression of the deformity, which is defined as pathological genu varum (infantile tibia vara). Johnston⁷¹ claimed that infantile tibia vara was always progressive, but Hagglund et al⁶⁰ suggested that spontaneous improvement might occur. Blount indicated that the deformity may resolve spontaneously and that the value of braces or other types of supportive treatment was unknown. Langenskiold and Riska ⁷⁹ reported spontaneous resolution in only two of 71 patients. Unfortunately, there are few reports^97,103 of the natural history of infantile tibia vara since treatment by splints or surgery is generally advised. Shinohara¹⁰³ observed the natural history of 46 limbs in 29 patients with ITV and a TMDA of more than 11º. In 22 limbs, which were not in Langenskiold stages II to III the condition resolved spontaneously without treatment. Of the remaining 24, which were in stages II to III, in 18 ITV resolved spontaneously by the age of six years, but six showed little or no improvement. There was no difference in the rate of resolution of the deformity between those patients who had been treated by a brace and those who had received no treatment. The authors failed to identify the BMI or weight-to-length percentile of the patients, in which the weight of the patient has been strongly correlated to the onset or advancement of the disease.

Orthotic

Observation or a trial of bracing is used most frequently for children aged 2-5 years. However, progressive deformity usually requires osteotomy.^33,101,121 No recommendation for operative treatment has been made for children younger than 2 years because the existing deformity may be an exaggerated physiologic genu varum.³³

Differentiating physiological bowing from infantile tibia vara in its early stages is very difficult. Several diagnostic criteria have been suggested. Levine andDrennan⁸¹ reported that 29 of 30 limbs with an MDA that was more than 11º developed Blount's disease. Zayer¹²³, however, reported that ten patients with MDAs of more than 11º (11 to 21º) showed spontaneous resolution. Eggert and Viemann⁴² concluded that neither the FTA nor the TMDA allowed differentiation between physiological bowing and infantile tibia vara. Hagglund et al⁶⁰ reported that in individual cases a single measurement of the TMDA couldn't be used to determine whether the bowing is progressive and requires treatment. Davids et al³⁰ suggest that children between the ages of 1 and 3 years of age with TMDA < 10º, or =10º and EMA = 20º, are at less risk for development of Blount's disease. Children with TMDA =10º and EMA > 20º are at greater risk for development of Blount's disease and should be followed closely. Finally, Tachdjian et al¹¹⁵ differentiate nonoperative treatment from orthotic treatment when the deformity is increasing or if the child has a TFA greater than 15º, a TMDA greater than 11º, and a TMEA of 25-30º.

In a child older than 2 years, orthotic treatment can be used when the deformity is increasing or if the child has a TFA greater than 15º, a TMDA of greater than 11º, and a TMEA of 25-30º¹¹⁵. Ambulatory daytime bracing using an above-the-knee brace with a free ankle may favorably alter the natural history of patients with tibia vara who are younger than 3 years and who have Langenskiold stage I or II deformity because the deformity is often reversible at these stages¹²⁵. Nonetheless, documentation of the effectiveness of bracing is difficult because tibia vara can resolve spontaneously³³.

Obesity, female gender, and a poor social situation are poor prognostic signs for successful bracing.⁵⁶ Brace treatment may be effective in very early infantile Blount's disease,^97,98 but most patients achieve optimal results with early corrective osteotomy of the proximal tibia and fibula (71m,79,121).

Orthotic Designs

The orthosis prescribed for children with ITV is an above the knee, knee-ankle-foot-orthosis (KAFO). Most KAFO designs discussed in the literature incorporate a free ankle, single medial upright and either no hinge joint at the knee or a locking hinged knee joint. A lateral cuff or elastic band around the knee pulls the leg into valgus.

Management Protocol

Brace treatment for children with Langenskiold stages I and II will be effective in only one-half of the cases. This differs from previous reports.^77,101 There was non-predictive value of brace success or failure on the basis of presenting angular measurements. Loder et al⁸² recommend that bracing is indicated only for children between 1.5 and 2.5 years of age presenting with stage I or II disease and that braces should be worn during weight-bearing so that compressive stresses on the medial physis are minimized.²⁶ If after 1 year of bracing, correction to a 0deg tibial-femoral angle is not achieved, and then tibial osteotomy is indicated.

Prognosis and treatment recommendations depend significantly on the age of diagnosis, which should be the age at which treatment begins. Orthotic treatment in a child under age three years with lesions no greater than Langenskiold II is recommended and justifiable, since 50% or more of these conditions can be adequately corrected using braces.^82,101 There may be a tendency to brace patients before a Blount's lesion is visible roentgenographically, especially in tibiae with a metaphyseal-diaphyseal angle (TMDA) predictive of progression. Thus, good results reported from bracing must be retrospectively evaluated with the knowledge that some of the patients were treated for physiologic genu varum before a roentgenographic lesion could develop. Nevertheless, full-time orthotic, as opposed to nighttime orthotic treatment, as opposed to nighttime or non weight-bearing treatment is now recommended for even the earliest treatment. Valgus correction should be increased every two months until standing roentgenograms demonstrates an absolute valgus mechanical axis. Weaning from the brace can then occur over a period of several months. To ensure lasting correction, resolution of the metaphyseal lesion should commence while the mechanical axis is corrected and should be complete, or nearly so, when use of the orthosis is discontinued completely.⁷¹

Some authors suggest observation at 6-month intervals without treatment until the age of four years, even in those children with Langenskiold stage II or stage III, and corrective osteotomy undertaken only in those who show no improvement after this age.¹⁰³ Zionts¹²⁵ suggests that ambulatory daytime bracing using an above-the-knee brace will favorably alter the natural history of patients with tibia vara who are younger than 3 years and who have Langenskiold stage I or II deformity because the deformity is often reversible at these stages. If the deformity persists or increases to stage III or IV with daytime brace treatment, osteotomy is required. If possible, it is preferable to perform the osteotomy before the child is aged 4 years to prevent recurrence (40). If deformity is severe, Langenskiold stage V or VI, operative correction is essential. Orthotic devices are ineffective in controlling the varus deformity in adolescents, and the treatment is surgical.

Orthotic treatment is probably not indicated after the age of three years, since a maximum trial of one year of bracing is presently recommended. If correction in a child younger than age three years is not obtained after one year of bracing, it is still possible to perform definitive osteotomy by age four. A good result from this single osteotomy occurs in nearly 90% of cases.⁸²

Expanding the indication for bracing to include children older than three years of age risks a delay in performing corrective osteotomy, if orthotic treatment is to be given an adequate trial of one year.

Daytime vs. Nighttime Bracing

Although some authors recommend nocturnal use only^58,108 others⁵⁶ believe that wearing of the brace 22-23 hours a day provides greater potential for correction of ITV. If a child is not able to tolerate full-time brace wear, then the time out of the brace should be while the child sleeps. The study by Raney et al suggests that nighttime bracing is as efficacious as full-time bracing, and a prospective study has been initiated. Daytime brace wear is recommended because standing and walking increases the compressive, growth-inhibiting forces and the physis needs protection during these activities.

Orthotic Treatment Results

Many authors^82,97,98,125 believe that treatment by bracing is important in the early stages of infantile tibia vara and have reported successful outcomes. Levine and Drennan⁸¹ found that children with a TMDA greater than 11º developed Blount's disease in 29 of 30 cases. Only 3 of 58 patients with a TMDA of less than 11º developed Blount's disease. Feldman and Schoenecker⁴⁶, however, found that one third of children with physiological bowing and a tibial-femoral angle (TFA) of more than 10º had a TMDA exceeding 11º. They recommended presumption of Blount's disease, if the TMDA is more than 16º. Hagglund et al⁶⁰ concluded that the TMDA has a limited prognostic value for distinguishing between physiological bowing and Blount's disease. It was stressed that in an individual case a single measurement of the TMDA cannot be used to determine whether the bowing will be progressive, and require treatment. Even a bowing with a TMDA over 20º can occasionally recover spontaneously. Davids et al³⁰ realized the limitations of a single non-standardized TMDA measurement in determining the progression of bowlegs and therefore treatment. In their investigation, they concluded that children with TMDA < 10º, or TMDA =10º and EMA =20º, are at less risk for development of Blount disease and may be followed clinically by their primary physician at routine intervals, with no further radiographic studies. Children with TMDA =10º and EMA >20º appear to be at greater risk for development of Blount disease and should be followed closely.

Richards et al⁹⁸ reported improvement after brace treatment in 65% of patients with Langenskiold stage II patients in whom 18 of 24 limbs (75%) resolved spontaneously. Zionts and Shean¹²⁵ reported that treatment with braces for early infantile tibia vara, which showed no improvement by two years of age, was effective in 29 of 42 limbs (69%). According to these indications, Shinohara et al¹⁰³ would have to apply braces to 40 limbs (87%), which showed spontaneous recovery without treatment. Raney et al⁹⁷ advised brace treatment for patients with MDAs of >16° or between 9° and 16° who had clinical risk factors. If the authors¹⁰³ had applied these criteria, 27 limbs in their series would have required braces, whereas only three did not resolve spontaneously. The rate of spontaneous resolution approximates to the successful outcomes reported for brace treatment. Shinohara et al concluded that brace treatment may not be necessary even if the MDA is > 11º and the proximal medial tibia is classified as Langenskiold stage II to stage III.

Schoenecker et al¹⁰¹ performed a retrospective review on 32 patients seen for Blount's disease. Five patients were definitively treated with bracing; five extremities were rated as good and one poor. The average initial TMDA was 14.8º and a 17.1º TFA. All patients in this study had a TMDA of >11º which increased in direct proportion to the extent of involvement. This review demonstrated good results if brace treatment was initiated early. Currently, the authors suggest bracing children < 2 years of age with Langenskiold stage I or II Blount's disease and varus deformity of ≥15º. If the deformity does not resolve with brace treatment, surgical correction is indicated.¹⁰¹

Zionts et al¹²⁵ reviewed 24 children (42 extremities) who had a diagnosis of early infantile tibia vara treated with bracing. The indication for bracing was either a varus deformity that was not improving by age 18-24 months, or a persistent varus deformity seen in a patient older than 24 months. The braces were worn during the day and removed at night. Results revealed that 29 extremities were in Langenskiold stage I, 11 were stage II, and two were stage III. Before treatment, the TMDA averaged 16.4º. Forty of the 42 extremities had TMDA of >11º, and 20 were >16º. Based on the criteria of the authors, the outcome was good in 29 extremities, nine fair, and four poor. The authors concluded that daytime, ambulatory brace treatment may favorably alter the natural history of tibia vara in patients who are younger than 3 years and who have Langenskiold stage I or II deformity.

Kumar et al⁷⁷ presented a series of 18 patients with infantile tibia vara. All were Langenskiold stages I and II. They were treated with nighttime bracing in either a Blount brace or a Denis-Browne splint. Although the authors noted improvement in the TFA, they conceded that the tibial-plateau depression had not improved by the time the braces were stopped. Loder and Johnston⁸² described 23 involved tibiae treated in either mermaid splints or bilateral upright knee-ankle-foot orthoses. Their treatment regimen was not described. They did note 12 successes and 11 failures with nonoperative treatment. In a follow-up study from the same institution that included 28 involved tibiae, Dales et al.²⁹ reported a 57% failure rate of brace treatment.

In a study by Richards et al⁹⁸ the effectiveness of brace treatment in early infantile Blount's disease of 27 with Langenskiold stage II were studied. Ten patients had bilateral disease (two of the patients had stage III disease affecting one side). Successful outcomes were achieved in 19 (70%) patients, the majority of them having unilateral disease. Of the 37 affected extremities, 24 (65%) had successful outcomes. Eight patients (13 extremities) required tibial osteotomies and were classified as bracing failures. Seven of the eight patients had bilateral disease. Therefore, bracing failed in seven (70%) of 10 of the patients with bilateral infantile Blount's disease. Only one of 17 patients with unilateral involvement failed the brace program. Eighteen patients were at or above the 95th percentile for weight. The authors concluded that bracing appears to be effective in stage II infantile Blount's disease, particularly in those with unilateral involvement.

Raney et al⁹⁷ reviewed outcomes of orthotic treatment in patients who received orthoses for genu varum due to pathologic tibia vara with risk of progression. The focus of the study was those patients with a TMDA of >16º or between 9º and 16º with a clinical risk factor for progression. In 1993, Feldman and Schoenecker⁴⁶ noted that for TMDAs >16º or < 9º, the confidence interval of a diagnosis of ITV increases to 95%. Orthotic treatment was initiated in patients with a TMDA of >16º, but < 9º, no treatment was recommended. Those patients with a TMDA between 9 and 16º were observed closely and treated if ligament laxity was present, as demonstrated by a lateral thrust on ambulation. Risk factors considered were ligamentous instability, obesity, asymmetry, and being black, or Hispanic. Thirty-eight patients with 60 tibiae were included. The success rate was 90% for those treated orthotically. Risk factors for failure (six cases) were instability, obesity, and delayed bracing. In cases with TMDAs >16 deg, the success rate was 86%. The results of orthotic treatment, restricted to patients meeting the stated parameters, represent improvement on the reported natural history.

Surgical Treatment

If the deformity does not improve with orthotic treatment and the disease progresses radiographically to advanced stage II or stage III deformity, surgical correction is indicated. Furthermore, surgery is recommended for a deformity that is increasing in severity and disabling the child, or if the child has a TFA greater than 15º, a TMDA greater than 14º, and a TMEA greater than 30º³³ Absolute definite indications for surgery are depression of the tibial plateau, impending closure of the medial physis of the upper tibia (stage IV), and ligamentous laxity of the knee¹¹⁵ Generally, operative treatment in the infantile form is recommended for severe or progressive angular deformity. No author has recommended surgery for children < 2 years of age because the deformity may be exaggerated physiologic genu varum.¹⁰⁷ Hofmann et al⁶⁵ stated that 3 years is the minimal age for considering osteotomy for Langenskiold stages I-III disease, whereas Schoenecker and others^40,101 suggested that 4 years might be the critical age beyond which there is a greater chance of recurrence of deformity after osteotomy. Doyle et al⁴⁰ noted that failure to correct the tibia vara deformity early results in permanent physeal damage, with resultant development of degenerative intraarticular knee pathology.

Complications associated with the surgical treatment of Blount's disease may include loss of alignment, vascular impairment, pathologic fractures, wound infection, and malalignment.^22,33,101

OBESITY

Obesity is the most prevalent disorder among children and adolescents in the United States, approximately 1 in 5 children in the United States is now overweight.⁶ Obesity in childhood and adolescence represents a serious concern and a challenge to the medical and lay communities. Major impacts include effects on blood pressure, intermediary metabolism, respiratory function, psychological well being, social adaptation, and educational performance. Obesity is associated with significant adult morbidity, including long-term effects on cardiovascular health and premature mortality. A number of orthopedic disorders, including genu valgum, slipped capital femoral epiphysis, and tibia vara, are observed more commonly in children with obesity.⁵¹

Operational definitions of obesity in adults are derived from statistical data analyzing the association between body mass and risks of acute and long-term morbidity and mortality.⁹² Because acute medical complications of obesity are less common in children and adolescents than in adults, and because longitudinal data on the relation between childhood weight and adult morbidity and mortality are limited and difficult to interpret, no single definition of obesity in childhood and adolescence has gained universal approval. Some investigators have used the terms overweight, obese, and morbidly obese to refer to children and adolescents whose weights exceed those expected for heights by 20%, 50% and 80-100%, respectively. Given that weight varies in a continuous rather than a stepwise fashion, the use of these arbitrary criteria is problematic and may be misleading.⁵¹

The body mass index (BMI) is a continuous, though imperfect, measure of body fatness. Calculated as weight (kg) divided by height (m²), BMI corrects for body size and can be quantified readily and reliably in clinical settings. The BMI correlates closely with total body fat scan in children who are overweight and obese. Recently, consensus committees have recommended that children and adolescents be considered overweight or obese if the BMI exceeds the 85th or 95th percentiles on curves generated from the 1963-1965 and 1966-1970 surveys or is more than 30 kg/m² at any age.⁹² For children 2 years or older, BMI-for-age is used to assess overweight. Five percent of children are expected to be above the 95th percentile of BMI-for-age, defined as overweight, due to normal biologic variation. A prevalence greater than the expected rate of 5 percent indicates that the population has a higher proportion of individuals with overweight than would be expected in the general population. There is no BMI-for-age references or consistent definitions for overweight for children younger than 2 years. However, nutrition programs have used weight-for-length recommendations to determine overweight.^19,67 Consequently, overweight in this age group is defined as at or above the 95th percentile of weight–for-length.

Obesity is a common disease in industrialized countries and we observe an increasing prevalence of early onset in childhood: at present it is the most prevalent nutritional disease of children and adolescents in the United States.³⁵ Obesity is frequently a factor when patients present with infantile Blount's.²⁸ It has been suggested that Blount's Disease represents a form of Obesity.²⁵

During childhood and adolescence, accumulation of excess fat mass occurs when total energy intake exceeds total energy expenditure, including the allowance for normal growth. This energy imbalance can result from excessive energy intake and /or reduced energy expenditure for body metabolism, thermoregulation, and physical activity. Genetic and hormonal disorders, however, do not explain the excess weight gain observed in most patients who have obesity and are referred to physicians for evaluation and treatment. Most overweight children have a familial form of obesity that results from multiple environmental factors. Correlations between parent and child habitus likely reflect, at least in part, the family patterns of food intake, exercise, selection of leisure activity, and family and cultural patterns of food selection. Nevertheless, evidence from twin, adoption, and family studies suggests that genetic factors also play a considerable role in the development of childhood obesity.⁵¹

Incidence/Prevalence of Childhood Obesity

The definitions of overweight and obesity in children differ between epidemiological studies, making comparisons of cross-sectional prevalence data difficult. Nevertheless, several studies have examined change in prevalence within populations over time, and the results of these analyses are astounding. Rates have increased 2-3 fold to 3-3 fold over about 25 years in the USA, 2-0 fold to 2-8 fold over 10 years in England, and 3-9 fold over 18 years in Egypt.^{24,32,48,83,89,91,120} The distribution of BMI has shifted in a skewed fashion, such that the heaviest children, at greatest risk of complications, have become even heavier.⁴⁹ This epidemic has affected a wide age range, most ethnic groups, and people of every socioeconomic status, though sometimes in disproportionate ways.^14,109 In the USA, prevalence rose more than twice as fast among minority groups compared with white groups, exacerbating pre-existing racial-ethnic disparities.¹⁰⁹ The urban poor in developed countries might be especially vulnerable because of poor diet⁷⁰, and limited opportunity for physical activity.⁵⁵ Conversely, childhood obesity is most frequent in upper socioeconomic strata of developing nations, where over nutrition and under nutrition coexist, probably owing to adoption of an increasingly Western lifestyle.^39,41,85,96

Using the BMI criteria, the most recent national surveys demonstrate that 21-24% of American children and adolescents are overweight and that 10-11% have obesity. These findings indicate that the prevalence of overweight (BMI = ≥85th percentile) children and adolescents in the United States has increased by 50-60% in a single generation, while the prevalence of obesity has doubled.

The long-term implications of obesity during infancy and early childhood on subsequent health are less clear. In general, the proportion of children with obesity who have obesity as adults increases with increased age at onset of obesity, such that 26-41% of preschoolers with obesity have obesity as adults, compared to 42-63% of school-aged children.⁵¹

There is no doubt that an association between obesity and several musculoskeletal disorders exist. The clinical characteristics of most study groups with tibia vara are very similar and often focus on marked obesity besides normal height, black race and slowly progressive genu varum.^34,59 Dietz et al³⁴ reported a series of 18 patients with infantile- and juvenile- onset disease. Twelve children (67%) had weights-for-height greater than 120% ideal body weight (mean 156% ideal body weight) as well as a highly significant correlation between the body weight and the TFA; the authors concluded that the degree of obesity might be a primary determinant of tibial deformity.

DISCUSSION

Tibia vara (Blount's disease) is a disease of unknown etiology that affects the metaphysis, the growth plate and the epiphysis of the posteromedial aspect of the proximal tibia, resulting in a varus and internal torsion deformity.^11,60 The principle of orthotic management in infantile tibia vara is alteration of abnormal compressive forces so that normal growth will resume and the genu varum will be corrected. In 1966 Blount recommended treatment in all infants with excessive bowing that does not begin to correct at 18 months should be placed in braces. Extreme deformity at any age requires immediate osteotomy.¹²

The diagnosis of ITV is based on the radiographic criteria of Langenskiöld and Riska.⁷⁹ In the early stage, it is radiographically difficult to distinguish between physiological bowing and Blount's disease. The tibial metaphyseal-diaphyseal angle (TMDA), described Levine and Drennan,⁸¹ was considered helpful in distinguishing cases that did not yet have the typical radiographic changes in Blount's disease, despite measurement error.

Until recently, the Levine-Drennan tibial metaphyseal-diaphyseal angle has been the recommendation for prognosis and treatment of children with ITV in the clinical setting. Davids et al³⁰ showed that errors in the radiographic technique used to produce the Levin-Drennan angle might lead to many false-positive results. These errors include a failure to consider the effect of transverse plane alignment, knee flexion and the inclusion of children who already exhibit Langenskiold changes on the initial radiograph.^46,60,81 Therefore, Davids et al³⁰ recommends a standardized radiographic technique to control for rotational alignment of the lower extremity with the application of both the tibial metaphyseal-diaphyseal angle as well as the epiphyseal-metaphyseal angle, when combined produce the lease amount of false-positive and the most amount of false-negative results.

The results of the only known published prospective randomized study by Shinohara et al¹⁰³ evaluated the natural history study without treatment of 46 limbs in 29 patients with ITV and a TMDA of more than 11º. In 22 limbs, which were not in Langenskiold II to III, 18 resolved spontaneously by age of six years. There was no difference in the rate of resolution of the deformity between those patients who had been treated by a brace and those who had received not treatment. Thus, the authors do not recommend initial treatment, even in patients with Langenskiold stage-II to stage-III deformity. When a deformity persists or progresses, brace treatment or surgical intervention should then be carried out.

There is continued controversy regarding treatment of Blount's disease. Some authors claim that the disease is always progressive and that treatment with orthoses or surgery should begin without delay.⁷¹ However, spontaneous improvement has been described.^{12,81,107,123} Significantly, none of these articles reporting the natural history of spontaneous resolution (with the exception of Shinohara) documented specific inclusion criteria for patients.

In a study by Giwa et al⁵³ the authors explored the possible role of antioxidant micronutrients (zinc, copper and manganese) in the etiology of Blount's disease in the African region of Nigeria. Burnt-out rickets (patients with biochemical and radiological diagnosis of rickets who after treatment still have residual bone changes despite normal bone biochemistry) is the primary concern, but the patient's also present with similar clinical and radiological features as Blount's disease.

Bathfield and Beighton⁹ reported that results of routine laboratory investigations in patients suffering from Blount's disease were usually within normal limits. Although the importance of calcium and phosphate metabolism in bone disorders is well recognized, antioxidant micronutrients also play important roles in normal bone homeostasis, bone health and metabolism.¹¹⁸ The deficiency of these micronutrients may contribute to bone disorders. The serum levels of calcium, inorganic phosphate, zinc, copper, and alkaline phosphatase in 15 patients aged between two and five years with clinical and radiographic features of Blount's disease were determined. There were no patients who had a BMI greater than 30, disqualifying obesity, a finding which is at variance with some studies. The absence of strict obesity among the patients of this study may suggest that obesity may not be a key risk factor in the etiology of Blount's disease in an environment where malnutrition is still prevalent.

The serum concentrations of inorganic phosphate, copper and calcium, though lower in patients with Blount's disease compared with control, did not reach statistical significance. Alkaline phosphatase activity was increased in the serum of all patients with Blount's disease. In addition, there was an observed significant reduction in serum concentration of zinc compared to the control subjects. According to the authors, these biochemical observations, especially that of zinc, may serve as a basis for differentiation of clinically inseparable disorders such as Blount's and rickets and may aid in early differential diagnosis, appropriate treatment as well as prevention of complications (53).

CONCLUSIONS

Early diagnosis of ITV is important, because treatment outcomes are clearly superior in younger children, presumably because the biomechanical overload can be corrected prior to irreversible damage having been done to the proximal tibial growth mechanism.^{26,40,47,65,101,107} The definitive diagnosis of ITV remains documentation of progressive varus deformity over time, occurring in conjunction with the development of Langenskiold changes on plain radiographs of the lower extremity.^{11,30,46,71,79,82,101} Although the origin of infantile tibia vara has not been clearly established, most investigators believe mechanical factors play a key role.^{13,26,34,47,54,74,82,125} They postulate early walking, when physiologic genu varum is at its peak, leads to impaired growth of the proximal medial tibia because of the Heuter-Volkmann principle (increased pressure on an epiphysis inhibits growth). Intuitively one would expect weight bearing to be the most important factor, (i.e., daytime use), but some authors suggest nighttime-only bracing and is subject to further review.^56,97

Some authors believe that bracing has been ineffective (possibly because of difficulty maintaining a proper orthotic fit with growth, poor compliance, and discomfort from considerable pressures applied to the limbs with brace wearing. For these reasons brace compliance has been poor.³⁰ With documented progressive varus deformities and a Langenskiold stage 2 or greater surgical realignment appears to be the management of choice. Numerous authors have made reference to the merits of bracing in early Blount's disease.^{7,11,52,101,115}

Although in most investigations the relationship between the onset of obesity and the onset of Blount's disease could not be determined due to retrospective study designs, there is enough evidence to conclude a causal effect of elevated body weight in the pathogenesis of the disease. Therefore, it is justified to suggest that the development of obesity in a child with physiologic bowing should be viewed with concern and efforts should be directed at weight reduction. Childhood obesity is a multisystem disease with potentially devastating consequences.⁴¹ Considering the adverse effects of elevated body weight on the musculoskeletal system, we must increase our efforts to lower the incidence and prevalence rates of overweight and obesity in children, adolescents and adults.

The role of orthotic management and surgery in patients with Blount's disease has been debated. Some authors believe that brace treatment may have a role early in the course of the disease^{12,47,56,65,74,82,101,116}, whereas others believe that osteotomy is the most appropriate treatment.^{54,78,79,87,107,125} In treating Blount's disease, the effectiveness of orthotic devices is open to question because some cases are known to spontaneously resolve. This benign course for some cases makes it difficult to find a scientific explanation for the effectiveness of orthotic treatment.¹¹⁶

Infantile tibia vara (ITV) or Blount's disease is probably the most frequent type of pathologic bowleg. It is a developmental condition that has been very difficult to differentiate between physiologic genu varum, thus early diagnosis is critical for a positive prognosis and treatment regimen. For improved orthotic treatment outcomes the following should be applied; first, treatment regimens must be more accurately described. Second, the need to develop a more compliant design. Third, a classification system that can be readily applied, assist in treatment decisions or prognosis, and have an acceptable level of reproducibility and reliability.

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