Pediatric Genu Varum

Updated: Oct 26, 2017
  • Author: Peter M Stevens, MD; Chief Editor: Jeffrey D Thomson, MD  more...
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Overview

Background

Genu varum is a Latin term used to describe bow legs. This condition may present from infancy through adulthood and has a wide variety of causes. As it becomes more severe, the patient may exhibit lateral knee thrust and a waddling gait. There may be associated in-toeing and secondary effects on the hip and ankle. The problem may be unilateral, with a functional limb-length discrepancy, or bilateral. The family and medical history may reveal clues to the likelihood of persistence or progression.

It is widely recognized that up to age 2 years, infants may have physiologic bowing of the lower extremities. The hallmark of this condition is symmetrical and painless bowing, usually associated with in-toeing and often with a propensity for tripping. This problem will resolve spontaneously without treatment, as a result of normal growth. [1, 2, 3]  All that is required is parental education and periodic follow-up to verify resolution. During the wait for the predicted spontaneous correction, reversing the shoes may reduce the frequency of tripping.

The prevalence of this condition is not known, but it is frequent enough to be considered a variation of normal in toddlers. Nevertheless, it is a relatively common cause of parents’ seeking medical attention from their primary care providers, who should be knowledgeable in the triage of these conditions. Only in the most persistent or worrisome cases is orthopedic consultation warranted. Radiographs, though optional as a rule, may be needed to differentiate physiologic varus from pathologic conditions that call for treatment. [4]

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Pathophysiology

In normal alignment, the lower-extremity lengths are equal, and the mechanical axis (center of gravity) bisects the knee when the patient is standing erect with the patellae facing forward (see the image below). This position places relatively balanced forces on the medial and lateral compartments of the knee and on the collateral ligaments, while the patella remains stable and centered in the femoral sulcus.

Mechanical axis is measured on full-length weightb Mechanical axis is measured on full-length weightbearing radiograph by drawing line from center of femoral head to center of ankle. Normally, it should bisect knee, with joint horizontal and parallel to ground. Genu varum is defined by medial displacement of mechanical axis. Shown here is tibia vara and slight lateral ligamentous laxity contributing to deformity.

In children younger than 2 years, physiologic genu varum is common but is self-limiting and innocuous. In older children with pathologic genu varum, as the knee drifts laterally, the mechanical axis falls in the inner quadrant of the knee; in severe cases, it does not even cross the knee (see the image below).

Three factors contributing to genu varum: femur va Three factors contributing to genu varum: femur varum, ligamentous laxity, and tibia vara. Mechanical axis is further deviated medially.

As a result, the medial femoral condyle and the medial plateau of the tibia are subjected to pathologic loading. The Heuter-Volkmann effect will compress the physis and the cartilaginous anlage of these structures and inhibit the normal ossification of the epiphysis. The lateral collateral ligaments are stretched, sometimes beyond their compliance, permitting the characteristic lateral thrust of the knees during gait.

When the mechanical axis deviates into or beyond the medial quadrant of the knee, regardless of the etiology, a number of clinical problems may ensue. Lateral ligamentous strain may be associated with recurrent knee pain, lateral thrust, in toeing, and the evolution of a waddling gait.

The natural history of untreated genu varum is not benign. During the adult years, premature and eccentric stress on the knee may result in medial meniscal tears, tibiofemoral subluxation, articular cartilage attrition, and arthrosis of the medial compartment of the knee. Nonoperative management that relies on shoe modification, physical therapy, and so-called Forrest Gump bracing is of no proven value.

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Etiology

The recognized etiologies for genu varum include the following:

Tibia vara (Blount disease) is growth disturbance Tibia vara (Blount disease) is growth disturbance of proximal medial tibia that can present any time from infancy to adolescence. Natural history is one of inexorable progression, premature closure of upper medial tibial physis, lateral thrust, ligamentous laxity, and, ultimately, joint instability and degeneration. At age 5, guided growth would have been sufficient. After physeal closure, complex osteotomies are required.
Hypophosphatemic rickets is disturbance in vitamin Hypophosphatemic rickets is disturbance in vitamin D metabolism that weakens physes through delayed ossification. Consequent deformities may progress despite careful medical management and bracing. Deformities are typically bilateral, involving both femur and tibia.

An association between soccer playing and genu varum has been suggested. [5, 6]

Regardless of the etiology of pathologic genu varum and regardless of the patient’s age, surgical correction of significant and symptomatic malalignment is warranted.

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Epidemiology

Physiologic genu varum, defined as occurring in children younger than 2 years, is exceedingly common but is self-correcting. In contrast, pathologic genu varum, which is due to a variety of conditions, is much less prevalent, especially with increasing age. Among the known causes are tibia vara (Blount disease), rickets, and skeletal dysplasias. The collective frequency of these conditions is not specifically known, but they are common triggers for pediatric orthopedic referral.

In countries where malnutrition is widespread and access to medical care is limited, the overall incidence of genu varum is undoubtedly higher. Whereas polio has been largely eradicated, other infectious diseases and mistreated (or untreated) traumatic injuries make physeal damage a frequent cause of progressive and disabling clinical deformity.

Likewise, untreated congenital anomalies, genetic disorders, metabolic conditions, and rheumatologic diseases may all cause progressive genu varum. Finally, in any country, one may encounter iatrogenic postoperative genu varum.

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Prognosis

The outcome of guided growth for genu varum is dependent on patient selection and timing. As noted earlier, this technique is contraindicated for physiologic genu varum and will be of no benefit after skeletal maturity has been attained. At least 6 (and preferably 12) months of predicted growth is needed to derive any benefit.

For the remainder of patients, regardless of age or diagnosis, guided growth holds promise for complete correction of the deformity and may reduce or eliminate the need for more invasive osteotomies. For specific endocrinologic conditions, concomitant medical management is required.

The parents must have a vested interest in the success of the procedure and must understand that although the incisions are small and the correction gradual, the onus is on them to return for follow-up appointments at the specified intervals (typically every 3 months while the implants are in place).

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