Approach to the Problem
Angular deformities of the lower extremities, known as leg bowing (genu varum) and knock-knees (genu valgum), are common orthopedic diagnoses in early childhood. Leg bowing and knock-knees are most often physiologically normal, as the angle of the knee changes with age. Infants typically have bowlegs, which are often not noticed by parents until children begin to stand and walk. The varum angle declines until 3 years of age, when the majority of children appear knock-kneed. Valgus angulation lessens to the more neutral angle of adults by 6 to 7 years of age. Lack of gradual resolution, asymmetry of extremity findings, and progression of angulation are indications of a pathologic etiology, and require further evaluation and possible intervention.
Key Points in the History
• Deviation from the expected natural history or asymmetry of bowlegs and knock-knees are concerning for nonphysiologic etiologies.
• Growth history and timing of symptoms are essential to distinguishing between physiologic, systemic, and mechanical etiologies.
• Genu varum or valgum in infancy associated with a patient and family history of short stature could indicate skeletal dysplasia.
• Patients with hypophosphatemic rickets, also known as vitamin D-resistant rickets, often have a history of poor linear growth and a family history of genu varum.
• Nutritional rickets, also known as vitamin D-deficiency rickets, should be considered if the patient was breastfed without receiving vitamin D supplementation, has abnormal dietary habits, or has limited sun exposure.
• Infantile tibia vara, the more common form of Blount disease, is usually found in obese African American females younger than 3 years of age who walked before 11 months of age.
• Adolescent tibia vara is typically found in obese African American males older than 8 years of age who walked before 11 months of age.
• Asymmetric valgus or varus deformities can be found following lower-extremity fractures or infections.
• Worsening genu valgum during the ages of expected physiologic valgus, without a history of trauma or infection, is concerning for renal osteodystrophy.
Key Points in the Physical Examination
• If the child is less than 2 years old with symmetric bowing and a tibiofemoral metaphyseal–diaphyseal angle falling within two standard deviations of the mean and otherwise has a normal history and physical examination, it is considered to be physiologic genu varum.
• Physiologic bowing is often characterized by the entire lower extremity appearing bowed, whereas greater apparent deformity in the proximal tibia can indicate a nonphysiologic cause.
• If the child is 2 to 8 years old with symmetric knock-knees and a tibiofemoral metaphyseal–diaphyseal angle falling within two standard deviations of the mean and otherwise has a normal history and physical examination, it is considered to be physiologic genu valgum.
• The differential diagnosis can be narrowed depending on whether or not physical findings are asymmetric, are isolated to the lower extremities, or are associated with other anomalies, such as short stature.
• A lateral thrust of the knee joint in stance while observing walking is characteristic of pathologic genu varum; however, its absence does not always indicate a physiologic process.
• Worsening genu valgum on examination after age 8 is highly suggestive of underlying pathology.
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PHOTOGRAPHS OF SELECTED DIAGNOSES |
Figure 46-1 Infantile tibial bowing. Outward angulation of the tibia bilaterally in an infant. (Courtesy of Shriners Hospitals for Children, Houston, Texas.)
Figure 46-2 Infantile tibial bowing. Outward angulation of the tibia is also notable in the posterior view of the infant with tibial bowing. (Courtesy of Shriners Hospitals for Children, Houston, Texas.)
Figure 46-3 Genu varum. Outward angulation of the knees in a child. (Courtesy of Shriners Hospitals for Children, Houston, Texas.)
Figure 46-4 Genu varum. Posterior view of a child with genu varum. (Courtesy of Shriners Hospitals for Children, Houston, Texas.)
Figure 46-5 Blount disease. Genu varum deformity is seen in this obese male with Blount disease. (Courtesy of Shriners Hospitals for Children, Houston, Texas.)
Figure 46-6 Physiologic Genu Varum and Genu Valgum. Physiologic genu varum (bowlegs) in a toddler (left) and genu valgum (knock-knees) in a toddler (right), which is often seen in children between 2 and 6 years of age. (Used with permission from Weinstein S.L., Buckwalter J.A. [1994]. Turek’s orthopaedics [5th ed.] Philadelphia: J.B. Lippincott.)
Figure 46-7 Genu valgum. Inward angulation of the knees seen in this child. (Courtesy of Shriners Hospitals for Children, Houston, Texas.)
Figure 46-8 Genu valgum. A toddler with notable inward angulation of the knees. (Courtesy of Bettina Gyr, MD.)
DIFFERENTIAL DIAGNOSIS
Other Diagnoses to Consider
• Bony tumors or malignancies
• Connective tissue disorders (e.g., Ehlers–Danlos syndrome, Marfan syndrome)
• Fluoride or lead intoxication
• Hemophilia
• Lysosomal storage disorders (e.g., Gaucher disease, Morquio syndrome)
• Neurofibromatosis
• Osteoarthritis
• Osteogenesis imperfecta
• Osteoporosis
• Rheumatoid arthritis
• Tibial or fibular hemimelia (congenital genu varum or genu valgum)
When to Consider Further Evaluation or Treatment
• Patients should be evaluated clinically every 3–6 months if findings appear consistent with physiologic genu varum or genu valgum. Obtain radiographs, and consider referral to an orthopedic specialist if individual deviates from expected natural history of physiologic genu varum or valgum, such as persistence or progression of angulation beyond expected ages.
• Clinical history that includes dietary anomalies, prior trauma or infection, or growth anomalies (large or small for age) should raise suspicion for possible pathologic etiologies and warrants radiographic evaluation and possible evaluation for metabolic bone disease. Results of further evaluation should guide specialist referrals.
• Physical examination showing asymmetry or unilateral involvement of extremities or other anomalies, such as short stature or dysmorphic features, should increase suspicion for nonphysiologic causes. Obtain radiographs, and consider metabolic bone disease and/or dysplasia assessment. Results of further evaluation should guide specialist referrals.
• Genu varum and genu valgum in metabolic bone disease are initially managed medically. Referral to the appropriate specialist—typically an endocrinologist and/or nephrologist—is essential. Involvement by an orthopedic surgeon may still be required for surgical management later.
• Genu varum and genu valgum in children with skeletal dysplasias typically require orthopedic surgical intervention.
SUGGESTED READINGS
Cheema JI, Grissom LE, Harcke HT. Radiographic characteristics of lower-extremity bowing in children. Radiographics. 2003;23(4):871–880.
Cozen L. Knock-knee deformity in children. Congenital and acquired. Clin Orthop Relat Res. 1990;(258):191–203.
Do TT. Clinical and radiographic evaluation of bowlegs. Curr Opin Pediatr. 2001;13(1):42–46.
Herring JA, ed. Tachdjian’s Pediatric Orthopedics. 4th ed. Philadelphia, PA: NB Saunders Company; 2008:973–1004.
Morrissy RT, Weinstein SL, eds. Lovell and Winter’s Pediatric Orthopaedics. 6th ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2006:1165–1189.
Staheli LT, ed. Practice of Pediatric Orthopedics. 2nd ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2006:81–85.