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.

• 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.

• 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.

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