The natural progression of bow-leggedness in a 6-month-old boy

A 6-month-old boy presented with bowing of both lower legs. He was mostly breastfed and received Vitamin D supplementation. His past medical history was unremarkable. There was no history of trauma. On examination, his weight (60th percentile) and height (95th percentile) were normal. His lower extremities revealed severe bilateral intoeing and tibial torsion (Figure 1). His laboratory values for calcium, phosphate, alkaline phosphatase, and vitamin D were normal. At 3 years of age, the boy displayed knock-knees (Figure 2). His growth and development continued to be normal. Genu varum at 6 months of age. Note: the lower leg is angled inward (medially) in relation to the thigh’s axis, giving the limb an appearance of an archer’s bow. Genu varum at 6 months of age. Note: the lower leg is angled inward (medially) in relation to the thigh’s axis, giving the limb an appearance of an archer’s bow. Genu valgum at 3 years of age of the patient in Figure 1. Note: Genu valgum, commonly called ‘knock-knee’ is a condition in which the knees angle inward and touch each other when the legs are straightened. Genu valgum at 3 years of age of the patient in Figure 1. Note: Genu valgum, commonly called ‘knock-knee’ is a condition in which the knees angle inward and touch each other when the legs are straightened. Genu varum is the Latin term used to describe bowed legs. The condition may present at birth and gradually resolve by the second year of life, without medical intervention (1). The bow-legged appearance occurs as children externally rotates their tibia to put the foot straight ahead when ambulating. Consequently, there is an angular deformity at the knee where the apex of the deformity points away from midline. This deformity is referred to as developmental or idiopathic genu varum (2). However, during the third or fourth year of life, the deformity often progresses to genu valgum (Figure 2) or a knee misalignment characterized by in-turned knees. Spontaneous resolution is expected by about 7 years (1). The process is similar for boys and girls. A primary care protocol was constructed to differentiate pathological versus physiological genu varum. Characteristics of physiologic bow-leggedness include average age of ambulation at 10 months and mean age of presentation at 16 months. Further, sequential measurement of genu varum was found to be the most useful differentiator showing resolution and evolution into genu valgum by 3 years of age (2). Other features may include tibiofemoral angle within two standard deviation of normal, bilateral, and symmetrical involvement, no lateral thrust with ambulation, and normal stature and apparent good health. The most common form of pathological genu varum is Blount’s disease or tibia vara (3). This condition results from a growth disturbance in cartilage development localized to the postero-medial proximal tibial physis. In the initial stages, radiographical difference between Blount’s disease and physiological genu varum is difficult. As such, careful follow-up and subsequent radiological imaging is crucial (3). Other recognized etiologies of pathological genu varum are rickets, post-traumatic and skeletal dysplasia. These may be distinguished from physiological genu varum by their clinical course, time of initial presentation, and diagnostic imaging findings. Rickets is a disease characterized by poor bone mineralization resulting from a deficiency of vitamin D, calcium, or phosphate. Furthermore, radiographic discrepancies from physiological genu varum may include diminished bone density and widened metaphysis (4). Post-traumatic genu varum is frequently unilateral and does not appear in the first year of life (5). Achondroplasia, the most common skeletal dysplasia, is characterized by shortening and thickening of the long bones. Medical management of pathological genu varum depends on the underlying cause, such as rickets. Surgical therapy or brace treatment may be indicated for patients with Blount’s Disease or skeletal dysplasia (6). Prominent lower extremity deformities in healthy children are distressing to parents. Paediatricians can emphasize the benign nature of physiological genu varum, understand the natural history, and provide reassurance of its spontaneous resolution. Funding: There are no funders to report for this submission. Informed Consent: Family consent has been obtained in writing for publication of this case. Financial Disclosure: There are no financial relationships relevant to this article to disclose from all the identified authors. Potential Conflicts of Interest: All authors: No reported conflicts of interest. All authors have submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest. Conflicts that the editors consider relevant to the content of the manuscript have been disclosed.

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