Clinical evaluation of bowed legs in children

Early radiographic screening and/or referral to a clinical specialist are often used to distinguish between physiologic bow leg deformity and infantile tibia vara disease in young children. These practices are a consequence of the clinician's inability (based upon the clinical examination) to distinguish between the deformities associated with physiologic and pathologic bow legs. Because the great majority of these children have physiologic bowing, routine radiographic screening and referral are not cost effective and expose children to unnecessary radiation. This study describes and evaluates the efficacy of a simple clinical examination technique, the 'cover up' test, to identify young children with bow legs who are at high risk for having infantile tibia vara. The 'cover up' test qualitatively assesses the alignment of the proximal portion of the shank or lower leg 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. Eighteen children with infantile tibia vara, 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 infantile tibia vara had a positive 'cover up' test (sensitivity = 1.00). Eighteen of 25 children with a positive 'cover up' test actually had or developed infantile tibia vara (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). We conclude that the 'cover up' test is an effective screening tool for the assessment of bow legs in children between 1 and 3 years of age. 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.