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Approach to the child with knock-knees

Scott B Rosenfeld, MD
Section Editors
William Phillips, MD
Teresa K Duryea, MD
Deputy Editor
Mary M Torchia, MD


Knock-knees (genu valgum) is an angular deformity at the knee where the apex of the deformity points toward the midline (figure 1). Bow-legs (genu varum) is an angular deformity at the knee where the apex of the deformity points away from the midline.

Bow-legs and knock-knees are among the most common musculoskeletal anatomic variations encountered by pediatric primary care providers and a common reason for referral to a pediatric orthopedic surgeon. However, most children with knock-knees or bow-legs have variations of normal lower-extremity development and can be monitored by the primary care provider.

An understanding of the normal physiologic development of the lower extremity is essential in differentiating physiologic from pathologic alignment. Pathologic causes of knock-knees include posttraumatic (eg, Cozen fracture), rickets (eg, renal osteodystrophy), skeletal dysplasias, mucopolysaccharidosis, and neoplasms. Unlike physiologic knock-knees, these conditions generally do not improve over time and may require treatment with bracing or surgery.

This topic will provide an overview of normal physiologic alignment of the lower extremity, physiologic and pathologic causes of knock-knees, and an approach to the child with knock-knees. Bow-legs are discussed separately. (See "Approach to the child with bow-legs".)


An understanding of normal physiologic development of the lower extremity is essential to differentiation of physiologic from pathologic deformities. Lower-extremity alignment goes through a predictable progression from varus (bow-legs), to neutral, to valgus (knock-knees), and back towards neutral over the first seven years of life (figure 2 and figure 3) [1]. Final adult lower-extremity alignment is slightly valgus. There is a wide range of normal values [1,2].

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Literature review current through: Nov 2017. | This topic last updated: Jun 06, 2017.
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