Angular Variations: Genu Varum (Bowleg) and Genu Valgum (Knock-Knee)

CHAPTER 26

Angular Variations: Genu Varum (Bowleg) and Genu Valgum (Knock-Knee)

Introduction/Etiology/Epidemiology

• Physiologic angulation

— Angular variations at the knee (bowleg [varus] or knock-knee [valgus]) that fall within 2 standard deviations of the mean

— Angular orientation of the lower limbs follows a predictable pattern of normal development during childhood.

■Before 2 years of age, most children demonstrate up to 15 degrees of physiologic genu varum (bowleg).

■By 2 years of age, spontaneous improvement occurs and neutral alignment is the norm.

■Children then proceed to develop exaggerated valgus, which peaks by about 3 to 5 years of age and then corrects toward the normal adult value of 5 to 7 degrees of valgus by age 8 years.

■Physiologic genu varum and valgum are typically symmetrical.

• Idiopathic angulation

— Angular variations at the knee (bowleg or knock-knee) that fall outside 2 standard deviations of the mean (Figure 26-1).

— This variation may be familial.

— Idiopathic genu valgum (knock-knee) is commonly seen in girls with obesity.

■In the supine position with the knees fully extended, the distance between the medial malleoli is greater than 8 cm.

• Pathologic angulation

— Rickets may cause genu varum or valgum (see Chapter 68, Skeletal Dysplasias).

■Pathologic angulation is usually associated with short stature.

■Radiographs show characteristic widening of the physes and help to establish the diagnosis along with serum laboratory values (ie, calcium, phosphorous, alkaline phosphatase, vitamin D, parathyroid hormone).

— Blount disease is a pathologic cause of varus deformity at the knee in juveniles.

■Focal growth disturbance of the medial proximal tibial epiphysis produces tibia vara.

Figure 26-1. Normal values for the knee angle are shown in degrees and intercondylar in intermalleolar distance. Abbreviation: SD, standard deviation.

Reproduced from Heath CH, Staheli LT. Normal limits of knee angle in white children—genu varum and genu valgum. J Pediatr Orthop 1993;13:259–262 (https://journals.lww.com/pedorthopaedics/Abstract/2013/06000/Estimation_of_the_Recovery_of_Physiological_Genu.16.aspx), with permission from Wolters Kluwer Health and the Pediatric Orthopaedic Society of North America.

■This occurs commonly in children with overweight who walk at an early age and are of African descent.

■It is often associated with significant internal tibial torsion.

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