Paediatric Imaging

Coxa vara

hip deformity caused by a decreased angle between the femoral neck and shaft, generally defined as an angle of less than 120 as measured on an anteroposterior radiograph. However, coxa vara may be present with a slightly greater angle in young children.

The normal femoral neck-shaft angle in children changes with age, being approximately 150 at birth and gradually reducing to approach the adult value of 120130. It is important that the radiograph is taken with the patient correctly positioned with the leg held in a neutral position and the patellae facing forward as external rotation of the leg will increase and internal rotation will decrease the projected neck-shaft angle. With coxa vara there is resultant shortening of the affected leg, vertical orientation of the capital femoral physis and often femoral anteversion.

The radiographic appearance is sometimes described as a "shepherd's crook" deformity. The condition may be congenital (Fig.1) or developmental and usually presents with leg length discrepancy or painless limp.

Clinical examination reveals a Trendelenburg gait (abductor lurch) if unilateral or a waddling gait if bilateral and hip abduction and rotation is limited. Bilateral coxa vara may result from generalised bone softening as in rickets, renal osteodystrophy or osteogenesis imperfecta. Coxa vara also occurs in skeletal dysplasias such as metaphyseal chondrodysplasia (especially the Schmid type), achondroplasia, cleidocranial dysplasia, polyostotic fibrous dysplasia or proximal focal femoral deficiency. Isolated coxa vara may be of unknown aetiology or may follow trauma including displacement of the capital femoral epiphysis with non accidental injury in infants.

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Fig.1

a. AP radiograph of a 5-year-old child with bilateral congenital coxa vara. Note the short femoral necks, which are angulated, with mild widening of the growth plates, which are slightly irregular. These are the typical appearances of congenital coxa vara. b. Same child, aged 12. Mild coxa vara remains but the growth plates are now normal.
Coxa vara, Fig.1 (a)
Coxa vara, Fig.1 (b)