Congenital Coxa Vara
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Direct answer
Congenital coxa vara is a developmental deformity of the proximal femur in which the neck-shaft angle is reduced, usually to below about 120 degrees, producing a varus and often shortened limb. The radiological clues are a widened Hilgenreiner-epiphyseal angle and an inverted-V defect, a radiolucent area with a triangular metaphyseal fragment in the inferomedial femoral neck. It presents as a limp or short limb, and a valgus osteotomy is needed when the deformity progresses.
What you must remember
- Neck-shaft angle: about 150 degrees at birth, falling to roughly 125 degrees in adults; congenital coxa vara is a reduced angle well below the age-appropriate norm.
- Hilgenreiner-epiphyseal angle: measured between the Hilgenreiner line and a line along the physis; a widened angle signals a more severe deformity.
- Inverted-V defect: an inverted-Y radiolucent area in the inferomedial femoral neck, with a triangular metaphyseal fragment, associated with a poorer prognosis.
- Presentation: a limp, a short limb, a waddling gait and an abductor lurch, noticed in early childhood.
- Associations: fibrous dysplasia, including the McCune-Albright pattern, and cleidocranial dysplasia are recognised causes of a varus proximal femur.
- Valgus osteotomy: the standard correction for a progressive or functionally limiting deformity, aiming to restore the neck-shaft angle and the mechanical axis.
- Differentials: developmental dysplasia of the hip, Perthes disease and slipped capital femoral epiphysis must be excluded before the diagnosis is accepted.
Measuring the deformity and choosing when to operate
A two-year-old presents with a short, varus limb and a waddling gait, and the pelvis radiograph shows a low neck-shaft angle. The steps below turn these measurements into a decision about surgery.
- Confirm the angle: an anteroposterior pelvis radiograph measures the neck-shaft angle on each side, and an angle well below the age norm, sustained over serial films, establishes coxa vara.
- Measure the Hilgenreiner-epiphyseal angle: draw the Hilgenreiner line through the triradiate cartilages and a line along the physis of the affected femur; a widened angle indicates a more severe deformity.
- Look for the inverted-V defect: an inverted-Y radiolucency at the inferomedial neck suggests a poorer prognosis and supports the congenital diagnosis.
- Assess function: a limp, limb shortening, abductor weakness on examination and serial radiographs showing progressive varus define whether the deformity is limiting.
- Plan a valgus osteotomy: when the deformity is progressive or functionally limiting, a valgus intertrochanteric osteotomy is planned to restore the neck-shaft angle and the mechanical axis.
- Follow the hip after correction: serial review checks for recurrence, leg-length change and complications such as nonunion or avascular necrosis.
Where the exam tries to catch you
Examiners test the measurements, the prognostic signs and the reason an osteotomy is needed.
- Trap: calling every low neck-shaft angle congenital coxa vara. Correct: the angle must be read against age-based norms, and coxa vara has to be separated from Perthes disease, dysplasia of the hip and skeletal causes.
- Trap: operating on a mild, stable varus. Correct: observation is reasonable when the deformity is not progressing, with surgery reserved for progressive or functionally limiting cases.
- Trap: ignoring fibrous dysplasia in a varus hip. Correct: fibrous dysplasia is a recognised cause of coxa vara and must be excluded before the diagnosis of congenital deformity is accepted.
Frequently asked questions
What is the normal neck-shaft angle at different ages?
The femoral neck-shaft angle is about 150 degrees at birth and gradually falls to roughly 125 degrees in adulthood. Congenital coxa vara is diagnosed when the neck-shaft angle is reduced well below the age-appropriate norm, typically below about 120 degrees.
Which radiological signs predict a poor outcome in congenital coxa vara?
The Hilgenreiner-epiphyseal angle and the inverted-V defect are the main radiological predictors of outcome in congenital coxa vara. A widened Hilgenreiner-epiphyseal angle and an inverted-Y radiolucent defect in the femoral neck both indicate a more severe and progressive deformity.
When is valgus osteotomy indicated in congenital coxa vara?
Valgus osteotomy is indicated in congenital coxa vara when the varus deformity is progressive, causes a limp or significant limb shortening, or is unlikely to remodel. Criteria and timing differ between textbooks, so the decision is individualised to the child's radiographs and function.
Which conditions must be excluded in a child with a varus hip?
Developmental dysplasia of the hip, Perthes disease, slipped capital femoral epiphysis, fibrous dysplasia and skeletal dysplasias must be excluded in a child with a varus hip. Congenital coxa vara is therefore a diagnosis confirmed only after these differentials are considered on the radiographs.