Coxa Vara in Children and Adolescents

Introduction and Definitions

Coxa vara is a deformity of the proximal femur in which the neck-shaft angle is reduced below normal — typically below 120° in adults, with the corresponding lower threshold somewhat higher in children to reflect the normal change in neck-shaft angle through development. The deformity has multiple etiologies and presents in three principal clinical contexts in pediatric and adolescent practice: developmental (congenital) coxa vara, an isolated or syndromic disorder of the proximal femoral physis presenting in early childhood; acquired coxa vara secondary to other disorders (Legg-Calvé-Perthes disease, SCFE, osteomyelitis, trauma, fibrous dysplasia, multiple osteochondromatosis); and dysplastic coxa vara associated with various skeletal dysplasias. The clinical importance of recognizing coxa vara lies in its association with progressive deformity, gait abnormalities, abductor weakness, and accelerated degenerative arthritis of the hip in adulthood. This chapter synthesizes content from Tachdjian’s Pediatric Orthopaedics, Apley & Solomon’s, and Miller’s Review.

Developmental (Congenital) Coxa Vara

Definition and Epidemiology Developmental coxa vara — sometimes called infantile coxa vara — is a focal disorder of the proximal femoral physis in which a triangular fragment of bone separates from the inferomedial corner of the femoral neck along an oblique medial defect through the metaphysis. The condition is rare, with an incidence of approximately 1 in 25,000 live births. Both sexes are affected equally. Bilateral involvement occurs in approximately 30- 50% of cases. Etiology The cause is unknown but is generally thought to represent a primary developmental abnormality of the proximal femoral metaphysis or physis. Some cases occur in association with skeletal dysplasias including cleidocranial dysplasia, spondylometaphyseal dysplasia, and metaphyseal chondrodysplasia (Schmid type). A small number have been reported with proximal femoral focal deficiency. The familial pattern, when present, is consistent with autosomal dominant inheritance with variable penetrance. Pathological Anatomy The characteristic pathology is a triangular fragment of bone — the “Fairbank triangle” — that separates from the medial corner of the femoral neck along an oblique line extending from the inferior aspect of the metaphysis upward and laterally toward the lateral cortex. The defect in the bone progressively widens as the child grows, producing increasing varus deformity and shortening of the neck. The physis appears widened and irregular on imaging, particularly on its inferior aspect, and may progress toward complete physeal failure with development of a pseudarthrosis through the femoral neck in severe cases.

Tönnis described a “wandering” of the triangular fragment with growth that worsens the deformity over time. Clinical Features Presentation is typically in early childhood (age 2-6 years) with a painless limp, leg-length discrepancy, decreased hip abduction (often with abductor lurch — Trendelenburg gait), and apparent short stature on the affected side. Bilateral cases may present with waddling gait without obvious leg-length discrepancy. Examination reveals decreased hip abduction and internal rotation, with the limb in external rotation and adduction. There is typically no pain. Radiographic Features and the Hilgenreiner-Epiphyseal Angle The plain AP pelvis radiograph is diagnostic. Features include: decreased neck-shaft angle (varus); short, wide femoral neck; the triangular Fairbank fragment in the inferomedial corner of the metaphysis; widened, irregular medial portion of the proximal femoral physis; and sometimes a clear vertical defect through the medial femoral neck. The Hilgenreiner-epiphyseal angle (the angle between Hilgenreiner’s line — through the triradiate cartilages — and a line along the proximal femoral physis) is the principal quantitative measurement and the strongest predictor of progression. The angle is normally less than 25°. An angle of 45° or greater predicts progression and is generally accepted as an indication for surgical correction; an angle between 25° and 45° is intermediate and requires observation or correction depending on additional features.

Treatment The treatment of developmental coxa vara depends on the Hilgenreiner-epiphyseal angle, the rate of progression, and the patient’s clinical findings. Observation: Hilgenreiner-epiphyseal angles less than 45° in the asymptomatic patient may be observed with serial radiographs every 6-12 months. The angle may decrease spontaneously with growth in mild cases, but progression is the rule in moderate cases. Surgical correction: Valgus subtrochanteric osteotomy is the standard treatment for established coxa vara with Hilgenreiner-epiphyseal angle greater than 45°. The procedure typically involves: a subtrochanteric or intertrochanteric closing-wedge or opening-wedge osteotomy to bring the neck-shaft angle to approximately 140-150° (slight overcorrection is desirable, since some loss of correction with growth is the rule); rigid fixation with a pediatric blade plate or pediatric hip screw; and an extended period of postoperative protection. The combined Pauwels intertrochanteric Y-osteotomy with adduction component is favored by some authors. The principle is to convert the high-angle physeal orientation (which subjects the medial femoral neck to shear forces) into a more horizontal orientation that subjects the physis to compression, allowing the physis to heal. Surgical timing: Surgery is generally recommended between ages 3 and 6 years, with delay only if the angle is in the intermediate range and trending favorably. Earlier surgery in the toddler is technically more demanding because of the small size of the proximal

femur and the difficulty of fixation; later surgery permits less time for postoperative growth-related correction. Outcomes and Complications The outcomes of valgus osteotomy for developmental coxa vara are generally good, with restoration of a near-normal neck-shaft angle, improvement in hip abductor function, and prevention of progressive deformity. The principal long-term concerns include: premature closure of the proximal femoral physis (greater trochanteric overgrowth from the relatively continued growth of the trochanteric apophysis after central physeal arrest — this is common and may require greater trochanteric advancement in adolescence to restore normal abductor mechanics); leg-length discrepancy from physeal disturbance; recurrence of varus in severe cases or with inadequate correction; and progressive degenerative arthritis of the hip in adulthood. The trochanteric overgrowth deserves particular attention: as the central physis closes prematurely while the apophysis of the greater trochanter continues to grow, the relative height of the trochanter rises above the femoral head, the abductor moment arm is shortened, and a persistent Trendelenburg gait results. Trochanteric advancement (lateral and distal transfer of the trochanter) restores the abductor mechanics.

Acquired Coxa Vara

Acquired coxa vara may follow a variety of conditions affecting the proximal femoral physis or proximal femur. The principal etiologies include: Post-traumatic coxa vara: Following femoral neck or proximal femoral fractures with malunion in varus, or following physeal injury. The treatment is reconstructive valgus osteotomy with attention to leg length and hip function. Post-infectious coxa vara: Following neonatal or childhood septic arthritis with destruction of the proximal femoral physis and femoral head. The deformity is often severe with shortening, varus, and degenerative changes. Reconstruction is complex and is discussed under “Tom Smith arthritis” in the chapter on infantile osteoarthritis. Coxa vara in Perthes disease: As discussed in the chapter on Perthes disease, coxa magna and coxa breva with relative trochanteric overgrowth are common late features of Perthes; significant varus is less common but can occur. Valgus osteotomy and trochanteric advancement are options. Coxa vara in fibrous dysplasia: Polyostotic fibrous dysplasia involving the proximal femur produces the classical “shepherd’s crook” varus deformity. Surgical correction by intertrochanteric or subtrochanteric valgus osteotomy with intramedullary fixation is the standard treatment. Coxa vara in multiple hereditary exostoses (MHE): Involvement of the proximal femoral metaphysis by exostoses can produce varus deformity, often combined with shortening.

Coxa vara in skeletal dysplasias: Various skeletal dysplasias including cleidocranial dysplasia, spondylometaphyseal dysplasia, metaphyseal chondrodysplasia (Schmid type), and others may produce coxa vara as part of their wider phenotype. Coxa vara in osteogenesis imperfecta: Bowing of the proximal femur from multiple healed fractures produces a varus appearance. Telescoping intramedullary rod fixation and valgus osteotomy can address the deformity.

Pauwels Classification and Biomechanics

The Pauwels biomechanical analysis of the proximal femur, developed in the 1930s and 1950s, provides the conceptual basis for the surgical correction of coxa vara. Pauwels recognized that the angle of the proximal femoral physis relative to the horizontal (which is approximately the Hilgenreiner-epiphyseal angle) determines whether the loading across the physis is predominantly compressive (when the angle is low, near horizontal) or shear (when the angle is high, near vertical). Shear loading inhibits physeal healing; compressive loading promotes it. The Pauwels intertrochanteric Y-osteotomy, in which a Y-shaped wedge of bone is removed below the physis and the proximal fragment is rotated to bring the physis to a more horizontal orientation, is the historic surgical solution to coxa vara and remains the conceptual basis for modern valgus osteotomy techniques.

Differential Diagnosis

The differential diagnosis of pediatric coxa vara includes: Developmental dysplasia of the hip: DDH can produce a varus appearance of the proximal femur with neck shortening, particularly in late-treated cases. The history, the absence of the Fairbank triangle on radiographs, and the dysplastic acetabulum distinguish DDH. Legg-Calvé-Perthes disease: Perthes produces relative trochanteric overgrowth that mimics coxa vara on examination, but the radiographic features of femoral head changes and the typical age and presentation distinguish Perthes. Slipped capital femoral epiphysis: SCFE produces a relative varus appearance from the posterior slippage of the head, but the older age (adolescence), the characteristic radiographic features, and the underlying pathology distinguish SCFE. Cleidocranial dysplasia and other skeletal dysplasias: The systemic features and family history identify these conditions. Multiple hereditary exostoses: The multiple bony lumps and the family history identify MHE. Tom Smith arthritis (post-infectious): The history of neonatal sepsis and the radiographic features of destruction distinguish this condition.

Adolescent Coxa Vara

Coxa vara presenting in adolescence is most commonly due to acquired causes (Perthes sequelae, SCFE, post-traumatic) or to skeletal dysplasias. True developmental coxa vara presenting for the first time in adolescence is rare. The treatment principles are similar to those for childhood developmental coxa vara, with attention to the substantial residual growth and the implications for surgical planning. Hemiepiphysiodesis of the greater trochanteric apophysis has been used to control progressive trochanteric overgrowth in selected cases.

Outcomes and Long-Term Considerations

The natural history of untreated coxa vara is one of progressive deformity, abductor weakness, leg-length discrepancy, and eventual development of degenerative arthritis of the hip. Surgical correction with valgus osteotomy restores hip mechanics in the great majority of cases and prevents the progression of these complications. The long-term outcomes depend on the underlying etiology: developmental coxa vara without other anomalies has the best outcome; coxa vara in the setting of skeletal dysplasia or post- infectious changes is more variable. Trochanteric overgrowth, when it occurs, can be addressed by greater trochanteric advancement in adolescence with good restoration of abductor function. Total hip arthroplasty in adulthood is sometimes required for end-stage degenerative arthritis and is technically more demanding than primary THA because of the residual bony deformity, leg-length discrepancy, and altered hip mechanics.

Summary and Take-Home Points

Coxa vara in children and adolescents is a heterogeneous condition unified by the common feature of decreased femoral neck-shaft angle. Developmental coxa vara, presenting in early childhood with painless limp and decreased hip abduction, is characterized by the Fairbank triangle on the AP pelvis radiograph and quantified by the Hilgenreiner- epiphyseal angle, which predicts progression — angles greater than 45° generally requiring surgical correction by valgus subtrochanteric osteotomy. Acquired coxa vara has multiple etiologies including post-traumatic, post-infectious, Perthes-related, fibrous dysplasia, multiple hereditary exostoses, and the various skeletal dysplasias; each requires individualized assessment and treatment. The Pauwels biomechanical analysis provides the conceptual basis for surgical correction, with the principle of converting the high-angle physeal orientation to a more horizontal orientation that subjects the physis to compression rather than shear. The principal long-term concerns are trochanteric overgrowth with abductor dysfunction, leg-length discrepancy, and degenerative arthritis. Across all etiologies, the principles of accurate diagnosis, quantitative radiographic assessment, timely surgical correction in progressive cases, and attention to the late sequelae of trochanteric overgrowth and limb-length discrepancy determine successful outcomes.