Introduction
Coxa vara includes all forms of decrease of the femoral neck shaft angle to less than 120-135°. This condition has many etiologies: congenital, acquired, and developmental. Congenital coxa vara (CCV), also referred to as infantile or cervical coxa vara, is a condition in which a varus deformity exists that is assumed to be caused by either an embryonic limb bud abnormality or an intrauterine condition causing significant proximal femoral varus. CCV is, by definition, present at birth but manifests clinically during early childhood and commonly follows a clinical course that is progressive with growth.1,2,3
Congenital coxa vara. Determination of the Hilgenreiner epiphyseal angle, using the Hilgenreiner line as the horizontal axis and a line through the defect adjacent to the metaphysis as the diagonal axis.
As a specific entity, CCV has characteristic clinical and radiographic features that help differentiate it from other forms of coxa vara. It is commonly associated with a significant limb-length discrepancy, segmental shortening of the femur, or other abnormalities of the bony femur. Associated diagnoses include proximal femoral focal deficiency (PFFD), congenital short femur, and congenital bowed femur.
Congenital coxa vara. Surgical methods of valgus-producing proximal femoral osteotomies. (A) Pauwels Y-shaped osteotomy. (B) Langenskiöld intertrochanteric osteotomy. (C) Borden subtrochanteric osteotomy.
Acquired forms of coxa vara are varus deformities of the proximal femur that develop secondary to metabolic, neoplastic, or traumatic conditions. This group includes ricketic coxa vara, fibrous dysplasia, proximal physeal injury, and premature closure. Also included in this category are secondary varus changes due to generalized skeletal conditions or dysplasias such as Morquio disease (mucopolysaccharidosis type IV), cleidocranial dysostosis, metaphyseal diaphyseal dysplasia, and metaphyseal dysostosis.
History of the Procedure
Fiorani first clinically described congenital coxa vara (CCV) in 1881.4 Hofmeister, in 1894, first coined the term coxa vara and was the first to show radiographic evidence of a decreased neck shaft angle.5 In 1905, Hoffa was the first to report on the histologic changes associated with coxa vara, and in 1928, Fairbank described the progressive tendency of the proximal femoral deformity during growth in coxa vara observed in childhood.6,7 Duncan proposed in 1938 that progressive childhood coxa vara represented a deformity that appeared during the early years of growth, rather than being congenital, thus coining the term developmental coxa vara.8 This proposal, although not generally accepted initially, was supported by the work of Amstutz in 1970.9 Amstutz documented 2 patients who had normal findings on radiographs of the hips at birth but had radiographic evidence of coxa vara by age 2-3 years.
Problem
Abnormal development of the proximal femoral cartilaginous physis and defective ossification of the adjacent metaphysis are responsible for the progressive decrease of the neck shaft angle. In severe cases, a separate triangular fragment involving the inferior-medial aspect of the femoral neck may also be found. These anatomic and biologic factors underlying the biomechanical loading characteristics of the varus hip lead to a progressive inclination of the proximal epiphyseal plate, with shortening of the femoral neck and concomitant relative trochanteric overgrowth. A serious hip deformity, both clinically and radiographically, often results, for which the course is not always clear and the treatment is not always successful.
Frequency
Congenital coxa vara (CCV) is believed to be a relatively rare condition, with a reported incidence ranging from 1 per 13,000 population to 1 per 25,000 population. Relative to developmental dysplasia of the hip (DDH), it is estimated to occur less frequently, with the CCV-to-DDH ratio ranging from 1:13 to 1:20. No sex predilection appears to exist, and reported rates of right- and left-side involvement are essentially equal. Bilateral involvement seems to occur only half as often as unilateral involvement. Although some authors propose that no racial predilection exists, there is some suggestion that incidence is higher in persons of African descent than in whites. No clear pattern of inheritance has been elucidated, but familial involvement in a number of cases has suggested an autosomal dominant genetic pattern of transmission.
Etiology
The exact cause of congenital coxa vara (CCV) remains unknown. Many hypotheses have been proposed, including the following: mechanical intrauterine stresses affecting hip development; avascular necrosis involving selected areas of the proximal femoral physis/head and neck; and metabolic abnormalities causing deficient production of, or a delay in, the normal ossification process of the proximal end of the femur.
Pylkkanen proposed what remains the most widely accepted theory on the cause of CCV.10 He postulated that the proximal femoral deformity is the result of a primary ossification defect in the inferior femoral neck, on which physiologic shearing stresses (applied during weightbearing) cause fatigue of the local dystrophic bone, resulting in progressive varus deformity.
Pathophysiology
Histologic investigations by Chung and Riser and by Bos et al showed abnormalities in the proximal femoral physeal chondrocyte maturation, with disruption of the normal columnar architecture and abnormal calcification of the cartilaginous matrix.11,12 This abnormal enchondral ossification results in decreased production of metaphyseal bone, leading to a relative osteoporosis and subsequent weakness in this area. Notably, no evidence exists in these studies or others of an avascular-type process or of any pathologic or radiologic signs suggesting slippage of the proximal physeal plate as an underlying cause of the observed coxa vara.Biomechanically, the sheer effect causing progressive varus deformity is best understood in relation to the resultant force (R) at the femoral/acetabular articulation (see Image 1).13 In the normal hip, this resultant force is perpendicular and compressive (C) in nature with respect to the physis. The force transmitted to the proximal femoral neck includes a net tension force (T) at the superior or lateral cortex and a net compressive force (C) at the inferior or medial cortex.
Congenital coxa vara (CCV). Hip biomechanics in coxa vara. (A, B) Normal hip. (C) Abnormal varus hip. Biomechanically, the sheer effect causing progressive varus deformity is best understood in relation to the resultant force (R) at the femoral/acetabular articulation. In the normal hip, this resultant force would be perpendicular and compressive (C) in nature with respect to the physis. The force transmitted to the proximal femoral neck would include a net tension force (T) at the superior or lateral cortex and a net compressive force (C) at the inferior or medial cortex. In the case of CCV, the more vertical position of the proximal femoral physis would increase not only the sheer component (S) of the hip articulation resultant force but also the net medial compressive force (C) on the metaphyseal bone of the femoral neck. These forces overwhelm the mechanical strength of the abnormally ossified bone in this area. This may lead to a relentless and progressive cycle of deformity that oftencontinues unless these forces are corrected with surgical intervention.
In the case of congenital coxa vara (CCV), the more vertical position of the proximal femoral physis increases not only the sheer component (S) of the hip articulation resultant force, but also the net medial compressive force (C) on the metaphyseal bone of the femoral neck. These forces overwhelm the mechanical strength of the abnormally ossified bone in this area (see Image 1). This may lead to a relentless and progressive cycle of deformity that continues unless these forces are corrected with surgical intervention.
Presentation
Patients with congenital coxa vara (CCV) usually present with gait abnormalities. Affected children generally present between the time they begin ambulation and age 6 years.
In most patients, the gait abnormality is progressive and, notably, pain free. Unilateral involvement with an associated relative limb-length discrepancy and Trendelenburg limp may be noted. This discrepancy in limb lengths usually is mild, ranging from 1.5 to 4.0 cm. Patients with bilateral involvement commonly present with a waddling gait abnormality, similar to that of patients with bilateral DDH. The Trendelenburg sign is commonly elicited in the affected hip or hips.
A tabletop examination may reveal weak abductors, a prominent greater trochanter, decreased abduction due to a decreased articulo-trochanteric distance, and coxa vara. A decrease in internal rotation also is often noted, caused by decreased femoral anteversion or true retroversion associated with this condition.
Indications
Weinstein et al proposed a radiological means of quantifying CCV.14 This measure, the Hilgenreiner epiphyseal angle (HEA), is the angle subtended by the horizontal Hilgenreiner line through the triradiate cartilages and an oblique line through the proximal femoral capital physes (see Image 3). A study of normal values of the HEA found that the angle in children younger than 7 years averages 20°, with a wide variation of 4-35°. The mean value for those aged 8 years to maturity is 23°.
Congenital coxa vara. Determination of the Hilgenreiner epiphyseal angle, using the Hilgenreiner line as the horizontal axis and a line through the defect adjacent to the metaphysis as the diagonal axis.
Using this measurement, patients in whom surgery is indicated include the following:
- A child with a clinical limp and an HEA of more than 60°
- A child with a clinical limp and an HEA of 45-60° with documented progression of varus deformity
If left untreated, CCV historically was believed to be a relentless and progressive deformity leading to pain and a loss of hip function with the development of premature degenerative changes (see Image 4). Some authors have shown, however, that not all patients with the diagnosis of CCV necessarily follow this course. On the basis of the HEA, 3 relatively distinct groups have emerged:
Congenital coxa vara. Natural history of untreated progressive developmental coxa vara with premature degeneration of hip joint.
- In those with an HEA of less than 45°, the CCV is more commonly found to halt progression spontaneously and to heal without intervention.
- In patients with an HEA of more than 60°, the CCV follows a more traditional course of progressive deformity that can be aided only by surgical intervention.
- An intermediate group with angle measurements of 45-60° represent a so-called "gray zone"; they require observation for either healing or progression, the latter of which requires surgical intervention.
Relevant Anatomy
See Pathophysiology.
Contraindications
Treatment of CCV is contraindicated in children who demonstrate any of the following:
- Lack of symptoms on clinical assessment
- Radiographs showing an HEA of less than 45°
- Radiographs showing an HEA of 45-60° with no documented progression
In such situations, close clinical and radiographic follow-up is warranted.
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References
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Further Reading
Keywords
coxa vara, congenital coxa vara, CCV, developmental coxa vara, infantile coxa vara, cervical coxa vara, childhood coxa vara, proximal femoral varus, proximal femoral focal deficiency, PFFD, congenital short femur, congenital bowed femur
