Congenital (Infantile) Coxa Vara

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.[3, 4] 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 shear effect causing progressive varus deformity is best understood in relation to the resultant force (R) at the femoral-acetabular articulation (see the image below).[5] 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, shear effect causing progressive varus deformity is best understood in relation to resultant force (R) at femoral-acetabular articulation. In normal hip, this resultant force would be perpendicular and compressive (C) in nature with respect to physis. Force transmitted to proximal femoral neck would include net tension force (T) at superior or lateral cortex and net compressive force (C) at inferior or medial cortex. In CCV, more vertical position of proximal femoral physis would increase not only shear component (S) of hip articulation resultant force but also net medial compressive force (C) on metaphyseal bone of femoral neck. These forces overwhelm mechanical strength of abnormally ossified bone in this area. This may lead to relentless and progressive cycle of deformity that often continues unless these forces are corrected with surgical intervention.

In the case of CCV, the more vertical position of the proximal femoral physis increases not only the shear 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 continues unless these forces are corrected with surgical intervention.

Some studies in the literature have described CCV as a variant of a chronic slip, with the continued varus biomechanically predisposing to increased shear stresses across the proximal femoral physis. The changes found in the cartilage of this physis are suggested to resemble those found in slipped capital femoral epiphysis (SCFE).

Other studies suggest that imaging (eg, magnetic resonance imaging [MRI]) results are not similar to those of SCFE and that a chronic slip theory does not explain the bone changes found in the metaphyseal bone of the proximal femur. The authors believe that a more generalized bone abnormality is present that predisposes these patients to deformity. Future investigations may shed further light on this topic.

The exact cause of CCV remains unknown. Many hypotheses have been proposed, including the following:

• Mechanical intrauterine stresses affecting hip development
• Avascular necrosis (AVN) involving selected areas of the proximal femoral physis/head and neck
• Metabolic abnormalities causing deficient production of, or a delay in, the normal ossification process of the proximal end of the femur

DiFazio et al reported on four patients with coxa vara who had neonatal extracorporeal membrane oxygenation (ECMO).[6]

Pylkkanen proposed what remains the most widely accepted theory on the cause of CCV.[7] 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.

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 clear pattern of inheritance has been elucidated, but familial involvement in a number of cases has suggested an autosomal dominant genetic pattern of transmission.

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.

Serafin et al retrospectively reviewed 130 hips with CCV (mean follow-up, ~9 years).[8] The indication for surgery was a neck-shaft angle of less than 110°, and they suggested correction of the Hilgenreiner epiphyseal angle (HEA) to less than 35-40°. Surgical treatment yielded good results in 80% of 2- to 9-year-olds, 62% of 10- to 11-year-olds, and 52% of 12- to 16-year-olds. Growth disturbances noted were a decrease in femoral head size (87%), flattening (43%), shallowness and underdevelopment of the acetabulum (76%), and shortening of the femoral neck. The authors suggested that most of these changes were reversible to some extent if surgical correction was undertaken in children aged 2-9 years.

Desai et al reported their experience with valgus subtrochanteric osteotomies in 20 hips.[9] Patient age at evaluation averaged 7 years, with surgery at an average age of 8 years and 20-year follow-up. Preoperative HEAs averaged 66°, and postoperative HEAs averaged 30°. Five patients also underwent greater trochanteric apophysiodesis at the discretion of the surgeon.

Good radiographic outcomes were noted in 89% of these patients, with Iowa hip scores of more than 90 points in all but one patient.[9] They reported a recurrence rate of 16%, citing inadequate correction (mean HEA >43°), and there was eventual healing with repeat osteotomies. Trochanteric overgrowth was noted in 63% of patients, and adductor weakness was noted in 41%. No patients had a limb-length discrepancy greater than 2 cm, though two had undergone epiphysiodesis prior to maturity with projected discrepancies of 2 cm and 4.2 cm.

Weinstein et al reviewed 20 patients with 25 hips affected with CCV.[10] Average age at diagnosis was 5.75 years, age at treatment averaged 6.6 years, and mean follow-up was 15.3 years. Average HEA preoperatively measured 82.1°, and the preoperative mean head-shaft angle was 89.9°, corrected to 132.4°. Postoperative HEAs were not reported.

The authors noted that 85.3% of initial correction was maintained at final follow-up.[10] In patients older than 5 years at the time of surgery, 75% maintained better than 80% correction, whereas in patients younger than 5 years, only 37% maintained 80% correction or better. A possible reason for this rate of correction, as well as whether it was related to greater trochanteric overgrowth, expected to be more of an issue in the younger patient, was not elucidated. This was the landmark article introducing the concept of the HEA as a predictor of progression in developmental coxa vara.

Roberts et al evaluated the long-term outcomes of operative and nonoperative treatment of CCV in 32 patients (46 hips; mean age at presentation, 5.4 ± 4.9 years; mean follow-up, 11.8 ± 5.8 years).[11]  Initial deformity was greater in the operative group (n = 20; 27 hips) than in the nonoperative group (n = 12; 19 hips), but radiographic outcomes were similar at follow-up. Valgus osteotomy was found to correct severe deformity with improved clinical and radiographic outcomes. Repeat osteotomy was performed in six cases (22%). No significant predictors for recurrence were identified.

As with any treatment, long-term results remain the mainstay of evaluation of utility and effectiveness. Available long-term evaluations of CCV show that with the proper diagnosis and indications for surgery and, most important, adequate correction of the deformity of the proximal femur, an optimistic outlook can be adopted for most patients affected by this condition.

Patients who have 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 developmental dysplasia of the hip (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 articulotrochanteric 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.

Congenital coxa vara (CCV) is differentiated radiographically from other forms of proximal femoral varus by the characteristic finding of an inverted Y-shaped lucency (see the image below). This lucency is made up of the proximal physeal plate and a fragment of bone inferolateral to the physis, which represents a contained area of abnormal calcification.

Characteristic radiographic findings of congenital coxa vara. (A) Decreased neck shaft angle. (B) Smaller and flatter femoral head. (C) More vertical orientation of physeal plate. (D) Coxa brevis. (E) Abnormal bony fragment inferolateral to physeal plate and contained in inverted Y-shaped lucency.

Other, more generic radiographic features are shared with the other causes of coxa vara. These include the following:

• Decreased neck-shaft angle, often approaching or less than 90°
• Smaller and flatter femoral head
• More vertical orientation of the physeal plate
• Decreased femoral anteversion or even retroversion of the head on the femoral neck
• Coxa brevis
• Often, a shallow acetabulum with a more oval shape

Scrutinize films for evidence of acquired or metabolic causes of coxa vara, such as avascular necrosis, slipped capital femoral epiphysis (SCFE), septic destruction of capital femoral epiphysis or metaphysis, fibrous dysplasia, and rickets.

In a study that proposed quantifying CCV with the Hilgenreiner epiphyseal angle (HEA), Weinstein et al also suggested that rather than using the Hilgenreiner line, which can change with pelvic obliquity induced by the commonly associated limb-length discrepancy, a horizontal line parallel to the ground can be drawn instead.[10]  Values for hips affected with CCV average 40-70° but may be as high as 70-90°. This physeal angle remains the most commonly used means for quantification of vertical tilt of the proximal femoral physis at presentation and during follow-up, as well as for evaluating the amount of correction achieved with surgical intervention.

Computed tomography

Computed tomography (CT) with possible three-dimensional (3D) reconstructions can be used to help delineate the proximal femoral defect. It commonly reveals displacement of the proximal femoral epiphysis and associated metaphyseal spike of bone, from its normal superior-anterior position on the femoral neck to an inferior-posterior position. This results in relative femoral retroversion with respect to the head-shaft relationship.

CT may provide useful information regarding femoral anteversion or retroversion and the amount of bone stock in the area, which is important information for preoperative surgical planning.

Magnetic resonance imaging

Findings from magnetic resonance imaging (MRI) include widening of the growth plate with expansion of cartilage mediodistally between the capital femoral epiphysis and the femoral metaphysis. The usefulness of MRI as a preoperative imaging modality, in both diagnosis and surgical planning, is relatively limited.

A large percentage of patients with congenital coxa vara (CCV) will require surgical intervention (see Indications for and Goals of Surgical Intervention).

Treatment of CCV is contraindicated in children who demonstrate any of the following:

• Lack of symptoms on clinical assessment
• Radiographs showing a Hilgenreiner epiphyseal angle (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.

Many forms of nonoperative treatment have been proposed for CCV, including spica cast immobilization and skeletal pin traction with bed rest, with generally unsatisfactory results. It is generally accepted that no place remains for conservative nonoperative measures for individuals who require treatment of either symptomatic or progressive CCV.

Surgical indications

Weinstein et al proposed a radiologic means of quantifying CCV.[10] This measure, the 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 the image below). 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 Hilgenreiner epiphyseal angle, using Hilgenreiner line as horizontal axis and line through defect adjacent to metaphysis as diagonal axis.

On the basis of this measurement, patients in whom surgery is indicated include the following:

• A child with a clinical limp and an HEA greater than 60°
• A child with a clinical limp and an HEA of 45-60° with documented progression of varus deformity

Historically, CCV, if left untreated, 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 the image below).

Congenital coxa vara. Natural history of untreated progressive developmental coxa vara with premature degeneration of hip joint.

Some authors have shown, however, that not all patients with the diagnosis of CCV necessarily follow this course. On the basis of the HEA, three relatively distinct groups have emerged, as follows:

• In those with an HEA smaller than 45°, the CCV is more commonly found to halt progression spontaneously and to heal without intervention
• In patients with an HEA greater than 60°, the CCV follows a more traditional course of progressive deformity that can be aided only by surgical intervention
• An intermediate group, comprising patients with angle measurements of 45-60°, represents a so-called gray zone; these patients require observation for either healing or progression, the latter of which necessitates surgical intervention

Goals of treatment

As noted previously, surgical intervention is required in a large percentage of those with CCV. Accordingly, remembering the indications for surgery and clearly defining the goals of treatment are important for ensuring the best possible outcome and minimizing the number of surgical procedures the patient must undergo.

The goals of surgical intervention are as follows:

• Correction of the neck-shaft angle to a more physiologic angle and the HEA to less than 35-40° ^[12]
• Correction of femoral anteversion (or retroversion) to more normal values
• Ossification and healing of the defective inferomedial femoral neck fragment
• Reconstitution of the abductor mechanism through replacement of its normal length-tension relationship

Surgical options

The treatment of choice for CCV has followed the recommendations of early work by Amstutz, Freiberger, and Wilson in the use of either subtrochanteric or intertrochanteric osteotomies (see the image below).[13, 14]

Congenital coxa vara. Surgical methods of valgus-producing proximal femoral osteotomies. (A) Pauwels Y-shaped osteotomy. (B) Langenskiöld intertrochanteric osteotomy. (C) Borden subtrochanteric osteotomy.

Of the intertrochanteric osteotomies, the Pauwels Y-shaped and Langenskiöld valgus-producing osteotomies have yielded good results. It should be kept in mind, however, that these osteotomies have a somewhat limited ability to correct the associated femoral neck retroversion. The subtrochanteric valgus-producing osteotomies used by many authors also have provided good and lasting clinical results (see the image below). In the end, the actual type of osteotomy performed may be less important than ensuring that the goals of surgical correction, as outlined above, are achieved.[15, 16, 17, 18, 19, 20]

Surgical treatment of congenital coxa vara. Progression from preoperative radiographs at ages 2 and 5 years, with characteristic bony changes. Postoperative radiographs at ages 6 and 12 years, with early and late follow-up results.

Many issues have been raised surrounding surgical intervention, including the following:

• Amount of correction needed
• Associated procedures at the time of surgery to aid in the osteotomy and decrease hip joint forces
• Optimal age for operation

Postoperatively, good results have been achieved consistently when the HEA has been corrected to less than 35-40°. Although some have suggested the need to correct the neck-shaft angle to more than 130-135°, Carroll et al found no strong correlation between the postoperative neck-shaft angle and lasting good clinical outcomes.[21] They suggested that the most consistent and reliable predictor of outcome was the HEA.

Weighill emphasized the use of an adductor tenotomy in association with osteotomy, with adductor release removing the deforming force during reduction of the femoral bone fragments and aiding in postoperative stability of the osteotomy.[22] If required, a segment of proximal femur may be removed to facilitate reduction and reduce joint reactive forces at the hip joint. Unfortunately, this may further shorten an already short limb.

With regard to the optimal age for surgical intervention. Weighill suggested that the best time for correction may be as early as 18 months. Weinstein et al found that patients treated when older than 5 years maintained correction better than those treated when younger than 5 years.[10] Serafin et al suggested that correction in children younger than 9 years maximizes the remodeling potential of both the proximal femur and the acetabulum.[8]

Most patients seem to present for evaluation and are considered for treatment when aged 5-10 years. Femoral osteotomy procedures are technically easier in the older child because more bone stock is present. Earlier surgical intervention may allow the hip, including the acetabulum, to remodel more completely. However, this remodeling potential in very young children has been suggested to lead to higher recurrence rates after surgical correction. In young surgical patients, the incidence of greater trochanteric overgrowth is also higher. Most agree, however, that the milder the deformity, the easier the correction.

It is generally accepted that the age at correction is less important than the ability to correct the hip to meet the goals of surgery. Once the diagnosis is clear and progression is evident, few reasons remain to delay surgery beyond an age at which stable fixation can be achieved reliably. Long-term outcomes have supported the view that adequate realignment of the deformity is most important. The authors tend to operate as soon as patients meet radiographic and clinical criteria, regardless of their age or size.

Preparation for surgery

As with many surgical procedures, preoperative planning is essential to achieve a favorable outcome. Up-to-date imaging is necessary to determine the amount of bone to be resected and the size of implants to be used. Templating the operative plan is often invaluable to ensure that the proposed result will meet the surgical goals. Having hardware of various angles available is helpful if intraoperative measurements lead to alteration in the amount of bone resected.

Operative details

Position the patient supine on a radiolucent table, and ensure that adequate-quality images are available before beginning surgery. Rotate the affected hip under fluoroscopy to compensate for hip (femoral head) version, defining the maximal varus deformity. From this view, determine the size of the bone wedge to be resected. Use clinical rotation of the hip to decide whether derotation will be combined with wedge resection.

Free draping of the hip allows better intraoperative control. The proximal lateral femur is routinely exposed. Image intensification is used in implant insertion and bone resection. Confirm correct positioning once provisional fixation is achieved.

After skin closure in the usual fashion, with the use of wound suction as required, apply a 1.5 hip spica cast. Obtain postoperative radiographs through the spica cast for later comparison. Maintain a nonweightbearing status for the patient until early bone healing is demonstrated radiographically, at approximately 6-10 weeks after surgery.

Premature closure of the proximal femoral physis has been consistently noted, occurring along with or shortly after healing of the inferomedial fragment of metaphyseal bone. Carroll et al[21] reported that all of their patients had premature closure of the proximal femoral physis, as did Desai et al.[9] Closure occurred at an average of 3 years after surgical correction. Pylkkanen reported a 90% rate of premature closure.[7] This, along with any residual shortening due to the osteotomy, necessitates follow-up with the aim of contralateral physeal arrest or ipsilateral lengthening at the appropriate time, should a clinically significant limb-length discrepancy exist near maturity.

Associated with premature closure of the proximal femoral physis is the often-encountered overgrowth of the greater trochanter (see the image below). Desai et al found this to occur in 60% of their series, with just under 50% of these patients having abductor weakness at final follow-up.[9] There was  no overgrowth in cases where successful greater trochanteric apophysiodesis was achieved. All of these patents had a good clinical outcome. Undertake surgical epiphysiodesis or distal transfer if overgrowth of the greater trochanter is noted both radiographically and clinically on follow-up.

Greater trochanteric overgrowth in treated congenital coxa vara.

Perform an initial postoperative check 1 week after surgery, with radiographs to ensure maintenance of position and integrity of fixation. The patient should be seen every 2 weeks until early healing is present (~6-8 weeks after surgery). At that time, the spica cast is removed, and physiotherapy is begun for mobilization and range-of-motion instruction.

Close follow-up every 3-6 months is required to ensure that the deformity is resolving. Assess for greater trochanteric overgrowth and commonly encountered proximal femoral physeal closure. Carry out trochanteric apophysiodesis if indicated (see Complications). Perform a careful serial examination for a relative limb-length discrepancy, and treat as appropriate.