Michael B. Millis and Joshua A. Strassberg
DEFINITION
Coxa vara is a deformity of the proximal femur associated with a neck–shaft angle (NSA) of less than 110 degrees.12
Developmental coxa vara, also referred to as cervical or infantile coxa vara, is not present at birth, but rather develops in early childhood.
This is a rare disease entity with a worldwide incidence of 1 in 25,000 live births.
This form has not been connected to an increased association with other musculoskeletal abnormalities.
The varus deformity does frequently progress with time.
This entity must be distinguished from other forms of coxa vara, such as congenital or acquired.
As opposed to developmental coxa vara, the congenital form is present at birth. It is presumed to be caused by an embryonic limb bud abnormality, is associated with an increased incidence of musculoskeletal abnormalities and significant limb-length discrepancy (LLD), and shows minimal progression with growth.
The acquired forms of coxa vara are secondary to underlying disorders (eg, metabolic, traumatic, tumors).
ANATOMY
Growth of the proximal femur occurs at the proximal femoral physeal plate, the femoral neck isthmus, and the greater trochanteric apophysis.
The growth at these sites determines the size and shape of the proximal femur, specifically the length of the proximal femur and the NSA.
Any injury to the proximal physis will result in a varus deformity owing to continued growth of the femoral neck and trochanter.4
Between 3 and 6 months of age, the capital femoral epiphyseal ossification center may be seen.
The trochanteric secondary center of ossification begins to ossify at 4 years of age.
The NSA normally progresses to a more varus position with growth, starting at approximately 150 degrees at birth and finishing near 120 degrees at full maturity.
PATHOGENESIS
The exact cause of developmental coxa vara is unknown.
An attractive theory, proposed by Pylkkanen,8 postulates that the varus deformity is due to a primary ossification defect in the medial femoral neck that results in a more vertical physis.
Dystrophic bone forms on the medial aspect of the femoral neck.
The physiologic shearing stresses that occur during weight bearing fatigue the dystrophic bone in the medial femoral neck, resulting in progressive varus.8
Biopsies of the proximal femoral physis reveal findings similar to those seen in the proximal tibia in patients with Blount's disease or the proximal femoral physis in patients with metaphyseal chondrodysplasia (Schmid type),6revealing an enlarged growth plate with disorganized islands of cartilage in relatively reduced numbers.1,3,8
No evidence of osteonecrosis was seen.
NATURAL HISTORY
As described by Weinstein et al,12 the most reliable factor for progression is the Hilgenreiner–epiphyseal angle (HEA), measured between the line of Hilgenreiner and a line parallel to the proximal femoral physis (FIG 1).
Patients whose HEA is more than 60 degrees will invariably progress.
The increased varus and retroversion can cause a cam-type impingement.
This will then lead to premature degenerative arthritis with progressive pain and disability.
If left untreated, the decreased NSA may eventually create too great a strain on the femoral neck, leading to a stress fracture of the femoral neck and eventual nonunion.
Patients with an HEA between 45 and 60 degrees have a less defined prognosis and must be followed for progression of varus deformity or increased symptoms.
PATIENT HISTORY AND PHYSICAL FINDINGS
Developmental coxa vara is typically discovered sometime between the initiation of ambulation and 6 years of age.5,7
Patients commonly present with a progressive painless limp.
Pain is an uncommon finding.
FIG 1 • Hilgenreiner–epiphyseal angle. This is the angle formed by crossing the line of Hilgenreiner with a line parallel to the proximal femoral physis. This angle is thought to be the best predictor of progression and postoperative recurrence.
If a unilateral abnormality is present, the limp will be due to abductor weakness, as well as a minor LLD (usually less than 2.5 cm).
When present bilaterally, the patient will present with a waddling gait associated with increased lumbar lordosis, similar to what is seen in ambulatory children with bilaterally dislocated hips.
As opposed to patients with dislocated hips, however, no telescoping or signs of instability should be noted.5,8,10
The greater trochanter may be prominent and elevated.
Because the abductors are not at their optimal length, they will eventually weaken, leading to easy fatigability and muscle aching.
Abductor weakness may also lead to the development of a Trendelenburg gait.
Hip motion is typically limited (mostly abduction and internal rotation).
Additionally, hip flexion may be restricted secondary to impingement.
Physical examination should include several range-of-motion tests.
Passive abduction: Varus deformity may lead to decreased ability to abduct. Normal full abduction is 40 degrees.
Passive internal rotation: Decreased internal rotation may be secondary to retroversion or impingement.
Internal rotation is variable, but at least 20 degrees is expected.
Passive flexion: Loss of flexion may result from femoroacetabular impingement. Normal full flexion is 120 degrees.
A positive Trendelenburg sign—tilting of the pelvis down toward the nonstance leg—indicates abductor weakness.
LLD may indicate growth disturbance of the proximal femur.
IMAGING AND OTHER DIAGNOSTIC STUDIES
Evaluation consists primarily of an AP radiograph of the pelvis (FIG 2A).
The NSA is substantially decreased, often less than 90 degrees.
The proximal femoral physis is wider and more vertical, with a triangular metaphyseal fragment in the inferior neck surrounded by physis, giving an inverted Y pattern—the sine qua non of developmental coxa vara.
Also notable are decreased femoral anteversion, coxa breva, and possible mild acetabular dysplasia.
A frog-leg lateral radiograph (FIG 2B) as well as a CT (FIG 2C,D) or MRI may also be obtained to provide more information.
DIFFERENTIAL DIAGNOSIS
Congenital coxa vara
Proximal femoral focal deficiency
Skeletal dysplasia
Cleidocranial dysostosis
Metaphyseal dysostosis (Jansen type)
Spondylometaphyseal dysplasia (Kozlowski type)
FIG 2 • A. AP pelvic radiograph. This film shows the classic appearance of developmental coxa vara on the right side. Compared with the normal left hip, notice the decreased neck–shaft angle; the more vertical, widened physis; the inverted-Y pattern; the coxa breva; and the mild acetabular dysplasia. B. A frog-leg lateral radiograph helps to show some of the femoral retrotilt that is present. C. The retrotilt is even more evident on an axial CT. D. A 3D CT reconstruction gives a more detailed picture of the deformity and better shows the pathology of the proximal femoral physis, including the triangular metaphyseal fragment.
Avascular necrosis
After reduction for developmental hip dislocation
Trauma (femoral neck fracture or hip dislocation)
Septic joint
Slipped capital femoral epiphysis
Pathologic bone condition
Fibrous dysplasia
Osteogenesis imperfecta
Renal osteodystrophy
Osteopetrosis
SURGICAL MANAGEMENT
Patients with an HEA greater than 60 degrees are candidates for surgical intervention, as are patients with an HEA greater than 45 degrees who are symptomatic (limp or progressive deformity).
Preoperative Planning
Clinically assess range of motion (ROM) and LLD.
Review all images.
Determine the desired alignment (version, NSA, offset).
Choose implant type based on patient age and size.
Kirschner wire: for dwarves or children up to 4 years of age with bones too small for a plate
Custom-made high-angle blade plate: used for older children with bones too large for the Kirschner wire technique
Wagner plate: an alternative plate for patients with bones too big for the Kirschner wire technique when a custommade high-angle blade plate is not accessible
Positioning
The patient is supine on a radiolucent table with a folded blanket beneath the pelvis.
This elevation allows more room for movement, especially when working posteriorly or when trying to drop your hand to aim anteriorly.
Approach
The standard lateral approach to the proximal femur is used.
TECHNIQUES
EXPOSURE
The fascia lata is split longitudinally.
The vastus lateralis fascia is incised longitudinally about 5 to 10 mm anterior to the intermuscular septum and is elevated atraumatically from the femur.
This muscle is then released proximally from the femur with a transverse incision just below the level of the greater trochanteric apophysis.
The periosteum is incised along the anterolateral femur and subperiosteal dissection is performed circumferentially just proximal to the level of the lesser trochanter.
The anterior neck is visualized to assess femoral version.
The bone is scored longitudinally with an electrocautery or saw, or Kirschner wires can be placed proximal and distal to the osteotomy site to assess rotation after the osteotomy has been performed.
VALGUS OSTEOTOMY USING MULTIPLE KIRSCHNER WIRE FIXATION
Three Kirschner wires (7/64-inch are most common) are inserted in parallel (TECH FIG 1A), lined up in a transverse fashion, up the middle of the neck.11,13
The lateral cortex is entered 5 to 10 mm distal to the trochanteric apophysis, and the wires are directed up the neck in parallel and advanced into the femoral head.
Starting more proximally allows for more lateralization of the femoral shaft.
The starting point may be more anterior if there is increased retroversion.
The three Kirschner wires are then bent to the desired angle of correction determined preoperatively (typically about 160 degrees) and rotated proximally to be out of the way (TECH FIG 1B,C).
An additional Kirschner wire is inserted at the level of the lesser trochanter perpendicular to the shaft to act as a guide for the osteotomy.
A bone tenaculum is placed on the greater trochanter to allow for control of the proximal fragment after the osteotomy.
Two bone cuts are made parallel to the Kirschner wire, about 5 mm on either side of the wire, and then this cylindrical segment is removed (TECH FIG 1D).
This allows for some shortening to relieve pressure on the femoral head and to reduce medial soft tissue tension.
The thick medial periosteum must be divided to allow for valgus correction and lateralization of the shaft.
The lateral cortex of the proximal fragment is abraded with the saw or with a burr to promote healing.
Trial reduction is attempted by gently pushing down on the Kirschner wires (without stressing the Kirschner wires to prevent pullout) to adduct the proximal fragment while abducting and translocating the distal fragment.
The three Kirschner wires are then rotated distally and brought down to the shaft so that the lateral cortex of the proximal fragment lies on or is impacted into the proximal end of the distal fragment (TECH FIG 1E).
The fragments are temporarily stabilized by holding down the Kirschner wires to the lateral cortex of the distal fragment with a Verbrugge clamp.
An interfragmentary Kirschner wire may be inserted for added stability.
The Kirschner wires are then definitively secured to the shaft with a cerclage wire, a small semitubular plate, or both.
The vastus lateralis should be sutured securely to the greater trochanter to provide a lateral tension band.
TECH FIG 1 • Multiple Kirschner wire fixation. A. Insertion of three Kirschner wires. B. Bending Kirschner wires to desired angle. C. Rotating the three wires out of the way to make room for the osteotomy. D. The osteotomy cuts. E. Reduction of the proximal fragment on the shaft. Inserting the Kirschner wires more proximally would allow for more lateralization of the shaft.
VALGUS OSTEOTOMY USING WAGNER PLATE FIXATION
A Kirschner wire is inserted just proximal to the proposed insertion site parallel to the planned angle of the plate.
The 115-degree Wagner plate is impacted through the lateral cortex of the femur, starting just above the level of the trochanteric apophysis and aiming toward the inferior aspect of the neck, at a preoperatively determined angle (TECH FIG 2).
Starting more proximally allows for more lateralization of the femoral shaft.
A Kirschner wire is inserted at the level of the lesser trochanter perpendicular to the shaft to act as a guide for the osteotomy.
A bone tenaculum is placed on the greater trochanter to allow for control of the proximal fragment after the osteotomy.
Two bone cuts are made parallel to the Kirschner wire, about 5 mm on either side of the wire, and then this cylindrical segment is removed.
This allows for some shortening to relieve pressure on the femoral head.
The thick medial periosteum must be divided to allow for valgus correction and lateralization of the shaft.
Reduction should be attempted without stressing fixation (prevents pullout).
The lateral cortex of the proximal fragment is abraded with the saw or with a burr to promote healing.
The plate is then brought down to the shaft so that the lateral cortex of the proximal fragment lies on or is impacted into the end of the distal fragment and is secured with two screws.
An interfragmentary screw may be inserted for added stability.
The vastus lateralis should be sutured securely to the greater trochanter to provide a lateral tension band.
TECH FIG 2 • Wagner plate fixation. Insertion of the plate parallel to the proximal guidewire.
VALGUS OSTEOTOMY USING ADOLESCENT BLADE PLATE FIXATION
A Kirschner wire is inserted just proximal to the proposed insertion site parallel to the planned angle of the plate.
The blade plate chisel is impacted through the lateral cortex of the femur, starting just above the level of the trochanteric apophysis and aiming toward the inferior aspect of the neck, at a preoperatively determined angle.
Starting more proximally allows for more lateralization of the femoral shaft.
A Kirschner wire is inserted at the level of the lesser trochanter perpendicular to the shaft to act as a guide for the osteotomy.
A bone tenaculum is placed on the greater trochanter to allow for control of the proximal fragment after the osteotomy.
Two bone cuts are made parallel to the Kirschner wire, about 5 mm on either side of the wire, and then this cylindrical segment is removed.
This allows for some shortening to relieve pressure on the femoral head.
The thick medial periosteum must be divided to allow for valgus correction and lateralization of the shaft.
Reduction is attempted without stressing the plate (prevents pullout).
The lateral cortex of the proximal fragment is abraded with the saw or with a burr to promote healing.
The plate is then brought down to the shaft so that the lateral cortex of the proximal fragment lies on or is impacted into the end of the distal fragment and is secured with screws.
An interfragmentary screw may be inserted for added stability.
The vastus lateralis should be sutured securely to the greater trochanter to provide a lateral tension band.
POSTOPERATIVE CARE
Radiographs are evaluated to ensure that instrument placement and alignment are appropriate.
The child is placed in a well-padded spica cast for 4 to 6 weeks or until bony healing is evident.
OUTCOMES
If adequate valgus is achieved, the triangular defect will spontaneously close by 3 to 6 months after surgery in nearly all patients.5
Fifty percent to 89% of operated hips sustain a premature closure of the proximal femoral physis, which occurs 1 to 2 years postoperatively and has not been found to correlate with patient age, surgical trauma, or degree of valgus.5,9
Recurrence has been reported in 30% to 70% of patients, though correction of the HEA to less than 38 degrees has been shown to have a 95% success rate.2
These patients must be monitored for recurrent varus deformity or significant LLD that may require further surgical intervention.
COMPLICATIONS
Recurrence
Proximal femoral physeal closure
Avascular necrosis
Implant failure
Infection
REFERENCES
· Bos C, Sakkers R, Bloem J. Histological, biochemical and MRI studies of the growth plate in congenital coxa vara. J Pediatr Orthop 1989;9:660–665.
· Carroll K, Coleman S, Stevens P. Coxa vara: surgical outcomes of valgus osteotomy. J Pediatr Orthop 1997;17:220–224.
· Chung S, Rider W. The histological characteristics of congenital coxa vara. Clin Orthop Relat Res 1978;132:71–81.
· Hensinger R. Congenital dislocation of the hip. Clin Symp 1979; 31:1–31.
· Kehl D, LaGrone M, Lovell W. Developmental coxa vara. Orthop Trans 1983;7:475.
· Langenskiold A, Riska E. Tibia vara (osteochondrosis deformans tibiae). J Bone Joint Surg Am 1964;46A:1405–1420.
· Pavlov H, Goldman B, Freiberger R. Infantile coxa vara. Pediatr Radiol 1980;135:631–640.
· Pylkkanen P. Coxa vara infantum. Acta Orthop Scand 1960;48 (Suppl):1–120.
· Schmidt T, Kalamchi A. The fate of the capital femoral physis and acetabular development in developmental coxa vara. J Pediatr Orthop 1982;2:534–538.
· Serafin J, Szulc W. Coxa vara infantum, hip growth disturbances, etiopathogenesis and long-term results of treatment. Clin Orthop Relat Res 1991;272:103–113.
· Wagner H. Femoral osteotomies for congenital hip dislocation. In: Acetabular Dysplasia: Skeletal Dysplasias in Childhood. Germany: Springer-Verlag, 1978:85–105.
· Weinstein J, Kuo K, Millar E. Congenital coxa vara: a retrospective review. J Pediatr Orthop 1984;4:70–77.
· Widmann R, Hresko M, Kasser J, et al. Wagner multiple K-wire osteosynthesis to correct coxa vara in the young child: experience with a versatile “tailor-made” high-angle blade plate equivalent. J Pediatr Orthop 2001;10:43–50.