Unni G. Narayanan
DEFINITION
Femoral anteversion is the angle in the transverse plane by which the neck of the femur is directed (forward) relative to the transcondylar or coronal plane.
ANATOMY
Femoral anteversion is measured from the projection of the femoral neck axis and the transcondylar axis onto the (transverse) plane perpendicular to the long axis of the femur (FIG 1).
The terms femoral anteversion and femoral torsion are sometimes used interchangeably, the latter term preferred by those who believe that the orientation of the proximal femur relative to the distal condyles is a consequence of torsion occurring in the shaft of the femur rather than in the neck.6,17,20
PATHOGENESIS
At birth the femoral anteversion is estimated to be 30 to 50 degrees.
During normal development, as the child crawls, pulls up to stand, and then walks, hip extension against the anterior iliofemoral ligaments pushes back on the cartilaginous femoral head, gradually decreasing the femoral neck anteversion. The increased anteversion of infancy “unwinds” spontaneously with growth.
This natural remodeling process may be impaired because of abnormal hip anatomy, developmental delay, abnormal muscle tone, or ligamentous laxity, resulting in the persistence of the increased anteversion of infancy.21
Increased anteversion has been associated with a number of clinical conditions, including cerebral palsy, developmental hip dysplasia, and Perthes disease.2,7,12,24
NATURAL HISTORY
Physiologic Anteversion
In some children the increased anteversion of infancy may persist without any other identifiable pathology. This is the most common cause of in-toeing in children. Most of these cases resolve spontaneously with growth by the time of puberty.7
FIG 1 • Femoral anteversion is the angle in the transverse plane by which the neck of the femur is directed (forward) relative to the transcondylar or coronal plane.
In a few children, anteversion persists into adolescence. Most children compensate well and only in a small minority does this interfere with their gait or physical function.
Cerebral Palsy
Cerebral palsy is associated with developmental delay. By the time the child stands or walks, the more ossified femoral head and neck is less likely to remodel in response to increasing hip extension. This may be further compromised because of the presence of hip flexion contractures. Furthermore, spasticity of the muscles that internally rotate the femur, such as the medial hamstrings and anterior gluteals, may contribute to the development of increased anteversion. Consequently, the increased anteversion of infancy may persist or even increase.
To seat the femoral heads congruously within the acetabulum during walking, the limb is internally rotated and the pelvis tilted anteriorly (increased lumbar lordosis), resulting in significant gait anomalies.8
In the face of increased femoral anteversion, the greater trochanter and the insertion of the gluteus medius are located more posterior. This effectively reduces the abductor lever arm.1
In children with severe nonambulatory cerebral palsy, the increased anteversion and coxa valga are features of the hip at risk for dislocation.
Increased anteversion is a component of “miserable malalignment syndrome,” which has been implicated as a source of patellofemoral pain and instability.5,13
There is conflicting evidence linking abnormally increased or decreased femoral anteversion with osteoarthritis of the hip and knee.26,27
Slipped capital femoral epiphysis has been associated with decreased anteversion or even retroversion.9
PATIENT HISTORY AND PHYSICAL FINDINGS
This is a common cause for in-toeing in children.
Children are more likely to sit in the W position and may not be able to sit cross-legged (FIG 2). This is because their hips can rotate internally more than they can rotate externally.
Normal foot progression angle during walking is 5 to 10 degrees external. Internal foot progression angle accompanied by medial or internal rotation of the knee is attributable to increased internal rotation at the hip associated with increased femoral anteversion.
Normal or even abnormal external foot progression angle may be present in the face of increased femoral anteversion when it is accompanied by excessive external tibial torsion.
Examination of the torsional profile in the prone position indicates the presence of increased femoral anteversion. The arc of internal rotation exceeds the arc of external rotation of the hip.
FIG 2 • W-sitting (A) is easier than sitting cross-legged (B) for children with increased femoral anteversion.
The magnitude of anteversion can be quantified by physical examination using the palpable prominence of the greater trochanter as a proxy for the femoral neck axis. This method, first described by Netter,15was adapted by Ruwe and associates,19 who also described an intraoperative method to estimate anteversion that could be applied at the time of derotational osteotomy of the proximal femur.
The accuracy of the physical examination method has been evaluated by Davids and coworkers.3
IMAGING AND OTHER DIAGNOSTIC STUDIES
A number of imaging techniques have been described to estimate femoral anteversion, including plain radiography,11 fluoroscopy, CT,4,14,23 ultrasonography,25 and MRI10 (FIG 3).
DIFFERENTIAL DIAGNOSIS
Increased anteversion is encountered in the following situations:
Physiologic anteversion
“Miserable malalignment syndrome”
Cerebral palsy
Developmental hip dysplasia
Legg-Calvé-Perthes disease
NONOPERATIVE MANAGEMENT
Attempts to treat increased femoral anteversion with twister cables and other braces have been abandoned as the natural history of spontaneous remodeling came to be understood.22
SURGICAL MANAGEMENT
Indications
Increased anteversion with severe medial rotation of the lower extremity and increased internal foot progression angle that has failed to resolve by adolescence, and is interfering with gait and function due to tripping
Increased femoral anteversion associated with increased external tibial torsion and genu valgum, the so-called miserable malalignment syndrome when it is associated with patellar instability or patellofemoral pain refractory to nonoperative methods of treatment
Increased femoral anteversion in children with ambulatory cerebral palsy, in whom the increased internal rotation of the hip results in significant abductor “lever arm dysfunction,” leading to impaired gait efficiency, instability, and tripping. Increased femoral anteversion may be accompanied by increased external tibial torsion, which must be simultaneously addressed with internal tibial derotational osteotomies to optimize the ultimate foot progression angle while walking.
Increased anteversion along with coxa valga is a component of the abnormal proximal femoral anatomy in longstanding cases of congenital, developmental, or neurogenically acquired hip dislocations. In these instances, the proximal femoral derotational osteotomy is combined with varusization of the femoral neck. The proximal femoral varus derotational osteotomy is described in Chapter PE-27.
Preoperative Planning
Preoperative planning involves quantifying the extent of the femoral anteversion in order to guide the extent of derotation required.
Assessment of the torsional profile of the entire limb is critical because any proximal corrections will result in distal consequences if distal torsional malalignments are not taken into consideration and concurrently addressed.
In most children physical examination by the method described above is adequate to detect the presence of increased anteversion and to quantify it accurately enough to guide surgical correction. Generally, preoperative axial imaging such as CT scan is unnecessary, as the magnitude of intraoperative corrections is also based on the physical examination technique.
In children with ambulatory cerebral palsy whose femoral anteversion is possibly one of a number of multilevel lower extremity soft tissue and bony abnormalities, there may be great value in conducting a 3-D gait analysis. Gait analysis provides a dynamic assessment that can provide useful transverse plane kinematics and kinetics to help guide the decision regarding the need for and amount of derotation.
Plane radiographs are important, including an anteroposterior (AP) view of the pelvis to include the proximal femurs and frog-leg lateral views of each proximal femur.
FIG 3 • CT method of estimating femoral anteversion involves overlapping images of three slices: the femoral head, the femoral neck at the base, and the distal femur through the femoral condyles.
FIG 4 • A. Supine position. The line of incision along the proximal femur demarcated relative to the top of the greater trochanter. B,C. Prone position allows the torsional profile to be estimated intraoperatively.
Positioning
The supine position is preferred when other operations necessitating this position are necessary, such as intramuscular psoas lengthening, pelvic osteotomies, or rectus femoris transfers (FIG 4A).
The prone position has the advantage of permitting the same intraoperative assessment of the torsional profile as the preoperative assessment (FIG 4B,C). The exposure is facilitated by the reflected vastus lateralis falling away from the field of surgery owing to gravity.
The prone position allows other concomitant operations to be performed, such as posterior knee (hamstring lengthening) or posterior calf surgery.
This position does not permit anterior pelvic or hip surgery.
Approach
Standard lateral approach to the proximal femur
TECHNIQUES
PROXIMAL FEMORAL DEROTATIONAL OSTEOTOMY WITH 90-DEGREE AO BLADE PLATE: SUPINE TECHNIQUE
Positioning, Incision, and Exposure
The patient is positioned supine on the radiolucent table.
The image intensifier is set up perpendicular to the long axis of the table, from the contralateral side, to obtain clear AP and frog-leg lateral images of the proximal femur.
Both lower extremities are prepared and draped free to permit assessment and comparison of the torsional profile.
A longitudinal incision is made along the lateral aspect of the proximal thigh starting at the level of the greater trochanteric prominence and extended distally for about 10 to 12 cm in line with the femur.
The underlying fascia lata is divided in line with the skin incision to expose the vastus lateralis and the overlying bursa at the level of the greater trochanter.
The vastus lateralis is divided transversely at its origin on the trochanteric ridge, which corresponds to the inferior level of the insertion of the gluteus medius anteriorly (TECH FIG 1A).
The vastus lateralis separation is continued inferiorly in an L-shaped manner along its posterior margin just anterior to the insertion of the gluteus maximus (TECH FIG 1B).
TECH FIG 1 • Exposure of the proximal femur through a standard lateral approach. A. Origin of vastus medialis at the trochanteric ridge. B. Detaching the vastus lateralis from the trochanteric ridge in Lshaped cut. C. Subperiosteal elevation of the vastus lateralis from the lateral surface of the proximal femur. D. Exposure of the lateral surface of proximal femur, with the vastus lateralis reflected anteriorly.
To minimize injury to the muscle belly, the thin fascia over the vastus lateralis is divided along the posterior margin close to the linea aspera, and the muscle is peeled off the septum with a broad elevator or cautery until the subperiosteal surface of the lateral aspect of the proximal femur is exposed (TECH FIG 1C).
Care is taken to identify and cauterize the perforators as they are encountered.
The vastus lateralis is then elevated subperiosteally until the lateral surface of the femur is adequately exposed for sufficient distance to accommodate the length of the blade plate (TECH FIG 1D).
At the level of the planned osteotomy, at the upper end of the lesser trochanter, the periosteum is elevated circumferentially with a narrow curved elevator.
The transverse osteotomy at this level heals rapidly and permits the use of strong internal fixation (blade plate), obviating the need for casting or any other external immobilization.
Preparation for Osteotomy and Fixation
Using the image intensifier, a guide pin is inserted through the middle of the superior portion of the proximal femoral neck at an angle that is 90 degrees to the long axis of the femur.
An effective way of ensuring that the initial guide pin is in the middle of the femoral neck axis in the transverse plane is to internally rotate the lower extremity and hip until the prominence of the greater trochanter is directly lateral. This usually occurs when the neck axis has been horizontalized.
With the lower extremity held in this position, the guide pin can be inserted parallel to the floor.
Because the greater trochanter is set slightly posterior relative to the neck axis, the starting point is best made in line with the middle of the AP width of the femur just distal to the greater trochanter.
On the AP image the guide pin needs to be sufficiently proximal (superior) to provide enough room to permit the introduction of the seating chisel inferior to the guide pin (TECH FIG 2A).
On the frog-leg lateral view, the guide pin should lie in the middle of the femoral neck in line with the neck axis (TECH FIG 2B).
The seating chisel is then used to create the hole in the bone to accommodate the blade plate.
Depending on the age of the child and the size of the bone, the matching seating chisel corresponding to the appropriately sized blade plate is used (infant, toddler, child, adolescent, or adult).
The seating chisel must be inserted perpendicular to the long axis of the femur if derotation is the only objective (TECH FIG 2C). Any deviation from the perpendicular on the AP view will lead to varus or valgus changes in the neck–shaft axis.
The face of the seating chisel should also be perpendicular to the long axis (in the sagittal plane) to prevent unintended flexion or extension through the osteotomy (TECH FIG 2D).
The direction of the seating chisel for the blade plate can be adjusted if the guide pin is not perfectly aligned.
Alternatively, if a cannulated seating chisel is available, the guide pin must be placed in the correct position for the seating chisel.
The disadvantage of a cannulated system is that there is no room for error in the placement of the guide pin. Furthermore, the blade plate itself is not cannulated, which necessitates removal of the guide pin (in addition to the seating chisel) at the time of insertion of the blade plate, which removes an important guide for its introduction.
TECH FIG 2 • Intraoperative C-arm–guided insertion of the seating chisel for the blade plate. A. Insertion of the guide pin in the superior part of the neck at right angles to the long axis of the femur. B. Position of the guide pin along the midfemoral neck axis in the frog-leg lateral view. C.Position of the seating chisel parallel to the guide pin and perpendicular to the long axis of the femur. D. Position of the seating chisel parallel to the guide pin and along the midfemoral neck axis on the frog-leg lateral view. E. The seating chisel is backed out from its final position to disimpact the chisel before the osteotomy.
TECH FIG 3 • Completion of transverse osteotomy, derotation, and fixation with 90-degree blade plate. A. Level of the osteotomy is at upper end of the lesser trochanter 1.5 cm below the seating chisel. Two parallel AP guide pins proximal and distal to the osteotomy line are used to judge the magnitude of derotation. B,C. Transverse osteotomy parallel to the seating chisel and perpendicular to the long axis of the femur.
The seating chisel is advanced up to the depth of the selected blade length. The depth in millimeters of the seating chisel is marked on its inferior surface.
In older ambulatory children with healthy bone, the seating chisel should be intermittently backed out to prevent its impaction in the strong bone.
It is prudent to back the chisel out, short of its final resting position, before completion of the osteotomy to facilitate its removal in exchange for the blade plate (TECH FIG 2E).
Osteotomy
The level of the transverse osteotomy is marked on the bone with a marking pen or cautery. This is done about 1 to 1.5 cm below the level of the seating chisel, at the upper end or just proximal to the lesser trochanter (TECH FIG 3A).
The periosteum is elevated circumferentially at this level to allow placement of protective retractors during the osteotomy.
Two smooth pins (2.5-mm Kirschner wires) are placed in an anterior-to-posterior direction parallel to each other and perpendicular to the long axis, just proximal and distal to the proposed osteotomy site respectively (TECH FIG 3A).
These two pins will serve as useful retractors of the vastus lateralis muscle anteriorly, and as joysticks to retain effective control of the proximal and distal segments after the osteotomy.
At the time of the derotation, the angle between the distal and proximal pins accurately gauges the magnitude of correction obtained and maintained during fixation of the blade plate.
The transverse osteotomy is completed with an oscillating saw directed perpendicular to the long axis of the femur and parallel to the seating chisel above (TECH FIG 3B,C).
Derotation and Fixation
The seating chisel is removed in exchange for the matching 90-degree blade plate of appropriate blade length (TECH FIG 4A).
The blade is inserted manually into the seating hole using thumb pressure. The blade plate holder is struck with a mallet to advance the blade until the plate lies adjacent to the lateral surface of the femur (TECH FIG 4B).
The plate is held against the distal segment of the femur using a plate-holding clamp such as the Verbrugge clamp (TECH FIG 4C).
Before securing the plate, the lower extremity (along with the distal femoral segment) is externally rotated by the desired angle of derotation that can be estimated by the position of the distal pin relative to the proximal pin (TECH FIG 4D).
Since the guide pin in the femoral neck has been placed along the middle of the neck axis, it is relatively simple to estimate the new femoral anteversion.
If the lower extremity is held with the patella positioned anteriorly, then the angle between the femoral neck guide pin and the horizontal plane is the new angle of femoral anteversion.
Once the desired degree of derotation has been set, the plate is secured to the bone with standard fully threaded cortical screws (3.5 small fragment for the infant and toddler blade plates; 4.5 large fragment screws for the child size and up).
TECH FIG 4 • A. A 90-degree blade plate of appropriate blade length on the handle. B. Insertion of the blade plate after removal of the seating chisel. C. The plate is held against the femur with a plate-holding (Verbrugge) clamp. D. The distal fragment is externally rotated by the desired amount using the two AP pins to judge the angle of correction. E. The plate is secured with cortical screws and the osteotomy is compressed. F. An impacter is used to advance the blade plate to its full depth. G. AP view of the proximal femur. H. Frog-leg lateral view of the proximal femur.
After fixation with the first screw, the arc of rotation is estimated (with the hip extended) using the guide pins to quantify the amount of internal and external rotation from the neutral position.
At least two of the screws are placed eccentrically to compress the osteotomy site (TECH FIG 4E).
The impacter is used to advance the blade plate to its full depth (TECH FIG 4F).
The guide pins are removed and AP and frog-leg lateral images obtained to confirm satisfactory position of the blade plate (TECH FIG 4G,H).
Wound Closure
The vastus lateralis is reattached to its origin on the trochanteric ridge with absorbable braided 0 suture so that the entire plate is covered (TECH FIG 5). Two or three tacking sutures are used to reattach the posterior edge of the vastus fascia to the septum.
The wound is closed in layers, including the fascia lata, the subcutaneous tissue, and the skin. Absorbable running subcuticular suture will obviate the need for suture removal.
TECH FIG 5 • Repair of vastus lateralis to its origin to cover the blade plate.
PROXIMAL FEMORAL DEROTATIONAL OSTEOTOMY WITH 90-DEGREE AO BLADE PLATE: PRONE TECHNIQUE18
The patient is positioned prone on appropriate (low) bolsters to support the chest and iliac crests, keeping pressure off the abdomen and the genitalia.
The table mattress padding under the thigh segments can be built up to keep the hips relatively extended.
The approach and dissection are identical to those described for the supine technique; only the orientation must be remembered with the anterior vastus lateralis now falling away from the operative field (TECH FIG 6A).
The torsional profile in the prone position is much easier to verify and compare with the contralateral side (TECH FIG 6B,C).
TECH FIG 6 • Proximal femoral derotation osteotomy using the prone technique. A. Orientation of the exposure in the prone position. B,C. Intraoperative ability to estimate the torsional profile.
PROXIMAL FEMORAL DEROTATIONAL OSTEOTOMY WITH A REGULAR LOW-CONTACT DYNAMIC COMPRESSION (LCDC) PLATE
Using the identical approach described above, the derotational osteotomy can be stabilized with a regular LCDC plate.
For secure fixation, the osteotomy would have to be done lower, in the subtrochanteric region, to allow a sufficient number of screws (at least three) proximal to the osteotomy.
The fixation is not as strong as that afforded by a blade plate but might be adequate in most children.
This is not a good technique if derotation of the proximal femur is combined with varusization for hip instability.
DISTAL FEMORAL DEROTATIONAL OSTEOTOMY
There is controversy about whether a distal or proximal femoral osteotomy is the optimal method to address abnormal femoral torsion or anteversion.
The distal femoral derotational osteotomy is described elsewhere.
POSTOPERATIVE CARE
With secure blade plate fixation, external immobilization is seldom if ever required. External immobilization in the form of a below-knee cast or a knee immobilizer may be indicated for concomitant procedures, but not for the femoral derotational osteotomy per se.
Touch-down weight bearing (no more than the weight of the lower extremity) is permitted on the affected lower extremity.
If the procedure is done bilaterally, the child is unable to bear weight safely and a wheelchair is required.
Depending on the age and ambulatory status of the child, progressively increased weight bearing is permitted from 4 to 6 weeks postoperatively.
Supported weight bearing in a pool may be possible as early as 3 weeks postoperatively.
Once there is clinical and radiographic evidence of union and consolidation of the osteotomy, all restrictions can be lifted (FIG 5).
OUTCOMES
Little is known about the long-term outcomes of femoral derotational osteotomies, as these are seldom done in isolation.
FIG 5 • Postoperative AP and lateral radiographs.
If adequate correction is achieved, ambulatory patients can expect to experience noticeable benefits in the appearance of their gait. Whether there are measurable functional improvements is less clear.
In conditions like cerebral palsy, the primary pathology in the brain cannot be addressed. Consequently, the abnormal forces that created the increased anteversion in the first place may contribute to its recurrence in the growing child.
There is no clear indication for routine removal of hardware.
COMPLICATIONS
Undercorrection
Overcorrection
Unrecognized or unaddressed abnormal tibial torsion
Recurrence
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