Tom F. Novacheck
DEFINITION
Proximal femoral varus osteotomy can be useful for many conditions:
Coxa valga deformity
Hip subluxation (nearly all etiologies)
Containment for Perthes disease
Degenerative arthrosis
Correction in other planes can be accomplished simultaneously (derotation and extension–flexion). Proximal femoral varus osteotomy can be accomplished at any age as satisfactory implants are available for all bone sizes.
In some situations (eg, neuromuscular disease), it may be necessary to address the etiology of the proximal femoral deformity and hip disease simultaneously.
ANATOMY
The normal femoral neck–shaft angle is 135 degrees (range 120 to 150 degrees).
The true neck–shaft angle cannot be directly assessed from an anteroposterior (AP) pelvis radiograph unless femoral anteversion is compensated for by internally rotating the femur to eliminate it.
The tip of the greater trochanter is at the level of the center of the femoral head.
The neck–shaft angle at birth is typically 150 degrees, decreasing to 135 degrees by skeletal maturity.
Normal anteversion at birth is 45 degrees, decreasing to 10 degrees in boys and 15 degrees in girls by 8 years of age.
PATHOGENESIS
The development of normal femoral anatomy and resolution of fetal bone alignment requires the attainment of gross motor activities at a typical age and is dependent on normal musculoskeletal forces. Both of these can be affected by neuromuscular conditions such as cerebral palsy or myelomeningocele.
Patients with Perthes disease may have a subluxated or uncovered femoral head even with proximal femoral anatomy that is normal except for the avascular femoral head segment. Even so, with good neuromuscular function, varusizing the femur can be well tolerated and can improve the containment of the diseased femoral head.
Contributing factors to the hip joint pathology may include musculotendinous contractures, ligamentous laxity, and coexistent acetabular dysplasia. If present, these may also require direct treatment. Adductor lengthening, psoas lengthening, open reduction of the hip with capsulorrhaphy, and acetabuloplasty may need to be considered.
Proximal femoral deformity can have an adverse effect on hip joint development and exacerbates or contributes to muscle imbalance about the hip.1
NATURAL HISTORY
In neuromuscular conditions, if femoral head uncoverage exceeds 50% based on the Reimer migration index, then further subluxation and dislocation are likely.4
Femoral head uncoverage during the resorption and reossification stages of Perthes disease puts the hip at risk for a poor outcome with permanent deformity of the femoral head.2
A poor outcome radiographically predisposes to early hip degeneration.5
PATIENT HISTORY AND PHYSICAL FINDINGS
There are no physical findings that are diagnostic for coxa valga.
The typical history for neuromuscular conditions, developmental dysplasia of the hip, or Perthes disease will be present in patients who may be candidates for a proximal femoral varus osteotomy.
In these cases, the associated musculotendinous or joint contractures may be present on physical examination and could include hip flexion contracture, hip adduction contracture, or altered transverse plane rotation.
In Perthes disease, restricted internal hip rotation and abduction are common.
Femoral anteversion is tested by palpation.
When the trochanter is most prominent laterally, the femoral neck is horizontal. In the absence of tibial deformity (varus or valgus), the tibial shaft is essentially perpendicular to the posterior aspect of the femoral condyles. The angular difference between the tibial shaft and a vertical line indicates the anteversion. In an otherwise normal hip, the anteversion is about 20 degrees less than the maximum internal rotation range of motion (ROM).
Excessive femoral anteversion is typically seen in neuromuscular conditions and in developmental dysplasia of the hip and leads to excessive internal hip rotation and a corresponding lack of external hip rotation when tested in the prone position.
Examining the hip ROM is essential for a differential diagnosis and to evaluate associated problems such as joint contracture, muscle imbalance, and musculotendinous contracture.
Normal total transverse plane ROM of the hip is about 90 degrees. Normally a third of the available ROM is internal and two thirds is external.
Restricted ROM can indicate a joint abnormality, capsular contracture, or spasticity of the internal or external rotators of the hip.
Excessive ROM indicates relative ligamentous laxity.
Shifted ROM (eg, excessive internal ROM) indicates excessive femoral anteversion.
In adolescents and young adults being evaluated for early degenerative arthrosis, pain may be found at the extremes of ROM. Severe ROM restrictions could be a contraindication to consideration of realignment osteotomy in these cases.
IMAGING AND OTHER DIAGNOSTIC STUDIES
A plain AP pelvis radiograph with anteversion eliminated is diagnostic of coxa valga.
If anteversion is normal, no compensation for hip rotation is necessary.
If anteversion is excessive, the AP pelvis radiograph should be taken with the hip internally rotated to obtain a true AP view of the proximal femur.
Hip flexion and adduction deformities can be identified by asymmetries in femoral position or asymmetric pelvic position.
Acetabular dysplasia should be ruled out.
Hip subluxation or femoral head uncoverage is assessed. Signs of degenerative arthrosis are sought.
CT scans (including three-dimensional reconstruction) are not useful or needed for primary proximal femoral deformities but can be helpful in evaluating acetabular dysplasia or potentially in revision cases.
MRI may be useful in evaluating associated problems, including labral tears, hip joint effusions, narrowing of articular cartilage, and femoral head vascularity.
DIFFERENTIAL DIAGNOSIS
Hip joint contracture
Hip joint subluxation
Femoral anteversion or retroversion
Musculotendinous contracture
Acetabular dysplasia
NONOPERATIVE MANAGEMENT
Nonoperative management may be helpful for one of the associated conditions listed above.
There is no nonoperative treatment for bone deformity that is clinically significant and adversely affecting hip joint development.
SURGICAL MANAGEMENT
Preoperative Planning
The AP pelvis radiograph is reviewed.
The size of implant is chosen based on radiographic templates.
The amount of varusization can be determined based on radiographs preoperatively or on intraoperative findings. Other associated problems (musculotendinous contracture, joint instability, and acetabular dysplasia) are addressed concurrently.
There is no examination under anesthesia to determine the amount of varusization to accomplish. An examination under anesthesia can guide decision making regarding concurrent tendon lengthening.
Varusization will inevitably shorten the extremity. The effect on leg length can be controlled by altering the amount of varusization and the size of the wedge of bone removed (if any) depending on preoperative leg-length assessment. Varus can be accomplished using a medial closing or lateral opening osteotomy.
Positioning
Although some surgeons prefer to perform proximal femoral varus osteotomy with the patient supine, I prefer the prone position with the leg draped free (FIG 1).
This allows ease of exposure posterior to the muscle belly of the vastus lateralis.
The prone position also allows accurate control of femoral torsion comparable to the prone physical examination for femoral anteversion by palpation, thereby improving consistency of surgical realignment.
Approach
A direct lateral approach to the proximal femur is routine. The procedure involves placing the chisel for the blade plate in the appropriate position in the femoral neck corresponding to the amount of varus to accomplish (eg, 20-degree varus correction corresponds to 70-degree chisel placement relative to the lateral femoral cortical surface: 90-degree blade plate minus 70 degrees equals 20 degrees varusization), completing the osteotomy, and placing the 90-degree blade plate as detailed in the Techniques section.
FIG 1 • Prone positioning allows easy access to divide the vastus lateralis posteriorly and replicates the position for physical examination for femoral anteversion, allowing improved accuracy and reliability of assessment and correction of femoral torsional alignment.
TECHNIQUES
EXPOSURE
A longitudinal lateral incision is made over the proximal femur matching the length of the blade plate.
The fascia lata is divided in line with the skin incision (TECH FIG 1A).
The vastus lateralis is reflected from its proximal and posterior origins and elevated to expose the proximal femur subperiosteally.
Circumferential subperiosteal elevators are placed in the intertrochanteric area to protect the soft tissues (TECH FIG 1B).
TECH FIG 1 • A. The fascia of the vastus lateralis is divided transversely at the greater trochanteric apophysis and posteriorly in the periosteum of the intertrochanteric area and longitudinally adjacent to the insertion on the linea aspera (in the prone position, up is posterior). B.The vastus lateralis is elevated subperiosteally, and Crego retractors are placed circumferentially at the intertrochanteric level.
GUIDEWIRE PLACEMENT
A fluoroscope is used to guide placement of a guidewire in both the AP and lateral views.
The entry point is just below the greater trochanteric apophysis if the patient is skeletally immature and through the greater trochanter after maturity.
The entry point is chosen to allow insertion of the guidewire and chisel without violating the medial calcar.
The anterior-to-posterior placement is determined in the view obtained by flexing the hip and knee (with the knee over the edge of the operating table) and internally and externally rotating the hip until the fluoroscopic image shows the femoral neck and femoral shaft colinear with the guidewire placed centrally and parallel to the neck and shaft of the femur (TECH FIG 2A).
The orientation of the pin on the AP view is controlled with an osteotomy triangle (TECH FIG 2B,C).
If preoperative planning indicated a 15-degree varusization goal, a 75-degree triangle would be used (see the Approach section above).
Alternatively, determination can be made based on preoperative and desired postoperative alignment; for example, the preoperative neck–shaft angle (150 degrees) minus the desired postoperative neck–shaft angle (120 degrees) equals 30 degrees of varusization. In this case, the guidewire would be placed at a 60-degree angle to the femoral shaft when using the 90-degree plate.
The anteversion is determined (transverse plane) by the angle between the pin (placed as described above) and the tibial shaft (perpendicular to the posterior aspect of the femoral condyles when the knee is flexed, provided there is no tibial varus or valgus).
TECH FIG 2 • A. A guidewire placed just below the apophysis and in line with the femoral shaft. B. Intraoperative C-arm view showing the guidewire at a 110-degree angle to the femoral shaft. C. The ideal lateral projection with femoral neck, femoral shaft, and guidewire coplanar improves accuracy and consistency.
PLACEMENT OF THE BLADE PLATE CHISEL
The appropriate-size chisel for the blade plate is then placed just below and exactly parallel to the pin to the desired depth (greatest depth possible depending on anatomy and available length of the blade plate; TECH FIG 3).
The chisel should be dislodged 5 to 10 mm before the osteotomy to allow for ease of later removal.
TECH FIG 3 • A. The chisel is placed exactly in line with the pin. B. Anteversion in this case is 35 degrees. C,D. Chisel position confirmed in the AP and lateral projections.
PERFORMING THE OSTEOTOMY
The details of the osteotomy are based on preoperative planning.
To minimize the shortening effect of the osteotomy on leg length in a child, a single transverse osteotomy can be performed in the intertrochanteric area (TECH FIG 4).
This will result in a lateral opening osteotomy.
Alternatively, a wedge of bone can be removed to accomplish a medial closing osteotomy.
Wedge Osteotomy
The first osteotomy is performed parallel to the chisel.
The entry point for the osteotomy saw blade is determined by the implant (distance between the blade and the subsequent angle in the plate for medialization).
A second osteotomy is then performed perpendicular to the femoral shaft.
The starting level for this osteotomy varies depending on the desired amount of shortening of the extremity.
A beginning point identical to the entry point for the first osteotomy achieves full contact of the osteotomy after fixation.
A lateral starting level distal to the first removes a portion of the lateral femoral cortex, achieving more shortening, but is limited by the insertion of the psoas tendon on the lesser trochanter (typically should not be violated).
An entry point proximal (within the cut of the first osteotomy) leads to less shortening, but incomplete final apposition of the osteotomy surfaces.
TECH FIG 4 • A. An oscillating saw is used 10 to 12 mm distal and parallel to the chisel. B. The completed osteotomy. A second (optional) osteotomy could be performed at this point.
PLACEMENT OF THE BLADE PLATE
Realignment and fixation of the osteotomy are achieved by placing the blade plate.
The chisel is removed and the blade plate is placed in the chisel path parallel to the guidewire and impacted to its final position (TECH FIG 5A).
The femoral shaft is reduced to the plate and held in position with a Verbrugge clamp (TECH FIG 5B).
Final anteversion alignment is controlled at this point (TECH FIG 5C).
The first two screws are typically placed in compression to optimize fixation and promote rapid healing (TECH FIG 5D).
Alignment is checked after placement of the first screw both radiographically and by physical examination.
If satisfactory, the final screws are placed. If not, alignment is adjusted accordingly.
Final radiographs are taken in both views (TECH FIG 5E,F).
The wound is closed in layers.
TECH FIG 5 • A. The chisel has been replaced with the blade plate (guidewire is still in place). B. Correction of deformity by reducing the plate to the femoral shaft with a Verbrugge clamp. C. Anteversion is assessed before guide pin removal (corrected to 10 degrees). D.Fixation is complete (note well-apposed osteotomy surfaces). E,F. Postoperative AP and lateral views confirming implant placement, proper osteotomy alignment, and appropriate medialization of the femoral shaft to align the piriformis fossa with the intramedullary canal.
FIG 2 • Bilateral short leg casts with a Denis-Browne bar incorporated controls rotational alignment postoperatively. Knee immobilizers improve comfort by preventing flexion-extension caused by spasms of the hip flexors and hamstrings.
POSTOPERATIVE CARE
Weight-bearing status and immobilization depend on patient age, condition being treated, compliance, bone size, implant size, and bone quality.
Weight bearing can vary from toe-touch to non-weight bearing for the first 3 to 6 weeks.
With poor bone quality, small bone size, small implant size, or poor compliance, a spica cast should be applied.
In intermediate situations, bilateral short-leg casts with a Dennis Brown bar can be applied along with knee immobilizers (FIG 2).
Unrestricted range of motion without external immobilization may be allowed (eg, most adults).
A range-of-motion and strengthening program often is instituted at 3 to 4 weeks postoperatively.
Advancement to full weight bearing can be accomplished within 6 to 8 weeks of the procedure, depending on muscle strength.
OUTCOMES
Patients over 8 years of age with moderate Perthes disease (lateral pillar B or B/C border) have a better outcome with surgery.2
The complex spectrum of cerebral palsy hip subluxation, hip dysplasia, and dislocation can be treated successfully in most cases using a treatment algorithm that incorporates femoral varus and derotation osteotomy. While there is a risk of recurrence and complications, McNerney and associates3 reported excellent results with aggressive surgical management with a low rate of complications and repeat acetabuloplasty or varus osteotomy.
COMPLICATIONS
Excessive varusization leading to hip abductor insufficiency
Implant failure
Malunion
Nonunion
Deep venous thrombosis in adults
Infection
Avascular necrosis
Implant irritation contributing to Trendelenburg gait
Overcorrection or undercorrection
REFERENCES
1. Gage JR. Gait and lever arm dysfunction. In Gage JR, ed. The treatment of gait problems in cerebral palsy. London: MacKeith Press, 2004:180–204.
2. Herring JA, Kim HT, Browne R. Legg-Calve-Perthes disease, part II: prospective multicenter study of the effect of treatment on outcome. J Bone Joint Surg 2004;86A:2121–2133.
3. McNerney N, Murbarak S, Wenger D. One-stage correction of the dysplastic hip in cerebral palsy with the San Diego acetabuloplasty: results and complications in 104 hips. J Pediatr Orthop 2000; 20:93–103.
4. Reimers J. The stability of the hip in children: a radiological study of results of muscle surgery in cerebral palsy. Acta Orthop Scand Suppl 1980;184.
5. Stulberg SD, Cooperman DR, Wallensten R. The natural history of Legg-Calve-Perthes disease. J Bone Joint Surg 1981;63A:1095–1108.