Proximal Femoral Varus Osteotomy Using a 90-Degree Blade Plate

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 of the greater trochanter in the prone position.
- 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, one-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.
Computed tomography (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.
Magnetic resonance imaging (MRI) may be useful in evaluating associated problems, including labral tears, hip joint effusions, articular cartilage pathology, and femoral head vascularity.

NONOPERATIVE MANAGEMENT

Nonoperative management may be helpful for one of the associated conditions listed earlier.
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.