Coxa Vara

Normal Hip

• Neck-Shaft Angle: 135 degrees (Adult), 150 degrees (Infant).
• Neck Version: 15 degrees Anteversion.
• Physis: Generally horizontal, subjected to compressive loads. Compression stimulates growth (Heuter-Volkmann).
• Abductors: Gluteus Medius inserts on GT. Distance from center of rotation (Head) to GT provides the lever arm.

Normal mechanics favor joint stability.

This relationship is crucial for gait efficiency and prevention of abductor lurch.

Coxa Vara Deformity

• Neck-Shaft Angle: Decreased (less than 120 degrees). Often severe (less than 90 degrees).
• Physis: Vertical orientation.
  • Shear Stress: The vertical physis sees excessive shear.
  • Growth Arrest: Shear inhibits physeal growth, worsening the deformity (Vicious Cycle).
• Acetabulum: Often shallow (dysplastic) due to altered forces.
• Femur: Shortened. Retroverted.
• Fairbank's Triangle: An inverted V-shaped radiolucency in the inferior aspect of the neck. It represents the cartilaginous defect in ossification.

The deformity is self-perpetuating due to shear forces.

This is known as the Vicious Cycle of developmental varus.

Functional Implications

1. Abductor Weakness:
   • The Greater Trochanter is elevated (relatively).
   • The Femoral Neck is short.
   • Result: Functional shortening of the abductor lever arm.
   • Trendelenburg Gait: Gluteus medius cannot hold the pelvis level.
2. Joint Reaction Force:
   • Increased secondary to loss of mechanical advantage.
   • Accelerates degenerative changes (OA).
3. Shear:
   • Increased shear across the vertical physis predisposes to Sillipes (pseudo-slipped capital femoral epiphysis) or progression of deformity.

The biomechanics dictate the treatment strategy.

1. Congenital (Present at birth):

• Associated with femoral dysplasia/PFFD.
• Short femur.

2. Developmental (Infantile):

• Normal at birth.
• Presents at walking age (waddle).
• Classic type with Fairbank's triangle.

3. Acquired:

• Trauma: Physis arrest, Malunion.
• Infection: Septic hip destroying head/neck.
• Metabolic: Rickets, Renal Osteodystrophy.
• Dysplasia: Fibrous Dysplasia (Shepherd's Crook), Osteogenesis Imperfecta.
• Perthes: Sequel of head collapse.

The etiology guides the recurrence risk.

Based on Radiographic Appearance:

• Type 1: No visible physis defect.
• Type 2: Vertical physis with Fairbank's triangle (Classic).
• Type 3: Old healed or fused physis (Adult).

Note: The HE Angle is more useful for prognosis than the Amstutz types.

• Gait: Trendelenburg gait (lurching to affected side). If bilateral, "Waddling gait".
  • Stance: Positive Trendelenburg Test.
  • Leg Length: True Leg Length Discrepancy (Shortening on affected side).
  • ROM:
    • Abduction: Restricted (finding of impingement of GT on ilium).
    • Internal Rotation: Restricted (due to retroversion).
    • Flexion: Usually preserved.
  • Posture: Increased lumbar lordosis (if bilateral).

X-Ray Assessment

• Views: AP Pelvis (standing) and Frog Lateral.
• Neck-Shaft Angle: Measure intersection of neck axis and shaft axis. less than 120 is diagnostic.
• Fairbank's Triangle: Look for the triangular fragment in inferior neck.
• Hilgenreiner's Epiphyseal Angle (HEA):
  • Line through triradiate cartilages (Hilgenreiner's line).
  • Line through the capital femoral physis.
  • Normal: less than 25 degrees.
  • Pathologic: greater than 60 degrees.

Observation

• Indications:
  • HEA less than 45 degrees.
  • Asymptomatic.
  • No progression on serial X-rays.
• Protocol: X-rays every 6-12 months.
• Outcome: The majority of curves with HEA less than 45 will spontaneously correct as the child grows.

Shoe lifts can be used for leg length discrepancy but do not correct the deformity.

Surgical Correction

• Indications:
  • HEA greater than 60 degrees (Progression is certain).
  • HEA 45-60 degrees with documented progression.
  • Significant gait abnormality / Trendelenburg.
  • Pain (rare).
• Procedure: Valgus Intertrochanteric Osteotomy (VRO).
• Goal:
  • Correct NSA to greater than 140 (overcorrect).
  • Reduce HEA to less than 30 (horizontal physis).
  • Correct retroversion.

Valgus Intertrochanteric Osteotomy

Principle: A closing wedge valgus osteotomy (remove lateral wedge) or opening wedge medial. Closing wedge is safer for union.

Steps:

1. Setup: Supine on radiolucent table. Fluoroscopy.
2. Approach: Direct lateral approach to proximal femur. Elevate Vastus Lateralis.
   • Careful hemostasis of perforating vessels.
   • Expose the flare of the greater trochanter.
3. Guide Wire: Insert guide wire into femoral neck/head.
   • The angle of insertion determines correction.
   • If using a 130 deg blade plate, insert wire at predetermined angle to shaft to achieve desired valgus.
4. Seating Chisel: Insert seating chisel over/parallel to wire.
5. Osteotomy:
   • Perform intertrochanteric bone cut.
   • Remove a laterally based wedge of bone (calculated from preoperative tracing).
   • Tip: The size of the wedge (in mm) roughly equals the degrees of correction needed on some plating systems, but templates are safer.
6. Reduction: Abduct the shaft to close the osteotomy. The head/neck unit is now more valgus.
7. Fixation: Insert Blade Plate or Pediatric Locking Plate (cannulated screw system).
8. Rotation: Correct retroversion by internally rotating the distal fragment before plating (if needed).
9. Adductor Tenotomy: Often required (percutaneous) as valgus lengthens the leg and tightens adductors.

Post-Op: Spica cast usually needed for younger children (less than 6-8). Protected weight bearing for older.

Pitfalls to Avoid:

• Under-correction (High recurrence rate).
• Anterior penetration of the plate (femoral neck is retroverted).
• Injury to the trochanteric apophysis (posterior approach).

Careful preoperative planning is the key to avoiding these pitfalls.

Y-Osteotomy (Pauwels)

• Indication: Extremely severe deformity where simple valgus is insufficient.
• Concept: A Y-shaped intertrochanteric osteotomy.
• Effect: Corrects varus + retroversion + creates stability.
• Cons: Technically very demanding. Rarely performed now given better locking plates.

The Y-osteotomy is technically demanding but mechanically elegant. Most surgeons stick to standard closing wedge valgus osteotomy.

Technical Tip: "Measure twice, cut once." The wedge size is critical.