TKA Bone Cuts - Total Knee Arthroplasty

This lecture discusses the techniques and goals of bone cuts in Total Knee Arthroplasty (TKA) to achieve mechanical alignment. The primary focus is on the "Measured Resection" technique.

Techniques of Bone Cuts

• Measured Resection: Achieves mechanical alignment.
• Gap Balancing: Another technique discussed elsewhere.

Key Bone Cuts

1. Tibial Cut

• Objective: Perpendicular to the mechanical axis (0 degrees).
• Importance: Affects both flexion and extension gaps, serving as the foundation for TKA.
• Contact Points:
  • Anterior tibia: Major contact during extension.
  • Posterior tibia: Major contact during flexion.
• Rotation: Align anterior tibial component with the medial 1/3 of the patellar tendon.
  • Incorrect rotation increases the Q angle, risking dislocation.

2. Distal Femoral Cut

• Mechanical Alignment: Aim is neutral mechanical alignment, typically with a 6-degree valgus knee angle.
  • Intramedullary Referencing: Guides based on the anatomical axis.
• Extension Gap:
  • Proper bone cuts form a rectangular balanced gap.
  • Trapezoidal gaps indicate soft tissue imbalance.
• Joint Line Height:
  • Target depth is 9 mm for the distal femoral cut.
  • Changes in cut depth affect the joint line and gap sizes.

3. Anterior & Posterior Femoral Cuts (Flexion Gap, Rotation)

• Implant Size Determination: Use a sizing guide before cuts.
• Rotation:
  • Posterior femoral cut should be parallel to the tibial cut for a rectangular flexion gap.
  • Use external rotation jigs or landmarks for neutrality.
  • Neutral rotation is crucial for patellar tracking and flexion gap balance.
• Flexion Gap:
  • Aim for a 9 mm depth similar to the extension gap.
  • Posterior Referencing: Ensures normal posterior condyle offset.
  • Anterior Referencing: Ensures accurate anterior depth.

4. Patellar Resurfacing

• Standard: Common in the US, not globally.
• Thickness: Typically 9 mm for the patellar button.
• Cutting Guide: Adjust to native patella thickness.
• Risk: Cutting below 12 mm increases fracture risk.

5. Kinematic Alignment Cuts

• Goal: Maintain native joint line.
• Distal Femoral Cut: Parallel to the distal femur joint line (3-degree valgus).
• Posterior Femoral Cut: Set to 0 rotation.
• Tibial Cut: Slight varus cut with established neutral rotation axis.

These bone cuts enable proper mechanical alignment and joint function in TKA, highlighting the significance of precise measurements and adjustments across different cuts.