Cruciate Retaining TKR

Courtesy: Dr A Reddy, Ashok Shyam TV, Ortho

Introduction

• Focus: Cruciate-retaining (CR) total knee arthroplasty.

• Personal practice preference:

  • ~99% of primary TKAs performed as CR knees.

  • Used even in severe deformities.

• Transition from posterior-stabilized (PS) to CR:

  • Smaller knee sizes.

  • Thinner femoral condyles.

  • Concerns regarding box cuts in smaller bone stock.

---

Why Choose Cruciate Retaining?

Surgical Advantages

• No box cut required:

  • Preserves bone stock.

  • Shorter operative time.

  • Reduced risk of condylar fracture in small knees.

• Better bone available if revision becomes necessary.

---

Design-Related Concerns in Posterior-Stabilized Knees

• Patellar clunk syndrome (primarily seen in PS designs).

• Post-cam dislocation.

• Cam wear.

• Limited tolerance to hyperextension.

• Trial post vulnerability to wear from rotational malalignment.

• Rotational mismatch may occur:

  • Intraoperatively.

  • Dynamically during gait.

---

Biomechanical Advantages of CR Knee

• Preserves posterior cruciate ligament (PCL).

• Maintains more physiologic joint line.

• Better quadriceps efficiency.

• Improved stair-climbing mechanics (reported in literature).

• PCL contributes to:

  • Posterior stability.

  • Varus-valgus stability.

• Reduced constraint compared to PS designs.

• Potentially lower joint reaction forces.

---

Joint Line Considerations

• If PCL is sacrificed:

  • Flexion gap increases (~5 mm).

  • May require additional distal femoral resection.

  • Joint line elevation can occur.

  • Risk of mid-flexion instability increases.

CR design:

• Maintains joint line more consistently.

• Less risk of mid-flexion instability.

---

Addressing the “PCL is Non-Functional” Argument

• PCL does not need to be completely normal to be retained.

• Majority of primary TKAs can successfully preserve PCL with minor balancing.

---

When to Consider PCL Balancing

Clinical features predicting need for balancing:

• Limited preoperative range of motion.

• Flexion contracture.

• Significant varus or valgus deformity.

---

Essential Steps Before Assessing PCL Balance

1. Remove all deforming osteophytes.

2. Perform required soft tissue releases.

3. Align femoral component properly.

4. Match bone resection to implant thickness in:

   • Extension.

   • Flexion.

---

Assessing PCL Balance

The “Pull-Off” Test

• At 90° flexion:

  • If tibial trial can be pulled anteriorly ? Flexion gap too loose.

The “Lift-Off” (Nutcracker) Sign

• If tibia lifts anteriorly during flexion:

  • PCL too tight.

  • Posterior rollback restricted.

---

Managing a Tight PCL

Preferred method:

• Femoral-side release (rather than tibial side).

• Controlled release in intercondylar notch.

• Gradual balancing under direct visualization.

Alternative:

• Tibial bone island preservation technique.

  • Maintain central bone island with PCL insertion.

  • Carefully cut surrounding tibial bone.

---

When to Sacrifice the PCL

• Persistent instability.

• Excessive rollback.

• Uncorrectable imbalance.

• Restricted motion despite balancing.

Not dogmatic:

• Convert to PS if balance cannot be achieved.

• Approximately 1 in 10 may require sacrifice.

---

Technical Pearls for PCL Preservation

• Use specialized retractor with dual prongs:

  • Protects PCL during tibial cut.

• Avoid central posterior saw penetration.

• Lift osteotomized bone from medial and lateral sides.

• Use meniscal grasper to control tibial cut segment.

• Carefully outline and preserve PCL insertion during tibial resection.

---

Clinical Evidence

Studies suggest:

• Greater knee extensor moment during stair climbing in CR knees.

• Lower medial compartment loading compared to PS.

• Comparable or favorable long-term survivorship.

---

Personal Clinical Experience

• 4,000 primary CR knees over several years.

• Very low conversion rate to PS.

• No major CR-specific complications observed.

• Successful use even in severe deformities.

---

Common Misconception

CR knees are often considered:

• More technically demanding.

• Less forgiving.

Experience suggests:

• If surgeon can perform PS reliably, CR is equally manageable.

• Proper technique and balancing are key.

---

Summary Points

1. Cruciate-retaining TKA provides outcomes comparable to PS designs.

2. Bone preservation is a significant surgical advantage.

3. PCL need not be pristine to be retained.

4. Proper assessment and balancing are essential.

5. Conversion to PS should remain an option when required.