Courtesy: Dr S Macdonald, Ashok Shyam TV, Ortho

Significant extra-articular deformities are relatively uncommon in many Western practices but may be more frequently encountered in post-traumatic populations. Common causes include:

• Malunited fractures

• Prior osteotomies

• Metabolic bone disease (e.g., Paget’s disease)

The challenge is achieving proper limb alignment without compromising ligament stability.

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Three Treatment Options

When facing extra-articular deformity in a patient requiring TKA, there are three main strategies:

1. Intra-articular bone resection + soft tissue balancing

2. Simultaneous corrective osteotomy + TKA

3. Staged corrective osteotomy followed by delayed TKA

The decision depends on deformity magnitude, location, and impact on ligament attachments.

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Alignment Principles Remain the Same

Regardless of deformity:

• Distal femoral cut ? 90° to mechanical axis

• Tibial cut ? 90° to tibial mechanical axis

• Goal ? restore neutral mechanical alignment

Standard distal femoral valgus angle (5–7° to anatomical axis) still applies.

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Option 1: Intra-Articular Correction

When Is It Feasible?

• Femoral varus/valgus deformity < 20°

• Tibial deformity up to ~30°

• Flexion/extension deformity up to ~25°

• Deformity not compromising collateral ligament origin/insertion

Key Rule

If planned bone cuts do NOT violate the:

• Femoral origin of collateral ligaments

• Tibial insertion of collateral ligaments

? Correction can be achieved through intra-articular resection.

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Preoperative Planning

• Draw mechanical axis (hip ? knee ? ankle).

• Map resection lines.

• Determine whether ligament attachments will remain intact.

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Technical Consideration

Intramedullary guides may not be usable.

Alternative strategy:

• Extramedullary referencing.

• Fluoroscopy-assisted localization of femoral head center.

• Surface landmark referencing.

Posterior stabilized (PS) design is often preferred to simplify balancing.

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Advantages

• Single procedure.

• Avoids osteotomy healing complications.

• Reliable when deformity is moderate.

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Option 2: Simultaneous Osteotomy + TKA

Indications

• Deformity > 20°–30°

• Deformity close to joint line

• Intra-articular correction would destabilize knee

• Ligament attachments would be compromised

Key Technical Principle

• Perform corrective osteotomy.

• Use stemmed components to bypass osteotomy site.

• Restore alignment and protect fixation.

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Advantages

• One-stage correction.

• Immediate mechanical realignment.

Risks

• Nonunion

• Malunion

• Delayed healing

• Increased surgical complexity

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Option 3: Staged Osteotomy Then TKA

Increasingly preferred when:

• Deformity is remote from joint.

• Severe angular deformity.

• Custom long stems would be required.

• Risk of nonunion is high.

Approach

1. Correct deformity first.

2. Allow complete union.

3. Perform standard TKA later.

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Why Consider Staging?

Simultaneous correction may:

• Increase nonunion rates.

• Increase fixation complexity.

• Compromise long-term results.

Staged approach may provide:

• More predictable bone healing.

• Simpler TKA.

• Better long-term mechanical stability.

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Key Decision Factors

1?? Magnitude of Deformity

Greater deformity ? more likely to require osteotomy.

2?? Distance from Joint Line

Closer to joint ? more impact on ligament balancing.

3?? Ligament Integrity

If bone cuts would violate collateral ligaments ? osteotomy required.

4?? Rotational Deformity

Often underestimated.
CT scan may be required to assess internal/external rotation.

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Practical Thresholds (General Guidelines)

These are guidelines, not absolute rules.

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Common Pitfalls

• Ignoring rotational deformity.

• Underestimating ligament compromise.

• Attempting simultaneous osteotomy in very severe deformity.

• Not bypassing osteotomy with adequate stem length.

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Final Algorithm

1. Define deformity (long-leg films ± CT).

2. Draw mechanical axis.

3. Map resection lines.

4. Assess ligament attachment preservation.

5. Choose:

   • Intra-articular correction (if safe).

   • Simultaneous osteotomy + stemmed TKA.

   • Staged osteotomy followed by TKA.

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Take-Home Messages

• Most moderate deformities can be managed intra-articularly.

• Severe deformities near the joint often require osteotomy.

• Remote deformities may be better treated in stages.

• Stemmed implants are essential when osteotomy performed.

• Alignment goals remain unchanged despite deformity.