Courtesy: KrishnaKumar, Limb Reconstruction Surgeon, Trichur, Kerala, India

Correction of Extra-articular Deformity in Total Knee Arthroplasty

1. Basic Concept

Significant extra-articular deformity around the knee is relatively uncommon in some practices, but may be encountered following:

Malunited fractures
Previous osteotomies with residual malalignment
Metabolic bone disease

When performing TKA in the presence of extra-articular deformity, there are three broad options:

Intra-articular bone resection + soft-tissue balancing
- Correct the deformity through the standard TKA bone cuts and appropriate releases.
Corrective osteotomy at the time of TKA
- Perform the osteotomy together with the arthroplasty.
Staged corrective osteotomy followed by TKA
- Correct the deformity first.
- Allow the osteotomy to heal.
- Perform TKA subsequently.

2. Fundamental Principle: Map the Deformity Before Surgery

The key question is:

Can the extra-articular deformity be corrected through the planned intra-articular bone resection without compromising the collateral ligaments?

The surgeon should map:

Mechanical axis
Center of femoral head
Knee center
Planned distal femoral and proximal tibial resections
Location of the extra-articular deformity
Relationship of the planned cut to the collateral ligament attachments

Critical principle

If the required correction can be achieved without violating the origin or insertion of the collateral ligaments, the deformity can generally be addressed through the TKA bone cuts and soft-tissue balancing.

If correction would compromise the collateral ligament attachment, another strategy is required.

3. Normal Alignment Concepts

The lecture emphasizes the conventional alignment targets:

Distal femur

Distal femoral resection is approximately 5–7° valgus relative to the anatomical axis.
Alternatively, the distal femoral cut is approximately 90° to the mechanical axis.

Proximal tibia

Tibial resection is approximately 90° to the long axis of the tibia.

4. Intra-articular Correction + Soft-Tissue Balancing

This is the most commonly applicable scenario.

The process is:

Map the extra-articular deformity.
Determine the planned intra-articular resection.
Determine where the resulting cut will lie.
Establish whether the collateral ligament attachments will remain intact.
Perform the TKA with appropriate soft-tissue balancing.

Practical principle

The deformity can be corrected through the arthroplasty provided the necessary correction does not compromise ligament stability.

5. When Can Intra-articular Correction Be Used?

The lecture gives approximate limits:

Deformity	Approximate range
Femoral varus/valgus	<20°
Tibial varus/valgus	Up to ~30°
Flexion/extension deformity	~25°

These are presented as practical guidelines rather than absolute limits.

Important consideration

The location of the deformity is as important as its magnitude.

A deformity that is:

Greater in magnitude
Closer to the joint line

has a greater effect on the arthroplasty and makes correction more difficult.

6. Rotational Deformity

Rotational deformity is particularly difficult to assess on standard radiographs.

Key point

Internal and external rotation deformities may coexist with coronal and sagittal deformities.

They are not reliably assessed radiographically.

A preoperative CT scan may therefore be required when rotational deformity is suspected.

7. When Intra-articular Correction Becomes Difficult

When deformity becomes more severe—particularly around the >20° range in the femur—simply correcting everything through the intra-articular resection may:

Produce excessive bone resection
Compromise collateral ligament attachments
Affect knee stability
Make soft-tissue balancing difficult

The lecture particularly highlights severe deformities close to the joint.

Practical approach

Map the deformity first rather than relying solely on a numerical cutoff.

8. Corrective Osteotomy at the Time of TKA

For more severe deformities, a corrective osteotomy may be performed simultaneously with TKA.

Indications

Generally considered when:

Deformity is more severe
Approximately >20–30° depending on bone and location
Intra-articular correction would compromise stability or ligament attachments

Important technical principle

The osteotomy must be bypassed by the TKA implant.

This is achieved using:

Stemmed femoral/tibial components
Appropriate stem extensions

The stem provides fixation beyond the osteotomy site.

9. Example of Simultaneous Osteotomy + TKA

In a severe deformity, attempting to correct everything through the knee may compromise stability.

The alternative is:

Corrective osteotomy + TKA + stemmed components

The lecture describes an example with approximately 8-year follow-up in which this approach had done well.

10. Staged Corrective Osteotomy

The third strategy is:

Stage 1

Corrective osteotomy-

Allow the osteotomy to heal

Stage 2

Total knee arthroplasty

11. Why Consider Staging?

Historically, simultaneous osteotomy and TKA were used more readily.

However, the speaker describes changing his practice after encountering:

Nonunion
Malunion
Delayed union
Problems with osteotomy healing

The concern becomes greater when the deformity is remote from the joint and correction requires substantial osteotomy or a custom/long stem.

Speaker’s practical view

If the osteotomy is very close to the joint, simultaneous correction may be reasonable.

If it is remote and substantial, the speaker favors considering:

Osteotomy ? healing ? TKA

rather than trying to accomplish everything in one operation.

12. Why Remote Osteotomy Is Different

A remote deformity may require:

More extensive correction
Custom stem components or significant stem extensions
Greater dependence on the osteotomy healing successfully

Attempting simultaneous correction can therefore increase the biological and mechanical demands on the osteotomy.

The speaker describes a personal case in which a simultaneous procedure resulted in delayed union requiring bone grafting.

13. Alignment Without Navigation

The speaker describes a practical method for centers without computer navigation.

Problem

With significant extra-articular deformity:

Standard intramedullary femoral alignment may be unreliable.
The femoral canal may not provide an appropriate reference for the mechanical axis.

“Canadian navigation system”

The described technique uses fluoroscopy:

Use fluoroscopy to identify the center of the femoral head.
Place ECG leads over the skin to mark/palpate the femoral head center.
Use these external markers as a reference.
Use a dedicated extramedullary alignment guide.
“Gun-sight” the alignment rod toward the femoral head center.

The speaker acknowledges that this may not be as accurate as computer navigation, but provides a practical method when navigation is unavailable.

14. Surgical Planning Principle

The central planning sequence is:

Define deformity-

Map mechanical axis-

Determine planned intra-articular resection-

Check collateral ligament attachments-

Decide whether intra-articular correction is sufficient-

If adequate:

TKA + bone resection + soft-tissue balancing

If inadequate:

TKA + corrective osteotomy

Staged corrective osteotomy ? TKA

15. Comparison of the Three Strategies

Strategy	Best suited for	Main principle	Main concern
Intra-articular correction	Mild/moderate deformity	Correct through TKA bone cuts	Excessive resection/ligament compromise
Simultaneous osteotomy + TKA	Severe deformity near the joint	Correct deformity and replace joint in one operation	Osteotomy healing
Staged osteotomy ? TKA	Severe/remote deformity	Correct alignment first, then arthroplasty	Two operations

16. Important Technical Considerations

1. Collateral ligament preservation

This is one of the most important determinants of whether the deformity can be corrected through the intra-articular resection.

2. Deformity location

Closer to the joint = greater influence on the TKA.

3. Magnitude

As deformity increases, intra-articular correction becomes progressively less attractive.

4. Rotation

Do not rely solely on plain radiographs.

Consider CT when rotational deformity is clinically suspected.

5. Stem fixation

When performing simultaneous corrective osteotomy and TKA:

Bypass the osteotomy with stemmed components.

17. Key Take-Home Points

Extra-articular deformity does not automatically require a corrective osteotomy.
First map the deformity and planned bone cuts.
If correction can be achieved without compromising the collateral ligaments, intra-articular correction may be sufficient.
Practical deformity limits mentioned are approximately <20° femoral and up to 30° tibial coronal deformity.
Flexion/extension deformity of approximately 25° may also be addressed depending on the situation.
Rotational deformity is difficult to assess on X-ray; CT may be required.
Severe deformity may require corrective osteotomy with TKA.
If a simultaneous osteotomy is performed, stemmed components should bypass the osteotomy.
For a remote, substantial deformity, staged osteotomy followed by TKA may be preferable because of concerns regarding healing.
The ultimate goal remains the same: restore the desired mechanical alignment while maintaining a stable, balanced knee.

Exam Pearls

Three options: intra-articular correction, simultaneous osteotomy + TKA, staged osteotomy ? TKA.
First question: Can I correct the deformity without compromising the collateral ligaments?
Femur: intra-articular correction generally discussed for deformity <20°.
Tibia: may be possible up to approximately 30°.
Remote severe deformity: consider staged correction.
Simultaneous osteotomy: bypass with stems.
Rotational deformity: consider CT.
Closer to joint + greater deformity = more difficult correction.

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