Planning a Total Knee Replacement in a Valgus Knee
The lateral approach is the preferred method for total knee arthroplasty (TKA) in patients with valgus knee deformity as it allows better correction of the deformity, shorter operating times, and potentially less use of constrained implants compared to the medial approach. 1
Understanding Valgus Knee Deformity
Valgus knee deformity occurs in approximately 10% of patients undergoing TKA and presents specific challenges due to:
- Anatomical variations including lateral cartilage erosion, lateral condylar hypoplasia, and metaphyseal femur and tibial plateau remodeling 2
- Soft tissue contractures of lateral structures: lateral collateral ligament, posterolateral capsule, popliteus tendon, hamstring tendons, lateral head of gastrocnemius, and iliotibial band 2
Preoperative Planning
Imaging Assessment
- Standing AP and lateral radiographs and tangential axial view of the patellofemoral joint are essential for initial evaluation 3
- Full-length standing hip-to-ankle radiographs provide optimal assessment of alignment and mechanical axis 3
- CT scan may be used to determine axial rotation of the femoral component 3
Clinical Evaluation
- Assess the degree of deformity (Ranawat classification can be used) 4
- Evaluate soft tissue contractures and medial ligamentous laxity 2
- Determine the need for constrained implants based on ligamentous stability 2
Surgical Approach Options
Lateral Parapatellar Approach (Recommended)
- Provides direct access to tight lateral structures that need release 1
- Preserves medial blood supply to the patella 5
- Results in better patellar tracking and alignment stability 5
- Allows better correction of valgus deformity (10.8° vs 7.3° with medial approach) 1
- Shorter operating times (87 min vs 137 min with medial approach) 1
- May require less use of constrained implants (9% vs 16% with medial approach) 1
- Can be performed with a Z-capsuloplasty modification for severe deformities 4
Medial Parapatellar Approach
- Standard approach for TKA but less optimal for valgus deformity 1
- Often requires lateral release which may compromise patellar blood supply 5
- More technically challenging for accessing lateral tight structures 1
Soft Tissue Management
Sequential Lateral Release (when using lateral approach)
- Iliotibial band at Gerdy's tubercle (required in 88% of cases) 6
- Iliotibial band at joint level (required in 46% of cases) 6
- Lateral collateral ligament (required in 13% of cases) 6
- Popliteus tendon (required in 4% of cases) 6
Bone Cuts Considerations
- Distal femoral cut should be perpendicular to the mechanical axis 2
- Consider slight under-correction of severe deformities to prevent medial instability 2
- Tibial cut should be perpendicular to the mechanical axis with minimal resection 2
Implant Selection
- Standard posterior-stabilized implants are usually sufficient with proper soft tissue balancing 4
- Constrained implants may be necessary in cases with significant medial ligamentous attenuation or inability to balance the knee 2
- Lateral approach may reduce the need for constrained implants (9% vs 16% with medial approach) 1
Postoperative Management
- Radiographic follow-up should include standing AP and lateral views to assess alignment 3
- Early mobilization is recommended to reduce length of hospital stay 3
- Supervised exercise program during the first 2 months improves physical function 3
- Regular follow-up every 1-2 years is recommended for long-term monitoring 3
Potential Complications and Pitfalls
- Residual instability due to inadequate soft tissue balancing 2
- Patellar maltracking (less common with lateral approach) 5
- Transient common peroneal nerve palsy (reported in lateral approach) 4
- Recurrence of deformity due to under-correction 2