What are the recommended techniques for total knee replacement (TKR) cuts in a valgus knee?

Total Knee Replacement Bone Cuts in Valgus Knee

For valgus knee deformities undergoing TKR, use standard medial parapatellar approach with measured bone resection (distal femur and proximal tibia cuts to create balanced rectangular flexion-extension gaps) combined with sequential lateral soft tissue release, reserving posterior-stabilized implants for most cases. 1, 2

Preoperative Assessment and Planning

• Obtain standing full-length hip-to-ankle radiographs to accurately measure the mechanical axis and quantify the degree of valgus deformity, as standard AP knee films alone cannot assess true limb alignment 3
• Classify deformity severity: mild (<10°), moderate (10-20°), or severe (>20° valgus) to guide surgical strategy 4, 1
• Identify bone deficiencies including lateral condylar hypoplasia, lateral cartilage erosion, and metaphyseal remodeling that will affect bone cut planning 4
• Assess contracted lateral structures: lateral collateral ligament, posterolateral capsule, popliteus tendon, iliotibial band, and lateral head of gastrocnemius 4

Surgical Approach Selection

The medial parapatellar approach is the standard and most successful approach for valgus knees, providing excellent visualization and outcomes 2

• Medial parapatellar approach allows standard bone cuts with controlled lateral soft tissue release from inside-out 1, 2
• Lateral parapatellar approach with tibial tubercle osteotomy is reserved only for severe grade II-III deformities (>20° valgus) where patellar maltracking is anticipated 5
• Avoid lateral approach in mild-moderate valgus as it adds unnecessary complexity and risk of tibial tubercle complications 5

Bone Resection Technique

Perform measured bone cuts to create balanced rectangular flexion-extension gaps rather than relying solely on soft tissue releases 1, 2

Distal Femoral Cut

• Make distal femoral resection perpendicular to the mechanical axis (typically 5-7° valgus to anatomic axis) 1
• Resect sufficient bone to correct deformity while preserving bone stock 1
• Standard measured resection of 9-10mm from the less-worn (medial) condyle 2

Proximal Tibial Cut

• Cut perpendicular to tibial mechanical axis (typically 3° varus to anatomic axis) 1
• Resect adequate bone from lateral plateau to address lateral bone deficiency and create balanced gaps 1, 2
• Standard resection removes approximately 8-10mm from the less-worn side 2

Posterior Femoral Cuts

• Size femoral component to avoid overstuffing the flexion gap 1
• External rotation of femoral component (3° from posterior condylar axis) helps balance the flexion gap 1

Lateral Soft Tissue Release Sequence

Use the inside-out release technique through the medial approach, performing sequential releases until balanced rectangular gaps are achieved 1

Release Sequence (from least to most aggressive):

1. Release posterolateral capsule first using inside-out technique from the medial side 1
2. Pie-crust the iliotibial band with multiple small punctures rather than complete transection 1
3. Release popliteus tendon if needed for persistent lateral tightness 4, 1
4. Release lateral collateral ligament origin only if absolutely necessary for severe deformities 4, 1

Critical pitfall: Avoid over-releasing lateral structures, which causes late-onset instability—the primary complication in valgus TKR 1

Implant Selection

Posterior-stabilized implants are appropriate for the vast majority of valgus knees when proper bone cuts and balanced soft tissue releases are performed 1, 2

• Posterior-stabilized design provides adequate stability after lateral release in most cases 1, 2
• Reserve constrained condylar implants only for severe deformities with gross instability after maximal release or incompetent medial collateral ligament 4, 1
• Avoid routine use of constrained implants, as they increase stress at the bone-implant interface and risk of loosening 1

Expected Outcomes and Alignment Goals

• Target postoperative alignment: 3-7° valgus (anatomic axis) or 0° mechanical axis 2, 5
• Expect correction from average 15-23° preoperative valgus to 5-9° postoperative valgus 1, 2
• Range of motion typically maintained or improved (average 110-112° postoperatively) 1, 2
• Knee Society Scores improve from 22-44 points preoperatively to 81-93 points postoperatively 1, 2

Common Pitfalls to Avoid

• Do not under-resect bone and rely solely on soft tissue releases—this leads to residual deformity and instability 1
• Do not over-release lateral structures—this causes late-onset lateral instability, the most problematic complication 1
• Avoid using cruciate-retaining implants in valgus knees, as the PCL is often contracted and prevents proper balancing 1, 2
• Do not accept residual valgus >10° (anatomic axis), as this predisposes to lateral compartment overload and accelerated wear 2, 5

Postoperative Monitoring

• Obtain standing AP radiographs with 10° internal rotation to accurately assess final alignment 3
• Annual weight-bearing radiographs recommended to detect subclinical wear or alignment changes 3
• Monitor for late instability, which can occur years after surgery if lateral releases were excessive 1