Management of Extra-Articular Deformities in Total Knee Arthroplasty

Summary

Limb alignment,whether “intra-”, or “extra-” articular is the key to success of an arthroplasty. Malalignment of a knee replacement may result in component loosening, prosthetic wear, instability and patellar complications. It is the alignment of the entire limb, from the hip to the knee to the ankle and referred to as the mechanical axis, that is important, not just the alignment of the knee joint. Component position in the plane of motion of the joint is less important, but correct rotational positioning is essential.

A “neutral mechanical axis” or straight line through the centers of the hip, knee, and ankle results from the angular position of the tibial and femoral components. The joint must then be stabilized with either ligamentous releases or mechanically constrained implants. Extra-articular deformities pose technical challenges.

Bone deformities may be corrected outside or inside the arthroplasty. In the first case, a corrective osteotomy may be performed at the site of the deformity (a fracture malunion or the apex of a rickets deformity) or closer to the joint where it may be performed concurrent with the arthroplasty. If an extra-articular deformity is corrected inside the joint, aggressive and even innovative soft-tissue procedures or a constrained implant will be required to stabilize the knee.