Simulation of Total Knee Arthroplasty in 5° or 7° Valgus: A Study of Gap Imbalances and Changes in Limb and Knee Alignments From Native

This study calculated the frequency of occurrence of gap imbalances between medial and lateral compartments at 0 degrees flexion and within a compartment between 0 degrees and 90 degrees flexion, and changes in limb and knee alignment from native after computer simulation of total knee arthroplasty (TKA) with the knee set in 5 degrees or 7 degrees valgus at 0 degrees flexion. TKA was simulated on 49 3D bone models of native limbs. At 0 degrees flexion, the femoral component was set in 5 degrees or 7 degrees valgus from the anatomic axis of the femur, and the tibial component was set 0 degrees to the tibial anatomic axis. At 90 degrees flexion, internal-external rotation of the femoral component was set perpendicular to the anteroposterior axis of the trochlear groove (Method 1), parallel to the transepicondylar axis (Method 2), 3 degrees externally rotated to the posterior condylar axis (Method 3), and gap-balanced to the tibial resection at 0 degrees flexion (Method 4). For 5 degrees and 7 degrees valgus knees, the frequency of occurrence of TKAs (1) with >= 2mm gap imbalance between compartments at 0 degrees flexion was >= 49%, (2) with 2 >= mm gap imbalance within a compartment between 0 degrees and 90 degrees flexion ranged from 43-69% for Methods 1, 2, and 3, and (3) with >= 2 degrees change in limb and knee alignment from native was >= 47%. Achieving balanced gaps between compartments at 0 degrees flexion may often require soft tissue release. Unbalanced gaps within a compartment between 0 degrees and 90 degrees flexion represent a potential instability which is difficult to surgically correct. (C) 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc.