Abstract
Several concepts may be used to restore normal knee kinematics after total knee arthroplasty.
One is a kinematically aligned (KA) technique, which restores the native joint line
and limb alignment, and the other is the use of a medial pivot knee (MPK) design,
with a ball and socket joint in the medial compartment. This study aimed to compare
motions, contact forces, and contact stress between mechanically aligned (MA) and
KA (medial tilt 3° [KA3] and 5° [KA5]) models in MPK. An MPK design was virtually
implanted with MA, KA3, and KA5 in a validated musculoskeletal computer model of a
healthy knee, and the simulation of motion and contact forces was implemented. Anteroposterior
(AP) positions, mediolateral positions, external rotation angles of the femoral component
relative to the tibial insert, and tibiofemoral contact forces were evaluated at different
knee flexion angles. Contact stresses on the tibial insert were calculated using finite
element analysis. The AP position at the medial compartment was consistent for all
models. From 0° to 120°, the femoral component in KA models showed larger posterior
movement at the lateral compartment (0.3, 6.8, and 17.7 mm in MA, KA3, and KA5 models,
respectively) and larger external rotation (4.2°, 12.0°, and 16.8° in the MA, KA3,
and KA5 models, respectively) relative to the tibial component. Concerning the mediolateral
position of the femoral component, the KA5 model was positioned more medially. The
contact forces at the lateral compartment of all models were larger than those at
the medial compartment at >60° of knee flexion. The peak contact stresses on the tibiofemoral
joint at 90° and 120° of knee flexion were higher in the KA models. However, the peak
contact stresses of the KA models at every flexion angle were <20 MPa. The KA technique
in MPK can successfully achieve near-normal knee kinematics; however, there may be
a concern for higher contact stresses on the tibial insert.
Keywords
total knee arthroplasty - computer simulation - medial pivot knee - kinematics - contact
stresses
