Malposition of components and Femorotibial mechanical Axis changes on pressure distribution in Total knee arthroplasty.

BACKGROUND

To the best of our knowledge, no report has analyzed the postoperative results of poor prosthesis position, particularly when the femoral and tibial components are abnormally positioned relative to neutral lower limb alignment. We aimed to investigate pressure distribution in the knee at different lower limb alignments with diverse positions of femoral and tibial components.

METHODS

We established a three-dimensional model of the lower limb using computed tomography and simulated total knee arthroplasty. Tibial and femoral components were changed to 7°, 5°, and 3° of valgus and neutral and 3°, 5°, and 7° of varus positions in the coronal plane. Finite element analysis was performed after applying pressure to simulate weight-bearing, and pressure distribution on the tibial surface was analyzed. We also conducted biomechanical testing using a weight-bearing rig with six cadavers. We measured the pressure at the tibial surface with the position of different components and lower limb alignment.

FINDINGS

Peak pressure on the medial or lateral side of the tibia was determined by the mechanical axis. When tibial components are in 3°,5° and 7° of valgus/varus and femoral components are in 3°,5° and 7° of varus/valgus correspondence, no peak pressure was detected with normal alignment, despite malpositioned components.

INTERPRETATION

Lower limb alignment is more critical than the position of the component. Medial and lateral tibial compartment pressures were evenly distributed if the alignment was neutral. Malpositioned femoral or tibial components changed the femorotibial mechanical axis, and peak pressure of the proximal tibia was positively related to alignment.