Preservation of femoral and tibial coronal alignment to improve biomechanical effects of medial unicompartment knee arthroplasty: Computational study

BACKGROUND: Medial unicompartmental knee arthroplasty (UKA) could be concerned with wear of the cartilage or the wear in the polyethylene (PE) insert. Mechanical alignment determines the biomechanical effect in the long term. However, previous computational studies all found that femoral and tibial components alignment in the UKA were rare, and the results varied. OBJECTIVE: The purpose of this study was to evaluate the biomechanical effect of the femoral and tibial component coronal alignment in varus and valgus conditions through computational simulation. METHODS: A three-dimensional finite element model of the intact knee was constructed from medical image data of one healthy subject. A medial UKA model of neutral position and various coronal components was developed from the intact knee joint model. The tibial varus-femoral valgus and tibial valgus-femoral varus conditions were analyzed with parallel component angles of 3 degrees, 6 degrees and 9 degrees by using validated finite element models. We considered the contact stresses in the PE inserts and articular cartilage and the force on collateral ligament under gait cycle condition. RESULTS: Compared to the contact stress in the neutral position model, the contact stress on the PE insert increased in both tibial varus-femoral valgus and tibial valgus-femoral varus models. These trends were also observed in the case of the articular cartilage in remain compartment. However, the contact stress on the PE insert and articular cartilage increased largely in the tibial valgus-femoral varus model than in the tibial varus-femoral valgus model. The forces on the medial and lateral collateral ligaments increased in the tibial valgus-femoral varus model, whereas in the tibial varus-femoral valgus model, the forces decreased compared to the forces in the neutral position. The force on the anterior lateral ligament and popliteofibular ligament increased in the tibial varus-femoral valgus model as compared to the neutral position. CONCLUSIONS: Our study suggests that neutral alignment or less than 3 degrees tibial varus-femoral valgus alignment in the coronal plane can be recommended in medial UKA to reduce the postoperative complications and to enhance the life expectancy of implants.