Finite element analysis of femoral component positioning in medial UKA: A focus on varied bone quality

BackgroundThe optimal positioning range for the femoral component in unicompartmental knee arthroplasty (UKA) performed in osteoporotic bone remains undefined. Most existing biomechanical studies have been established using normal bone quality models, whereas limited evidence addresses abnormal bone conditions. Complications involving the operative-side compartment are closely associated with the high revision rates after UKA.MethodsCT and MRI scans of the right knee of a volunteer without pathological changes were used to construct a three-dimensional finite element model. A normal bone quality UKA model (NB group) was created, and an osteoporotic model (OP group) was generated by reducing the elastic modulus of bone tissue proportionally. Femoral component alignment was set at 0°, as well as 3°, 6°, and 9° of varus and valgus. Stress changes within operative-side structures were quantified and compared between the two models.Results(1) In both models, peak stress on the femoral component increased progressively with greater varus alignment, with the OP group consistently demonstrating higher stress values than the NB group. Compared to their respective 0° neutral position, the peak von Mises stress on the femoral component surface increased by 71.8% and 70.8% at 9° of varus in the NB and OP groups, respectively. (2) Peak stresses on the PE insert and on the cortical bone beneath the tibial component increased with both varus and valgus malalignment; the increase was more pronounced under varus. The OP group exhibited higher peak stresses and greater incremental changes than the NB group. Compared to their respective 0° neutral position, the peak von Mises stress on the cortical bone surface beneath the tibial component increased by 50.0% in the NB group and 40.8% in the OP group at 9° varus, and by 14.2% and 27.0%, respectively, at 9° valgus.ConclusionEven small coronal-plane deviations (±3°) in femoral component positioning during medial UKA may substantially elevate stresses within the operative-side compartment. Strict control of coronal alignment is essential to avoid varus or valgus and prevent abnormal stress concentrations around the implant. Additionally, the impact of osteoporosis on postoperative biomechanical stability warrants careful consideration to optimize implant design and surgical technique, thereby reducing the risks of aseptic loosening, periprosthetic fracture, and improving long-term outcomes.