ObjectiveTo investigate the biomechanical characteristics of the proximal tibia (including cortical bone, cancellous bone, and bone cement) after lateral unicompartmental knee arthroplasty (L-UKA) under conditions of normal bone mass, osteopenia, and osteoporosis through finite element analysis of the tibial plateau, and to evaluate the impact of osteoporosis on the risk of postoperative tibial fracture from a biomechanical perspective, focusing on stress, strain, and deformation distribution patterns. MethodsBased on CT data of the tibia from a healthy adult male volunteer, a three-dimensional finite element model of L-UKA was established, including the femoral component, tibial component, ultra-high molecular weight polyethylene insert, bone cement, medial tibial cartilage, and tibia (comprising cortical and cancellous bone). Three groups of bone density parameters were defined: normal bone mass (T-score ≥?1.0SD), osteopenia (T-score –2.5SD-–1.0SD), and osteoporosis (T-score ≤–2.5SD). Different bone conditions were simulated by adjusting the elastic modulus of cortical and cancellous bone. Boundary conditions included complete constraint of the distal tibia, application of a 600 N vertical load on the femoral component, and a 400 N vertical load on the medial tibial cartilage to simulate single-leg stance during slow walking. The maximum stress, maximum strain, and maximum deformation of key structures were measured. Results As bone mass decreased, the biomechanical responses of bone and bone cement changed significantly. Specifically, the maximum stress, maximum strain, and maximum deformation of cortical bone and the bone cement layer increased markedly. For cancellous bone, the maximum stress decreased, while the maximum strain and maximum deformation increased. The maximum stress of the insert were similar across the three groups, with minimal variation (<1%); the peak stress was located at the contact area between the insert and the femoral component. ConclusionThe biomechanical risk of tibial fracture after L-UKA significantly increases in patients with osteoporosis, particularly for periprosthetic stress or fragility fractures.