Biomechanical risk factors for tibial plateau fracture following Oxford unicompartmental knee arthroplasty: a finite element analysis under gait loading.

Background: Tibial plateau fractures following Oxford unicompartmental knee arthroplasty (UKA), though rare (<1% incidence), represent serious postoperative complications that often necessitate complex revision surgery. This study aimed to systematically investigate the biomechanical risk factors for tibial plateau fractures following Oxford UKA by evaluating the effects of prosthesis positioning parameters on tibial stress distribution under dynamic gait loading. Methods: Ten distinct models were analyzed under ISO-standardized gait cycle loading to assess the impact of coronal alignment angles (-7°, -3°, 0°, 3°, 7°), sagittal bone cut (1 mm, 3 mm, 8 mm), and femoral-tibial prosthesis positioning (3 mm, 5 mm shifts). Maximum von-Mises stress on the tibial cortex was measured, with particular focus on the posterior medial cortex. Both von Mises stress and Maximum Principal Stress were evaluated to assess general equivalent loads and specific tensile fracture risks, respectively. Results: In the neutral position, maximum stress measured 19.01 MPa post-gait loading. Varus positioning at -3° yielded the minimum stress (18.06 MPa), while 7° valgus resulted in dramatically elevated stress (48.15 MPa, 2.5-fold increase). Longitudinal sagittal bone cut significantly influenced stress distribution: 1 mm over-cut increased stress to 28.21 MPa, 3 mm to 29.23 MPa, and 8 mm depth reached 45.10 MPa (2.3-fold increase). Femoral prosthesis displacement of 5 mm relative to the tibial component elevated posterior cortex stress to 33.24 MPa (1.7-fold increase from neutral). Notably, eversion-induced stress increases exceeded those from inversion, and these parameters exhibited nonlinear interactions. Principal stress analysis revealed that severe valgus alignment (7°) and deep sagittal cuts (8 mm) drastically concentrated tensile stresses at the posterior tibial cortex, peaking at 15.1 MPa and 12.56 MPa, respectively. Conclusion: Prosthesis malalignment (particularly excessive valgus beyond 3°) and depth of tibial sagittal osteotomy (>3 mm) are primary contributors to elevated tibial stress. Based on these biomechanical findings, we recommend that the Oxford unicompartmental prosthesis should be positioned at 3° varus in the coronal plane, the femoral-tibial prosthesis distance should not exceed 3 mm, and the longitudinal sagittal bone cut should be limited to 3 mm depth.