Background <p>Tibial plateau fractures involving posterolateral fragments are challenging to fix internally because of the small surface area and the complex regional anatomy. This study aimed to compare the biomechanical performance of three plate fixation methods and to identify the construct most resistant to fracture displacement under axial loading.</p> Methods <p>Fifteen synthetic tibia models were used to simulate posterolateral split fractures. The models were randomized into three groups (n = 5 per group): Group A received an R-LOCK locking plate with 3.5 mm locking screws; Group B received a small T-oblique dynamic compression plate (DCP) with 3.5-mm cortical screws; and Group C received a distal radius T-oblique locking compression plate (LCP) with 2.7 mm locking screws. Vertical displacement was measured under sequential axial loads of 500, 1000, and 1500 N, followed by load-to-failure testing. Because each specimen was tested under multiple loading conditions, vertical displacement was analysed by mixed-design repeated-measures ANOVA (within-subject factor, loading condition; between-subject factor, implant group), equivalent in this balanced design to a random-intercept linear mixed-effects model with specimen as the random grouping factor. Per-load one-way ANOVAs were used as a secondary analysis for pairwise comparisons.</p> Results <p>For vertical displacement, the primary mixed-design repeated-measures ANOVA revealed a significant main effect of load (p &lt; 0.001), only a marginal main effect of implant group (p = 0.077), and a non-significant group × load interaction (p = 0.289). Based on secondary per-load analyses, Group C demonstrated significantly less vertical displacement than Group A and Group B under low-to-moderate axial loading at both 500 N (0.219 ± 0.036 mm vs. 0.359 ± 0.092 mm and 0.329 ± 0.055 mm; p = 0.005 and p = 0.021, respectively) and at 1000 N (0.382 ± 0.053 mm vs. 0.494 ± 0.114 mm and 0.576 ± 0.089 mm; p = 0.005). At 1500 N, Group C continued to exhibit the lowest mean displacement (0.592 ± 0.165 mm) compared with Group A (0.601 ± 0.182 mm) and Group B (0.757 ± 0.218 mm), although this difference did not reach statistical significance (p = 0.336). No statistically significant difference in load-to-failure was observed among the three constructs (p = 0.875), although a descriptive trend favoured Group C (3260.40 ± 351.76 N), followed by Group B (3178.80 ± 218.88 N) and Group A (3145.80 ± 461.66 N).</p> Conclusions <p>We demonstrated that the 2.7 mm distal radius T-oblique LCP was associated with comparatively lower vertical displacement under moderate axial loads (500–1000 N) compared to Groups A and B. All three constructs maintained vertical displacement below the 2 mm failure threshold across the tested loading range, suggesting that each is biomechanically adequate to resist normal physiological loads.</p> Trial registration <p>This study used only synthetic tibial bone models and did not involve human participants, human tissue, or animals; therefore, formal ethical approval and informed consent were not required. The protocol was nevertheless reviewed and registered by the Institutional Review Board of the Faculty of Medicine Vajira Hospital, Navamindradhiraj University (COE 031/2022).</p>