Objective <p>The purpose of this retrospective study was to investigate the differences in clinical efficacy and radiographic outcomes of the double-triangle locking compression plate (DT-LCP) and the T-shaped locking compression plate (T-LCP) fixation systems in open-wedge high tibial osteotomy (OWHTO).</p> Methods <p>A retrospective analysis was conducted on the clinical data of 127 patients who underwent OWHTO at the Affiliated Hospital of Qingdao University between January 2019 and May 2020. Patients were divided into two groups based on the different steel plate fixation systems used: the DT-LCP group with 65 patients and the T-LCP group with 62 patients. Both groups underwent clinical and radiographic assessments preoperatively and at 5 years postoperatively. Clinical assessments were performed using the Visual Analog Scale (VAS), the Lysholm score, and the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC). Radiographic evaluations included measurements of the hip-knee-ankle angle (HKA), medial proximal tibial angle (MPTA), weight-bearing line ratio (WBLR), joint line convergence angle (JLCA), and tibial posterior slope (PTS) to assess lower limb alignment correction postoperatively. The compensatory changes in adjacent joints were evaluated by measuring the hip abduction angle (HAA), talar tilt angle (TIA), and Carton-Deschamps index (CDI) in both groups. Complications were also analyzed for both groups.</p> Results <p>At the 5-year follow-up, the complication rate was 20% in the DT-LCP group and 24.19% in the T-LCP group (χ² = 0.324, <i>p</i> = 0.569). All radiographic measures of coronal alignment (HKA, MPTA, WBLR and JLCA) improved significantly from baseline in both groups (<i>p</i> &lt; 0.001). After adjustment for pre-operative values, ANCOVA showed no between-group difference in HKA or JLCA (<i>p</i> = 0.319 and <i>p</i> = 0.287, respectively). MPTA and WBLR reached statistical significance, but with small effect sizes (MPTA: 0.89°, 95% CI 0.28–1.51; WBLR: 0.06, 95% CI 0.03–0.08). PTS increased similarly in both groups (effect − 0.80°, 95% CI − 1.95 to 0.34, <i>p</i> = 0.114). Compensatory changes in adjacent-joint parameters (HAA, TIA and CDI) did not differ between groups: HAA 0.21° (95% CI − 0.13 to 0.55, <i>p</i> = 0.226), TIA − 0.50° (95% CI − 1.43 to 0.42, <i>p</i> = 0.151), and CDI 0.08 (95% CI − 0.01 to 0.17, <i>p</i> = 0.225). Peri-operatively, the DT-LCP group outperformed the T-LCP group, with smaller incision, shorter operative time, less intra-operative blood loss (all <i>p</i> &lt; 0.001) and lower hospitalization cost (<i>p</i> = 0.014). Clinical scores (VAS, WOMAC and Lysholm) improved markedly in both cohorts (<i>p</i> &lt; 0.001), with no significant between-group differences in the magnitude of improvement (all <i>p</i> &gt; 0.05).</p> Conclusion <p>This study demonstrates that both DT-LCP and T-LCP achieve favorable clinical outcomes after OWHTO, as evidenced by significant reductions in mean VAS scores and improvements in WOMAC and Lysholm ratings. The two fixation systems provide reliable correction in both the coronal and sagittal planes, with good alignment of lower-limb parameters such as HKA and MPTA, showing excellent durability and safety. Satisfactory functional results were obtained with either implant. However, the DT-LCP group demonstrated superior peri-operative performance, with a significantly lower incidence of implant-related irritation, thereby reducing the need for secondary hardware removal and resulting in a lighter economic burden.</p>