Objective To investigate the radiographic anatomical relationship between tibial plateau and distal femur and evaluate the impact of reset tibial plateau of various widths after reduction of the Schatzker IV-C tibial plateau fractures on postoperative outcomes. Methods We collected and reviewed the X-ray images of the normal knees of 207 standard neutrally-positioned adults （non-fracture group） and pre-and post-operative immediate anterior-posterior X-ray images of the knees of 60 patients with Schatzker IV-C fractures （fracture group） in our hospital from August 2012 to August 2022. We measured the proximal tibial joint width （TAW）， distal femoral width （DFW）， and distal femoral joint width （FAW） in both groups and calculated the TAW/DFW and TAW/FAW ratios. In the fracture group， the cases with TAW between FAW and DFW were assigned to the well-reduced group， while those with TAW outside this range between FAW and DFW to the poorly-reduced group. Both groups were assessed using the Hospital for Special Surgery knee score （HSS） one year after operation. Results In the non-fracture group， there were no significant differences in gender or affected side in terms of TAW/DFW and TAW/FAW ratios （P > 0.05）， while in the fracture group， there were statistically significant differences in the TAW/DFW and TAW/FAW ratios compared to the non-fracture group （P < 0.05）. There was a statistically significant difference in the one-year postoperative HSS scores between the well-reduced and poorly-reduced groups in the fracture group （P < 0.05）. Conclusion The radiographic anatomical relationship between the tibial plateau and distal femur in normal adults is relatively constant， providing a radiological reference for resetting the tibial plateau to a satisfactory width during reduction of Schatzker IV-C fractures. TAW/DFW > 1 or TAW/FAW < 1 indicates a poor reduction of the fracture and predicts poor postoperative recovery of knee joint function.