Background <p>Precise execution of preoperative 3D planning is critical in total knee arthroplasty (TKA), but current verification methods—postoperative imaging, navigation, robotics—have limitations: they often assess alignment indirectly or fail to directly compare planned and actual osteotomy surfaces. An in vivo method to quantitatively evaluate plan-execution discrepancies on resected surfaces is lacking. This study aimed to introduce a novel technique for acquiring the TKA osteotomy surface using intraoperative CT, and subsequently comparing it with the preoperative plan to accurately evaluate the precision of osteotomy. Furthermore, this technique was utilized to assess the reliability of osteotomy accuracy in patient-specific instrumentation (PSI) assisted TKA procedures.</p> Methods <p>In this case series study, intraoperative CT scans were acquired immediately after bone resection in 80 TKAs. 3D models of the resected surfaces were created and precisely superimposed onto the preoperative 3D planning models. Angular discrepancies between planned and achieved osteotomy planes (coronal, sagittal, axial) for femur and tibia were quantified. Outliers (&gt; 3°) were assessed.</p> Results <p>Excellent inter- and intra-observer reliability was confirmed, with Intra-class Correlation Coefficient (ICC) ranging from 0.807 to 0.959. Intraoperative CT verification demonstrated femoral deviations of 0.91° ± 0.71° (coronal plane, 2.5% outliers), 2.07° ± 1.98° (sagittal plane, 24.1%), and 1.45° ± 1.28° (axial plane, 19.0%). Tibial deviations were measured at 1.39° ± 0.93° (coronal plane, 5.2%), 2.49° ± 2.21° (sagittal plane, 31.2%), and 4.25° ± 3.82° (axial plane, 7.8%).</p> Conclusion <p>This study represented the first application of intraoperative CT for in vivo verification of osteotomy accuracy in TKA. Results demonstrated excellent consistency. The results for PSI-assisted TKA, validated by this innovative method, showed excellent performance in the coronal plane, with minimal angular deviations and low outlier rates. However, there were still deficiencies in the sagittal and axial planes. This novel verification method not only served as an effective tool for surgical evaluation, but also functioned as a powerful postoperative review and analysis instrumentation, providing critical insights for optimizing and enhancing related surgical techniques.</p> Level of evidence <p>IV, a case series study.</p> Trial registration <p>This trial was registered at Chinese clinical trial registry, registration number: ChiCTR2000039217, registration date: 22/10/2020).</p>