## 4 Discussion
Moreover, we can justify the lack of coincidence due to the measurements being derived from X-rays. In a study performed by [PERSON] et al. [23], a Bland-Altman plot demonstrated sufficient agreement to justify using the CT scan and X-rays interchangeably. [PERSON] et al. [24] evaluated the reliability of studies with measurements based on long leg radiographs, and they concluded that the post-operative evaluation could be performed with these radiological studies. However, intra- or inter-observer reliability appears to be better when the measurements are carried out on a CT scan. The high variance between assessments might be explained by two important factors: the accuracy of the landmarks and patient positioning at the time of the X-ray. [PERSON] et al. [25] showed differences between the pre-planning and postoperative measurements of 1.8\({}^{\circ}\) and 1.7\({}^{\circ}\) on the coronal plane of the femur and the tibia, respectively. Those assessments were made with a 3D CT scan in consideration of a lack of significant differences. [PERSON] et al. [11], measuring postoperatively with a 2D CT scan, found smaller differences of 1.2\({}^{\circ}\) in the coronal femur and 0.4\({}^{\circ}\) in the coronal tibia when using PSI technology. Considering our results and comparing them with other studies, it is easy to think that two of the most important factors involved in obtaining the most accuracy in measuring are probably the observers' training at the time of evaluation and having a strict imaging protocol in place in terms of patient positioning (axial and sagittal planes), following the indications published by [PERSON] et al. [26] and [PERSON] et al. [27]. In the analysis of the patient profiles in which bone cut accuracy was worse, the present study did not identify a clear, describable pattern for either obesity or preoperative deformity based on the results seen in the literature. Over the years, the BMI has been one of the most concerning factors when the surgeon attempts to position the implant. [PERSON] et al. [28] stated that there were no differences in tibial component alignment between stratified BMI groups. [PERSON] et al. [29] observed no significant differences between obese and non-obese patients in terms of femoral and tibial component alignment. Deformity prior to surgery is another important factor to analyse when considering the accuracy of bone cutting. [PERSON] et al. [30] observed that accuracy tends to diminish in bone cuts in patients with more than 10 degrees of varus in the hip-knee-ankle (HKA) angle. In that study, patients operated on with the CT-based PSI system saw a decrease in accuracy of over 15\({}^{\circ}\) of varus in the HKA. In our study, that association was also found. If one looks at the different technological systems aimed at helping surgeons achieve bone cut accuracy, the literature also reports discrepancies. [PERSON] et al. [31] showed interesting results in terms of accuracy using PSI guides. They saw a discrepancy of 0.5\({}^{\circ}\) in the distal femur and 0.1\({}^{\circ}\) in the coronal proximal tibia. However, that was with a limited number of patients. Then again, other studies [32] have shown a high proportion of outliers when using this PSI technology, or the same degree of accuracy when comparing PSI with conventional cutting guides [33]. Navigation systems may be a reliable tool to obtain precise results in bone cuts. [PERSON] et al. [34] observed that 95.5% and 90.1% of the patients were within the range of 3\({}^{\circ}\) varus/valgus in the tibia and femur, respectively. A recent [PERSON] et al. study [35] demonstrated that even with accelerometer- and navigation-improvedalignment, there were no differences in clinical outcomes, quality-of-life and satisfaction when compared to conventional instruments. Regarding robotics, there are several studies defending their greater accuracy in bone cutting [36; 37; 38]. However, further studies with longer follow-ups are needed to confirm the benefits of this new technology.