# Personalised High Tibal Osteotomy Surgery Is Accurate: An Assessment Using 3D Distance Mapping
## 4 Discussion  
High tibial osteotomy is a highly effective treatment for early-stage knee osteoarthritis [49]; however, it requires appropriate correction and also orthopaedic surgeons must be willing to offer the treatment. It is important to highlight that HTO and unicompartmental knee replacement (UKR) have similar outcomes [50], but HTO is joint preserving, thus offering more future options for treatment. The clinical concern about the difficulty in achieving the planned correction is well articulated by [PERSON] et al. [28], who state \"The accuracy of coronal alignment corrections using conventional HTO falls short\". The current study's main purpose was to determine how well a new personalised HTO system actually replicated the planned surgery, going beyond the global commonly used clinical measure of the hip-knee-ankle (HKA) angle. We were able to perform a unique set of measurements in a cohort who had both preoperative and postoperative CT scans. For the first time, a direct 3D comparison between planned and achieved HTO surgery was undertaken. Our findings demonstrate that personalised HTO performed with this system does actually replicate the planned surgery, with the achieved correction matching the planned 3D procedure very well. Overall, the planned osteotomy and fixation plate position was achieved with a discrepancy of considerably less than 2 millimetres (the largest value for the average Positive mean Distance was 1.4 \(\pm\) 0.5 mm, Table 1). The current study provides evidence that the planned correction can be achieved with the personalised HTO system used here, and this should provide orthopaedic surgeons the confidence in offering HTO to patients with early knee OA. The results from the distance map analyses are consistent with the changes in the clinical measurements of knee alignment using the hip-knee-ankle angle. As far as we are aware, there are no other studies which have used this methodology to examine the accuracy of surgically achieving the planned placement of osteotomy bone cuts and stabilisation plates. Thus, it is not possible to compare the findings of the current study with that of other work. A previous cadaver study has shown that the TOKA Personalised HTO procedure achieves a high level of fidelity to the planned correction in terms of changes to HKA [36], which supports the findings of the current study. Patient-specific cutting guides as a means of increasing the accuracy of HTO surgery have been investigated. [PERSON] et al., in a small number of patients, demonstrated that patient-specific  
Figure 7: Screenshot of DMA software depicting (iv) POST tibial plateau versus PRE tibial plateau. Data from the representative case above and the colour scale gives surface deviation in millimetres. cutting guides allowed HKA correction with two degrees [51]. [PERSON] et al. reported that personalised cutting guides increase the probability of achieving an accuracy of \(\pm 2^{\circ}\) in HKA correction compared to the standard HTO technique [52]. There are some limitations that need to be discussed and some of these are related to the way the 3D surfaces used in the DMA methodology were derived. The PRE and POST geometries were obtained by segmenting CT data, and thus there will be a difference between the PRE dataset and the POST dataset, although these were not significant in terms of the tibial bone models in the present study. The introduction of a metallic implant creates streaking artefacts in CT scans; however, the use of metal artefact reduction processing, such as the one used here, can reduce this considerably [53]. This artefact will give rise to noise in the reconstructed surfaces, as can be seen in our results when using POST data for comparisons. The PLA plate surfaces were generated from Computer-Aided Design (CAD) processes, which have considerably less noise than those from CT data; a very clear reduction in DMA standard deviation is seen for this situation in Figure 3(iii-a).