Over the past 15 years, there has been a dramatic rise in surgical-assisted instruments being developed using CT scans and MRI imaging data. Among those, 3D templating and the using of PSI in THA demonstrated superior effects on preoperative planning and postoperative outcomes. The digital data of patients will be segmented to create a customized digital 3D anatomy model, specifically the hip joint and the whole lower limb. Those digital models enable surgeons to observe images in the form of slices, multi-planar reconstructions of CT images, or 3D models that closely resemble reality, thus accurately determine the femoral and acetabular component positioning. Furthermore, 3D software supports calculating the offset of acetabulum, femur, and the precise measurement of leg length discrepancy, thereby minimizing potential complications of the surgery. Lastly, 3D software provides a visualization of the cup orientation and the range of motion of the artificial hip joint in three-dimensional space, offering surgeons a comprehensive understanding of the implant's orientation and movement for enhanced surgical planning.[11, 12]
The main findings of this study highlighted that 3D printing PSI technique accurately reproduced dynamic planning with regard to the size of the joint components. A study conducted by Mainard in 2017 demonstrated that the sizing of the stem measured using 3D technology achieved an accuracy of 84%, compared to 68% accuracy when measured using 2D methods. Similarly, the sizing of the cup component was found to be 92% accurate when measured with 3D technology, compared to 87% accuracy with 2D methods.[13] According to Di Laura (2020), the use of 3D templates supports in accurately predicting the stem size in 93% of cases and the acetabular cup size in 89% of cases. This significantly reduces the need for hospital inventory reserves by 61%.[14] These aforementioned findings is similar to that in our study, which the accuracy in selection of cup and stem size were 94% and 91% of the cases respectively. Although our study had a smaller sample size and only utilized one system of hip implants, it still indicates the advantage of using that 3D templating in preoperative planning for the anticipated size of the joint components. By accurately predicting the size of the acetabular cup and stem, as well as determining the optimal placement of the components and the osteotomy location, the surgical time can be shortened, the complications such as implant dislocation, early loosening or wear of the joint, periprosthetic fractures, and limb length discrepancies can be controlled.[15],[16]
Regarding the accuracy of using PSI for positioning the acetabular component, there is no significant difference of the mean inclination and anteversion values among preoperatively planned data and postoperatively achieved results in this study (44,90 compared with 44.20 and 18.30 compared with 19.20, respectively). From chart in Fig. 5, approximately 64.7% of the cases had a absolute deviation of acetabular component placement within ± 50 range and 94.1% of the cases had a absolute deviation of acetabular component placement within ± 100 range comparing planned data and achieved values. Among them, 70.6% of the cup were completely placed within the safe zone of Lewinnek. These values indicate an acceptable level of PSI usage accuracy. Spencer (2016) reported achieved inclination and anteversion values of 41.80 and 25.10, respectively; with the absolute deviation of 3.90 and 3.60, respectively. Approximately 54% of the cases achieved the patient-specific target of inclination and anteversion within ± 50 range and 91% within ± 100 range.[17] Findings from Inoue's study (2018) utilizing MRI-based PSI demonstrates that the achieved inclination and anteversion angles were 45.60 and 27.40, respectively, with a deviation of 2.80 and 3.20 degrees from the planned values. Notably, 100% of the inclination measurements fell within the range of ± 10° deviation from the expected values.[18] Ferretti (2021) assess the accuracy of PSI with laser guidance from OPS system (Corin, UK) revealed that the achieved inclination and anteversion angles were 38.40 and 18.30, respectively and 92% of cases, both inclination and anteversion values were within ± 10° absolute deviation range from the planned values. The aforementioned findings indicate that the utilization of PSI point-of-care manufactured, based on the landmarks of the acetabular bone and using the parameters from 3D templating, can ensure accurate determination of the optimal position for the placement of the artificial acetabular component, even in cases with bone deformities. However, in the practical implementation, we realized that in terms of preparation and the utilization of PSI during surgery, it is suggested that senior surgeons are the requirement to facilitate the surgery. Our current PSI design still needs to be improved, especially if we aim to use it for various surgical approaches and different surgeons. The PSI model used in the study was specifically designed for the THA using a posterolateral approach and requiring an additional 2cm incision length compared to conventional methods. As a CT-based approach, it can sometimes be influenced by the acetabular cartilage layer, and we assumed a 0.5mm offset for this cartilage layer to overed that disadvantage.
According to the results in Table 2, the use of PSI for femoral neck osteotomy and stem placement showed a slightly decreasing trend in the stem anteversion angle compared to the achieved angle, although the difference was minimal and not statistically significant (18.90 and 18.10). The height of femoral neck osteotomy and the leg length discrepancy post-operation both achieved the planned targets. The achieved femoral neck osteotomy height varied from the predicted 11.5mm to 12.3mm in actual. With an average leg length discrepancy of 2.1mm, most patients did not perceive any discomfort during movement. This indicates that, unlike PSI for the acetabulum, PSI used for femoral bone osteotomy is relatively easy to use (as it involves less interference with soft tissue around cutting side) while still providing high accuracy. The precise placement of the femoral neck osteotomy plays an important role in establishing reference points for achieving proper leg length and anteversion alignment during stem insertion. In our study, all stems were placed press-fit, with the majority having a center-directed stem axis, maximizing the longevity of the stem and minimizing complications such as thigh pain during ambulation. According to Hassani (2014), the restoration of balanced leg length reached 88% with an average discrepancy between the two legs of only 0.3mm.[19] According to Mishra (2020), the use of PSI can achieve a leg length discrepancy between the planned and achieved measurements as low as 0.15mm.[20] Ferretti's findings demonstrate that the leg length discrepancy and osteotomy height were accurately placed according to the plan, with differences of 2.5mm and 10.3mm expected versus 2.4mm and 10mm observed, respectively.[21]
In terms of safety and initial clinical outcomes, as described in Table 3, according to several authors, the average surgical time when using PSI is longer compared to conventional methods but much shorter than when using robotic or navigation system.[22] According to Spencer, the preparation steps for PSI take approximately 3–5 minutes.[17] In Mishra's study, the surgical time was reported as 99.39 minutes compared to the control group, which had a surgical time of 92.33 minutes.[20], in Xing's study, the surgical time was reported as 138.4 minutes compared to the control group, which had a surgical time of 88.9 minutes.[23]. Meanwhile, according to Xiao (2020), it was found that PSI did not prolong the surgical time.[6] The results of our study showed a shorter surgical time of 82.5 minutes, which could be attributed to the majority of patients in our study using smaller implant sizes and performing surgery on patients without severe deformities, leading to a faster preparation time. The average blood loss in our study was 317.7 mL, which did not differ significantly from conventional hip replacement procedures and was comparable to other studies such as Ito (2017) with a blood loss of 356ml[24] and Xing with 453.3ml [23]. Less intraoperative blood loss can be explained by the shorter operative time in our study. All cases in our study did not experience any intraoperative complications, thereby demonstrating the safety of this method. In addition, in some parameters such as the time to walk early after surgery (1–3 days, of which 64.7% could walk on the day of surgery) compared with many other common surgery studies, PSI was used for THA shows similarity. Many studies have demonstrated the benefits of getting patients to walk again in the day of hip arthroplasty surgery to reduce hospital stay and significantly improve rehabilitation.[25, 26] For example, in Xing's study, the Forgotten Joint Score (FJS-12) for the PSI group was 80 compared to 68.5 in the control group, and the Harris Hip Score also showed improved results[23]. However, it is important to note that our study was conducted with a small sample size, had a short follow-up period, and limited clinical outcomes assessed. Therefore, these findings may not yet provide a definitive conclusion.
Despite listing some advantages above, the 3D planning and patient-specific instrument (PSI) utilization in THA still have some significant drawbacks that are gradually being addressed. Firstly, there is a high cost associated with 3D printers, softwares investment and the issues of CT scans, making it unaffordable for every facility to implement. Additionally, patients are exposed to higher levels of radiation. Moreover, the time required for designing and printing a set of instruments can sometimes extend to 1–3 days, increasing the waiting time (although it is faster compared to ordering from other commercial companies worldwide). Furthermore, the data from CT scans does not accurately assess certain pathologies and abnormalities in cartilage and soft tissues surrounding the joint, maybe leading to inaccuracies in the surgical instruments.