Introduction
Restoring the neutral mechanical alignment is usually considered as one of the prerequisites for a successful total knee arthroplasty (TKA). Previous literature has shown that malalignment or malposition of the components are often closely associated with complications such as polyethylene wear and aseptic loosening [
1‐
3]. However, the incidence of the lower limb malalignment or malposition of the components after conventional TKA is as high as 20–30% [
4,
5].
To overcome the limitations of the conventional method for TKA, many modified surgical techniques have been adopted. The proponents of computer navigation believe that this method can achieve more accurate osteotomy by adding about 10 min of registration time during the surgery [
6,
7]. And robotics can reduce the occurrence of outliers in the lower limb [
8‐
10]. However, compared with conventional methods, there are deficiencies in computer navigation and robotics such as longer surgical time [
8,
11], higher surgery costs [
8,
12], a substantial learning curve [
8,
10], and more complications. Furthermore, during the surgery, the percentage of temporarily changing from robotic technology to conventional method due to various reasons is as high as 22% [
13]. Patient-specific instrumentation (PSI) is regarded to enable better component positions and lower limb alignment with decreased operative steps, less blood loss and fat embolism, and shorter operative time [
14,
15]. However, more and more literatures have shown that compared with the conventional method, PSI has no obvious advantages in lower limb alignment, component position, and postoperative knee function [
14,
16‐
19]. Some authors even argued that PSI was worse at the control of the lateral tibial component (LTC) angle [
17‐
20].
In this study, on the basis of summarizing the principles, advantages, and disadvantages of the conventional method and the modified techniques, we adopted a novel technique of CT-based patient-specific three-dimensional preoperative design combined with conventional osteotomy instruments. The advantages of this technique include personalized preoperative design, precise intraoperative positioning, no need to purchase new equipment, better control of the surgical time and cost, and easier application due to similar procedures with the conventional method.
Patients were divided into the novel technique group and the conventional group to evaluate the operation and early clinical effect of the novel technique compared with the conventional method.
Discussion
The postoperative outcomes of total knee replacement are related to many factors, and the surgical factors often include the placement position of components, the alignment and soft tissue balance of the lower limbs, and the bone cement technique [
36]. Among them, the neutral alignment of the lower limbs and the component position may be the key to avoiding the early failures of TKA. In order to obtain the desired postoperative lower limb alignment and components position, technologies such as patient-specific instrumentation, computer navigation, and robot-assisted TKA came into being, but these high-tech technologies are also accompanied by various disadvantages, such as longer operation time [
8], higher operation cost [
8,
37], more potential complications [
13,
38], and the possibility to switch to conventional TKA for various reasons during the operation [
11,
13]. In addition, TKA is no longer limited to large hospitals, and many small hospitals have also carried out such operations, but most of the smaller hospitals do not have the equipment or technology related to the above high-tech technologies. Is there a TKA surgical technique that is simpler and more economical than the abovementioned high-tech techniques, but more precise than conventional methods in controlling the alignment of the lower limbs and the position of the components? The novel technique of CT-based patient-specific 3D preoperative design combined with conventional osteotomy instruments provides one possibility.
The LTC of the novel technique group was better than the conventional group [4.23° ± 2.57° vs (9.48° ± 3.74°,
P < 0.001), and the percentage of outliers was also significantly smaller than the conventional group (31.68% vs 95.05%,
P < 0.001). The results demonstrated that the novel technology group is superior to the conventional group in controlling the position of the tibial components. The conventional method usually determines the position of the positioning rod and the retroversion angle of the osteotomy instrument by the surgeon’s visual assessment, whereas the novel technique uses the positioning pin of the extramedullary positioning rod to accurately restore the pre-designed fix point of the guide pin and accurately control the position of the distal end of the positioning rod based on the thickness of the soft tissue of the anterior tibial of the patient to ensure the accurate intraoperative implementation of the preoperative design. The precise patient-specific preoperative design and its accurate implementation are the main reasons why the novel technique group has significantly better control of the LTC than the conventional group (
P < 0.001). The LTC angle after TKA would significantly affect the knee joint movement, the fixation of implants, and the wear of polyethylene pads, etc .[
39‐
41]. Therefore, this angle is one of the important evaluation indexes of the radiographic evaluation of the American Knee Society [
31]. Yan et al. randomly divided 90 OA knee joints into three groups and performed a randomized controlled trial on the lower extremity alignment of PSI, computer navigation, and conventional method. They found that the average LTC values and outliers of the three methods had no statistical differences postoperatively [
16]. Rhee et al. summarized and evaluated 5 studies on the sagittal alignments of the tibial component and found that the number of outliers in LTC included 131 of 1020 cases in the computer-navigated TKA and 154 of 1026 cases in the conventional TKA group; the difference was not significant (
P = 0.17) [
42]. More researches have indicated that PSI is even worse than the conventional method in controlling LTC [
17‐
20]. In the control of FTC, both groups performed well without statistical differences in this study. Previous studies of computer navigation, PSI, and robotics have shown that in the control of FTC, these more expensive techniques might not have obvious advantages compared with the conventional method [
6,
7,
14,
16,
43‐
45]. This may be because the experienced surgeons in those studies could control FTC well during the surgery without deviation.
The conventional method usually chooses the apex of the intercondylar notch as the medullary entry point and uses the HKS angle measured on FLX for distal femoral osteotomy. Preoperative 3D design can more accurately evaluate the medullary entry point and measure the valgus osteotomy angle. In most patients, the femoral medullary cavity is larger than the intramedullary positioning rod, and the swing of the drill when drilling may cause the intramedullary diameter larger than the diameter of the intramedullary positioning rod, resulting in a 1° deviation [
46]; in addition, during distal femoral osteotomy, the osteotomy instrument can only select an integer, which may result in intraoperative selection bias. The above factors have reduced the accuracy of intraoperative implementation of HKS to a certain extent, which may be one of the main reasons for the two groups to have no significant difference in the femoral component position. However, from postoperative results, the control of the femoral component position in the novel technique group and conventional group are both acceptable. Computer-navigated and robotics use technologies such as intraoperative navigation and second calibration to achieve more accurate intramedullary positioning and femoral osteotomy. However, many studies have proven that they are not superior to the conventional method in the femoral component position [
16,
42‐
44,
47]; PSI also does not provide better results in this field [
14,
45].
Compared with the conventional group, the novel technique group had a lower percentage of HKA outliers (17.43% vs 40.37%, P < 0.001) and percentage of HKA overcorrection (11.01% vs 26.61%, P = 0.003), although the mean value of HKA between the two groups was not statistically significant. This demonstrates that the novel technology can reduce the occurrence of lower limb alignment outliers than the conventional one.
The operation time and tourniquet time of the novel technology group were significantly less than those of the conventional group. After excluding the influence of related confounding factors, we believed that the longer tourniquet time in the conventional group was mainly due to repeated adjustment and confirmation of the femoral medullary entry point and tibial positioning system during the surgery, while the novel technology group mainly needed to confirm the positioning system according to the preoperative plan, reducing the incidence of repeated adjustments, thereby reducing both tourniquet time and operation time by about 13 min on average.
There was no significant difference between the two groups in the scores of VAS and NEW-KSS at 6 and 12 months after the operation. However, in the VAS pain score at 1 month after the operation, the novel technology group was better than the conventional group(3.58 ± 0.71 vs 4.32 ± 0.65), and the difference was statistically significant (P < 0.05). In each item of the NEW-KSS score 1 month after the operation, the novel technology group had a tendency to be superior to the conventional group, but the difference was not statistically significant (P > 0.05). In the case that the two groups of early rehabilitation and pain management were consistent, this indicated that the novel technique group was superior to the conventional group in early pain and recovery, which may be related to the shorter tourniquet time and operation time in the novel technique group.
This study also has some deficiencies. First, it does not include computer-navigated, robotics, or PSI technology to compare with the novel technique. Second, it has not conducted mid- or long-term follow-up and functional scoring of the patients. Third, it is a single-center study and the CT-based patient-specific three-dimensional preoperative design all came from one manufacturer. Multi-center studies and execution with other manufacturers are needed for further verification.
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