From January 2021 to December 2021, patients requiring total hip replacement surgery at our hospital were included in our study. The inclusion criteria were (1) patients undergoing primary total hip arthroplasty and (2) patients diagnosed with a femoral neck fracture, osteonecrosis of the femoral head, and hip osteoarthritis. Patients were excluded from the study if (1) undergoing revision hip arthroplasty, (2) diagnosed with development dysplasia of the hip (DDH), and (3) having life-threatening comorbidities such as respiratory and cardiac insufficiency. This study was approved by the IRB Ethics Institute of Guangzhou First People's Hospital (K-2018-137-04). Patient-specific information is given in Table 1.

All patients in our study underwent preoperative anteroposterior (AP)-lateral hip radiography and pelvic CT scanning. A 64-slice spiral CT was used to conduct thin-sliced plain scans of the affected hip joint, with a layer distance and thickness of 0.625 mm. The DICOM data were then imported into medical image processing software Mimics20.0 (Materialize Software, Leuven, Belgium). A three-dimensional anatomical model of the hip joint was generated and digitally processed into an STL format. The STL data model was then imported into reverse engineering software Imageware13.0 (UGS Corporation, Plano, TX, USA), and the anatomical structures involved in THA preoperative planning (femoral head spherical boundaries, femoral head and neck axis, femoral shaft axis) were measured. The hip replacement systems utilized in our study were obtained from a single product line [Smith and Nephew (SN), London, United Kingdom]. The prosthetic parameters of the entire SN product line (including the acetabular and femoral component) were digitized using a laser scanner and processed using Imageware to obtain 3D STL data (Figure 1). This included diameter, depth, femoral stalk length, width, angular structure, and curvature, with a degree of error up to 0.05 mm, which can be directly utilized for preoperative planning and surgical simulations.

Intraoperative acetabular cup implantation was simulated in the software with a standardized abduction angle of 40° and an anteversion angle of 15°; the femoral prosthesis was inserted along the medullary canal. The selection of the most suitable acetabular component size was based on a standardized total hip arthroplasty templating criterion, ensuring that the outer metallic curvature of the acetabular cup made contact with the acetabular subchondral bone and the inferior border of the metallic cup lay within and parallel to the transverse ligament. The most suitable femoral implant size was selected according to the intramedullary diameter of the proximal femur. The proximal stem was positioned parallel to the site of femoral neck osteotomy and can be evaluated intraoperatively by hand-rotating the femoral stem after placement to assess for axial stability. The overall preoperative planning process in our study is shown in Figure 2.

All patients underwent a standard posterolateral approach for THA, performed by the same surgical team. After anesthesia induction, a curved 6–8 cm posterolateral incision was made over the greater trochanter. The soft tissue layer was dissected to expose the joint capsule, and the femoral head was then removed by osteotomy. Subsequently, the joint capsule was dissected to expose the medial side of the acetabulum. The cup implant and polyethylene lining were placed after grinding the acetabular soft tissue using an acetabular reamer. The soft tissue lining of the acetabular surface was removed, followed by femoral broaching to expose the femoral canal for insertion of the femoral prosthesis, completing the implantation of both femoral and acetabular components. All of the final sizes used were in accordance with the intraoperative findings, with preoperative sizing mainly used as a reference. After successful reduction, the exposed articular cavity was washed with saline, and 30 ml of cocktail solution was injected into the surrounding soft tissues. The hip capsule was then reconstructed, followed by repair of the posterior tissue envelope. Finally, the surgical incision was sutured and closed.

Preoperative antibiotics were administered 30 min prior and 24 h after surgery to prevent postoperative infection. Low-molecular-weight heparin was administered starting from the second postoperative day to prevent deep vein thrombosis, and quadriceps exercises were encouraged for all patients as soon as possible. Standard postoperative radiographs were taken on the second postoperative day to evaluate the accuracy and stability of the implanted prosthetics. Some of the patients were further evaluated using a postoperative CT scan of the operated limb. Patients were followed up at 1, 3, and 6 months postoperatively. Prosthetic loosening and dislocation were confirmed using femoral x-rays during the follow-up period, and the Harris hip function score was evaluated at the final follow-up (6 months post-operation) to further evaluate hip function recovery.

SPSS22.0 statistical software was used for all of our data analysis. Data measurements in our study were expressed as mean ± standard deviation. A record was made of the instances where the acetabular and femoral component sizes were selected according to the preoperative planning vs instances where they differed from preoperative planning. These values were compared and analyzed. The intraoperative time, blood loss, postoperative observation time, and postoperative Harris hip score of the two groups were analyzed by independent sample t-tests. All data with a p-value <0.05 indicated statistical difference.

A total of 62 patients were included, with 31 patients in the CAD simulation group and 31 patients in the traditional x-ray interpretation control group. There were no significant differences in gender, age, and preoperative Harris hip scores between the two groups (P > 0.05). Details of all the patients are presented in Table 1.

Data analysis of the comparison between the acetabular component selected during preoperative planning and the actual component used during the surgery showed accuracies of 80.6% and 61.3% and 83.9% and 67.7% for the femoral component between the CAD group and the control group, respectively. The number the implants used during surgery as compared to the preoperative planning of the two groups are presented in Figure 3 and Table 2.

Intraoperative time, blood loss, duration of postoperative hospital stay, and final follow-up Harris hip score of the two groups were compared. The CAD group showed better results in all the recorded parameters (operation time, intraoperative blood loss, duration of postoperative hospital stay, and postoperative Harris hip score). The average operation time and intraoperative blood loss were found to be significantly lower in the CAD group than in the control group (operation time: 84.2 ± 19.8 vs. 100.3 ± 25.9 min, P = 0.008; blood loss: 177.4 ± 45.5 vs. 231.0 ± 76.7 ml, P = 0.002). The duration of postoperative hospital stay was also significantly lower in the CAD group than in the control group (6.5 ± 3.0 vs. 9.1 ± 3.9 days, P = 0.003). The Harris hip scores evaluated during follow-up at 6 months postoperatively were also significantly higher for the CAD group than for the control group (81.9 ± 6.5 and 74.7 ± 11.1, P = 0.003) (Table 3).

All patients underwent successful THA and were discharged after satisfactory wound healing without any incidence of surgical site infection during their hospital stay. There were no recorded incidences of acetabular penetration or proximal femoral fracture during prosthetic implantation. Patients achieved satisfactory joint stability and range of motion after surgery and were discharged without any incidence of surgical site infection. During discharge, all patients were asked to be followed up at 1, 3, and 6 months. Throughout the follow-up period, we did not encounter any incidence of infection, implant dislocation, periprosthetic fracture, or perioperative comorbidities (severe pneumonia, deep vein thrombosis, etc.). The stability of the implant was mainly evaluated by follow-up hip radiographs, which showed no evidence of loosening. Patients underwent physical examinations during their follow-ups to assess postoperative Harris hip scores. All patients in our study were able to return to regular daily activities without hip pain at 1–2 months after surgery. A sample case is presented in Figure 4.

We do acknowledge the limitations of our study, including the small population size and the lack of a multicenter large sample comparative study. In our study, we only included the different sizes from one series of prostheses and did not perform an analysis on the positioning of the prostheses during surgery. This may also lead to problems with postoperative rehabilitation in some patients. However, with CAD, the appropriate placement of the implant prostheses can be tailored for each patient with the usage of personalized surgical guide plates. Our future studies will aim to include the usage of surgical guide plates to further incorporate CAD in the proper placement of implant prostheses.

Personalized treatment is a current aim in the development of orthopedic surgical treatment because patients require specialized preoperative planning and surgical treatment plans unique to each individual to achieve an accurate diagnosis, treatment, and postoperative rehabilitation (19, 20). THA, as the end-stage therapy of choice for numerous hip diseases, is becoming a common surgical procedure with numerous strategies to improve surgical outcomes. Our study results show that implementing CAD in the preoperative planning of THA leads to better surgical outcomes compared to traditional radiograph assessment for implant sizing. This is reflected by a more accurate selection of the required implant size, resulting in a shorter surgical duration, reduced surgical blood loss, shorter postoperative hospital stay, and improved short-term postoperative functional recovery. The utilization of CAD in the preoperative planning of DDH, complex hip arthroplasties, and revision hip arthroplasties has been studied and shown to have evident benefits. Our study results show that CAD is also beneficial in the preoperative planning of regular total hip replacements.

Proper preoperative planning and the selection of suitable implant prostheses of both acetabular and femoral components used during surgery determine the surgical outcome and affect the postoperative quality of life. Inappropriate selection of an acetabular prosthesis that is too large for the acetabular rim leads to excessive degeneration of the polyethylene lining and increases the risk of pelvic wall penetration during surgery. This leads to implant instability and is one of the reasons for postoperative chronic pain. Conversely, selecting a cup implant that is too small leads to overall instability of the acetabular complex due to being unable to achieve a suitable press-fit, resulting in an inability to restore the physiological axis of the operated limb, further increasing the risk of wear and dislocation. Selecting an appropriate femoral implant size plays a vital role in the overall implant lifespan. Inappropriate selection of a femoral prosthesis that is too small for the intramedullary canal severely increases the risk of aseptic loosening (2, 10). Postoperative loss of trabecular bone volume causes the implant to lose the support of the surrounding tissue due to not having a press-fit relation with the surrounding bone tissue. On the other hand, selecting a femoral prosthesis that is too large directly increases the risk of periprosthetic fracture intraoperative and postoperatively (21–23). Therefore, appropriate preoperative planning and accurate intraoperative prosthesis selection are the first and most crucial steps in determining the success of total hip arthroplasty.

The usage of CAD in our study allows for a 3D reconstruction of the operated area, providing an accurate understanding of the hip joint, including the severity of osteophyte growth surrounding the acetabular structures, the degree of degeneration of the acetabulum and femoral head, the accurate position of fractures and bony fragments, and the precise degree of fracture dislocation. For patients with femoral neck fractures, this offers guidance for determining the appropriate site of osteotomy. CAD mainly allows for the accurate measurement of acetabular margins, including both the diameter and depth in 3D, allowing for the most appropriate selection of a suitable prosthetic size. Preoperative surgical simulation by CAD allows for perioperative assessment of the operated limb, including length and axis changes, evaluation of the surgical plan, and early recognition and avoidance of the limitations and possible surgical complications. In our study, CAD greatly assisted in the preoperative planning for osteoporotic patients requiring THA. A 3D reconstruction of the affected limb allowed for a better understanding of the hip and femoral bone mineral density, enabling proper avoidance of regions of vulnerability, thus preventing hospital-related injuries. Proper selection of prosthesis size also helps prevent prosthesis implant-related fractures, providing guidance as to whether the acetabular prosthesis further requires the usage of screws.

In our study, we utilized CAD during preoperative planning to allow the surgeon to accurately predict the appropriate size of implant prostheses required. This allowed for a better selection of the size of the reamer and broach used instead of having to progressively increase the size of the instrument over a wide range. This contributes to effectively reducing the amount of time needed for reaming the soft tissue layer of the acetabulum and broaching the intramedullary canal of the femur, thus reducing the overall surgical time (which was recorded from making the surgical incision to suturing the surgical wound). The reduced amount of intraoperative trauma to surrounding tissue then reduces the overall amount of blood loss and the need for blood transfusions, effectively eradicating the risk associated with it. These factors promote patient postoperative rehabilitation and success to a certain degree. This is in accordance with Moyer et al., who reported that early postoperative rehabilitation relies on a precise surgical procedure (24). Our results show that the CAD group has a more accurate prediction of the acetabular prosthesis than the control group. Considering the postoperative evaluation, this means that there is a reduction in overall postoperative hospital stay and treatment costs. Postoperative follow-up also showed better results for the CAD group than for the control group, further proving the benefits of CAD in preoperative planning. In our study, we also recorded that the patients with an apparent preoperative leg length difference achieved simultaneous correction. Preoperative simulation, estimating the postoperative limb length difference after implanting the femoral prosthesis, allows for selecting a suitable femoral head component, which mainly relies on the subjective decision of each surgeon in the control group and would then be standardized through CAD simulation.

In our study, most of the elderly female patients require total hip replacement due to femoral neck fractures. The higher incidence of osteoporosis in this age group explains their susceptibility to fractures and requirement for additional attention in selecting appropriate implant prosthesis sizes to prevent pelvic wall penetration and femoral fractures during prosthesis implantation. Evidence of osteoporosis also provides a reminder of the necessity of osteoporotic treatment postoperatively. Consequently, the elderly male patients in our group require THA primarily due to osteonecrosis of the femoral head and their smoking and drinking habits. In this group of patients, the incidence of osteoporosis is relatively lower but mainly requires the cessation of their smoking and drinking habits postoperatively and postoperative vasoactive supportive treatment.