Using Three-Dimensional Printing Technology to Solve Complex Primary Total Hip Arthroplasty Cases: Do We Really Need Custom-Made Guides and Templates? A Critical Systematic Review on the Available Evidence

The burden of osteoarthritis (OA) is around 300 million people affected worldwide, with the hip representing a commonly affected joint. Total hip arthroplasty (THA) has been used with notable success as a definitive treatment to improve pain and function in hip OA patients. The recent advent of new technologies, such as 3D printing, has pushed the application of these new concepts toward applications for the well-known THA. Currently, the evidence on the use of 3D printing to aid complex primary THA cases is still scarce. Methods: An extensive literature review was conducted to retrieve all articles centered on the use of 3D printing in the setting of primary THA. Results: A total of seven studies were included in the present systematic review. Four studies investigated the use of 3D-printed surgical guides to be used during surgery. The remaining three studies investigated the benefit of the use of 3D-printed templates of the pelvis to simulate the surgery. Conclusions: The use of 3D printing could be a promising aid to solve difficult primary total hip arthroplasty cases. However, the general enthusiasm in the field is not supported by high-quality studies, hence preventing us from currently recommending its application in everyday practice.


Introduction
On a worldwide scale, up to 300 million people are affected by osteoarthritis (OA), with the hip representing one of the most involved joints [1].The pain is just the tip of the constellation of OA consequences, which include the almost unbearable social and economic costs, which are estimated to be around 303 billion yearly, both due to healthcare expenses and loss of profit [2][3][4].Since its introduction in the 1960s [5], total hip arthroplasty (THA) has proven its effectiveness in reducing symptoms and improving function, hence leading to an overall improvement in quality of life and reduction of healthcare service usage [6,7].In order to ensure the longest implant survival and avoid reoperation procedures, several studies and approaches [8,9] were developed, considering the osteointegration of the prosthetic materials, biomaterial wear, and the prosthetic component positioning, thus ensuring the hip biomechanics [10][11][12].Joint replacement surgery, with its focus on implants, instruments, and surgical devices, is well suited for the application of three-dimensional (3D) printing: a process of design and manufacturing and layer-by-layer construction of anatomically detailed models and surgical guides, with the promise to revolutionize medicine and healthcare [13].In the operating room, 3D printers are working to assist the orthopedic surgeon both intraoperatively, through cutting guides facilitating crucial surgical steps, and even before surgery, via 3D templates better reflecting each patient's peculiar anatomy [14][15][16].Previous studies also assessed its efficacy in decreasing the operative time, blood and bone loss, and trauma for the patient [17,18].In fact, the use of 3D printing templates is able to provide the surgeon with more information on patient-specific anatomy that can be hands-on investigated prior to surgery in complex procedures, hopefully giving a better understanding than the conventional two-dimensional (2D) radiographic reconstructions [19].The adoption of this new perioperative asset has been recently investigated in the setting of total hip and knee revision arthroplasties, reporting satisfactory clinical and radiological outcomes [20].However, only a few studies investigated 3D printing, intended both as templates and guiding devices, to assist complex primary THA.Such technologies have been proposed as an additional aid in the setting of complex cases of the hip undergoing THA.Furthermore, 3D-printed templates of the patient's pelvic anatomy are intended to be used during a prior surgical simulation to better plan the THA procedure, whereas 3D-printed cutting guides have been developed to be used during surgery to improve the accuracy of both the acetabular cup and femoral stem placement.Hence, the aim of the present systematic review is to summarize the existing literature on the application of such 3D-printed technologies in complex primary THA, evaluating the potential benefits and eventual disadvantages.

Materials and Methods
Literature research was performed on PubMed, Embase, and Google Scholar databases on the 23 September 2023, utilizing the following search string: "3D printing" OR "three dimensional printing" OR "3D assisted" OR "3D guides" OR "three dimensional guides" OR "printed template" AND "primary total hip arthroplasty" OR "primary THA" OR "primary total hip replacement" OR "primary THR".The screening process was performed by two independent reviewers (G.A. and P.C.).The first step was the initial screening based on titles and articles, considering the following inclusion criteria: (1) randomized controlled trials (RCTs); retrospective or prospective studies on humans; (2) English language; (3) published in indexed journals; and (4) evaluating the outcomes of 3D printing technology for difficult primary total hip arthroplasties.Exclusion criteria were articles written in other languages, pre-clinical studies, reviews and meta-analyses, and studies on the use of 3D printing for different procedures.Furthermore, this study was focused on 3D-printed technologies that help surgeons in complex THA procedures; therefore, reports on 3D-printed custom-made implantable prostheses have not been included.
Upon concluding the initial screening phase, full texts of included articles were evaluated, and the reference list of all the retrieved articles was further evaluated for identification of potentially relevant studies.A PRISMA flowchart of the selection process is reported in Figure 1.
Discrepancies encountered between the two reviewers were solved by a senior investigator (M.L.).The full texts included underwent data extraction and subsequent collection for the purposes of the present project.Discrepancies encountered between the two reviewers were solved by a senior investigator (M.L.).The full texts included underwent data extraction and subsequent collection for the purposes of the present project.

Results
A total of seven studies were included in the present systematic review.Four studies [21][22][23][24] investigated the use of 3D-printed surgical guides: in all four studies, a preoperative CT scan of the pelvis was performed, and, with the aid of specific software, 3D surgical guides were designed and printed.Those guides were then sterilized and temporarily fixed to the patient's pelvis during THA surgery to guide the surgeon and to improve the accuracy of acetabular cup placement (all four studies previously mentioned) or even femoral osteotomy [22] in primary complex THA.
The remaining three studies investigated the benefit of the use of 3D-printed templates of the pelvis in complex primary THA [18,25,26].In all three studies, a CT scan was conducted, and an entire 3D-printed template of the specific patient's pelvis was produced to perform a pre-surgery simulation of the THA procedure.The aim of producing those real-size anatomical templates was to better plan the cup positioning and to more precisely estimate cup dimensions and the eventual need for additional specific surgical devices such as augments and contouring plates.Compared to surgical guides, templates were not used during surgery but exclusively during the preoperative simulation.

Quality Assessment of the Retrieved Studies
For randomized controlled trials (RCTs), the risk of bias was assessed using the Cochrane Risk of Bias Tool 2 for Randomized Controlled Trials (RoB 2 tool) [27].Seven types of bias were analyzed and classified into "low risk", "high risk", or "unclear risk".For both the studies analyzed, the randomization process and the allocation concealment method were not sufficiently described, leading to some concerns in the overall judgment (Table 1).Then, the results of this evaluation were converted to Agency for Healthcare Research and Quality standards, which ultimately ranked the trials as "good quality", "fair quality", and "poor quality".None of the randomized controlled trials included in the present systematic review reached a standard of "good quality", and both the RCTs reached a standard of "fair quality".2020) [21] such as augments and contouring plates.Compared to surgical guides, templates were not used during surgery but exclusively during the preoperative simulation.

Quality Assessment of the Retrieved Studies
For randomized controlled trials (RCTs), the risk of bias was assessed using the Cochrane Risk of Bias Tool 2 for Randomized Controlled Trials (RoB 2 tool) [27].Seven types of bias were analyzed and classified into "low risk", "high risk", or "unclear risk".For both the studies analyzed, the randomization process and the allocation concealment method were not sufficiently described, leading to some concerns in the overall judgment (Table 1).Then, the results of this evaluation were converted to Agency for Healthcare Research and Quality standards, which ultimately ranked the trials as "good quality", "fair quality", and "poor quality".None of the randomized controlled trials included in the present systematic review reached a standard of "good quality", and both the RCTs reached a standard of "fair quality".templates of the pelvis in complex primary THA [18,25,26].In all three studies, a CT scan was conducted, and an entire 3D-printed template of the specific patient's pelvis was produced to perform a pre-surgery simulation of the THA procedure.The aim of producing those real-size anatomical templates was to better plan the cup positioning and to more precisely estimate cup dimensions and the eventual need for additional specific surgical devices such as augments and contouring plates.Compared to surgical guides, templates were not used during surgery but exclusively during the preoperative simulation.

Quality Assessment of the Retrieved Studies
For randomized controlled trials (RCTs), the risk of bias was assessed using the Cochrane Risk of Bias Tool 2 for Randomized Controlled Trials (RoB 2 tool) [27].Seven types of bias were analyzed and classified into "low risk", "high risk", or "unclear risk".For both the studies analyzed, the randomization process and the allocation concealment method were not sufficiently described, leading to some concerns in the overall judgment (Table 1).Then, the results of this evaluation were converted to Agency for Healthcare Research and Quality standards, which ultimately ranked the trials as "good quality", "fair quality", and "poor quality".None of the randomized controlled trials included in the present systematic review reached a standard of "good quality", and both the RCTs reached a standard of "fair quality".For studies with a non-randomized design, the risk of bias was carried on through the ROBINS-I tool ("Risk Of Bias In Non-randomised Studies-of Interventions") [28], which evaluates the eventual benefit or harm of an intervention in studies that did not use the randomization process.(Table 2).Two studies reported a "moderate" overall risk of bias [25,26], and one study reported a "serious" risk of bias [24], mainly caused by participants' selection and outcomes' measurements.
For studies with a non-randomized design, the risk of bias was carried on through the ROBINS-I tool ("Risk Of Bias In Non-randomised Studies-of Interventions") [28], which evaluates the eventual benefit or harm of an intervention in studies that did not use the randomization process.(Table 2).Two studies reported a "moderate" overall risk of bias [25,26], and one study reported a "serious" risk of bias [24], mainly caused by participants' selection and outcomes' measurements.

3D-Printed Surgical Guides
A synopsis of the included studies evaluating 3D printing in the setting of the development of intraoperative guides is reported in Table 3. such as augments and contouring plates.Compared to surgical guides, templates were not used during surgery but exclusively during the preoperative simulation.

Quality Assessment of the Retrieved Studies
For randomized controlled trials (RCTs), the risk of bias was assessed using the Cochrane Risk of Bias Tool 2 for Randomized Controlled Trials (RoB 2 tool) [27].Seven types of bias were analyzed and classified into "low risk", "high risk", or "unclear risk".For both the studies analyzed, the randomization process and the allocation concealment method were not sufficiently described, leading to some concerns in the overall judgment (Table 1).Then, the results of this evaluation were converted to Agency for Healthcare Research and Quality standards, which ultimately ranked the trials as "good quality", "fair quality", and "poor quality".None of the randomized controlled trials included in the present systematic review reached a standard of "good quality", and both the RCTs reached a standard of "fair quality".Table 1.Quality assessment for the included RCTs using the Cochrane RoB 2 tool.
templates of the pelvis in complex primary THA [18,25,26].In all three studies, a CT scan was conducted, and an entire 3D-printed template of the specific patient's pelvis was produced to perform a pre-surgery simulation of the THA procedure.The aim o producing those real-size anatomical templates was to better plan the cup positioning and to more precisely estimate cup dimensions and the eventual need for additional specific surgical devices such as augments and contouring plates.Compared to surgical guides templates were not used during surgery but exclusively during the preoperative simulation.

Quality Assessment of the Retrieved Studies
For randomized controlled trials (RCTs), the risk of bias was assessed using the Cochrane Risk of Bias Tool 2 for Randomized Controlled Trials (RoB 2 tool) [27].Seven types of bias were analyzed and classified into "low risk", "high risk", or "unclear risk" For both the studies analyzed, the randomization process and the allocation concealmen method were not sufficiently described, leading to some concerns in the overall judgmen (Table 1).Then, the results of this evaluation were converted to Agency for Healthcare Research and Quality standards, which ultimately ranked the trials as "good quality" "fair quality", and "poor quality".None of the randomized controlled trials included in the present systematic review reached a standard of "good quality", and both the RCTs reached a standard of "fair quality".For studies with a non-randomized design, the risk of bias was carried on through the ROBINS-I tool ("Risk Of Bias In Non-randomised Studies-of Interventions") [28] which evaluates the eventual benefit or harm of an intervention in studies that did not use the randomization process.(Table 2).Two studies reported a "moderate" overall risk o bias [25,26], and one study reported a "serious" risk of bias [24], mainly caused by participants' selection and outcomes' measurements.
For studies with a non-randomized design, the risk of bias was carried on through the ROBINS-I tool ("Risk Of Bias In Non-randomised Studies-of Interventions") [28], which evaluates the eventual benefit or harm of an intervention in studies that did not use the randomization process.(Table 2).Two studies reported a "moderate" overall risk of bias [25,26], and one study reported a "serious" risk of bias [24], mainly caused by participants' selection and outcomes' measurements.

3D-Printed Surgical Guides
A synopsis of the included studies evaluating 3D printing in the setting of the development of intraoperative guides is reported in Table 3.
J. Clin.Med.2024, 13, 0 such as augments and contouring plates.Compared to surgical guides, templates used during surgery but exclusively during the preoperative simulation.

Quality Assessment of the Retrieved Studies
For randomized controlled trials (RCTs), the risk of bias was assessed u Cochrane Risk of Bias Tool 2 for Randomized Controlled Trials (RoB 2 tool) [27 types of bias were analyzed and classified into "low risk", "high risk", or "uncle For both the studies analyzed, the randomization process and the allocation conc method were not sufficiently described, leading to some concerns in the overall ju (Table 1).Then, the results of this evaluation were converted to Agency for He Research and Quality standards, which ultimately ranked the trials as "good quali quality", and "poor quality".None of the randomized controlled trials include present systematic review reached a standard of "good quality", and both the RCTs a standard of "fair quality".Table 1.Quality assessment for the included RCTs using the Cochrane RoB 2 tool.
templates of the pelvis in complex primary THA [18,25,26].In all three stu was conducted, and an entire 3D-printed template of the specific patien produced to perform a pre-surgery simulation of the THA procedur producing those real-size anatomical templates was to better plan the cup p to more precisely estimate cup dimensions and the eventual need for add surgical devices such as augments and contouring plates.Compared to s templates were not used during surgery but exclusively during the simulation.

Quality Assessment of the Retrieved Studies
For randomized controlled trials (RCTs), the risk of bias was asse Cochrane Risk of Bias Tool 2 for Randomized Controlled Trials (RoB 2 to types of bias were analyzed and classified into "low risk", "high risk", or For both the studies analyzed, the randomization process and the allocatio method were not sufficiently described, leading to some concerns in the ov (Table 1).Then, the results of this evaluation were converted to Agency Research and Quality standards, which ultimately ranked the trials as " "fair quality", and "poor quality".None of the randomized controlled tri the present systematic review reached a standard of "good quality", and reached a standard of "fair quality".For studies with a non-randomized design, the risk of bias was carr the ROBINS-I tool ("Risk Of Bias In Non-randomised Studies-of Interv which evaluates the eventual benefit or harm of an intervention in studies t the randomization process.(Table 2).Two studies reported a "moderate" bias [25,26], and one study reported a "serious" risk of bias [24], mai participants' selection and outcomes' measurements.
For studies with a non-randomized design, the risk of bias was carried on thro ROBINS-I tool ("Risk Of Bias In Non-randomised Studies-of Interventions") [28 evaluates the eventual benefit or harm of an intervention in studies that did the randomization process.(Table 2).Two studies reported a "moderate" ove of bias [25,26], and one study reported a "serious" risk of bias [24], mainly ca participants' selection and outcomes' measurements.

3D-Printed Surgical Guides
A synopsis of the included studies evaluating 3D printing in the setting of th opment of intraoperative guides is reported in Table 3.
J. Clin.Med.2024, 13, 0 such as augments and contouring plates.Compared to surgical gu used during surgery but exclusively during the preoperative sim

Quality Assessment of the Retrieved Studies
For randomized controlled trials (RCTs), the risk of bias Cochrane Risk of Bias Tool 2 for Randomized Controlled Trials types of bias were analyzed and classified into "low risk", "high For both the studies analyzed, the randomization process and th method were not sufficiently described, leading to some concern (Table 1).Then, the results of this evaluation were converted t Research and Quality standards, which ultimately ranked the tria quality", and "poor quality".None of the randomized controll present systematic review reached a standard of "good quality", a a standard of "fair quality".Table 1.Quality assessment for the included RCTs using the Cochrane R templates of the pelvis in complex primary THA [18,25,26].was conducted, and an entire 3D-printed template of the produced to perform a pre-surgery simulation of the T producing those real-size anatomical templates was to better to more precisely estimate cup dimensions and the eventua surgical devices such as augments and contouring plates.C templates were not used during surgery but exclusive simulation.

Quality Assessment of the Retrieved Studies
For randomized controlled trials (RCTs), the risk of Cochrane Risk of Bias Tool 2 for Randomized Controlled T types of bias were analyzed and classified into "low risk", " For both the studies analyzed, the randomization process an method were not sufficiently described, leading to some con (Table 1).Then, the results of this evaluation were convert Research and Quality standards, which ultimately ranked "fair quality", and "poor quality".None of the randomized the present systematic review reached a standard of "good reached a standard of "fair quality".For studies with a non-randomized design, the risk of the ROBINS-I tool ("Risk Of Bias In Non-randomised Stu which evaluates the eventual benefit or harm of an intervent the randomization process.(Table 2).Two studies reported bias [25,26], and one study reported a "serious" risk of participants' selection and outcomes' measurements.
For studies with a non-randomized design, the risk of bias w ROBINS-I tool ("Risk Of Bias In Non-randomised Studies-of Int evaluates the eventual benefit or harm of an intervention in the randomization process.(Table 2).Two studies reported a of bias [25,26], and one study reported a "serious" risk of bias participants' selection and outcomes' measurements.

3D-Printed Surgical Guides
A synopsis of the included studies evaluating 3D printing i opment of intraoperative guides is reported in Table 3.

Quality Assessment of the Retr
For randomized controlled Cochrane Risk of Bias Tool 2 fo types of bias were analyzed and For both the studies analyzed, th method were not sufficiently des (Table 1).Then, the results of th Research and Quality standards, quality", and "poor quality".N present systematic review reache a standard of "fair quality".Table 1.Quality assessment for the templates of the pelvis in compl was conducted, and an entire produced to perform a pre-su producing those real-size anatom to more precisely estimate cup surgical devices such as augme templates were not used dur simulation.

Quality Assessment of the Ret
For randomized controlled Cochrane Risk of Bias Tool 2 fo types of bias were analyzed and For both the studies analyzed, t method were not sufficiently de (Table 1).Then, the results of t Research and Quality standard "fair quality", and "poor qualit the present systematic review r reached a standard of "fair qual For studies with a non-ran the ROBINS-I tool ("Risk Of B which evaluates the eventual be the randomization process.(Tab bias [25,26], and one study re participants' selection and outco For studies with a non-rand ROBINS-I tool ("Risk Of Bias In evaluates the eventual benefit the randomization process.(Ta of bias [25,26], and one study r participants' selection and outco templates of the p was conducted, a produced to per producing those r to more precisely surgical devices s templates were simulation.

Quality Assess
For random Cochrane Risk of types of bias wer For both the stud method were not (Table 1).Then, t Research and Qu "fair quality", an the present system reached a standar For studies w the ROBINS-I to which evaluates t the randomizatio bias [25,26], and participants' selec For studies ROBINS-I tool evaluates the e the randomizat of bias [25,26], participants' se such as augments and contouring plates.Compared to surgical guides, templates were not used during surgery but exclusively during the preoperative simulation.

Quality Assessment of the Retrieved Studies
For randomized controlled trials (RCTs), the risk of bias was assessed using the Cochrane Risk of Bias Tool 2 for Randomized Controlled Trials (RoB 2 tool) [27].Seven types of bias were analyzed and classified into "low risk", "high risk", or "unclear risk".For both the studies analyzed, the randomization process and the allocation concealment method were not sufficiently described, leading to some concerns in the overall judgment (Table 1).Then, the results of this evaluation were converted to Agency for Healthcare Research and Quality standards, which ultimately ranked the trials as "good quality", "fair quality", and "poor quality".None of the randomized controlled trials included in the present systematic review reached a standard of "good quality", and both the RCTs reached a standard of "fair quality".Table 1.Quality assessment for the included RCTs using the Cochrane RoB 2 tool.
The remaining three studies investigated the benefit of the use of 3D-printed templates of the pelvis in complex primary THA [18,25,26].In all three studies, a CT scan was conducted, and an entire 3D-printed template of the specific patient's pelvis was produced to perform a pre-surgery simulation of the THA procedure.The aim of producing those real-size anatomical templates was to better plan the cup positioning and to more precisely estimate cup dimensions and the eventual need for additional specific surgical devices such as augments and contouring plates.Compared to surgical guides, templates were not used during surgery but exclusively during the preoperative simulation.

Quality Assessment of the Retrieved Studies
For randomized controlled trials (RCTs), the risk of bias was assessed using the Cochrane Risk of Bias Tool 2 for Randomized Controlled Trials (RoB 2 tool) [27].Seven types of bias were analyzed and classified into "low risk", "high risk", or "unclear risk".For both the studies analyzed, the randomization process and the allocation concealment method were not sufficiently described, leading to some concerns in the overall judgment (Table 1).Then, the results of this evaluation were converted to Agency for Healthcare Research and Quality standards, which ultimately ranked the trials as "good quality", "fair quality", and "poor quality".None of the randomized controlled trials included in the present systematic review reached a standard of "good quality", and both the RCTs reached a standard of "fair quality".For studies with a non-randomized design, the risk of bias was carried on through the ROBINS-I tool ("Risk Of Bias In Non-randomised Studies-of Interventions") [28], which evaluates the eventual benefit or harm of an intervention in studies that did not use the randomization process.(Table 2).Two studies reported a "moderate" overall risk of bias [25,26], and one study reported a "serious" risk of bias [24], mainly caused by participants' selection and outcomes' measurements.
For studies with a non-randomized design, the risk of bias was carried on through the ROBINS-I tool ("Risk Of Bias In Non-randomised Studies-of Interventions") [28], which evaluates the eventual benefit or harm of an intervention in studies that did not use the randomization process.(Table 2).Two studies reported a "moderate" overall risk of bias [25,26], and one study reported a "serious" risk of bias [24], mainly caused by participants' selection and outcomes' measurements.

3D-Printed Surgical Guides
A synopsis of the included studies evaluating 3D printing in the setting of the development of intraoperative guides is reported in Table 3. such as augments and contouring plates.Compared to surgical guides, templates were not used during surgery but exclusively during the preoperative simulation.

Quality Assessment of the Retrieved Studies
For randomized controlled trials (RCTs), the risk of bias was assessed using the Cochrane Risk of Bias Tool 2 for Randomized Controlled Trials (RoB 2 tool) [27].Seven types of bias were analyzed and classified into "low risk", "high risk", or "unclear risk".For both the studies analyzed, the randomization process and the allocation concealment method were not sufficiently described, leading to some concerns in the overall judgment (Table 1).Then, the results of this evaluation were converted to Agency for Healthcare Research and Quality standards, which ultimately ranked the trials as "good quality", "fair quality", and "poor quality".None of the randomized controlled trials included in the present systematic review reached a standard of "good quality", and both the RCTs reached a standard of "fair quality".Table 1.Quality assessment for the included RCTs using the Cochrane RoB 2 tool.
The remaining three studies investigated the benefit of the use of 3D-printed templates of the pelvis in complex primary THA [18,25,26].In all three studies, a CT scan was conducted, and an entire 3D-printed template of the specific patient's pelvis was produced to perform a pre-surgery simulation of the THA procedure.The aim o producing those real-size anatomical templates was to better plan the cup positioning and to more precisely estimate cup dimensions and the eventual need for additional specific surgical devices such as augments and contouring plates.Compared to surgical guides templates were not used during surgery but exclusively during the preoperative simulation.

Quality Assessment of the Retrieved Studies
For randomized controlled trials (RCTs), the risk of bias was assessed using the Cochrane Risk of Bias Tool 2 for Randomized Controlled Trials (RoB 2 tool) [27].Seven types of bias were analyzed and classified into "low risk", "high risk", or "unclear risk" For both the studies analyzed, the randomization process and the allocation concealmen method were not sufficiently described, leading to some concerns in the overall judgmen (Table 1).Then, the results of this evaluation were converted to Agency for Healthcare Research and Quality standards, which ultimately ranked the trials as "good quality" "fair quality", and "poor quality".None of the randomized controlled trials included in the present systematic review reached a standard of "good quality", and both the RCTs reached a standard of "fair quality".For studies with a non-randomized design, the risk of bias was carried on through the ROBINS-I tool ("Risk Of Bias In Non-randomised Studies-of Interventions") [28] which evaluates the eventual benefit or harm of an intervention in studies that did not use the randomization process.(Table 2).Two studies reported a "moderate" overall risk o bias [25,26], and one study reported a "serious" risk of bias [24], mainly caused by participants' selection and outcomes' measurements.
For studies with a non-randomized design, the risk of bias was carried on through the ROBINS-I tool ("Risk Of Bias In Non-randomised Studies-of Interventions") [28], which evaluates the eventual benefit or harm of an intervention in studies that did not use the randomization process.(Table 2).Two studies reported a "moderate" overall risk of bias [25,26], and one study reported a "serious" risk of bias [24], mainly caused by participants' selection and outcomes' measurements.

3D-Printed Surgical Guides
A synopsis of the included studies evaluating 3D printing in the setting of the development of intraoperative guides is reported in Table 3.
J. Clin.Med.2024, 13, 0 such as augments and contouring plates.Compared to surgical guides, templates used during surgery but exclusively during the preoperative simulation.

Quality Assessment of the Retrieved Studies
For randomized controlled trials (RCTs), the risk of bias was assessed u Cochrane Risk of Bias Tool 2 for Randomized Controlled Trials (RoB 2 tool) [27 types of bias were analyzed and classified into "low risk", "high risk", or "uncle For both the studies analyzed, the randomization process and the allocation conc method were not sufficiently described, leading to some concerns in the overall ju (Table 1).Then, the results of this evaluation were converted to Agency for He Research and Quality standards, which ultimately ranked the trials as "good quali quality", and "poor quality".None of the randomized controlled trials include present systematic review reached a standard of "good quality", and both the RCTs a standard of "fair quality".Table 1.Quality assessment for the included RCTs using the Cochrane RoB 2 tool.
The remaining three studies investigated the benefit of the use templates of the pelvis in complex primary THA [18,25,26].In all three stu was conducted, and an entire 3D-printed template of the specific patien produced to perform a pre-surgery simulation of the THA procedur producing those real-size anatomical templates was to better plan the cup p to more precisely estimate cup dimensions and the eventual need for add surgical devices such as augments and contouring plates.Compared to s templates were not used during surgery but exclusively during the simulation.

Quality Assessment of the Retrieved Studies
For randomized controlled trials (RCTs), the risk of bias was asse Cochrane Risk of Bias Tool 2 for Randomized Controlled Trials (RoB 2 to types of bias were analyzed and classified into "low risk", "high risk", or For both the studies analyzed, the randomization process and the allocatio method were not sufficiently described, leading to some concerns in the ov (Table 1).Then, the results of this evaluation were converted to Agency Research and Quality standards, which ultimately ranked the trials as " "fair quality", and "poor quality".None of the randomized controlled tri the present systematic review reached a standard of "good quality", and reached a standard of "fair quality".For studies with a non-randomized design, the risk of bias was carr the ROBINS-I tool ("Risk Of Bias In Non-randomised Studies-of Interv which evaluates the eventual benefit or harm of an intervention in studies t the randomization process.(Table 2).Two studies reported a "moderate" bias [25,26], and one study reported a "serious" risk of bias [24], mai participants' selection and outcomes' measurements.
For studies with a non-randomized design, the risk of bias was carried on thro ROBINS-I tool ("Risk Of Bias In Non-randomised Studies-of Interventions") [28 evaluates the eventual benefit or harm of an intervention in studies that did the randomization process.(Table 2).Two studies reported a "moderate" ove of bias [25,26], and one study reported a "serious" risk of bias [24], mainly ca participants' selection and outcomes' measurements.
Table 2. ROBINS-I tool for the risk of bias assessment of the non-RCTs included studies.

Selection of Reported Results
Ove o

3D-Printed Surgical Guides
A synopsis of the included studies evaluating 3D printing in the setting of th opment of intraoperative guides is reported in Table 3.
J. Clin.Med.2024, 13, 0 such as augments and contouring plates.Compared to surgical gu used during surgery but exclusively during the preoperative sim

Quality Assessment of the Retrieved Studies
For randomized controlled trials (RCTs), the risk of bias Cochrane Risk of Bias Tool 2 for Randomized Controlled Trials types of bias were analyzed and classified into "low risk", "high For both the studies analyzed, the randomization process and th method were not sufficiently described, leading to some concern (Table 1).Then, the results of this evaluation were converted t Research and Quality standards, which ultimately ranked the tria quality", and "poor quality".None of the randomized controll present systematic review reached a standard of "good quality", a a standard of "fair quality".Table 1.Quality assessment for the included RCTs using the Cochrane R The remaining three studies investigated the benefi templates of the pelvis in complex primary THA [18,25,26].was conducted, and an entire 3D-printed template of the produced to perform a pre-surgery simulation of the T producing those real-size anatomical templates was to better to more precisely estimate cup dimensions and the eventua surgical devices such as augments and contouring plates.C templates were not used during surgery but exclusive simulation.

Quality Assessment of the Retrieved Studies
For randomized controlled trials (RCTs), the risk of Cochrane Risk of Bias Tool 2 for Randomized Controlled T types of bias were analyzed and classified into "low risk", " For both the studies analyzed, the randomization process an method were not sufficiently described, leading to some con (Table 1).Then, the results of this evaluation were convert Research and Quality standards, which ultimately ranked "fair quality", and "poor quality".None of the randomized the present systematic review reached a standard of "good reached a standard of "fair quality".For studies with a non-randomized design, the risk of the ROBINS-I tool ("Risk Of Bias In Non-randomised Stu which evaluates the eventual benefit or harm of an intervent the randomization process.(Table 2).Two studies reported bias [25,26], and one study reported a "serious" risk of participants' selection and outcomes' measurements.
For studies with a non-randomized design, the risk of bias w ROBINS-I tool ("Risk Of Bias In Non-randomised Studies-of Int evaluates the eventual benefit or harm of an intervention in the randomization process.(Table 2).Two studies reported a of bias [25,26], and one study reported a "serious" risk of bias participants' selection and outcomes' measurements.
Table 2. ROBINS-I tool for the risk of bias assessment of the non-RCTs i such as augments and contouring plates.Compa used during surgery but exclusively during the

Quality Assessment of the Retrieved Studies
For randomized controlled trials (RCTs), Cochrane Risk of Bias Tool 2 for Randomized C types of bias were analyzed and classified into For both the studies analyzed, the randomizatio method were not sufficiently described, leading (Table 1).Then, the results of this evaluation w Research and Quality standards, which ultimatel quality", and "poor quality".None of the rand present systematic review reached a standard of " a standard of "fair quality".

Table 1. Quality assessment for the included RCTs us
The remaining three studies investiga templates of the pelvis in complex primary TH was conducted, and an entire 3D-printed te produced to perform a pre-surgery simula producing those real-size anatomical template to more precisely estimate cup dimensions an surgical devices such as augments and conto templates were not used during surgery simulation.

Quality Assessment of the Retrieved Studies
For randomized controlled trials (RCTs Cochrane Risk of Bias Tool 2 for Randomize types of bias were analyzed and classified int For both the studies analyzed, the randomiza method were not sufficiently described, leadin (Table 1).Then, the results of this evaluation Research and Quality standards, which ultim "fair quality", and "poor quality".None of th the present systematic review reached a stan reached a standard of "fair quality".For studies with a non-randomized desi the ROBINS-I tool ("Risk Of Bias In Non-r which evaluates the eventual benefit or harm the randomization process.(Table 2).Two stu bias [25,26], and one study reported a "ser participants' selection and outcomes' measur For studies with a non-randomized design, ROBINS-I tool ("Risk Of Bias In Non-randomis evaluates the eventual benefit or harm of an the randomization process.(Table 2).Two stu of bias [25,26], and one study reported a "seri participants' selection and outcomes' measurem The remaini templates of the p was conducted, a produced to per producing those r to more precisely surgical devices s templates were simulation.

Quality Assess
For random Cochrane Risk of types of bias wer For both the stud method were not (Table 1).Then, t Research and Qu "fair quality", an the present system reached a standar For studies w the ROBINS-I to which evaluates t the randomizatio bias [25,26], and participants' selec For studies ROBINS-I tool evaluates the e the randomizat of bias [25,26], participants' se  For randomized controlled trials (RCTs), the risk of bias was as Cochrane Risk of Bias Tool 2 for Randomized Controlled Trials (RoB 2 types of bias were analyzed and classified into "low risk", "high risk", For both the studies analyzed, the randomization process and the alloca method were not sufficiently described, leading to some concerns in the (Table 1).Then, the results of this evaluation were converted to Agen Research and Quality standards, which ultimately ranked the trials as "g quality", and "poor quality".None of the randomized controlled tria present systematic review reached a standard of "good quality", and both a standard of "fair quality".Table 1.Quality assessment for the included RCTs using the Cochrane RoB 2 to templates of the pelvis in complex primary THA [18,25,26].In all t was conducted, and an entire 3D-printed template of the specifi produced to perform a pre-surgery simulation of the THA p producing those real-size anatomical templates was to better plan t to more precisely estimate cup dimensions and the eventual need surgical devices such as augments and contouring plates.Compa templates were not used during surgery but exclusively du simulation.

Quality Assessment of the Retrieved Studies
For randomized controlled trials (RCTs), the risk of bias w Cochrane Risk of Bias Tool 2 for Randomized Controlled Trials ( types of bias were analyzed and classified into "low risk", "high r For both the studies analyzed, the randomization process and the method were not sufficiently described, leading to some concerns (Table 1).Then, the results of this evaluation were converted to Research and Quality standards, which ultimately ranked the tr "fair quality", and "poor quality".None of the randomized contr the present systematic review reached a standard of "good quali reached a standard of "fair quality".For studies with a non-randomized design, the risk of bias w the ROBINS-I tool ("Risk Of Bias In Non-randomised Studies-o which evaluates the eventual benefit or harm of an intervention in the randomization process.(Table 2).Two studies reported a "mo bias [25,26], and one study reported a "serious" risk of bias [ participants' selection and outcomes' measurements.
For studies with a non-randomized design, the risk of bias was carri ROBINS-I tool ("Risk Of Bias In Non-randomised Studies-of Intervent evaluates the eventual benefit or harm of an intervention in studies the randomization process.(Table 2).Two studies reported a "mode of bias [25,26], and one study reported a "serious" risk of bias [24], m participants' selection and outcomes' measurements.

3D-Printed Surgical Guides
A synopsis of the included studies evaluating 3D printing in the se opment of intraoperative guides is reported in Table 3.
, Some concerns; J. Clin.Med.2024, 13, 0 such as augments and contouring plates.Compared to surgical guides, used during surgery but exclusively during the preoperative simulatio

Quality Assessment of the Retrieved Studies
For randomized controlled trials (RCTs), the risk of bias was a Cochrane Risk of Bias Tool 2 for Randomized Controlled Trials (RoB types of bias were analyzed and classified into "low risk", "high risk" For both the studies analyzed, the randomization process and the alloc method were not sufficiently described, leading to some concerns in th (Table 1).Then, the results of this evaluation were converted to Age Research and Quality standards, which ultimately ranked the trials as "g quality", and "poor quality".None of the randomized controlled tri present systematic review reached a standard of "good quality", and bot a standard of "fair quality".Table 1.Quality assessment for the included RCTs using the Cochrane RoB 2 t templates of the pelvis in complex primary THA [18,25,26].In all was conducted, and an entire 3D-printed template of the spec produced to perform a pre-surgery simulation of the THA producing those real-size anatomical templates was to better plan to more precisely estimate cup dimensions and the eventual nee surgical devices such as augments and contouring plates.Comp templates were not used during surgery but exclusively d simulation.

Quality Assessment of the Retrieved Studies
For randomized controlled trials (RCTs), the risk of bias Cochrane Risk of Bias Tool 2 for Randomized Controlled Trials types of bias were analyzed and classified into "low risk", "high For both the studies analyzed, the randomization process and the method were not sufficiently described, leading to some concerns (Table 1).Then, the results of this evaluation were converted to Research and Quality standards, which ultimately ranked the t "fair quality", and "poor quality".None of the randomized cont the present systematic review reached a standard of "good qual reached a standard of "fair quality".For studies with a non-randomized design, the risk of bias the ROBINS-I tool ("Risk Of Bias In Non-randomised Studieswhich evaluates the eventual benefit or harm of an intervention in the randomization process.(Table 2).Two studies reported a "m bias [25,26], and one study reported a "serious" risk of bias participants' selection and outcomes' measurements.
For studies with a non-randomized design, the risk of bias was car ROBINS-I tool ("Risk Of Bias In Non-randomised Studies-of Interven evaluates the eventual benefit or harm of an intervention in studie the randomization process.(Table 2).Two studies reported a "mod of bias [25,26], and one study reported a "serious" risk of bias [24], participants' selection and outcomes' measurements.Among the four studies investigating the use of surgical jigs, two presented a randomized design [21,23]: one was a prospective trial [22], and one was a case-control study [24].
Yan et al. [21] published an RCT comparing 12 THA performed with the 3D-printed navigation templates for the acetabulum versus 13 THA with the standard technique in patients affected by OA secondary to developmental dysplasia of the hip (DDH).A Computer Tomography (CT) scan was utilized to evaluate the positioning of the implants.They found a statistically significant reduction in operative time, intra-operative bleeding, and postoperative hemorrhage and a statistically significant increase in the Harris Hip Score (HHS) at 6 months in the 3D-printed group.They also found no statistically significant difference in abduction and anteversion angle and distance between the center of rotation (COR) and the ischial tuberosity from the affected side and the prosthesis in the 3D-printed group, while the anteversion angle and the distance were larger in the control group.
Mishra et al. [23] evaluated the difference in cup placement between two groups in their RCT (18 hips each); one group operated with the aid of a 3D-printed jig to help in the cup reaming and positioning, and the other operated with the standard technique.They evaluated the results with postoperative X-rays, and in the 3D-printed jig group, the anteversion angles were significantly closer to their proposed safe zone compared to the other one.They did not find any statistically significant difference in surgical time, blood loss, surgical time for cup placement, or cup abduction angle.
Tu et al. [22] evaluated the accuracy and the results of the use of 3D-printed jigs for acetabular cup placement and femoral shortening osteotomy for the treatment of Crowe type IV DDH.This was a prospective study on 12 patients (12 hips) with an average followup of 72.42 months (38-135 months).The authors found that the guiding template faithfully matched the bony landmark of the acetabulum and proximal femur.The HHS improved from 34.2 ± 3.7 preoperatively to 85.2 ± 4.2 postoperatively.Leg length discrepancy decreased from 51.5 ± 6.5 mm preoperatively to 10.2 ± 1.5 mm postoperatively.The visual analog scale for pain score decreased from 6.2 ± 0.8 preoperatively to 1.3 ± 0.3 postoperatively.They reported one dislocation 2 weeks after surgery and one sciatic nerve palsy, both resolved without surgery.
Hananouchi et al. [24] investigated the accuracy of the cup placement with and without the use of a 3D-printed guide.The authors divided the patients into two groups: one operated with a standard technique (38 hips) and one with a surgical guide (31 hips).Afterward, they evaluated the number of outliers, defined as a cup placed beyond 10 • from preoperatively planned alignment.All of the patients had a preoperative CT scan for surgical planning and a postoperative CT scan to evaluate the cup orientation.The use of the surgical guide reduced the number of outliers (0%; zero out of 31 cases) compared with the group operated with the standard technique (23.7%; 9 out of 38 cases).This result was achieved with no difference in operative time (p = 0.06) or blood loss (p = 0.73) between the two groups.
Furthermore, among the studies using surgical jigs, both resin and polylactic acid were used to realize the model, with variable costs, reported in detail in Table 4.  PLA: polylactic acid.

3D-Printed Models for Surgical Simulations
A synopsis of the included studies assessing the use of 3D printing to produce surgical phantoms is reported in Table 5.
Of the three studies investigating the benefit of the use of a 3D-printed model of the pelvis to simulate the surgery, one was a retrospective study [26], one was a prospective study [25], and the last one was a pilot study with surgical simulation.
Zhang et al. [26] investigated the use of a 3D-printed model in 21 difficult primary THA (17 patients) and evaluated their ability to assess the bone defect size and the clinical and radiological outcomes.The bone defect evaluation shows no statistically significant difference between the sizes of bone defects in the 3D-printed model and during surgery (4.58 ± 2.47 cm 2 in the simulation and 4.55 ± 2.57 cm 2 in the surgery; t = 0.03, p = 0.97).There was a high rate of agreement between the size of the cup preoperatively planned and the one implanted (ICC = 0.93).The mean vertical and horizontal distances of the hip rotation center on the pelvic radiographs were restored to 15.12 ± 1.25 mm and 32.49 ± 2.83 mm, respectively.Xu et al. [25] published a prospective study on 10 patients (14 hips) who underwent THA with the aid of a 3D-printed model for OA due to DDH.The mean follow-up was 23.1 ± 5.9 (14-30) months.The mean HHS at the last examination was 83.3 ± 5.7 (pre-op: 37.7 ± 6.8).No perceptible limb length discrepancy (LLD) was reported after a six-month follow-up.The authors evaluated the position and the bone coverage of the cups on the X-rays showing a mean abduction angle of 45.1 • (40.2 • -53.5 • ), a mean horizontal location of the hip center from the teardrop of 21.7 mm (15.0-31.2mm), a mean height of the hip center from the inter-teardrop baseline of 18.8 mm (11.5-25.8mm), and at least 80% of the cup contained by bone in each case.At the last follow-up, no implants showed signs of mobilization.There was a higher rate of agreement with the size of the cup preoperatively planned with the 3D simulation than the one planned with the 2D template.The difference in excellence rate (a difference of ≤two sizes) in the prediction of the prosthesis between 3D preoperative planning and 2D template measuring method was of statistical significance (χ 2 = 8.023, p= 0.05).Jiang et al. [18] published a pilot study investigating the usefulness of 3D-printed models and the properties of different materials in simulated preoperative surgery and compared them with preoperative planning based on 2D CT scans and X-ray imaging.Seven patients (seven hips) with complex anatomy were enrolled, and patient-specific models were 3D-printed in plaster, resin, and nylon.Resin models provided the most realistic trials of implant impaction; conversely, nylon models underwent rapid bony distortion under reaming.In conclusion, the authors referred to a superior clinical, logistical, and educational outcome when using the 3D model planning compared to the 2D CT scan and X-ray imaging model planning.
Costs and materials used to produce a surgical model for preoperative simulation are reported in Table 4.

Discussion
The main finding of the present systematic review is that 3D printing offers no disadvantages in the setting of complex primary total hip arthroplasty cases.The investigation of clinical and radiological superiority of this new technique over traditional surgery is undermined by the wide heterogeneity of the studies, including notable differences in the baseline condition (DDH, Perthes disease, OA, and pelvic fractures), material used, and outcome measures assessed.
The introduction of 3D printing in the context of the surgical field arises as an interconnected mixture of modern digital capture technology, computer-aided design, numerical control technology, laser or electron beam technology, and the most innovative materials all being integrated [29].Significant recent breakthroughs have been made in 3D printing technology and associated software [30].In the medical industry, a combination of 3D printing and CT scanning technology allows for the capture of a digital grid model in biological forms to 3D print a corresponding physical model with the same shape and internal structure as the biological anatomical part [31].A new age has begun with the development of 3D printing, which makes it possible to convert patient-specific imaging data into realistic three-dimensional models that the surgeon can evaluate with hands-on experience prior to surgery.As a result, the use of 3D printing technology in medical reconstruction has given rise to a new discipline known as digital medicine [32].Indeed, orthopedic surgeons can now reach previously unachievable insights into each patient's distinct anatomy, enabling a thorough comprehension that goes beyond the limitations of conventional planning techniques.Surgeons may now examine, explore, and understand the patient's hip joint in three dimensions, which paves the way for a paradigm change.Since the development of this new technology, limitless potential has been perceived in orthopedics, especially in the field of joint replacements.The systematic review conducted by Zhang et al. [20] analyzed the outcomes obtained by ten studies that used 3D printingassisted surgery for revision total hip and knee arthroplasty.Only two out of ten studies examined reported the presence of a control group; nonetheless, the authors conclude that this technology can offer satisfactory radiological and clinical outcomes.Conversely, we retrieved only articles focused on the use of 3D printing to assist primary THA, and only three [21,23,24] of them had a control group.Moreover, despite all the authors adopting this new technique for complex cases, we realized that there is no univocal definition of a complex primary THA since it is usually an operator-related definition rather than radiologically dependent.However, many of the authors tend to use this adjective to outline the most advanced cases of developmental dysplasia of the hip (DDH), rated according to the Crowe classification [33].Five [18,21,22,25,26] out of the seven studies included considered the advanced DDH as a criterion able to increase the surgical complexity, in particular, related to the cup positioning.Moreover, we made a distinction between 3D printing to produce surgical guides and 3D printing to produce surgical models.Not unexpectedly, the studies with a randomized design belong to the first group; however, the patients included may appear quite diverse.Yan et al. [21] included patients affected by DDH Crow II-IV; conversely, Mirsha et al. [23] included patients with no further specified complex anatomy, leading to a major concern regarding comparisons between the two studies.In fact, the former [21] reports superior outcomes when 3D-printed surgical guides are used, while the latter [23] does not assess such differences, reporting comparable inter-group results.Furthermore, they even reported different outcomes, including cup anteversion, a concept that has to be integrated with the combined anteversion and the pelvic tilt [34,35], making the radiological comparison even more challenging.
Furthermore, the reduction in surgical times is one of the most common outcomes assessed in the included studies.In fact, one of the most promising applications of 3Dprinted aided surgery is the shortening of surgery.This aspect is ultimately related to the consequent reduction in the occurrence of postoperative infection.With an incidence rate ranging between 0.4% and 1.4% [36][37][38], the corollary of a periprosthetic hip infection can deeply impact both the patient's life and the healthcare system.Indeed, the 5-year survival after a diagnosis of periprosthetic hip infection is even lower than common malignancies such as melanoma, breast cancer, and other common tumors [39], with outrageous annual direct and indirect costs, estimated to be up to USD 753.4 million annually by 2030 [40].Hence, we believe that each effort is fundamental to reducing the occurrence rate of this disastrous complication.Among the studies included in the present systematic review, only the RCT by Yan et al. [21] reported a decreased surgical duration compared to conventional surgery.None of the other studies adopting the 3D printing surgical guides reported significant differences.Furthermore, none of the studies evaluating the use of 3D-printed templates mentioned eventual variations in surgical times compared to conventional surgery.Despite that, we can hypothesize that exact knowledge of a patient's threedimensional anatomy, assessed by the surgeon's hand and instruments, would significantly shorten the surgery time compared to a simple assessment of bidimensional radiological imaging.However, the lack of a control group makes this assumption a mere opinion of the authors based on their own experience in this field.
Nonetheless, even if the customization and the advent of tailored medicine, built on the patient, for the patient, make the use of 3D printing a cutting-edge piece of technology for each orthopedic surgeon, at the end of the day, a cost-benefit analysis appears necessary.The cost of each surgical case ranged from USD 4 to USD 1500; however, most of the included studies did not account for the additional indirect expenses due to the preoperative CT scan and outsourcing of the procedure.Moreover, different prices are mostly a result of the type of material used, and we do not exactly have sufficient data to assess if the material characteristics are comparable [18].Hence, the ability to strike a balance between therapeutic benefits and budgetary considerations is critical for the long-term incorporation of this technology into everyday practice.
However, we are well aware that these conclusions should be considered only as a photograph of the available evidence and taken as a bouquet of indications for future research rather than a definitive judgment.As shown in the risk of bias assessment of the retrieved studies (Tables 1 and 2), the quality of the current data is still insufficient to provide categorical recommendations for the application of 3D printing in the fields analyzed.
However, we believe that the major strength of our study is the novelty of the topic examined and the collection of all the available evidence in such a limited research corner.However, the present systematic review is not free from limitations.Firstly, the broadened definition of 'complex' primary THA is not scientifically accepted and includes a wide variety of conditions, anatomies, and patients, hence diluting any scientific consideration.Specifically, a wide variety of conditions were found to be considered 'complex' cases in the included studies, spanning from Perthes disease to DDH, pelvic fractures, and advanced primary hip OA.The different types of 3D printers used and the different materials contribute to the addition of further variability to our findings.Furthermore, a major burden of the current evidence is represented by the often inadequate methodological quality of the included studies, which is particularly undermined by the lack of high-quality RCTs, inadequate patient selection, and diverse outcome measures reported.Moreover, the exiguous number of both patients and studies included leads us to believe we are still in the learning curve phase of this new era, maybe in a premature time to draw hasty conclusions.

Conclusions
The use of 3D printing could be a promising aid to solve complex primary THA surgeries, but the current evidence is undermined by the small number of cases, different materials and techniques, and diverse outcomes assessed.Hence, the lack of high-quality studies does not justify the general enthusiasm in the field, preventing us from currently recommending its application in everyday practice.
Author Contributions: G.A. and M.L., conceptualization; G.A. and P.C., methodology and data collection; G.A. and E.G., writing-original draft preparation; P.C., V.D.M., E.K. and G.G., writingreview and editing; M.L., supervision; M.L., project administration.All authors have read and agreed to the published version of the manuscript.

Figure 1 .
Figure 1.PRISMA (Preferred Reporting Items for Systematic Review and Meta-Analysis) flowchart of the systematic literature review.

Figure 1 .
Figure 1.PRISMA (Preferred Reporting Items for Systematic Review and Meta-Analysis) flowchart of the systematic literature review.
Domains: D1: Bias arising from the randomization process.D2: Bias due to deviations from intended intervention.D3: Bias due to missing outcome data.D4: Bias in measurement of the outcome.D5: Bias in selection of the reported result.Judgement: J. Clin.Med.2024, 13, 0 such as augments and contouring plates.Compared to surgical guides, t used during surgery but exclusively during the preoperative simulation 3.1.Quality Assessment of the Retrieved Studies

Table 1 .
Quality assessment for the included RCTs using the Cochrane RoB 2 tool.

Table 1 .
Quality assessment for the included RCTs using the Cochrane RoB 2 tool.

Table 1 .
Quality assessment for the included RCTs using the Cochrane RoB 2 tool.

Table 2 .
ROBINS-I tool for the risk of bias assessment of the non-RCTs included studies.

Table 1 .
Quality assessment for the included RCTs using the Cochrane RoB 2 tool.

Table 1 .
Quality assessment for the included RCTs using the Cochrane RoB 2 tool.

Table 2 .
ROBINS-I tool for the risk of bias assessment of the non-RCTs included studies.

Table 1 .
Quality assessment for the included RCTs using the Cochr

Table 2 .
ROBINS-I tool for the risk of bias assessment of the non-

Table 1 .
Quality assessment for the

Table 2 .
ROBINS-I tool for the risk o

Table 1 .
Quality a

Table 1 .
Quality ass

Table 1 .
Quality assessment for the included RCTs using the Cochrane RoB 2 tool.

Table 2 .
ROBINS-I tool for the risk of bias assessment of the non-RCTs included studies.

Table 1 .
Quality assessment for the included RCTs using the Cochrane RoB 2 tool.

Table 2 .
ROBINS-I tool for the risk of bias assessment of the non-RCTs included studies.

Table 1 .
Quality assessment for the included RCTs using the Cochrane RoB 2 tool.

Table 1 .
Quality assessment for the included RCTs using the Cochr

Table 1 .
Quality assessment for the included RCTs

Table 2 .
ROBINS-I tool for the risk of bias

Table 1 .
Quality a

Table 1 .
Quality ass

Table 1 .
Quality assessment for the included RCTs using the Cochrane Ro

Table 2 .
ROBINS-I tool for the risk of bias assessment of the non-RCTs included

Table 1 .
Quality assessment for the included RCTs using the Cochrane R

Table 2 .
ROBINS-I tool for the risk of bias assessment of the non-RCTs include

Table 3 .
Synopsis of the studies focused on the use of 3D-printed jigs.

Table 4 .
Material and costs of the 3D equipment used.

Table 5 .
List of the studies using 3D models for surgical simulation.