Introduction

Robotics was first introduced into orthopedics surgery in the 1980s to improve the accuracy in implant positioning, prosthesis alignment and to reduce the rate of complications compared to conventional manual techniques [28]. Robotic total knee arthroplasty enhances the surgeon’s preoperative planning capabilities and real-time intra-operative dynamic referencing to allow for continuous assessments of range of motion and ligamentous tensioning. The real-time intra-operative kinematic assessment allows the comparison between the osteoarthritic knee and the new prosthetic knee [22]. However, with a lack of long-term evidence comparing clinical and functional results with conventional TKA and associated with increased costs and longer operative time, the trust in robotic TKA is restricted [14]. We are now in a pivotal time when data are emerging on robotic technologies, which makes it prudent to objectively examine whether their potential benefits are being realized.

In orthopedic surgery, every procedure is associated with some complications. Hence, it is fundamental to systematically examine the complications to improve the understanding and decrease these complications. It is also necessary to systematically assess the complications of this new technology before it can be widely used. In a recent systematic review [35], pin-hole fractures were reported in robotic TKA. But, to authors’ knowledge, no systematic review is available that comprehensively described all reported complications and downsides of robotic TKA. Therefore, we performed a systematic review of studies that reported complications and downsides of robotic TKA. Based on the results of the study, surgeons can perform appropriate risk stratification, which can help to counsel patients and their families, when selecting patients for robotic TKA. The hypothesis was that robotic TKA is associated with certain complications and downsides.

Materials and methods

This systematic review followed Preferred Reporting Items for Systematic Reviews and Meta-analysis (PRISMA) Guidelines for literature search and it was registered on the PROSPERO International prospective register of systematic reviews (ID CRD42022303970).

Search strategy

A literature review was performed using a strategy search designed to collect articles regarding complications and flaws of robotic TKA. Two independent authors (A.M., C.N.) conducted a comprehensive search across multiple databases (PubMed/MEDLINE, Cochrane Central Register of Controlled Trials, Scopus, and Google Scholar) and reviewed each article’s title and abstract for studies available until December 2021. Identified articles and their corresponding references were also reviewed according to selection criteria for additional eligible articles. The keywords used for initial screening were ((TKA) OR (TKR) OR (Total Knee Replacement) OR (Total Knee Arthroplasty)) AND ((Robot) OR (Robotic) OR (Robotic Surgical Procedure) OR (Robotic Arm Assisted)) AND ((Complication) OR (Disadvantage)). The full texts of the articles were obtained and evaluated when eligibility could not be assessed from the title and abstract. The eligibility of studies was independently assessed by these two authors and disagreements were resolved by consensus discussion between the authors, and a third author (C.F.) was consulted if the disagreement could not be resolved.

Inclusion and exclusion criteria

All articles of any study design directly reporting on complications and downsides of the robotic system in TKA were considered for inclusion. Intraoperative complications, such as pin-hole fracture, iatrogenic soft tissue and bony injury, excessive blood loss, longer operative duration, aborting a robotic TKA due to different reasons and postoperative issues, such as pin-related infection, longer hospital stays and post-TKA stiffness, were noted. Any other complications and downsides of this technology were also reported. Non-English studies, non-peer-reviewed studies, review articles, case reports, surgical techniques, conference abstracts, non-clinical studies as well as studies solely focused on robotic unicompartmental knee arthroplasty, computer-assisted total knee arthroplasty, or navigated total knee arthroplasty were excluded.

The Cochrane risk of bias (RoB1) tool for randomized controlled trials [12] and methodological index for non-randomized studies (MINORS) tool [33] for observational studies was used for the quality assessment of the included studies. Two authors (A.M, C.N.) independently performed the quality assessment for each article. A third author (C.F.) was consulted in case of disagreement.

Results

There were 530 potentially relevant studies identified in the initial comprehensive search across multi-databases and reference lists. Following the elimination of duplicate titles, abstracts were screened and pre-defined inclusion and exclusion criteria were applied. A large proportion of robotic-assisted surgeries was performed on unicompartmental knee arthroplasty (UKA) instead of TKA and hence, these studies were also excluded. A further 33 studies were excluded from analysis for various reasons after review of 54 full-text articles and one of the main reasons for exclusion was that data about complications were not available. Through discrete screenings, a total of 21 studies were included (Table 1), consisting of 4 randomized controlled trials, 7 prospective studies and 10 retrospective studies. A selection process flow diagram to identify included studies is presented in Fig. 1.

Table 1 Baseline characteristics included studies, (A) Semi-active system, (B) Active system, (C) Robotic system not mentioned
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Fig. 1
figure 1

A selection process flow diagram to identify included studies

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Methodological quality assessment

The Cochrane risk of bias (RoB1) tool was used for the quality assessment of 4 RCT studies. The MINORS criteria were used for the quality assessment of 17 observational studies and the average score was 15.9, ranging from 8 to 20. The quality assessment data are shown in Tables 2 and 3.

Table 2 The Cochrane risk of bias (RoB) quality assessment data for RCT studies
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Table 3 The MINORS criteria for the quality assessment of observational studies
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Pin-hole fracture [11, 29, 38, 39], pin-related infection [11, 15, 32, 36], iatrogenic injuries [11, 29, 36], more blood loss [11, 17] in the robotic TKA and stiffness after robotic TKA [20, 34] were the reported complications. Whereas, longer operative duration [7, 9, 11, 13, 17, 24, 26, 32, 34, 36, 38], longer hospital stays [27], higher intraoperative cost [2, 9], learning curve [15, 20, 22, 31, 32, 38], aborting a robotic TKA due to different reasons [8, 19, 32] were reported downsides. Iatrogenic injuries were more common in the active robotic system and abortion of the robotic TKA was reported only with active robotic TKA. The results of included studies are illustrated in Table 4.

Table 4 Comparison of complications and downsides between MTKA and RATKA
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Discussion

The most important finding of this systematic review was that robotic TKA is associated with longer operative time. Iatrogenic injuries were more common in the active robotic system and abortion of the robotic TKA was reported only with active robotic TKA.

Both, robotic and conventional systems have their advantages and disadvantages. Advantages of robotic TKA include accurate placement of prosthesis which results in fewer outliers in the component positions, superior implant alignment accuracy, precise bony cuts, and soft tissue balancing which are all considered a prerequisite for good functional outcome and endurance in TKA. A recent meta-analysis found improved short-term patient-reported outcomes (KSS and WOMAC) in the robotic group compared to the conventional TKA group [41]. However, these advantages of better clinical scores, patient satisfaction, and implant survivorship remain to be confirmed in long-term follow-up [18].

Three different robotic systems are available, based on the amount of autonomy delivered to both the surgeon and the robot, which include passive, active and semi-active. In a passive robotic system, the surgeon has continuous and direct control, while, an active robotic system is completely independent of the surgeon for performing a designated task. Therefore, active robotic systems are associated with increased chances of iatrogenic soft tissue injury. To ensure accuracy and safety against iatrogenic soft tissue or neurovascular injury, semi-active systems developed which provide tactile feedback to the surgeon, thus, helping define specific boundaries (i.e., for surgical resection or safety). The major goals of a semi-active system are to prevent gross intraoperative errors and reduce deviations from the surgical plan to ensure a safe procedure with well-aligned components. Although constant efforts have been made to improve the robotic system and decrease the associated complication, certain complications and downsides have been reported in the literature.

Femoral or tibial shaft fracture due to mechanical weakness caused by the pinholes is one of the most dreaded complications of the robotic TKA. In their study of 385 TKAs Beldame et al. [4] found the incidence of pin-site femoral fracture fractures to be 1.4%. They found a unique pattern of pin-site fracture where fractures occur an average of 12.6 weeks after arthroplasty, and before fracture episodes, patients experienced unusual pain for several days in the thigh. These fractures were associated with minor or indirect trauma and all of them were treated by intramedullary fixation. Yun et al. [39] and Baek et al. [3] recommended periarticular pin placement because the bone at this site is more robust to torsional and bending stresses than the diaphysis. Vermue et al. [38] advised for the smaller pins to prevent this complication. Preoperatively, all the patients should be informed about the potential risk of pin-hole fractures because it is not rare. Pin-site infection is another specific complication of tracker pin that may require antibiotics and dressing for an additional duration. However, the incidence of pin-site infection was reported to be low in general (0.47%) [11].

Iatrogenic soft tissue and bony injuries include patellar tendon rupture, dislocation of the patella, patellar fracture, and peroneal nerve injury [29]. Patellar tendon rupture was also seen in the study by Held et al. [11] and the patient underwent surgical repair. Although Kayani et al. [16] reported that Robotic TKA was associated with reduced bone and soft tissue injury compared to conventional TKA, other studies documented the opposite [11, 29, 36]. Iatrogenic injures were more common in active robotic system. Therefore, surgeons should be aware and try to avoid any iatrogenic injury while taking bone cuts.

In a recent study, Held et al. [11] found greater estimated blood loss in the robotic group which may be attributed to the prolonged operative time. In another long-term study by Kim et al. [17], the robotic group was associated with more blood loss and postoperative drainage volume. Bohl et al. [6] reported that longer surgical duration in hip and knee arthroplasty may require transfusion. However, it is important to recognize that robotic TKA does not require opening of the femoral canal which should theoretically result in less blood loss. Therefore, studies are needed with a large sample size to examine the difference in blood loss between these two groups.

Surgical robots are suggested to decrease post-TKA stiffness incidence by the accurate placement of a prosthesis and precise alignment but, this systematic review found studies that reported stiffness following robotic TKA. However, stiffness after TKA is multifactorial, in their recent systematic review, Zaffagini et al. [40] found modifiable and non-modifiable causes for post-TKA stiffness. Robots may help to correct the modifiable causes, such as prosthesis malalignment and overstuffing of joint but, other factors may not be corrected using robotic surgery.

This systematic review also identified some downsides of robotic systems compared to conventional instrumentation. The most consistent finding among different studies was longer intraoperative time with robotic systems. This longer duration is due to insertion and removal of pins in the femur and tibia, registration of the knee joint with the robotic system, and intraoperative planning. Longer surgical time is associated with a higher risk of infection which may result in devastating outcomes of TKA [25]. Pugely et al. [30] reported that after 120 min of surgical time the risk of infection increases to 1.8 times in joint arthroplasty. Two recent systematic reviews reported that the incidence of deep prosthetic joint infection was higher in robotic group at 1.6–1.7% compared to 0.44–1.0% in conventional TKA [21, 28]. Moreover, prolonged surgical duration is in part responsible for the higher intraoperative costs of robotic TKA. Other factors responsible for higher intraoperative costs were higher anesthesia costs, operation theater supplies, robotic maintenance costs, robotic-specific disposables costs, software requirements, and additional diagnostic imaging. On the other hand, some authors believe that robotic systems may improve TKA survivorship which would result in a decreased cost for future revision. However, to date, there is a lack of conclusive data on the relationship between the use of robotic systems and the longevity of TKA implants [1, 2, 10, 37]. Due to the additional time and expense associated with robotic systems in their long-term study, Kim 2019 et al. [17] did not recommend widespread use of robotic TKA.

There is conflicting evidence with respect to the length of hospital stay after robotic TKA. Most of the included studies reported shorter hospital stays in the robotic group, except for one study [27]. This was a nationwide database study from 2010 to 2017 which reported on significantly longer hospital stays following robotic TKA. Therefore, further research is needed for clarification of this matter.

Aborting a robotic TKA was another downside identified in this systematic review. Although all these studies used active robotic system. Regardless of the robotic system, reported abortion rates for robotic arthroplasty are between 1 and 12% [5]. Therefore, the surgeon should be aware of potential problems with the robotic system used, to avoid them upfront or to cope with them.

Another challenge with new technology is the learning curve. TKA robotics is associated with a learning curve that affects the comfort level of the surgical team. It has been shown that during this initial learning phase, the robotic system was associated with heightened levels of anxiety among the surgical team. This is an important consideration because stress and mental strain are correlated with diminished surgical performance, poor decision-making, and reduced technical skills [23]. The learning curve probably depends on the surgeon's previous experience and the general level of competence in robotics in surgery [20]. Therefore, surgeons starting with robotics TKA should foresee enough time to cope with this learning curve during initial cases.

This study has some key limitations. First, the heterogeneous approaches adopted in evaluating complications and downside of the robotic system did not allow a meta-analysis of the retrieved data. Second, the selection criteria, such as the exclusion of robotic unicompartmental knee arthroplasty, computer-assisted total knee arthroplasty or navigated total knee arthroplasty may have excluded relevant studies. Third, there are few studies on robotic TKAs and most of them are with small sample sizes with short-term follow-up. Future studies with large sample sizes and long-term follow-up will be needed to provide more conclusive findings in assessing the complications and downside of this system. Analysis of the national registry data will be a key finding to look out for the relevant complication associated with robotic TKA. Fourth, these studies used different robotic systems in different populations so there may be bias in the reporting of the complication.

The ultimate goal of the TKA is to create a stable, painless, long-lasting joint, which may be achieved by both conventional and robotic-assisted methods. The surgeon should be aware that despite the potential advantages of the robotic system, this new technology, may be associated with certain complications and downsides. This emerging technology is a tool, available to surgeons and they should decide which techniques will provide them and their patients with the optimum outcomes.

Conclusion

Robotic TKA is associated with certain advantages and disadvantages. Therefore, surgeons need to be familiar with the system to use it effectively. Widespread adoption of the robotic system should always be evidence-based.