Robotics in total knee replacement: Current use and future implications

Abstract

Robotic total knee replacement (TKR) surgery has evolved over the years with the aim of improving the overall 80% satisfaction rate associated with TKR surgery. Proponents claim higher precision in executing the pre-operative plan which results in improved alignment and possibly better clinical outcomes. Opponents suggest longer operative times with potentially higher complications and no superiority in clinical outcomes alongside increased costs. This editorial will summarize where we currently stand and the future implications of using robotics in knee replacement surgery.

Core Tip: The use of robot-assisted total knee replacement surgery has rapidly gained popularity and shows improved radiological outcomes with no difference in complication rates. It is associated with less soft tissue injuries and blood loss intraoperatively. However, this has not translated into better long-term clinical outcomes within the limited published literature. On the other hand, there are installation and maintenance costs and longer operative times during the learning curve which are partly compensated by reduced hospital stay and 90 d readmission rates.

INTRODUCTION

The prevalence of knee osteoarthritis (OA) has surged dramatically in the last few decades due to the negative impact of modern lifestyle. It is estimated that among adults aged 60 years or older, the prevalence of knee OA is approximately 10% in men and 13% in women[1]. On the other hand, recent advancements in medicine and technology have raised patients’ expectations for physical activity and mobility.

Total knee replacement (TKR) is a safe and cost-effective operation that is in high demand worldwide, with a significant impact on pain reduction and the restoration of joint function. Satisfactory outcomes have been reported in more than 80% of patients[2]. However, technical difficulties including inaccurate prosthesis placement and inadequate recovery of the mechanical axis, remain a concern and may be related to the overall 20% dissatisfaction rates after TKR surgery. These difficulties are often attributed to subjective measurements for the required cuts performed by the surgeon leading to deviations of up to 30% from the desired measurements in angles, rotation, offset of the implant in the sagittal, coronal, and axial planes. The drawbacks of these surgeries include a significant reliance on the surgeon’s skills and a lack of consistent reproducible results. These challenges can contribute to patient dissatisfaction, increased wear on polyethylene, and premature loosening of the implant, requiring early revision surgery[3,4]. Hence, optimal prosthesis placement along with proper lower limb axis alignment according to the surgeon’s preferred philosophy of alignment method are of utmost importance and may be associated with improved clinical outcomes and patient satisfaction rates, prolonging prosthesis survival, and enhancing long-term TKR outcomes[5].

Thus, seeking to address the existing flaws and enhancing what has already been built, the introduction of robotics in TKR surgery was pursued by utilizing the most recent advances in technology.

The use of robots in surgery was first documented in 1988 by neurosurgery where it was utilized to perform precise neurosurgical biopsies[6]. Subsequently, many specialties followed and in the late 1980s, a revolutionary robotic-assisted TKR (rTKR) was first performed. The aim was to increase the accuracy of the cuts and minimize the possibility of human error[7,8]. Theoretically, rTKR reduces soft tissue damage and the amount of bone resection[9]. One robotic device that showed great promise in the last two decades was the Acrobot (Imperial College, London, United Kingdom). It underwent extensive research following the initial series of clinical trials in 2002. Following that a double-blind, randomized controlled trial (RCT) comparing the Acrobot and traditional TKR in 2004 revealed that the robotic system made it feasible to position the prosthetic implant consistently and accurately, which the traditional method was unable to achieve[10].

With tremendous literature being published lately, the comparison between conventional TKR (cTKR) and rTKR has been under intense scrutiny to decide which one is better. This editorial will summarize where we currently stand and the future implications of using robotics in knee replacement surgery. We will particularly focus on the latest evidence comparing cTKR and rTKR, including intraoperative parameters, patient-reported outcomes, radiological assessment, and the associated financial burden.

INTRA-OPERATIVE PARAMETERS: OPERATION TIME, LEARNING CURVE, SOFT TISSUE RELEASE, PERIARTICULAR INJURIES, AND BLOOD TRANSFUSION

Assessing operative time and intraoperative blood loss is crucial in every surgical procedure due to their direct influence on patient well-being and indirect effects on overall surgical outcomes and financial considerations.

Operative time and learning curve

Generally, it was noted that rTKR exhibited a significantly prolonged operation time, with the rTKR group encountering an additional 45 minutes compared to the conventional group[11]. This observation is subject to various confounding factors, among which the surgeon's experience level plays a significant role. As reported by Kayani et al[12], surgeons initially using rTKR experienced longer operative times, leading to increased anxiety within the surgical team during the first seven cases accounting for the learning curve of rTKR surgery. However, with increasing familiarity of robotic technology, operative times progressively decreased over time[12].

In a meta-analysis conducted by Zhang et al[8] in 2020, they found that operating times decreased notably after the initial 7 to 11 cases, indicating an adaptation phase in surgical techniques. Interestingly, no learning curve was observed for the accuracy of implant positioning. However, achieving higher proficiency required a broader range of cases, typically between 20 to 80. Moreover, reaching mastery of rTKR techniques was generally attained after approximately 80 cases, resulting in consistently shorter operating times thereafter[8].

Soft tissue release and periarticular injuries

Preservation of the surrounding soft-tissue envelope is a cornerstone in knee replacement surgery as it does not only provide crucial anatomical support but also plays a significant role in postoperative rehabilitation and overall knee function. As a result, injury to the periarticular soft-tissue structures imposes enduring consequences on joint stability and the durability of the implanted prosthesis[13-16]. Thus, the delicate balance between soft-tissue preservation and technical accuracy highlights an important parameter for the comparison between different surgical approaches. To correct complex deformities and achieve balance in TKRs, soft tissue releases are indispensable. However, their execution is arbitrary and subjective, often regarded as an art[17]. Advanced technologies allow for the creation of digital models that represent soft tissue laxity and the required soft tissue releases for achieving balance. Surgeons can utilize these digital tools alongside clinical evaluation to assess and plan their steps accordingly[18].

Plaskos et al[19] demonstrated that robotic-assisted gap-balancing required fewer soft tissue releases compared to robot-assisted measured resection and conventional measured resection, as part of a multicenter investigation. The overall rate of soft tissue release was notably lower in the robotic gap-balancing group, with 31% of knees needing one or more releases, compared to 50% (P = 0.001) in the robotic measured resection group and 66% (P < 0.001) for conventional measured resection. Similarly, Selvanathan et al[18] found that only 29.7% of patients undergoing rTKR needed a soft tissue release. Clark et al[20] demonstrated that rTKR provides notable short-term benefits when compared to cTKR due to less soft tissue releases, including better range of motion, lower pain scores on day one, and decreased narcotic usage on day two. As a result, there was a decrease in total morphine-equivalent dosage, facilitating early mobilization and discharge, thereby shortening hospital stays. However, despite these early benefits, no long-term advantages were observed, with no discernible differences between the groups in terms of Oxford knee score (OKS) or Forgotten knee score at the two-year mark.

Another crucial aspect to consider is that employing manual techniques used in conventional knee replacement surgery runs the risk of unintentionally disrupting the delicate periarticular soft-tissue structures[13]. However, these intraoperative injuries tend to be underreported[21]. On the contrary, in rTKR, saw blade movements are confined within a predetermined, fixed stereotactic field. This confinement theoretically reduces the likelihood of iatrogenic intraoperative bone and soft-tissue injuries, providing a safer surgical approach compared to manual techniques[22]. Hampp et al[22] conducted a cadaveric study which compared soft-tissue injuries between rTKR and cTKR groups. They found mild posterior cruciate ligament injuries in 28% of cTKR patients, whereas none were observed in the rTKR group. Additionally, upon careful visual evaluation, cTKR resulted in more overall soft tissue trauma, whereas the rTKR group showed better periarticular soft tissue preservation.

Blood loss

In terms of blood loss, some robotic systems present a notable advantage by using small-diameter bone pins instead of intramedullary instrumentation. Furthermore, some systems integrate an automatic stop feature for the saw blade, which activates if there is any deviation beyond a predefined cutting area[23]. Theoretical factors contributing to elevated blood loss in cTKR include the use of intramedullary guides during femoral canal instrumentation, excessive bone resection, and iatrogenic soft-tissue trauma[23,24].

According to a recent study published in 2021 that primarily focused on assessing blood loss and risk of blood transfusion, it was shown that patients undergoing rTKR exhibited a 23.7% reduction in blood loss compared to those undergoing cTKR (911 mL vs 1193 mL, respectively, P < 0.01). Additionally, there was an 83% relative risk reduction in the likelihood of receiving a blood transfusion in the rTKR group (2% of patient vs 12%, respectively, P = 0.02). Hence, the use of robotic surgical systems in TKR surgery not only reduced blood loss but also diminished the risk of requiring a blood transfusion[24].

In line with this, Kayani et al[16] reported that patients undergoing cTKR experienced a more pronounced reduction in postoperative hemoglobin levels compared to those undergoing rTKR. Only two of forty patients in the rTKR group required blood transfusion, while in the cTKR group, four of forty patients required blood transfusion postoperatively. Neither group utilized a pneumatic tourniquet during the procedures[25].

Unlike many existing studies, Stimson et al[26] did not identify any statistically notable difference in postoperative blood loss or transfusion rates between the rTKR and cTKR groups. Some factors which may have influenced those findings include preoperative hemoglobin levels, tourniquet application, strict postoperative transfusion criteria, and the administration of perioperative tranexamic acid[26].

CLINICAL SCORES, PATIENT REPORTED OUTCOMES AND COMPLICATIONS

TKR outcomes are influenced by factors such as the surgeon’s experience, patient and implant-related factors[27]. Consequently, attributing minute differences to each surgical method can prove challenging. Many studies have aimed to compare the short and long outcomes between both methods, yet a definitive consensus remains inconclusive.

In the realm of postoperative pain experience, there is a noteworthy body of evidence suggesting that the use of rTKR is associated with reduced pain levels contributing to an overall improvement in the patient experience and recovery process[27,28].

Patients who underwent rTKR exhibited markedly lower Visual Analog Scale pain scores during periods of rest and activity at both the two and six week intervals. Additionally, they demonstrated a substantial reduction in opioid usage at the six-week period, a significantly higher probability of being opioid-free at 6 weeks, and a shorter length of hospital stay compared to patients undergoing cTKR[28]. Meta-analyses reported statistically significant improvements in the Hospital for Special Surgery (HSS) and Knee Society scores (KSS) in the short to mid-term follow-up in the rTKR compared to the cTKR group[8,29]. A more recent study published in 2022 that was conducted on patients who underwent bilateral TKRs with one side undergoing rTKR and the other cTKR, showed that a higher percentage of patients expressed greater satisfaction after rTKR. Many patients reported that their knees felt less painful and more natural with rTKR compared to cTKR at the final follow-up (P < 0.01). The majority of patients expressed a willingness to undergo rTKR again and recommended it to others[23].

On the contrary, a RCT published in 2020[30] reported no statistically significant differences in all clinical outcomes between rTKR and cTKR. These outcomes included mean total KSS, residual pain, Western Ontario and McMaster University Osteoarthritis Index (WOMAC) scores, range of motion, and University of California at Los Angeles activity scores[26]. Few studies reported on the long-term functional outcomes comparing both methods and found no difference in HSS, WOMAC, OKS, KSS or short form-12 scores between them at a minimum of 10 years follow-up[31,32].

Upon evaluating the incidence of postoperative complications between the two methods, it was observed that there was no statistically significant difference in complication rates between the rTKR and cTKR. The comparative analysis did not reveal any substantial difference in the occurrence of complications, suggesting a similar level of safety and complication risk associated with both methods[8,32].

RADIOLOGICAL ASSESSMENT

The primary objective of robotic surgery is to enhance surgical precision regardless of the surgeon’s preferred philosophy of alignment techniques. While recent literature debates the superiority of robotic surgery over conventional methods across various factors, consensus among researchers is emerging regarding radiological parameters. Most studies acknowledge the superior precision of rTKR, leading to improved prosthesis placement and overall joint alignment[8,29]. According to a meta-analysis involving 12 RCTs, rTKR achieved more precise placement of prosthetic components and improved joint alignment accuracy compared to cTKR. The pooled analysis demonstrated fewer outliers in various joint angles including the hip-knee-ankle (HKA) angle, femoral component (coronal) angle, femoral component (sagittal) angle, tibial component (coronal) angle, and tibial component (sagittal) angle, with significant differences (P < 0.0001, P = 0.0006, P = 0.009, P = 0.05, P = 0.01, respectively). Additionally, the postoperative HKA angle was significantly more neutral in the rTKR group, with a mean difference of 20.77 (P < 0.0001)[33]. This enhancement in precision was further highlighted in radiographic findings at 90 d post-operation in an RCT published in 2022. The study reported a statistically significant lower frequency of lateral tibial component angle outliers in the rTKR group compared to the cTKR group (3.0% vs 29.4%, P = 0.003)[34].

ECONOMICAL IMPACT

The introduction of new technology often sparks debates, and a key aspect under scrutiny is its cost-effectiveness. While the literature is replete with studies evaluating clinical outcomes, there is a noticeable gap in evidence concerning economic implications and healthcare resource utilization outcomes. A recent meta-analysis published in 2023 reported that rTKR resulted in reduced hospital stay, increased likelihood of home discharge, and lower 90-d readmission rates compared to cTKR. The extended operating times and the presence of a learning curve for rTKR aligned with previous findings[35].

Cool et al[36] conducted a case-controlled study in the United States to investigate the cost implications of the two methods. Their investigation showed that rTKR was associated with substantially lower 90-d episode-of-care costs compared to cTKR [mean difference (MD) = US$ 2391, P < 0.001]. These cost savings stemmed primarily from reduced index facility costs (MD = US$ 640, P < 0.001) due to a shorter length of stay (MD = 0.69 d, P < 0.001), along with diminished post-acute services costs (MD = US$ 1744, P < 0.001) including the higher probability of discharge to home and lower readmission rates compared to patients undergoing cTKR. However, the inclusion of computed tomography scan costs for pre-operative planning slightly diminished the total cost savings to US$ 2182. Alongside preoperative imaging, it is noteworthy that the installation and maintenance of the robotic device incurs substantial costs to healthcare providers according to the type of robot and category of application systems used and this may range between US$ 600000 and US$ 1.5 million[36]. Therefore, the potential cost value of rTKR warrants further detailed exploration in future studies.

FUTURE IMPLICATIONS

Whilst the evidence continues to evolve regarding rTKR surgery, the use of robotics continues to attract great interest from surgeons and patients alike. The ability to execute the preoperative plan precisely results in better alignment. However, long-term evidence from high quality RCTs confirming superiority in clinical outcomes is still lacking at this stage. On the other hand, there is continuous interest in improving how robotics are performing and the introduction of rTKR in training of junior staff may result in it becoming the norm for how this surgery is going to be performed in the future.

CONCLUSION

Robotic TKR surgery improves radiological outcomes, precision of prosthesis placement and overall joint alignment with no difference in complication rates compared to conventional TKR surgery. It is associated with less soft tissue injuries and blood loss intraoperatively. However, this has not translated into better long-term clinical outcomes within the limited published literature. On the other hand, there are installation and maintenance costs and longer operative times during the learning curve which are partly compensated by reduced hospital stay and 90 d readmission rates.