Jelle P. van der List, MD, Harshvardhan Chawla, BS, and Andrew D. Pearle, MD
Authors’ Disclosure Statement: Dr. Pearle reports that he is a paid consultant to Mako/Stryker, is a member of the scientific advisory board for Blue Belt Technologies, and is a consultant to Biomet. The other authors report no actual or potential conflict of interest in relation to this article.
Unicompartmental knee arthroplasty and total knee arthroplasty are reliable treatment options for osteoarthritis. In order to improve survivorship rates, variables that are intraoperatively controlled by the orthopedic surgeon are being evaluated. These variables include lower leg alignment, soft tissue balance, joint line maintenance, and tibial and femoral component alignment, size, and fixation methods. Since tighter control of these factors is associated with improved outcomes of knee arthroplasty, several computer-assisted surgery systems have been developed.
These systems differ in the number and type of variables they control. Robotic-assisted systems control these aforementioned variables and, in addition, aim to improve the surgical precision of the procedure. Robotic-assisted systems are active, semi-active, or passive, depending on how independently the systems perform maneuvers.
Reviewing the robotic-assisted knee arthroplasty systems, it becomes clear that these systems can accurately and reliably control the aforementioned variables. Moreover, these systems are more accurate and reliable in controlling these variables when compared to the current gold standard of conventional manual surgery.
At present, few studies have assessed the survivorship and functional outcomes of robotic-assisted surgery, and no sufficiently powered studies were identified that compared survivorship or functional outcomes between robotic-assisted and conventional knee arthroplasty. Although preliminary outcomes of robotic-assisted surgery look promising, more studies are necessary to assess if the increased accuracy and reliability in controlling the surgical variables leads to better outcomes of robotic-assisted knee arthroplasty.
Unicompartmental knee arthroplasty (UKA) and total knee arthroplasty (TKA) are 2 reliable treatment options for patients with primary osteoarthritis. Recently published systematic reviews of cohort studies have shown that 10-year survivorship of medial and lateral UKA is 92% and 91%, respectively,1 while 10-year survivorship of TKA in cohort studies is 95%.2 National and annual registries show a similar trend, although the reported survivorship is lower.1,3-7
In order to improve these survivorship rates, the surgical variables that can intraoperatively be controlled by the orthopedic surgeon have been evaluated. These variables include lower leg alignment, soft tissue balance, joint line maintenance, and alignment, size, and fixation of the tibial and femoral component. Several studies have shown that tight control of lower leg alignment,8-14 balancing of the soft tissues,15-19 joint line maintenance,20-23 component alignment,24-28 component size,29-34 and component fixation35-40 can improve the outcomes of UKA and TKA. As a result, over the past 2 decades, several computer-assisted surgery systems have been developed with the goal of more accurate and reliable control of these factors, and thus improved outcomes of knee arthroplasty.
These systems differ with regard to the number and type of variables they control. Computer navigation systems aim to control one or more of these surgical variables, and several meta-analyses have shown that these systems, when compared to conventional surgery, improve mechanical axis accuracy, decrease the risk for mechanical axis outliers, and improve component positioning in TKA41-49 and UKA surgery.50,51 Interestingly, however, meta-analyses have failed to show the expected superiority in clinical outcomes following computer navigation compared to conventional knee arthroplasty.48,52-55 Furthermore, authors have shown that, despite the fact that computer-navigated surgery increases the accuracy of mechanical alignment and surgical cutting, there is still room for improvement.56 As a consequence, robotic-assisted systems have been developed.
Similar to computer navigation, these robotic-assisted systems aim to control the surgical variables; in addition, they aim to improve the surgical precision of the procedure. Interestingly, 2 recent studies have shown that robotic-assisted systems are superior to computer navigation systems with regard to less cutting time and less resection deviations in coronal and sagittal plane in a cadaveric study,57 and shorter total surgery time, more accurate mechanical axis, and shorter hospital stay in a clinical study.58 Although these results are promising, the exact role of robotic surgery in knee arthroplasty remains unclear. In this review, we aim to report the current state of robotic-assisted knee arthroplasty by discussing (1) the different robotic-assisted knee arthroplasty systems that are available for UKA and TKA surgery, (2) studies that assessed the role of robotic-assisted knee arthroplasty in controlling the aforementioned surgical variables, (3) cadaveric and clinical comparative studies that compared how accurate robotic-assisted and conventional knee surgery control these surgical variables, and (4) studies that assessed the cost-effectiveness of robotic-assisted knee arthroplasty surgery.
Robotic-Assisted Knee Arthroplasty Systems
Several systems have been developed over the years for knee arthroplasty, and these are usually defined as active, semi-active, or passive.59 Active systems are capable of performing tasks or processes autonomously under the watchful eye of the surgeon, while passive systems do not perform actions independently but provide the surgeon with information. In semi-active systems, the surgical action is physically constrained in order to follow a predefined strategy.
In the United States, 3 robotic systems are FDA-approved for knee arthroplasty. The Stryker/Mako haptic guided robot (Mako Surgical Corp.) was introduced in 2005 and has been used for over 50,000 UKA procedures (Figure 1). There are nearly 300 robotic systems used nationally, as it has 20% of the market share for UKA in the United States. The Mako system is a semi-active tactile robotic system that requires preoperative imaging, after which a preoperative planning is performed. Intraoperatively, the robotic arm is under direct surgeon control and gives real-time tactile feedback during the procedure (Figure 2).
Furthermore, the surgeon can intraoperatively virtually adjust component positioning and alignment and move the knee through the range of motion, after which the system can provide information on alignment, component position, and balance of the soft tissue (eg, if the knee is overtight or lax through the flexion-arch).60 This system has a burr that resects the bone and when the surgeon directs the burr outside the preplanned area, the burr stops and prevents unnecessary and unwanted resections (Figure 3).
The Navio Precision Free-Hand Sculptor (PFS) system (Blue Belt Technologies) has been used for 1500 UKA procedures, with 50 robots in use in the United States (Figure 4). This system is an image-free semi-active robotic system and has the same characteristics as the aforementioned Mako system.61 Finally, the OmniBotic robotic system (Omnilife Science) has been released for TKA and has been used for over 7300 procedures (Figure 5). This system has an automated cutting-guide technique in which the surgeon designs a virtual plan on the computer system. After this, the cutting-guides are placed by the robotic system at the planned location for all 5 femoral cuts (ie, distal, anterior chamfer, anterior, posterior chamfer, and posterior) and the surgeon then makes the final cuts.57,62
