Robotic total knee arthroplasty: clinical outcomes and directions for future research.

The term ‘robot’ originates from the Czech word ‘robota’, which means forced labour or activity. Karel Capek first used the term in his 1921 play Rossum’s Universal Robots, in which robots were a series of factory-manufactured artificial people made from synthetic material that undertook mundane tasks for their human masters. The robots eventually became frustrated with their roles and masterminded a robotic rebellion, leading to the extinction of the human race. Since then, robotics has evolved to describe an array of computer machines that perform preprogrammed, precise, and repetitive procedures. These computer machines have now become integrated into the routine workforce of several industries, including aviation, military, healthcare, finance, construction, and engineering.[1,2] Robotic technology has helped each of these sectors to achieve and sustain levels of precision, productivity, and efficiency that were not possible with humans alone. Within each of these sectors that have integrated robotic technology into the workforce, the use of this technology has never diminished or exited from the industry.[2]

The first robotic surgical procedure was performed by Kwoh et al[3] in 1988 using the PUMA 560 robotic system (Westinghouse Electric, Pittsburgh, Pennsylvania) to undertake neurosurgical biopsies with improved precision. The same robotic platform was used by Davies et al[4] in 1991 to undertake transurethral resections of the prostate with greater accuracy and reduced iatrogenic soft-tissue injury. Over the following two decades, several other surgical robotic devices were developed, including the Zeus (Computer Motion, Inc., Goleta, California) and Da Vinci (Intuitive Surgical, Sunnyvale, California) robotic platforms, which enabled a variety of surgical procedures to be performed remotely using robotically controlled arms and a 3D camera to improve the visual field.[5,6] These robotic devices have been used to perform cholecystectomy, hysterectomy, lobectomy, mitral valve replacement, coronary artery bypass grafting, and prostatectomy. Compared with conventional open surgery or laparoscopic surgery, robotic surgery with these devices is associated with smaller skin incisions, improved precision of soft-tissue dissection, better visualization of the surgical field, and more comprehensive data capture for surgical training.[6,7] Clinically, this has translated to robotic surgery enabling faster postoperative rehabilitation and decreased length of hospital stay compared with conventional and laparoscopic surgery for these procedures.[5-8]

Total knee arthroplasty (TKA) is an effective and cost-efficient procedure that is performed in over 90 000 patients per year in the United Kingdom.[9] Implant survivorship, assessed with revision as the primary endpoint, is greater than 90% at ten years’ follow-up.[10,11] However, patient satisfaction and functional outcomes remain inferior to total hip arthroplasty, with up to 20% of patients remaining dissatisfied following TKA.[12,13] Accurate implant positioning, balanced flexion-extension gaps, proper ligament tensioning, and preservation of the periarticular soft-tissue envelope are important surgeon-controlled variables that affect functional outcomes, implant stability, and long-term implant survivorship.[14-16] Conventional jig-based TKA uses preoperative radiographic films, intraoperative anatomical landmarks, and manually positioned alignment jigs to guide bone resection and implant positioning. However, these handheld techniques are associated with poor reproducibility of alignment-guide positioning, inadvertent sawblade injury to the periarticular soft-tissue envelope, and limited intraoperative data on gap measurements or ligamentous tensioning to fine-tune implant positioning.[17-19] Suboptimal implant positioning or gap balancing may lead to poor functional recovery, reduced clinical outcomes, increased instability, and reduced implant survivorship.[14-16]

Robotic TKA uses computer software to convert anatomical information into a virtual patient-specific 3D reconstruction of the knee joint. The anatomical information may be obtained using preoperative CT (image-based) or a combination of preoperative radiographs and intraoperative osseous mapping (imageless). The surgeon uses this virtual model to plan optimal bone resection, implant positioning, bone coverage, and limb alignment based on the patient’s unique anatomy. An intraoperative robotic device helps to execute this preoperative patient-specific plan with a high level of accuracy.[20-26] The action of the sawblade is confined to the preoperative surgical plan for femoral and tibial resection, which limits iatrogenic periarticular soft-tissue injury and bone trauma.[27,28] Although the first robotic TKA was performed in 1988 using the ACROBOT robotic system (Imperial College, London, United Kingdom), there has been a surge in robotic TKA over the last decade.[29] This has been attributed to recent developments in computer software and technology, and the ease with which modifications can be made to existing technology such as computer navigation.[1,2] Computer-navigated TKA provides patient-specific anatomical data with recommendations for bone resection and optimal component positioning. Robotic TKA takes this one step further by actively controlling and/or restraining the surgeon’s motor function to improve the accuracy of achieving the planned bone resection and implant positioning.

There are a variety of robotic TKA devices, some of which actively perform all parts of femoral and tibial bone resections (fully active), while others enable the surgeon to undertake the procedure while providing live intraoperative feedback to help control bone resection to the confines of the preoperative surgical plan (semi-active). ROBODOC (THINK Surgical Inc., Fremont, California) is an example of a fully active robotic TKA application system.[30] The surgeon performs the surgical approach, positions retractors to protect the periarticular soft tissues, and then secures the limb into a fixed device. The robotic device then independently executes the planned bone resections. The Mako Robotic Arm Interactive Orthopaedic System (Stryker Ltd, Kalamazoo, Michigan) is an example of an image-guided semi-active robotic system for robotic TKA.[31] The robotic arm has visual, tactile, and audio feedback that help the surgeon to control the force and direction of saw blade action within the confines of the femoral and tibial bone resection windows. The Navio Surgical system (Smith & Nephew, Andover, Texas) is an imageless semi-active robotic system that uses a handheld platform to intraoperatively map osseous anatomy and guide bone resection.[32] The Rosa Knee System (Zimmer Biomet, Warsaw, Indiana) offers a computer software program to convert 2D knee radiographs into a 3D patient-specific bone model, and a robotic device to help position the cutting blocks and execute the planned bone resections with greater accuracy.[33] Omnibotic (OMNIlife Science Inc., East Taunton, Massachusetts) is a robotic device that uses patented intraoperative Bone Morphin technology to create a 3D model of the osseous anatomy using plain radiographs.[34] This may be combined with the BalanceBot Ligament Balancer (OMNIlife Science Inc.), which uses an intraoperative robotic device to balance the soft tissues. Together, these technologies may help surgeons place implants anatomically while minimizing the need for soft-tissue releases.[34]

Robotic TKA is associated with improved accuracy of achieving the planned femoral and tibial implant positioning, joint line restoration, limb alignment, and posterior tibial slope compared with conventional jig-based TKA.[20,24] This has been attributed to the stereotactic boundaries that confine the action of the sawblade to the preplanned haptic femoral and tibial windows. Song et al[20,21] performed a prospective randomized study on 100 patients undergoing primary TKA, and found that robotic TKA was associated with improved accuracy and reduced outliers in achieving the planned alignment compared with conventional manual TKA. Bellemans et al[22] reviewed outcomes in 25 patients undergoing robotic TKA and reported femoral and tibial implant positioning within 1° of the planned positions in all three planes. Hampp et al[23] performed a study on six cadaveric specimens and found that robotic TKA was associated with improved accuracy of femoral and tibial implant positioning in the coronal, sagittal, and axial planes compared with conventional manual TKA. Improved accuracy in achieving these radiological outcomes has been previously correlated to increased patient satisfaction, greater stability, and improved kinematics through the arc of motion following TKA.[1,25,26] Furthermore, robotic TKA is associated with a learning curve of six to 20 cases for operative times, but there is no learning curve for achieving the planned femoral or tibial implant positioning.[35,36] This is important for the safe implementation of this technology into routine arthroplasty practice and offers an avenue for low-volume arthroplasty surgeons to achieve high levels of accuracy in implant positioning.

Balanced flexion-extension gaps and proper mediolateral ligamentous tensioning are important technical objectives in TKA for optimizing knee kinematics, stability, and long-term implant survivorship.[14-16] Conventional jig-based TKA techniques often utilize controlled soft-tissue releases to achieve balanced flexion-extension gaps and mediolateral soft-tissue tension. Assessing intraoperative gap measurements and periarticular soft-tissue laxity is challenging, and is often dependent on the skill and expertise of the operating surgeon.[36-38] Robotic TKA uses optical motion capture technology to assess intraoperative alignment, component positioning, range of movement, flexion-extension gaps, and mediolateral laxity. This real-time intraoperative data can then be used to fine-tune bone resection and guide implant positioning, in order to achieve the desired knee kinematics and limit the need for additional soft-tissue releases.[27,28] Kayani et al[28] conducted a prospective cohort study comparing bone trauma and periarticular soft tissue injury in 30 patients undergoing conventional jig-based TKA versus 30 patients receiving robotic TKA. The study found that robotic TKA enabled better preservation of the periarticular soft-tissue envelope in both correctible and non-correctible coronal plane deformities, and robotic TKA was associated with less trauma to the residual femoral and tibial bone resection surfaces. Khlopas et al[27] conducted a cadaveric study in which six blinded observers reported soft-tissue trauma following bone resection in cruciate-retaining TKAs, and found that robotic TKA was associated with reduced posterior cruciate ligament injury, decreased tibial subluxation, and reduced patella eversion compared with conventional jig-based TKA.

Improved preservation of the periarticular soft envelope secondary to reduced iatrogenic periarticular soft-tissue injury in robotic TKA may help to limit the local inflammatory response, decrease pain, and reduce postoperative swelling compared with conventional jig-based TKA. Siebert et al[39] conducted a retrospective study on 70 patients undergoing robotic TKA versus a matched historic cohort of 50 conventional jig-based TKAs, and observed reduced postoperative soft-tissue swelling in the robotic group. Kayani et al[40] conducted a prospective cohort study comparing early functional outcomes in 40 conventional manual UKAs followed by 40 robotic TKAs. The authors found that robotic TKA was associated with reduced postoperative pain, decreased analgesia requirements, shorter time to straight leg raise, increased knee flexion at discharge, and reduced need for inpatient physiotherapy compared with conventional jig-based TKA. Median time to hospital discharge in robotic-arm assisted TKA was 77 hours (interquartile range (IQR) 74 to 81) compared with 105 hours (IQR 98 to 126) in conventional jig-based TKA (p < 0.001). Marchand et al[41] compared outcomes in 28 robotic TKAs matched with 20 conventional jig-based TKAs and showed that pain, patient satisfaction, and physical function scores, as measured using Western Ontario and McMaster Universities Arthritis Index (WOMAC), were better in the robotic group compared with the conventional group at six months after surgery.

Improved accuracy of implant positioning and enhanced postoperative rehabilitation in robotic TKA have not translated to any differences in middle- to long-term functional outcomes compared with conventional jig-based TKA. Song et al[20,21] reported no difference in Hospital for Special Surgery (HSS) or WOMAC scores between 50 conventional jig-based TKAs and 50 robotic TKAs at two years’ follow-up. Liow et al[42] conducted a prospective randomized trial in 29 conventional jig-based TKAs versus 31 robotic TKAs, and found that there was no difference between the two treatment groups with respect to the Oxford Knee Score (OKS) and KSS at two years’ follow-up. Yang et al[43] conducted a prospective cohort study on 71 robotic TKAs versus 42 conventional jig-based TKAs, and found no difference in HSS and WOMAC scores at a minimum of ten years’ follow-up. As with all new technology in medicine and surgery, there is a paucity of prospective randomized controlled trials reporting on longer-term outcomes.

Fixed femoral and tibial arrays provide novel intraoperative data on fixed flexion deformity, range of movement, limb alignment, flexion-extension gaps, and mediolateral ligamentous laxity, which may be used for research and development purposes. For example, existing studies assessing functional alignment in TKA have used patient-specific implants or alignment guides to achieve the preplanned alignment. Robotic technology offers an opportunity to accurately execute the planned bone resection and implant positioning to achieve functional alignment, and fixed intraoperative femoral and tibial arrays enable the surgeon to confirm that this alignment has been achieved. Similarly, changes in gap measurements and alignment following specific ligamentous resection may provide data on ligament biomechanics and kinematics. In anterior and posterior cruciate ligament reconstructions, robotic technology potentially offers an avenue to improve accuracy and reduce outliers in correct femoral and tibial tunnel positioning. Robotic technology may minimize human error and provide objective, real-time data for scientists, clinicians, and engineers to accurately record changes in knee kinematics and function. Intraoperative data on the various stages of robotic TKA may also be used for teaching purposes to improve surgical proficiency.

Robotic technology is associated with several limitations that must be acknowledged when understanding the current role and future potential of this technology in TKA. The robotic device is expensive to install and separate applications may need to be required for total hip arthroplasty, TKA, and unicompartmental knee arthroplasty. The robotic device is only compatible with a limited number of implants from the manufacturer of the robotic device, and additional costs are incurred for preoperative imaging, increased operating times during the learning phase, training the surgical team, updating of computer software and servicing contracts, and consumables. Image-guided robotic TKA requires preoperative CT scans that require extra time and radiation exposure. Additional time is also required for remote preoperative planning and segmentation using the patient-specific virtual models, and a robotic product specialist is required in the operating room to capture data and facilitate the operative procedure. Fully active robotic TKA systems have also been reported to cause periarticular soft-tissue injury, and technical issues with robotic device have required intraoperative conversion to conventional jig-based TKA.[1,17]

Overall, robotic technology enables TKA to be undertaken with improved accuracy of implant positioning and reduced periarticular soft-tissue injury compared with conventional jig-based TKA. This has translated to improved inpatient functional rehabilitation and earlier time to hospital discharge compared with conventional jig-based TKA. Robotic technology offers potential for further research by providing objective data on gap measurements and knee kinematics following specific ligamentous releases, and provides an avenue for executing preplanned implant positioning and alignment with greater precision and reproducibility for study purposes. These advantages must be acknowledged while respecting the limitations of robotic TKA, which include additional costs for installation and maintenance of the robotic machine, additional radiation exposure, and paucity of long-term data showing any functional benefit over conventional jig-based TKA. The results of further high-quality studies with longer term follow-up on functional outcomes, implant survivorship, complications, and cost-effectiveness are awaited.