Technique and first clinical results of robot-assisted total knee replacement

Computer-Assisted Orthopedic Surgery: Current State and Future Perspective

Introduced about two decades ago, computer-assisted orthopedic surgery (CAOS) has emerged as a new and independent area, due to the importance of treatment of musculoskeletal diseases in orthopedics and traumatology, increasing availability of different imaging modalities, and advances in analytics and navigation tools. The aim of this paper is to present the basic elements of CAOS devices and to review state-of-the-art examples of different imaging modalities used to create the virtual representations, of different position tracking devices for navigation systems, of different surgical robots, of different methods for registration and referencing, and of CAOS modules that have been realized for different surgical procedures. Future perspectives will also be outlined.

Robotic-assisted knee arthroplasty

Robotics in total knee arthroplasty (TKA) has undergone vast improvements. Although some of the systems have fallen out of favor due to safety concerns, there has been recent increased interest for semi-active haptic robotic systems that provide intraoperative tactile feedback to the surgeon. The potential advantages include improvements in radiographic outcomes, reducing the incidence of mechanical axis malalignment of the lower extremity and better tissue balance. Proponents of robotic technology believe that these improvements may lead to superior functional outcomes and implant survivorship. We aim to discuss robotic technology development, outcomes of unicompartmental and total knee arthroplasty and the future outlook. Short-term follow-up studies on robotic-assisted knee arthroplasty suggest that, although some alignment objectives may have been achieved, more studies regarding functional outcomes are needed. Furthermore, studies evaluating the projected cost-benefit analyses of this new technology are needed before widespread adoption. Nevertheless, the short-term results warrant further evaluation.

Robotic surgery in trauma and orthopaedics: a systematic review

The use of robots in orthopaedic surgery is an emerging field that is gaining momentum. It has the potential for significant improvements in surgical planning, accuracy of component implantation and patient safety. Advocates of robot-assisted systems describe better patient outcomes through improved pre-operative planning and enhanced execution of surgery. However, costs, limited availability, a lack of evidence regarding the efficiency and safety of such systems and an absence of long-term high-impact studies have restricted the widespread implementation of these systems. We have reviewed the literature on the efficacy, safety and current understanding of the use of robotics in orthopaedics.

Robot-assisted total knee arthroplasty accurately restores the joint line and mechanical axis. A prospective randomised study

Robot-assisted Total Knee Arthroplasty (TKA) improves the accuracy and precision of component implantation and mechanical axis (MA) alignment. Joint-line restoration in robot-assisted TKA is not widely described and joint-line deviation of>5mm results in mid-flexion instability and poor outcomes. We prospectively randomised 60 patients into two groups: 31 patients (robot-assisted), 29 patients (conventional). No MA outliers (>±3° from neutral) or notching was noted in the robot-assisted group as compared with 19.4% (P=0.049) and 10.3% (P=0.238) respectively in the conventional group. The robot-assisted group had 3.23% joint-line outliers (>5mm) as compared to 20.6% in the conventional group (P=0.049). Robot-assisted TKA produces similar short-term clinical outcomes when compared to conventional methods with reduction of MA alignment and joint-line deviation outliers.

Can technology improve alignment during knee arthroplasty

Component malalignment remains a concern in total knee arthroplasty (TKA); therefore, a series of technologies have been developed to improve alignment. The authors conducted a systematic review to compare computer-assisted navigation with conventional instrumentation, and assess the current evidence for patient-matched instrumentation and robot-assisted implantation. An extensive search of the PubMed database for relevant meta-analyses, systematic reviews and original articles was performed, with each study scrutinised by two reviewers. Data on study characteristics and outcomes were extracted from each study and compared. In total 30 studies were included: 10 meta-analyses comparing computer-assisted navigation and conventional instrumentation, 13 studies examining patient-matched instrumentation, and seven investigating robot-assisted implantation. Computer-assisted navigation showed significant and reproducible improvements in mechanical alignment over conventional instrumentation. Patient-matched instrumentation appeared to achieve a high degree of mechanical alignment, although the majority of studies were of poor quality. The data for robot-assisted surgery was less indicative. Computer-assisted navigation improves alignment during TKA over conventional instrumentation. For patient-matched instrumentation and robot-assisted implantation, alignment benefits have not been reliably demonstrated. For all three technologies, clinical benefits cannot currently be assumed, and further studies are required. Although current technologies to improve alignment during TKA appear to result in intra-operative benefits, their clinical impact remains unclear, and surgeons should take this into account when considering their adoption.

Accuracy of a freehand sculpting tool for unicondylar knee replacement

BACKGROUND

Unicondylar knee replacement is technically challenging and malalignment of the implant components is one of the factors that results in high failure rates. Surgical robotics with navigation is emerging as a potential solution to improve the accuracy of implant placement.

METHODS

The accuracy of performing unicondylar knee replacement using a freehand sculpting, semi-active robotic tool was investigated using 20 synthetic femurs and tibia. Resultant femoral and tibial implant placement was compared to the planned implant position.

RESULTS

The maximum rotational error was 3.2(o) and RMS angular error was 1.46(o) across all orientations, for both the tibia and femoral implants. The maximum translational error was 1.18 mm and the RMS translational error across all directions was 0.61 mm.

CONCLUSIONS

The freehand sculpting tool produced accurate implant placement with small errors comparable to those reported by other robotic-assistive devices on the market for unicondylar knee replacement.

A comparison of classical and anatomical total knee alignment methods in robotic total knee arthroplasty: classical and anatomical knee alignment methods in TKA

The purpose of this study was to compare the clinical and radiological outcomes achieved using classical and anatomical alignment methods in primary total knee arthroplasty (TKA). One hundred and seventeen patients were randomly assigned to undergo robotic-assisted TKA using either the classical (56 patients) or the anatomical alignment method (61 patients). Clinical outcomes including varus and valgus laxities, ROM, HSS and WOMAC scores and radiological outcomes were evaluated after a minimum follow-up of 2 years. Varus and valgus laxity assessments showed no significant inter-group differences (P>0.05). Moreover, no significant differences were observed in ROM, HSS and WOMAC scores (P>0.05). We could not find any significant difference in mechanical alignment of the lower limb. The results of this study show that two alignment methods provide comparable clinical and radiological outcomes after primary TKA.

A perspective on robotic assistance for knee arthroplasty

Knee arthroplasty is used to treat patients with degenerative joint disease of the knee to reduce pain and restore the function of the joint. Although patient outcomes are generally quite good, there are still a number of patients that are dissatisfied with their procedures. Aside from implant design which has largely become standard, surgical technique is one of the main factors that determine clinical results. Therefore, a lot of effort has gone into improving surgical technique including the use of computer-aided surgery. The latest generation of orthopedic surgical tools involves the use of robotics to enhance the surgeons' abilities to install implants more precisely and consistently. This review presents an evolution of robot-assisted surgical systems for knee replacement with an emphasis on the clinical results available in the literature. Ever since various robotic-assistance systems were developed and used clinically worldwide, studies have demonstrated that these systems are as safe as and more accurate than conventional methods of manual implantation. Robotic surgical assistance will likely result in improved surgical technique and improved clinical results.

Cooperative force control of a hybrid Cartesian parallel manipulator for bone slicing

Over the past two decades, robots have been increasingly used in biomedical applications such as bone cutting. Traditional automated manufacturing processes are often unable to meet the safety and accuracy requirements for such applications, particularly for cutting inhomogeneous constitutions of bone. In this case, human–robot cooperation may prove to be an effective approach. In this paper, we demonstrate that a hybrid parallel manipulator under cooperative force control can achieve accurate bone cutting with sufficient safety guaranteed. First, a hybrid parallel manipulator was constructed to provide the required rigidity for bone cutting. Then a two-loop controller was designed to implement the human–robot cooperation in bone cutting. The position control loop of adaptive fuzzy control is responsible for achieving high-tracking performance by overcoming varying friction forces from the mechanism. The force control loop of the cooperative force control adjusts the feed rate of the cutter according to the bone slicing conditions and operator's supervisory commands. The experimental results show that the proposed controller can effectively achieve the required accuracy in bone cutting with required safety.

Robotic-assisted TKA reduces postoperative alignment outliers and improves gap balance compared to conventional TKA

BACKGROUND

Several studies have shown mechanical alignment influences the outcome of TKA. Robotic systems have been developed to improve the precision and accuracy of achieving component position and mechanical alignment.

QUESTIONS/PURPOSES

We determined whether robotic-assisted implantation for TKA (1) improved clinical outcome; (2) improved mechanical axis alignment and implant inclination in the coronal and sagittal planes; (3) improved the balance (flexion and extension gaps); and (4) reduced complications, postoperative drainage, and operative time when compared to conventionally implanted TKA over an intermediate-term (minimum 3-year) followup period.

METHODS

We prospectively randomized 100 patients who underwent unilateral TKA into one of two groups: 50 using a robotic-assisted procedure and 50 using conventional manual techniques. Outcome variables considered were postoperative ROM, WOMAC scores, Hospital for Special Surgery (HSS) knee scores, mechanical axis alignment, flexion/extension gap balance, complications, postoperative drainage, and operative time. Minimum followup was 41 months (mean, 65 months; range, 41-81 months).

RESULTS

There were no differences in postoperative ROM, WOMAC scores, and HSS knee scores. The robotic-assisted group resulted in no mechanical axis outliers (> ± 3° from neutral) compared to 24% in the conventional group. There were fewer robotic-assisted knees where the flexion gap exceeded the extension gap by 2 mm. The robotic-assisted procedures took an average of 25 minutes longer than the conventional procedures but had less postoperative blood drainage. There were no differences in complications between groups.

CONCLUSIONS

Robotic-assisted TKA appears to reduce the number of mechanical axis alignment outliers and improve the ability to achieve flexion-extension gap balance, without any differences in clinical scores or complications when compared to conventional manual techniques.

Robot-assisted implantation improves the precision of component position in minimally invasive TKA

Minimally invasive and robot-assisted procedures have potential advantages when used for total knee arthroplasty (TKA). The purpose of this cadaveric study was to examine whether robot-assisted minimally invasive procedures improve TKA alignment after modifying the robotic techniques and instruments. Total knee arthroplasties were performed on 10 pairs of fresh cadaveric femora. Ten knees were replaced using the robot-assisted minimally invasive technique and 10 using the conventional minimally invasive technique. After prosthesis implantation, limb and prosthesis alignments were investigated by measuring mechanical axis deviation, femoral and tibial sagittal and coronal inclination, and femoral rotational alignment with 3-dimensional computed tomography scans. Postoperative alignment accuracy of the implanted prostheses was better in the robot-assisted minimally invasive TKA group than in the conventional minimally invasive TKA group as judged by the rotational alignment of the femoral component (0.7°±″.3° vs 3.6°±2.2°, respectively) and the tibial component sagittal angle (7.8°±1.1° vs 5.5°±3.6°, respectively). One sagittal inclination outlier for the tibial side existed in the robotic minimally invasive TKA group, and 2 outliers for the mechanical axis, 2 for the tibial side sagittal inclination, and 2 for the femoral rotational alignment existed in the conventional minimally invasive TKA group. Higher implanted prostheses accuracy and fewer outliers in postoperative radiographic alignments can be attained with robot-assisted TKA. Minimally invasive TKA in combination with an improved robot-assisted technique is an alternative option to compensate for the shortcomings of conventional minimally invasive TKA.

Comparison of robot-assisted and conventional total knee arthroplasty: a controlled cadaver study using multiparameter quantitative three-dimensional CT assessment of alignment

INTRODUCTION

A functional total knee replacement has to be well aligned, which implies that it should lie along the mechanical axis and in the correct axial and rotational planes. Incorrect alignment will lead to abnormal wear, early mechanical loosening, and patellofemoral problems. There has been increased interest of late in total knee arthroplasty with robotic assistance. This study was conducted to determine whether robot-assisted total knee arthroplasty is superior to the conventional surgical method with regard to the precision of implant positioning.

MATERIALS AND METHODS

Twenty knee replacements, comprising ten robot-assisted procedures and ten conventional operations, were performed on ten cadavers. Two experienced surgeons performed the surgeries. Both procedures on each cadaver were performed by the same surgeon. The choice of which procedure was to be performed first was randomized. Following implantation of the prosthesis, the mechanical axis deviation, femoral coronal angle, tibial coronal angle, femoral sagittal angle, tibial sagittal angle, and femoral rotational alignment were measured via 3D CT scanning. These variables were then compared with the preoperatively planned values.

RESULTS

In the knees that underwent robot-assisted surgery, the mechanical axis deviation ranged from -1.94° to 2.13° (mean: -0.21°), the femoral coronal angle from 88.08° to 90.99° (mean: 89.81°), the tibial coronal angle from 89.01° to 92.36° (mean: 90.42°), the tibial sagittal angle from 81.72° to 86.24° (mean: 83.20°), and the femoral rotational alignment from 0.02° to 1.15° (mean: 0.52°) in relation to the transepicondylar axis. In the knees that underwent conventional surgery, the mechanical axis deviation ranged from -3.19° to 3.84° (mean: -0.48°), the femoral coronal angle from 88.36° to 92.29° (mean: 90.50°), the tibial coronal angle from 88.15° to 91.51° (mean: 89.83°), the tibial sagittal angle from 80.06° to 87.34° (mean: 84.50°), and the femoral rotational alignment from 0.32° to 4.13° (mean: 2.76°) in relation to the transepicondylar axis. In the conventional knee replacement group, there were two instances of outliers outside the range of 3° varus/valgus for the mechanical axis deviation. The robot-assisted knee replacements showed significantly superior femoral rotational alignment results compared with conventional surgery (p = 0.006). There was no statistically significant difference between robot-assisted and conventional total knee arthroplasty with regard to the other variables. All the measurements showed high intra-observer and inter-observer reliability.

CONCLUSION

Robot-assisted total knee arthroplasty showed excellent precision in the sagittal and coronal planes of the 3D CT scan. In particular, the robot-assisted technique showed better accuracy in femoral rotational alignment compared to the conventional surgery, despite the fact that the surgeons who performed the operations were more experienced and familiar with the conventional method than with robot-assisted surgery. It can thus be concluded that robot-assisted total knee arthroplasty is superior to conventional total knee arthroplasty.

ACCURACY CHARACTERIZATION OF AN INTEGRATED OPTICAL-BASED METHOD FOR LOADS MEASUREMENT IN COMPUTER AIDED SURGERY

Generally in the anterior cruciate ligament (ACL) injury assessment specific laxity tests (i.e., Lachman, drawer tests) are clinically performed to evaluate the presence of ligamentous lesion. At present these tests are qualitatively evaluated by the surgeon and some quantitative measurements can be performed only for Lachman/drawer tests by means of dedicated devices. This study aimed to characterize the accuracy of a novel integrated optical-based method that can be used both in intra-operative and in office assessment of ACL injuries; in particular this technology was addressed to measure the loads/torques applied during clinical laxity tests, extending the current possible quantitative evaluations. The system, based on a commercial optical localizer and common springs, was spatially characterized in order to verify displacement/rotation and corresponding applied load/torque measurements. Evaluated limits of agreement between measured and applied loads were from –0.541 to 1.781 N, with a bias of 0.621 N (P = 0.05) in a dedicated clinical-like setup. This approach reported an excellent accuracy in load measurements, showing its possible integration in computer-aided surgery (CAS).

THE ACROBOT® SYSTEM FOR ROBOTIC MIS TOTAL KNEE AND UNI-CONDYLAR ARTHROPLASTY

The concept of the Acrobot® system is described. The technical details of the complete system are then outlined, including the pre-operative planner which incorporates 3D CT models together with CAD models of prostheses that can be used to plan the leg alignment, position the prostheses, plan the shape of the cuts required and generate the regions within which cuts must be constrained. The robotic system is also described, together with the methods for locating and clamping the patient. An outline is given of the means by which the preoperative model is registered or aligned to the intra-operative position of the patient and of the robot, without the need for fiducial markers. Post-operative results are given, for both total knee replacement and also for the more recent clinical trials using a minimally invasive robotic procedure for uni-condylar arthroplasty.

Simultaneous bilateral total knee arthroplasty with robotic and conventional techniques: a prospective, randomized study

PURPOSE

The authors performed this study to compare the outcomes of robotic-assisted and conventional TKA in same patient simultaneously. It was hypothesized that the robotic-assisted procedure would produce better leg alignment and component orientation, and thus, improve patient satisfaction and clinical and radiological outcomes.

METHODS

Thirty patients underwent bilateral sequential total knee replacement. One knee was replaced by robotic-assisted implantation and the other by conventional implantation.

RESULTS

Radiographic results showed significantly more postoperative leg alignment outliers of conventional sides than robotic-assisted sides (mechanical axis, coronal inclination of the femoral prosthesis, and sagittal inclination of the tibial prosthesis). Robotic-assisted sides had non-significantly better postoperative knee scores and ROMs. Robotic-assisted sides needed longer operation times (25 min, SD ± 18) and longer skin incisions. Nevertheless, postoperative bleeding was significantly less for robotic-assisted sides.

CONCLUSION

The better alignment accuracy of robotic TKA and the good clinical results achieved may favorably influence clinical and radiological outcomes.

Causes and patterns of aborting a robot-assisted arthroplasty

For a successful robot-assisted arthroplasty, every step should be executed harmoniously. However, when we encounter serious obstacles during surgery, it is sometimes better to abort the procedure in a timely manner. This study investigated the possible causes and patterns of aborted robot-assisted arthroplasties. Of 100 consecutively planned robot-assisted arthroplasties, 22 cases were aborted. Most involved total knee arthroplasty (21/22 cases). We classified the causes according to the stage at which they occurred and the type of error. Abortions after starting the milling procedure and abortions due to an interactive factor were the most common. We believe that this study can guide surgeons to effective decision making during robot-assisted arthroplasty.

Robotic surgery: from autonomous systems to intelligent tools

A brief history of robotic surgery is provided, which describes the transition from autonomous robots to hands-on systems that are under the direct control of the surgeon. An example of the latter is the Acrobot (for active-constraint robot) system used in orthopaedics, whilst soft-tissue surgery is illustrated by the daVinci telemanipulator system. Non-technological aspects of robotic surgery have often been a major impediment to their widespread clinical use. These are discussed in detail, together with the role of navigation systems, which are considered a major competitor to surgical robots. A detailed description is then given of a registration method for robots to achieve improved accuracy. Registration is a major source of error in robotic surgery, particularly in orthopaedics. The paper describes the design and clinical implementation of a novel method, coined the bounded registration method, applied to minimally invasive registration of the femur. Results of simulations which compare the performance of bounded registration with a standard implementation of the iterative closest point algorithm are also presented, alongside a description of their application in the Acrobot hands-on robot, used clinically for uni-condylar knee arthroplasty.

Robot-assisted unicompartmental knee arthroplasty

The outcomes of unicompartmental knee arthroplasties (UKAs) have demonstrated inconsistent long-term survival. We report the first clinical series of UKA using a semiactive robotic system for the implantation of an inlay unicondylar knee arthroplasty. Ten patients were selected for this study. Preoperative mechanical leg alignment values ranged from 0.3 degrees varus to 9.8 degrees varus. A haptic guidance system was used; a detailed description is given in the manuscript. The setup time for the robot was 41 minutes; intraoperative registration process, 7.5 minutes (6-13 minutes); skin incision, 8 cm; robot-assisted burring, 34.8 minutes (18-50 minutes); mean tourniquet time, 87.4 minutes (68-113 minutes); and overall operation time, 132 minutes (118-152 minutes). The planned and intraoperative tibiofemoral angle was within 1 degrees. The postoperative long leg axis radiographs were within 1.6 degrees. Haptic guidance in combination with a navigation module allows for precise planning and execution of both inlay components in UKA.

Robotic devices in surgery

Robotic devices are defined wich can be used as an aid to surgery. A classification system is proposed that reflects the manner of use and the safety of the systems. Typical benefits and problems of using robots are discussed, and a number of applications are reviewed. These cover "autonomous" systems, that involve no intervention from the surgeon; "hands-on" systems, that require the direct involvement of the surgeon; and "Master/Slave" (or Telemanipulator) systems, that are somewhere between these two and involve some degree of indirect surgeon activity. A number of predictions for the future of medical robotics are provided.

Robot-assisted total knee arthroplasty

Increasing evidence suggests performing total knee arthroplasty using computer navigation can lead to more accurate surgical positioning of the components and knee alignment compared to a conventional operating technique without computer assistance. The use of robotic technology could theoretically take this accuracy one level further because it uses navigation in combination with ultimate mechanical precision, which could eliminate or reduce the inevitable margin of error during mechanical preparation of the bony cuts of total knee arthroplasty by the surgeon. We prospectively followed 25 consecutive cases using an active surgical robot. The minimum followup was 5.1 years (mean, 5.5 years; range, 5.1-5.8 years). Our results demonstrate excellent implant positioning and alignment was achieved within the 1 degree error of neutral alignment in all three planes in all cases. Despite this technical precision, the excessive operating time required for the robotic implantation, the technical complexity of the system, and the extremely high operational costs have led us to abandon this procedure and direct our interest more toward smart semiactive robotic systems.

LEVEL OF EVIDENCE

Level IV, therapeutic study. See the Guidelines for Authors for a complete description of levels of evidence.

Influence of intra-operative joint gap on post-operative flexion angle in osteoarthritis patients undergoing posterior-stabilized total knee arthroplasty

Recently, we developed a new tensor for total knee arthroplasty (TKA) procedures enabling soft tissue balance assessment throughout the range of motion while reproducing post-operative joint alignment with the patello-femoral (PF) joint reduced and the tibiofemoral joint aligned. Using the tensor with a computer-assisted navigation system, we investigated the relationship between various intra-operative joint gap values and their post-operative flexion angles. An increased value during the extension to flexion gap and a decreased value during the flexion to deep flexion gap with PF joint reduced, not everted, showed an inverse correlation with post-operative knee flexion angle, not pre-operative flexion angle. In conclusion, understanding the characteristics of joint gap kinematics in posterior-stabilized TKA under physiological and reproducible joint conditions may enable the prediction of the post-operative flexion angle and help to determine the appropriate intra-operative joint gap.

Soft tissue balance measurement in anterior cruciate ligament-resected knee joint: cadaveric study as a model for cruciate-retaining total knee arthroplasty

BACKGROUND

The soft tissue balancing procedure remains a difficult issue during total knee arthroplasty, as much depends on the surgeon's "feel." Although computer-assisted navigation technology has been attempting to evaluate the joint stability, we have no definitive answer to an ideal soft tissue balance of the knee joint. The purpose of the present study was to determine the soft tissue balance in an anterior cruciate ligament (ACL)-resected normal knee joint throughout the range of knee flexion, which may provide reference data for cruciate-retaining total knee arthroplasty (TKA).

METHODS

We investigated joint stability in 10 ACL-resected normal cadaver knees throughout the range of flexion under consistent joint distraction force using a specially developed tensioning device for TKA. We measured both medial and lateral joint gaps as the separation distance between the articular surfaces with 40 lb (18.7 kg) of joint distraction force.

RESULTS

Both medial and lateral joint gaps at 0 degrees of flexion were significantly smaller than those at other flexion angles. The medial joint gap was almost consistent during knee flexion; however, the lateral joint gap increased with knee flexion and showed a significantly larger value at 60 degrees-120 degrees of flexion than the medial joint gap.

CONCLUSIONS

These characteristics of joint stability in the ACL-resected normal knee need to be taken into consideration in soft tissue balancing during cruciate-retaining TKA.

[The history and development of computer assisted orthopaedic surgery]

Computer assisted orthopaedic surgery (CAOS) was developed to improve the accuracy of surgical procedures. It has improved dramatically over the last years, being transformed from an experimental, laboratory procedure into a routine procedure theoretically available to every orthopaedic surgeon. The first field of application of computer assistance was neurosurgery. After the application of computer guided spinal surgery, the navigation of total hip and knee joints became available. Currently, several applications for computer assisted surgery are available. At the beginning of navigation, a preoperative CT-scan or several fluoroscopic images were necessary. The imageless systems allow the surgeon to digitize patient anatomy at the beginning of surgery without any preoperative imaging. The future of CAOS remains unknown, but there is no doubt that its importance will grow in the next 10 years, and that this technology will probably modify the conventional practice of orthopaedic surgery.

Robotic control in knee joint replacement surgery

A brief history of robotic systems in knee arthroplasty is provided. The place of autonomous robots is then discussed and compared to more recent ‘hands-on’ robotic systems that can be more cost effective. The case is made for robotic systems to have a clear justification, with improved benefits compared to those from cheaper navigation systems. A number of more recent, smaller, robot systems for knee arthroplasty are also described. A specific example is given of an active constraint medical robot, the ACROBOT system, used in a prospective randomized controlled trial of unicondylar robotic knee arthroplasty in which the robot was compared to conventional surgery. The results of the trial are presented together with a discussion of the need for measures of accuracy to be introduced so that the efficacy of the robotic surgery can be immediately identified, rather than have to wait for a number of years before long-term clinical improvements can be demonstrated.

Surgical navigation for total knee arthroplasty: A perspective

A new generation of surgical tools, known as surgical navigation systems, has been developed to help surgeons install implants more accurately and reproducibly. Navigation systems also record quantitative information such as joint range of motion, laxity, and kinematics intra-operatively. This article reviews the history of surgical navigation for total knee arthroplasty, the biomechanical principles associated with this technology, and the related clinical research studies. We describe how navigation has the potential to address three main challenges for total knee arthroplasty: ensuring excellent and consistent outcomes, treating younger and more physically active patients, and enabling less invasive surgery.

Very low-dose computed tomography for planning and outcome measurement in knee replacement

Surgeons need to be able to measure angles and distances in three dimensions in the planning and assessment of knee replacement. Computed tomography (CT) offers the accuracy needed but involves greater radiation exposure to patients than traditional long-leg standing radiographs, which give very little information outside the plane of the image.

There is considerable variation in CT radiation doses between research centres, scanning protocols and individual scanners, and ethics committees are rightly demanding more consistency in this area.

By refining the CT scanning protocol we have reduced the effective radiation dose received by the patient down to the equivalent of one long-leg standing radiograph. Because of this, it will be more acceptable to obtain the three-dimensional data set produced by CT scanning. Surgeons will be able to document the impact of implant position on outcome with greater precision.

Joint Gap Kinematics in Posterior-Stabilized Total Knee Arthroplasty Measured by a New Tensor With the Navigation System

Background: The management of soft tissue balance during surgery is essential for the success of total knee arthroplasty (TKA) but remains difficult, leaving it much to the surgeon’s feel. Previous assessments for soft tissue balance have been performed under unphysiological joint conditions, with patellar eversion and without the prosthesis only at extension and 90 deg of flexion. We therefore developed a new tensor for TKA procedures, enabling soft tissue balance assessment throughout the range of motion while reproducing postoperative joint alignment with the patellofemoral (PF) joint reduced and the tibiofemoral joint aligned. Our purpose in the present study was to clarify joint gap kinematics using the tensor with the CT-free computer assisted navigation system. Method of Approach: Joint gap kinematics, defined as joint gap change during knee motion, was evaluated during 30 consecutive, primary posterior-stabilized (PS) TKA with the navigation system in 30 osteoarthritic patients. Measurements were performed using a newly developed tensor, which enabled the measurement of the joint gap throughout the range of motion, including the joint conditions relevant after TKA with PF joint reduced and trial femoral component in place. Joint gap was assessed by the tensor at full extension, 5 deg, 10 deg, 15 deg, 30 deg, 45 deg, 60 deg, 90 deg, and 135 deg of flexion with the patella both everted and reduced. The navigation system was used to obtain the accuracy of implantations and to measure an accurate flexion angle of the knee during the intraoperative joint gap measurement. Results: Results showed that the joint gap varied depending on the knee flexion angle. Joint gap showed an accelerated decrease during full knee extension. With the PF joint everted, the joint gap increased throughout knee flexion. In contrast, the joint gap with the PF joint reduced increased with knee flexion but decreased after 60 deg of flexion. Conclusions: We clarified the characteristics of joint gap kinematics in PS TKA under physiological and reproducible joint conditions. Our findings can provide useful information for prosthetic design and selection and allow evaluation of surgical technique throughout the range of knee motion that may lead to consistent clinical outcomes after TKA.

Hands-on robotic unicompartmental knee replacement: a prospective, randomised controlled study of the acrobot system

We performed a prospective, randomised controlled trial of unicompartmental knee arthroplasty comparing the performance of the Acrobot system with conventional surgery. A total of 27 patients (28 knees) awaiting unicompartmental knee arthroplasty were randomly allocated to have the operation performed conventionally or with the assistance of the Acrobot. The primary outcome measurement was the angle of tibiofemoral alignment in the coronal plane, measured by CT. Other secondary parameters were evaluated and are reported. All of the Acrobot group had tibiofemoral alignment in the coronal plane within 2 degrees of the planned position, while only 40% of the conventional group achieved this level of accuracy. While the operations took longer, no adverse effects were noted, and there was a trend towards improvement in performance with increasing accuracy based on the Western Ontario and McMaster Universities Osteoarthritis Index and American Knee Society scores at six weeks and three months. The Acrobot device allows the surgeon to reproduce a pre-operative plan more reliably than is possible using conventional techniques which may have clinical advantages.

Computer-assisted total knee arthroplasty using patient-specific templating

Current techniques used for total knee arthroplasty rely on conventional instrumentation that violates the intramedullary canals. Accuracy of the instrumentation is questionable, and assembly and disposal of the numerous pieces is time consuming. Navigation techniques are more accurate, but their broad application is limited by cost and complexity. We aimed to prove a new concept of computer-assisted preoperative planning to provide patient-specific templates that can replace conventional instruments. Computed tomography-based planning was used to design two virtual templates. Using rapid prototyping technology, virtual templates were transferred into physical templates (cutting blocks) with surfaces that matched the distal femur and proximal tibia. We performed 45 total knee arthroplasties on 16 cadaveric and 29 plastic knees, including a comparative trial against conventional instrumentations. All operations were performed using patient-specific templates with no conventional instrumentations, intramedullary perforation, tracking, or registration. The mean time for bone cutting was 9 minutes with a surgical assistant and 11 minutes without an assistant. Computer-assisted analyses of six random computed tomography scans showed mean errors for alignment and bone resection within 1.7 degrees and 0.8 mm (maximum, 2.3 degrees and 1.2 mm, respectively). Patient-specific templates are a practical alternative to conventional instrumentations, but additional clinical validation is required before clinical use.

Robotic clinical trials of uni-condylar arthroplasty

A randomised clinical trial has been completed for uni-condylar arthroplasty. The trial, under the auspices of the UK MHRA, comprised 15 knees of patients undergoing conventional surgery, and 13 knees of patients who had robotic surgery using the Acrobot hands-on robotic system. The results of the trial were checked by comparing post-op CT scans with pre-op CT-based plans, and show a significant improvement in accuracy using the robot. The technical concept of the Acrobot approach is also described. Details of the complete system are outlined, including the pre-operative planner. The plan incorporates 3D CT models of the leg, together with CAD models of prostheses that can be used to plan the leg alignment, position the prostheses, plan the shape of the cuts required and generate the regions within which cuts must be constrained. The robotic system is also described, together with the methods for locating, clamping, cutting and monitoring the patient. An outline is given of the means by which the preoperative model is registered or aligned to the intra-operative position of the patient and of the robot, without the need for fiducial markers. Results of the randomised clinical trial are also discussed.

A hand-eye robotic model for total knee replacement surgery

This paper presents a hand-eye robotic model for total knee replacement (TKR) surgery. Unlike existent robot assisted TKR surgery, the proposed model is a surgical robot that combines with a movable hand-eye navigation system, which would use the full potential of both computer-assisted systems. Without using CT images and landmark pins in the patient's bones, it can directly measure the mechanical axis with high precision. This system provides a new approach of the minimally invasive surgery. Experiment results show that the proposed model is promising in the future application.

Robotic total knee arthroplasty: the accuracy of CT-based component placement

BACKGROUND

Accurate alignment of the components in total knee arthroplasty is important. By use of postoperative CT controls, we studied the ability of a robotic effector to accurately place and align total knee arthroplasty (TKA) components according to a purely CT-based preoperative plan.

PATIENTS AND METHODS

Robotic TKA was performed in 13 patients (6 men) with primary gonarthrosis. Locator screws were placed into femur and tibia under spinal anesthesia. A CT-scan including the femoral head, knee and ankle was performed. In the preoperative planning software, virtual components were positioned into the CT volume. In a second operation, the robot milled femur and tibia with a high-speed milling tool according to the preoperative plan. On the 10th day, CT controls were performed following the same protocol as preoperatively.

RESULTS

The mean deviation of the postoperative from the preoperatively planned mechanical axis was 0.2 degrees (95% CI: -0.1 degrees to 0.5 degrees ). The accuracy of angular component placement in frontal, sagittal and transverse planes was within +/-1.2 degrees , and the accuracy of linear component placement in mediolateral, dorsoventral and caudocranial directions was within +/-1.1 mm.

INTERPRETATION

Robotic TKA allows placement of components with unparalleled accuracy, but further development is mandatory to integrate soft-tissue balancing into the procedure and make it faster, easier and cheaper.

Robots in the operating theatre—chances and challenges

The use of surgical robots and manipulators is still being frequently discussed in the mass media as well as in the scientific community. Although it was already noted in 1985 that the first patient was treated by a joint team of robot and surgeon, today such systems are not routinely used. This can be explained by the high complexity of such systems and the often limited usability, but also, that it is difficult for surgeons to accept "automatic" machines. In this paper the possibilities and chances of robots and manipulators will be explained and it will be shown that robots will never work alone in the operating theatre as it is common in industry today. On the other hand, also limitations and challenges will be outlined. Therefore first a review on today's systems is given in different disciplines including oral- and cranio-maxillofacial surgery, then advantages and disadvantages are shown.

Computer-assisted orthopedic surgery

Computer-assisted surgery (CAS) utilizing robotic or image-guided technologies has been introduced into various orthopedic fields. Navigation and robotic systems are the most advanced parts of CAS, and their range of functions and applications is increasing. Surgical navigation is a visualization system that gives positional information about surgical tools or implants relative to a target organ (bone) on a computer display. There are three types of surgical planning that involve navigation systems. One makes use of volumetric images, such as computed tomography, magnetic resonance imaging, or ultrasound echograms. Another makes use of intraoperative fluoroscopic images. The last type makes use of kinetic information about joints or morphometric information about the target bones obtained intraoperatively. Systems that involve these planning methods are called volumetric image-based navigation, fluoroscopic navigation, and imageless navigation, respectively. To overcome the inaccuracy of hand-controlled positioning of surgical tools, three robotic systems have been developed. One type directs a cutting guide block or a drilling guide sleeve, with surgeons sliding a bone saw or a drill bit through the guide instrument to execute a surgical action. Another type constrains the range of movement of a surgical tool held by a robot arm such as ACROBOT. The last type is an active system, such as ROBODOC or CASPAR, which directs a milling device automatically according to preoperative planning. These CAS systems, their potential, and their limitations are reviewed here. Future technologies and future directions of CAS that will help provide improved patient outcomes in a cost-effective manner are also discussed.