Computer assisted knee replacement

Computer-assisted navigation increases precision of component placement in total knee arthroplasty

In our clinical study, 200 total knee arthroplasties were evaluated to compare the use of the OrthoPilot system with conventional mechanical instrumentation. Long-term outcome of total knee replacement depends mainly on the accuracy of implant positioning and restoration of the mechanical leg axis. Our experience was that navigation could achieve a greater degree of accuracy concerning the aforementioned aspects. Among 513 primary-inserted total knee replacements, 100 navigated knees were compared with 100 conventionally implanted knees after matching the two groups of patients by gender, body mass index, age, preoperative deformities, radiographic findings, and operating time. Three weeks after surgery, the radiographic results were significantly better in the computer-assisted group compared with the results in the conventional group when we assessed component positioning in four axes. Only the sagittal tibial component angle was not significantly different. Total knee arthroplasty using the OrthoPilot system led to increased precision of tibial and femoral component positioning in comparison with hand-guided replacement surgery. An additional 10 minutes of operating time was acceptable. Navigation-specific complications were not seen, and the number of outliers decreased. Because computer navigation in orthopaedics is a new technology, data regarding long-term outcomes are not available.

LEVEL OF EVIDENCE

Diagnostic study, Level II-1 (retrospective study). See the Guidelines for Authors for a complete description of levels of evidence.

The use of computer-assisted surgical navigation to prevent malalignment in unicompartmental knee arthroplasty

We reviewed the outcome of 30 consecutive primary unicompartmental knee arthroplasties (UKAs) performed by a single surgeon over a 26-month period. All operations were performed to treat osteoarthritis of the medial compartment of the knee. Fifteen Allegretto (Sulzer, Winterthur, Switzerland) UKAs were implanted without computer navigation whereas 15 EIUS (Stryker-Howmedica, Allendale, NJ) UKAs were implanted using navigation. The patients were assessed clinically using the Oxford knee score and radiologically using long-leg weight-bearing films and non-weight-bearing computed tomography leg alignment films. No patients operated on were lost to follow-up. Unicompartmental knee arthroplasty performed with computer-assisted surgical navigation resulted in a more accurate and reproducible limb alignment than UKA performed without surgical navigation.

An algorithm for locating the center of the ankle joint in knee navigation surgery

The primary aim of computer-assisted knee arthroplasty is to improve the alignment of the implanted prostheses. Accurate component alignment is dependent on the establishment of accurate anatomical reference points. Current techniques for establishing the center of the ankle joint, especially in the coronal plane, rely solely on clinical judgment in relation to the position of the center of the ankle joint. The aim of this study was to determine if an algorithm could be developed, based on establishing the most prominent points on the medial and lateral malleoli on 3D CT scans, to accurately and reproducibly establish the position of the center of the ankle joint. To determine this, images of 20 ankles were obtained and axial, coronal, and sagittal 2D reconstructions were manipulated on a workstation. Two observers independently performed relevant measurements and calculations. The calculated data was found to be reproducible with a very small standard deviation in each plane. This algorithm is able to provide accurate measurements of the ankle joint in knee navigation surgery. Caution must be exercised in anatomically abnormal ankles, as the calculations of the ankle center were found to be significantly different.

Prosthetic alignment and sizing in computer-assisted total knee arthroplasty

We implanted 60 posterior stabilized total knee prostheses (P.F.C. Sigma, DePuy, Warsaw, USA). In 30 cases, we used a CT-free navigation system (Vector Vision, Brain LAB, Heimstetten, Germany), and in 30 matched-paired controls, we used a conventional manual implantation. We compared postoperative long-leg radiographs in the two groups. The results revealed a significant difference in favor of navigation. In addition, we compared the preoperative anteroposterior dimension of the femoral condyle with the postoperative value. While there were no significant differences in the preoperative anteroposterior dimension of the femoral condyle between the two groups, the postoperative value in the navigation group was significantly larger than that of the preoperative value. Therefore, surgeons using navigation systems should guard against the possibility of oversizing when determining the size of the femoral component.

Kniegelenksendoprothetik

Today the most common application in the field of computer-assisted surgery is navigated total knee arthroplasty. During the last 5 years the imageless kinematic navigation systems have gained wide acceptance. As several prospective randomized studies could show, the standard deviation of the mechanical axis is reduced significantly by these techniques. However, the direction of the mechanical axis is only one factor which influences the long-term results of total knee arthroplasty. Further important factors are ligament balancing and position of the femoral and tibial components in all three planes. Up to now no studies have been able to show a significantly better functional result, a more rapid recovery, or a decreased complication rate. Drawbacks of the navigation systems are the additional costs and the additional operation time between 15 and 20 min. Therefore, navigated total knee arthroplasty is not yet a standard procedure, but this technique is well on the way to becoming the gold standard in the future.

New indications for computer-assisted surgery: tumor resection in the pelvis

The resection of recurrent malignant pelvic tumors was supported by a commercially available navigation system in three patients. Preoperatively three-dimensional images from the pelvis were obtained by computed tomography or magnetic resonance imaging to identify the tumor extension. During surgery navigated tools oriented the surgeon to excise the tumor with adequate virtual margins. Navigation was helpful for tumor identification in one patient with a recurrent presacral mesenchymal chondrosarcoma. In the other two patients the tumor resection in the bone was done with three-dimensional observation of the osteotomies in the sacrum. In all three patients the histopathologic analysis confirmed that the neoplasms were excised accurately within their margins. We think that computer-assisted surgery is a potential method to increase the accuracy of tumor resections.

[Integration of modern technologies in therapy of sarcomas of the pelvis. Computer-assisted hemipelvectomy and implantation of a "custom-made" Bonit gentamycin coated partial pelvic prosthesis]

The resection of primary malignancies in the pelvis is technically demanding as organs and structures are to be preserved and reconstruction of the defect as well as the postoperative function and rehabilitation are dependent on an optimal prosthesis. We present two patients with a sarcoma of the pelvis where for the first time a structured concept of technology integration led to a press-fit implantation of a hemipelvic prosthesis. This concept includes the design and production of a "custom-made" prosthesis as a hemipelvic substitute and the coating of this prosthesis with Bonit, a second-generation calcium phosphate, and gentamycin in watery solution. The tumor resection was done with computer-assisted surgery based on computed tomographies (CT) of the pelvis model done by rapid prototyping rather than on the CT of the patients' pelvis. With this procedure the presurgically simulated resection could be executed precisely with complete resection of the tumors and an accuracy which allowed an exact implantation of the prosthesis. The course was uneventful with primary healing and no sign of an infection or loosening after 6 months.

Use of the Cusum technique for evaluation of a CT-based navigation system for total knee replacement

Most of the early failures of total knee replacements are related to technical flaws. Conventional ancillary devices achieve good alignment in the frontal plane in only an average of 75% of total knee replacements. Computer-assisted surgery may improve the technical quality of implantation surgery. The aim of our study was to evaluate the use of computer-assisted surgery using a quality control process. Seventy-eight total knee arthroplasties were done with a CT-based computer-assisted surgery system. The outcomes studied were alignment of the lower limb, implant positioning, and operative time. The target for alignment was 180 degrees +/- 3 degrees. Cusum analysis showed that the three outcomes were controlled during the study. The cusum test identified any existing outliers. Because few data were available at the beginning of this study regarding computer-assisted surgery for total knee replacement, a randomized study was not relevant. However, a control of the procedure was mandatory. The cusum technique allowed continuous evaluation of the performance of the new procedure, and is a useful tool in assessing new technology. The results of this study showed that it is possible to do a randomized study to determine if computer-assisted surgery can improve the technical result of total knee replacement.

Low reproducibility of the intra-operative measurement of the transepicondylar axis during total knee replacement

BACKGROUND

The transepicondylar axis is often used for positioning of the femoral component in knee replacement.

METHODS

We studied the reproducibility of the intra-operative palpation of the transepicondylar axis for rotational alignment of the femoral component in 20 total knee replacement (TKR) implantations with a non-image-based navigation system. 2 surgeons defined the transepicondylar axis 3 times each without changing the reference plane.

RESULTS

The angle between the reference plane and the transepicondylar axis was measured by the navigation system. The mean intra-observer ranges of variation were 5 degrees and 6 degrees for both surgeons, with a maximum of 15 degrees. The mean inter-observer range of variation was 9 degrees, with a maximum of 15 degrees. Variations occurred in either internal or external rotation. Intra-observer agreement was considered good for one surgeon and poor for the other. There was no agreement between the two observers.

INTERPRETATION

To define the rotational alignment of the femoral component of a TKR according to the intra-operative palpation of the transepicondylar axis may not be as reproducible as expected. However, the exact effect of this variability on the outcome after TKR should be studied.

Radiological results of image-based and non-image-based computer-assisted total knee arthroplasty

Restoration of the mechanical limb axis and accurate component orientation are two major factors affecting the long-term results after total knee replacement (TKR). Different navigation systems are available to improve the outcome. Image-based systems require pre-operative CT scans, while non-image-based systems gain all necessary information intra-operatively during a registration process. We studied 130 patients who received a TKR either using the CT-based (Knee 1.1) or the CT-free module (CT-free Knee 1.0) of the BrainLAB Vector-Vision Navigation System. Post-operative leg alignment and component orientation was determined on long-leg coronal and lateral X-rays. Sixty of 65 patients in the CT-based group and 63/65 patients in the CT-free group had a post-operative leg axis between 3 degrees varus/valgus. No significant differences were found for varus/valgus orientation of the femoral and tibial components.

In vivo evaluation of a computer planning system for total knee arthroplasty

In this paper we report the analysis of a preoperative computer planner for total knee arthroplasty (TKA), when applied to a set of patients by different surgeons. The goal of this work was to study the repeatability and reliability of computer planning, the ergonomy of the system, identify the useful features of this technique and the possible drawbacks. The planning system allows the surgeon to interactively stimulate the implant on a 3D model of the patient computed from computerized tomography (CT) images. In this paper, we summarize the main results of a series of evaluation trials carried out by four surgeons on ten patients. We measured the variability of the main application parameters, evaluated the efficacy and usefulness of the automatic prosthesis positioning provided by the system and carefully analyzed the system ergonomy. The system showed satisfactory repeatability in the interactive definition of the essential parameters. Moreover it showed to be easy to use, consistent, focused on the most important parameters and able to improve the surgeon's insight and confidence in the outcome. Further steps include clinical studies and direct comparison with standard technique.

How accurate is current TKR instrumentation?

Mechanical total knee replacement (TKR) alignment systems have fundamental limitations that limit their ultimate accuracy. This study uses an image-free computer-assisted navigation system to assess the accuracy of a currently available conventional mechanical, intramedullary instrumentation system. Mechanical instrumentation allows reasonably accurate and reproducible (within 3 degrees varus-valgus) frontal and sagittal limb alignment. There is a tendency to leave the knee in slight flexion, to hyperextend the femoral component and to posteriorly tilt the tibial implant with mechanical AP guides. There also is a consistent tendency to internally rotate the femoral implant. Although almost all of the 20 TKRs resulted in final limb alignment within 3 degrees of the frontal and sagittal mechanical axes, only four TKRs were done in which all of the measured steps were within 3 degrees of the optimal positions. If implant longevity, pain-relief, and function are related to the accuracy with which TKRs are done, this study emphasizes that current mechanical instrumentation does not result in a high incidence of accuracy when each step of the procedure is measured. Computer-assisted techniques permit measurement of the steps of the TKRs procedure with a high degree (error < 1 degree) of accuracy.

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.

Total knee arthroplasty implanted with and without kinematic navigation

Between September 2000 and February 2002 we inserted 120 total knee arthroplasties. In 60 patients we used the standard technique, and in 60 patients we used the OrthoPilot navigation system. Postoperatively all patients had standing long radiographs of the lower extremity from the hip joint to the ankle. We considered the ideal value of the anatomic lateral tibiofemoral angle (LTFA) to be 174 degrees. In the standard group the mean value of LTFA was 174.9 degrees and in the navigation group 174.3 degrees. A deviation between 0 degrees and 2 degrees from the ideal value was seen in 42 cases in the standard group and in 53 cases in the navigation group. In the standard group 18 cases had a deviation of more than 2.1 degrees, whereas there were only seven cases in the navigation group with a deviation exceeding 2.1 degrees. There were no complications related to the use of the navigation system. The system affords a possibility to place femoral and tibial components precisely with less axis deviation than with the conventional technique.

Computer assisted orthopaedic and trauma surgery. State of the art and future perspectives

In recent years computer technologies have become more and more integrated in surgical procedures. The potential advantages of computer assisted surgery (CAS) are: increase of accuracy of surgical interventions, less invasive operations, better planning and simulation and reduction of radiation exposure for both patient and surgeon. After introduction of CAS in neurosurgery, the clinical applications of this technique expanded also into trauma and orthopaedic surgery. The first application of this new technique in orthopaedic and trauma surgery was for placement of lumbar pedicle screws. After its introduction into spine surgery, CAS was applied in other fields of orthopaedic surgery like hip, knee and skeletal trauma surgery. In this article the technical background and the various clinical applications and future perspectives of computer assisted orthopaedic and trauma surgery are outlined.

Unicompartmental knee prosthesis implantation with a non-image-based navigation system: rationale, technique, case-control comparative study with a conventional instrumented implantation

The accuracy of implantation is an accepted prognostic factor for the long-term survival of unicompartmental knee prostheses (UKP). We developed a non-image-guided navigation system for UKP implantation without any extramedullary or intramedullary guiding device. The 30 patients operated on with the navigation system (group A) were matched to 30 patients operated on with the conventional technique (group B) using age, sex, body mass index, preoperative coronal mechanical femorotibial angle, and severity of the preoperative degenerative changes. All patients had a complete radiological examination in the first 3 months after the index procedure, with anteroposterior and lateral plain knee radiographs and anteroposterior and lateral long leg radiographs. Coronal femorotibial mechanical angle and both coronal and sagittal orientations of the femoral and tibial components were measured. There were no significant differences in the mean numerical values of all measured angles except for the sagittal orientation of the tibial component, with a significant excessive posterior tibial slope in group B. There was a significant increase in the rate of prostheses implanted in the desired angular range for all criteria except the coronal mechanical femorotibial angle in group A. An optimal implantation with all optimal items was obtained by 18 cases in group A and 6 cases in group B. Navigated implantation of a UKP with the used, non-image-based system improved the accuracy of the radiological implantation without any significant inconvenience and with little change in the conventional operative technique. The only inconvenience was a 20-min longer operative time. This improvement could be related to a longer survival of such implanted prostheses.

Bone cutting errors in total knee arthroplasty

Although achieving precise implant alignment is crucial for producing good outcomes in total knee arthroplasty, the contribution of the bone-cutting process to overall variability has not been measured previously. Eight orthopaedic surgeons with varying amounts of total knee arthroplasty experience performed 85 resections on 19 cadaver femora and tibiae, and the planes of the resulting cut surfaces were compared with the guide planes. Varus-valgus alignment variability ranged from 0.4 degrees to 0.8 degrees SD for expert and trainee surgeons. Sagittal variability was approximately 1.3 degrees SD for both surgeon groups. Slotted cutting guides reduced the variability and eliminated the bias in the sagittal plane for experienced surgeons but did not improve significantly frontal plane alignment variability. Guide movement contributed 10% to 40% of the total cutting error, depending on cut and guide type.

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

Total knee replacement (TKR) is a common procedure for treatment of severe gonarthrosis, but the outcome may be unsatisfactory due to primary malalignment of the prosthetic components. In order to improve precision and accuracy of this surgical procedure, a commercial robotic surgical system (CASPAR) has been adapted to assist the surgeon in the preoperative planning and intraoperative execution of TKR. So far, 70 patients with idiopathic gonarthrosis were successfully treated with a robot-assisted technique in our institution. No major adverse events related to the use of the robotic system have been observed. The mean difference between preoperatively planned and postoperatively achieved tibiofemoral alignment was 0.8 degrees (0-4.1 degrees ) in the robotic group vs. 2.6 degrees (0-7 degrees ) in a manually operated historical control group of 50 patients. A clear advantage of robot-assisted TKR seems to be the ability to execute a highly precise preoperative plan based on computed tomography (CT) scans. Due to better alignment of the prosthetic components and improved bone-implant fit, implant loosening is anticipated to be diminished which may be most evident in non-cemented prostheses. Current disadvantages such as the need for placement of fiducial markers, increased operating times and higher overall costs have to be resolved in the future.

Robotics for surgery

Robotic technology is enhancing surgery through improved precision, stability, and dexterity. In image-guided procedures, robots use magnetic resonance and computed tomography image data to guide instruments to the treatment site. This requires new algorithms and user interfaces for planning procedures; it also requires sensors for registering the patient's anatomy with the preoperative image data. Minimally invasive procedures use remotely controlled robots that allow the surgeon to work inside the patient's body without making large incisions. Specialized mechanical designs and sensing technologies are needed to maximize dexterity under these access constraints. Robots have applications in many surgical specialties. In neurosurgery, image-guided robots can biopsy brain lesions with minimal damage to adjacent tissue. In orthopedic surgery, robots are routinely used to shape the femur to precisely fit prosthetic hip joint replacements. Robotic systems are also under development for closed-chest heart bypass, for microsurgical procedures in ophthalmology, and for surgical training and simulation. Although results from initial clinical experience is positive, issues of clinician acceptance, high capital costs, performance validation, and safety remain to be addressed.

CRIGOS: a compact robot for image-guided orthopedic surgery

The CRIGOS (compact robot for image-guided orthopedic surgery) project was set up for the development of a compact surgical robot system for image-guided orthopedic surgery based on user requirements. The modular system comprises a compact parallel robot and a software system for planning of the surgical interventions and for supervision of the robotic device. Because it is not sufficient to consider only technical aspects in order to improve in clinical routine the therapeutic outcome of conventional interventions, a user-centered and task-oriented design process has been developed which also takes human factors into account. The design process for the CRIGOS system was started from requirement analysis of various orthopedic interventions using information gathered from literature, questionnaires, and workshops with domain experts. This resulted in identification of conventional interventions for which the robotic system would improve the medical and procedural quality. A system design concept has been elaborated which includes definitions of components, functionalities, and interfaces. Approaches to the acquisition of calibrated X-rays will be presented in the paper together with design and evaluation of a first human-computer interface. Finally, the first labtype parallel robot based on low-cost standard components is presented together with the first evaluation results concerning positioning accuracy.

An overlapping subzone technique for MR-based elastic property reconstruction

A finite element-based nonlinear inversion scheme for magnetic resonance (MR) elastography is detailed. The algorithm operates on small overlapping subzones of the total region of interest, processed in a hierarchical order as determined by progressive error minimization. This zoned approach allows for a high degree of spatial discretization, taking advantage of the data-rich environment afforded by the MR. The inversion technique is tested in simulation under high-noise conditions (15% random noise applied to the displacement data) with both complicated user-defined stiffness distributions and realistic tissue geometries obtained by thresholding MR image slices. In both cases the process has proved successful and has been capable of discerning small inclusions near 4 mm in diameter. Magn Reson Med 42:779-786, 1999.