Robot-patient registration for optical tracker-free robotic fracture reduction surgery.

BACKGROUND AND OBJECTIVE: Image-guided robotic surgery for fracture reduction is a medical procedure in which surgeons control a surgical robot to align the fractured bones by using a navigation system that shows the rotation and distance of bone movement. In such robotic surgeries, it is necessary to estimate the relationship between the robot and patient (bone), a task known as robot-patient registration, to realize the navigation. Through the registration, a fracture state in real-world can be simulated in virtual space of the navigation system. METHODS: This paper proposes an approach to realize robot-patient registration for an optical-tracker-free robotic fracture-reduction system. Instead of the optical tracker which is a three-dimensional position localizer, X-ray images are used to realize the robot-patient registration, combining the relationship of both the robot and patient with regards to C-arm. The proposed method consists of two steps of registration, where initial registration is followed by refined registration which adopts particle swarm optimization with the minimum cross-reprojection error based on bidirectional X-ray images. To address the unrecognizable features due to interference between the robot and bone, we also developed attachable robot features. The allocated robot features could be clearly extracted from the X-ray images, and precise registration could be realized through the particle swarm optimization. RESULTS: The proposed method was evaluated in phantom and ex-vivo experiments involving a caprine cadaver. For the phantom experiments, the average translational and rotational errors were 1.88 mm and 2.45°, respectively, and the corresponding errors in the ex vivo experiments were 2.64 mm and 3.32° The results demonstrated the effectiveness of the proposed robot-patient registration. CONCLUSIONS: The proposed method enable to estimate the three-dimensional relationship between fractured bones in real-world by using only two-dimensional images, and the relationship is accurately simulated in virtual reality for the navigation. Therefore, a reduction procedure for successful treatment of bone fractures in image-guided robotic surgery can be expected with the aid of the proposed registration method.

A shape-partitioned statistical shape model for highly deformed femurs using X-ray images.

To develop a patient-specific 3 D reconstruction of a femur modeled using the statistical shape model (SSM) and X-ray images, it is assumed that the target shape is not outside the range of variations allowed by the SSM built from a training dataset. We propose the shape-partitioned statistical shape model (SPSSM) to cover significant variations in the target shape. This model can divide a shape into several segments of anatomical interest. We break up the eigenvector matrix into the corresponding representative matrices for the SPSSM by preserving the relevant rows of the original matrix without segmenting the shape and building an independent SSM for each segment. To quantify the reconstruction error of the proposed method, we generated two groups of deformation models of the femur which cannot be easily represented by the conventional SSM. One group of femurs had an anteversion angle deformation, and the other group of femurs had two different scales of the femoral head. Each experiment was performed using the leave-one-out method for twelve femurs. When the femoral head was rotated by 30°, the average reconstruction error of the conventional SSM was 5.34 mm, which was reduced to 3.82 mm for the proposed SPSSM. When the femoral head size was decreased by 20%, the average reconstruction error of the SSM was 4.70 mm, which was reduced to 3.56 mm for the SPSSM. When the femoral head size was increased by 20%, the average reconstruction error of the SSM was 4.28 mm, which was reduced to 3.10 mm for the SPSSM. The experimental results for the two groups of deformation models showed that the proposed SPSSM outperformed the conventional SSM.

Novel C-arm-based planning robotic spinal surgery in a cadaver model using quantitative accuracy assessment methodology.

BACKGROUND: This preclinical study emulating the clinical environment quantitatively analysed the accuracy of pedicle screw insertion using a navigated robotic system. METHODS: Pedicle screws were placed from T7 to L5 in the whole-body form of a cadaver. After the insertion of multiple artificial markers into each vertebra, errors between the planned insertion path and the inserted screw were quantified using the Gertzbein-Robbins system (GRS) and offset calculation. RESULTS: A total of 22 screws were placed. Almost all (95.45% [21/22]) were classified as GRS A or B, while one (4.55%) was GRS C. The mean and standard deviations of entry, tip, and angular offset were 1.78 ± 0.94 mm, 2.30 ± 1.01 mm, and 2.64 ± 1.05°, respectively. CONCLUSIONS: This study demonstrated that pedicle screw insertion using a navigated robotic system had high accuracy and safety. A future clinical study is necessary to validate our findings.

Heterogeneous Stitching of X-ray Images According to Homographic Evaluation.

The C-arm X-ray system is a common intraoperative imaging modality used to observe the state of a fractured bone in orthopedic surgery. Using C-arm, the bone fragments are aligned during surgery, and their lengths and angles with respect to the entire bone are measured to verify the fracture reduction. Since the field-of-view of the C-arm is too narrow to visualize the entire bone, a panoramic X-ray image is utilized to enlarge it by stitching multiple images. To achieve X-ray image stitching with feature detection, the extraction of accurate and densely matched features within the overlap region between images is imperative. However, since the features are highly affected by the properties and sizes of the overlap regions in consecutive X-ray images, the accuracy and density of matched features cannot be guaranteed. To solve this problem, a heterogeneous stitching of X-ray images was proposed. This heterogeneous stitching was completed according to the overlap region based on homographic evaluation. To acquire sufficiently matched features within the limited overlap region, integrated feature detection was used to estimate a homography. The homography was then evaluated to confirm its accuracy. When the estimated homography was incorrect, local regions around the matched feature were derived from integrated feature detection and substituted to re-estimate the homography. Successful X-ray image stitching of the C-arm was achieved by estimating the optimal homography for each image. Based on phantom and ex-vivo experiments using the proposed method, we confirmed a panoramic X-ray image construction that was robust compared to the conventional methods.

Navigation-assisted anchor insertion in shoulder arthroscopy: a validity study.

BACKGROUND: This study aimed to compare conventional and navigation-assisted arthroscopic rotator cuff repair in terms of anchor screw insertion. METHODS: The surgical performance of five operators while using the conventional and proposed navigation-assisted systems in a phantom surgical model and cadaveric shoulders were compared. The participating operators were divided into two groups, the expert group (n = 3) and the novice group (n = 2). In the phantom model, the experimental tasks included anchor insertion in the rotator cuff footprint and sutures retrieval. A motion analysis camera system was used to track the surgeons' hand movements. The surgical performance metric included the total path length, number of movements, and surgical duration. In cadaveric experiments, the repeatability and reproducibility of the anchor insertion angle were compared among the three experts, and the feasibility of the navigation-assisted anchor insertion was validated. RESULTS: No significant differences in the total path length, number of movements, and time taken were found between the conventional and proposed systems in the phantom model. In cadaveric experiments, however, the clustering of the anchor insertion angle indicated that the proposed system enabled both novice and expert operators to reproducibly insert the anchor with an angle close to the predetermined target angle, resulting in an angle error of < 2° (P = 0.0002). CONCLUSION: The proposed navigation-assisted system improved the surgical performance from a novice level to an expert level. All the experts achieved high repeatability and reproducibility for anchor insertion. The navigation-assisted system may help surgeons, including those who are inexperienced, easily familiarize themselves to of suture anchors insertion in the right direction by providing better guidance for anchor orientation. LEVEL OF EVIDENCE: A retrospective study (level 2).

Simultaneous Optimization of Patient-Image Registration and Hand-Eye Calibration for Accurate Augmented Reality in Surgery.

OBJECTIVE: Augmented reality (AR) navigation using a position sensor in endoscopic surgeries relies on the quality of patient-image registration and hand-eye calibration. Conventional methods collect the necessary data to compute two output transformation matrices separately. However, the AR display setting during surgery generally differs from that during preoperative processes. Although conventional methods can identify optimal solutions under initial conditions, AR display errors are unavoidable during surgery owing to the inherent computational complexity of AR processes, such as error accumulation over successive matrix multiplications, and tracking errors of position sensor. METHODS: We propose the simultaneous optimization of patient-image registration and hand-eye calibration in an AR environment before surgery. The relationship between the endoscope and a virtual object to overlay is first calculated using an endoscopic image, which also functions as a reference during optimization. After including the tracking information from the position sensor, patient-image registration and hand-eye calibration are optimized in terms of least-squares. RESULTS: Experiments with synthetic data verify that the proposed method is less sensitive to computation and tracking errors. A phantom experiment with a position sensor is also conducted. The accuracy of the proposed method is significantly higher than that of the conventional method. CONCLUSION: The AR accuracy of the proposed method is compared with those of the conventional ones, and the superiority of the proposed method is verified. SIGNIFICANCE: This study demonstrates that the proposed method exhibits substantial potential for improving AR navigation accuracy.

Compact Bone Surgery Robot With a High-Resolution and High-Rigidity Remote Center of Motion Mechanism.

OBJECTIVE: Two important and difficult tasks during a bone drilling procedure are guiding the orientation of the drilling axis toward the target and maintaining the orientation against the drilling force. To accomplish these tasks, a remote center of motion (RCM) mechanism is adopted to align the orientation of the drilling axis without changing the entry point. However, existing RCM mechanisms do not provide sufficient resolution and rigidity to address hard tissue cases. METHODS: We propose a new type of RCM mechanism that uses two sets of linear actuators and a gearless-arc guide to have a high resolution and rigidity. In addition, we designed a single motor-based drilling mechanism based on rolling friction. To achieve automatic control of the guiding and drilling process, we incorporated a computer-tomography-based navigation system that was equipped with an optical tracking system. RESULTS: The effectiveness of the integrated robotic system was demonstrated through a series of experiments and ex vivo drilling tests on swine femurs. The proposed robotic system withstood a maximum external force of 51 N to maintain the joint angle, and the average drilling error was less than 1.2 mm. CONCLUSION: This study confirms the feasibility of the proposed bone drilling robotic system with a high-resolution and high-rigidity RCM mechanism. SIGNIFICANCE: This drilling system is the first successful trial based on an RCM mechanism and a single motor-based drilling mechanism, reducing the footprint and required motors with respect to previous bone surgical robots.

Wire-driven flexible manipulator with constrained spherical joints for minimally invasive surgery.

PURPOSE: One of the main factors that affect the rigidity of flexible robots is the twist deformation because of the external force exerted on the end effector. Another important factor that affects accuracy is the fact that such robots do not have a constant curvature. The conventional kinematic model assumes that the curvature is constant; however, in reality, it is not. To improve the rigidity and accuracy of flexible robots used in minimally invasive surgery via preventing the twist deformation while ensuring a constant curvature, we propose a novel flexible manipulator with ball-constrained spherical (BCS) joints and a spring. METHODS: The BCS joints are used to prevent the twist deformation in the flexible robot. The joints have two degrees of freedom (DOFs), which limit the rotation about the axial direction. The rotation is limited because the ball that is inserted into a BCS joint can move only along the ball guide. To obtain a constant curvature, springs are installed among the BCS joints. The springs receive the uniform compression force generated among the joints, thus achieving a constant curvature. The proposed BCS joint is designed based on the diameter of the forceps, desired workspace, and desired bending angle. RESULTS: To evaluate the proposed mechanism, three experiments were performed using a 20-mm-diameter prototype consisting of 13 BCS joints with a two-DOF motion. The experimental results showed that the prototype can realize a constant curvature with a mean error of 0.21°, which can support up to 5 N with no apparent twist deformation. CONCLUSIONS: We developed a flexible manipulator with BCS joints for minimally invasive surgery. The proposed mechanism is anticipated to help prevent the twist deformation of the robot and realize a constant curvature. Accordingly, it is expected that rigidity is improved to ensure accuracy.

CT-based Navigation System Using a Patient-Specific Instrument for Femoral Component Positioning: An Experimental in vitro Study with a Sawbone Model.

PURPOSE: The intraoperative version of the femoral component is usually determined by visual appraisal of the stem position relative to the distal femoral condylar axis. However, several studies have suggested that a surgeon's visual assessment of the stem position has a high probability of misinterpretation. We developed a computed tomography (CT)-based navigation system with a patient-specific instrument (PSI) capable of three-dimensional (3D) printing and investigated its accuracy and consistency in comparison to the conventional technique of visual assessment of the stem position. MATERIALS AND METHODS: A CT scan of a femur sawbone model was performed, and pre-experimental planning was completed. We conducted 30 femoral neck osteotomies using the conventional technique and another 30 femoral neck osteotomies using the proposed technique. The femoral medullary canals were identified in both groups using a box chisel. RESULTS: For the absolute deviation between the measured and planned values, the mean two-dimensional anteversions of the proposed and conventional techniques were 1.41° and 4.78°, while their mean 3D anteversions were 1.15° and 3.31°. The mean θ1, θ2, θ3, and d, all of which are parameters for evaluating femoral neck osteotomy, were 2.93°, 1.96°, 5.29°, and 0.48 mm for the proposed technique and 4.26°, 3.17°, 4.43°, and 3.15 mm for the conventional technique, respectively. CONCLUSION: The CT-based navigation system with PSI was more accurate and consistent than the conventional technique for assessment of stem position. Therefore, it can be used to reduce the frequency of incorrect assessments of the stem position among surgeons and to help with accurate determination of stem anteversion.

Perspective pinhole model with planar source for augmented reality surgical navigation based on C-arm imaging.

PURPOSE: For augmented reality surgical navigation based on C-arm imaging, accuracy of the overlaid augmented reality onto the X-ray image is imperative. However, overlay displacement is generated when a conventional pinhole model describing a geometric relationship of a normal camera is adopted for C-arm calibration. Thus, a modified model for C-arm calibration is proposed to reduce this displacement, which is essential for accurate surgical navigation. METHOD: Based on the analysis of displacement pattern generated for three-dimensional objects, we assumed that displacement originated by moving the X-ray source position according to the depth. In the proposed method, X-ray source movement was modeled as variable intrinsic parameters and represented in the pinhole model by replacing the point source with a planar source. RESULTS: The improvement which represents a reduced displacement was verified by comparing overlay accuracy for augmented reality surgical navigation between the conventional and proposed methods. The proposed method achieved more accurate overlay on the X-ray image in spatial position as well as depth of the object volume. CONCLUSION: We validated that intrinsic parameters that describe the source position were dependent on depth for a three-dimensional object and showed that displacement can be reduced and become independent of depth by using the proposed planar source model.

Augmented reality-based electrode guidance system for reliable electroencephalography.

BACKGROUND: In longitudinal electroencephalography (EEG) studies, repeatable electrode positioning is essential for reliable EEG assessment. Conventional methods use anatomical landmarks as fiducial locations for the electrode placement. Since the landmarks are manually identified, the EEG assessment is inevitably unreliable because of individual variations among the subjects and the examiners. To overcome this unreliability, an augmented reality (AR) visualization-based electrode guidance system was proposed. METHODS: The proposed electrode guidance system is based on AR visualization to replace the manual electrode positioning. After scanning and registration of the facial surface of a subject by an RGB-D camera, the AR of the initial electrode positions as reference positions is overlapped with the current electrode positions in real time. Thus, it can guide the position of the subsequently placed electrodes with high repeatability. RESULTS: The experimental results with the phantom show that the repeatability of the electrode positioning was improved compared to that of the conventional 10-20 positioning system. CONCLUSION: The proposed AR guidance system improves the electrode positioning performance with a cost-effective system, which uses only RGB-D camera. This system can be used as an alternative to the international 10-20 system.

A cadaver study of mastoidectomy using an image-guided human-robot collaborative control system.

Objective: Surgical precision would be better achieved with the development of an anatomical monitoring and controlling robot system than by traditional surgery techniques alone. We evaluated the feasibility of robot-assisted mastoidectomy in terms of duration, precision, and safety. Study Design: Human cadaveric study. Materials and Methods: We developed a multi-degree-of-freedom robot system for a surgical drill with a balancing arm. The drill system is manipulated by the surgeon, the motion of the drill burr is monitored by the image-guided system, and the brake is controlled by the robotic system. The system also includes an alarm as well as the brake to help avoid unexpected damage to vital structures. Experimental mastoidectomy was performed in 11 temporal bones of six cadavers. Parameters including duration and safety were assessed, as well as intraoperative damage, which was judged via pre- and post-operative computed tomography. Results: The duration of mastoidectomy in our study was comparable with that required for chronic otitis media patients. Although minor damage, such as dura exposure without tearing, was noted, no critical damage to the facial nerve or other important structures was observed. When the brake system was set to 1 mm from the facial nerve, the postoperative average bone thicknesses of the facial nerve was 1.39, 1.41, 1.22, 1.41, and 1.55 mm in the lateral, posterior pyramidal and anterior, lateral, and posterior mastoid portions, respectively. Conclusion: Mastoidectomy can be successfully performed using our robot-assisted system while maintaining a pre-set limit of 1 mm in most cases. This system may thus be useful for more inexperienced surgeons. Level of Evidence: NA.

A portable surgical navigation device to display resection planes for bone tumor surgery.

INTRODUCTION: Surgical navigation has been used in musculoskeletal tumor surgical procedures to improve the precision of tumor resection. Despite the favorable attributes of navigation-assisted surgery, conventional systems do not display the resection margin in real time, and preoperative manual input is required. In addition, navigation systems are often expensive and complex, and this has limited their widespread use. In this study, we propose an augmented reality surgical navigation system that uses a tablet personal computer with no external tracking system. MATERIAL AND METHODS: We realized a real-time safety margin display based on three-dimensional dilation. The resection plane induced by the safety margin is updated in real time according to the direction of sawing. The minimum separation between the saw and the resection plane is also calculated and displayed. The surgeon can resect bone tumors accurately by referring to the resection plane and the minimum separation updated in real time. RESULTS: The effectiveness of the system was demonstrated with experiments on pig pelvises. When the desired resection margin was 10 mm, the measured resection margin was 9.85 ± 1.02 mm. CONCLUSIONS: The proposed method exhibits sufficient accuracy and convenience for use in bone tumor resection. It also has favorable practical applicability due to its low cost and portability.