Providing visual information to validate 2-D to 3-D registration.

This paper addresses a key issue of providing clinicians with visual information to validate the accuracy of 2-D/3-D registration for robot-assisted total hip replacement (THR) surgery. Although numerous registration approaches have been presented, the topic of registration validation has scarcely been addressed in the literature. In practice, clinicians rely on post-operative X-rays to assess the accuracy of implant placement. Motivated by this, we simulate a set of post-operative X-ray images by superimposing the implant positioned pre-operatively onto the intra-operatively collected and calibrated images of the femur, through a transformation computed by the 2-D/3-D registration. With these images, a judgment on the registration accuracy can be made. In addition, this paper introduces methods for superimposing pre-operative data on intra-operative X-ray images that were not corrected for distortion, by applying the same image distortion to the data. This paper also introduces a new framework for incorporating surface normals in the objective function for registration. A comparison between marker-based and image-based registration is conducted. The advantage of our approach is that the simulated post-operative X-ray images are very familiar to clinicians and, therefore, easy for them to interpret. As an added benefit, this technique provides new means for comparing the marker-based and image-based registration for robot-assisted THR surgery. This approach can be extended to other interventions where intra-operative images are used for registration.

A C-arm fluoroscopy-guided progressive cut refinement strategy using a surgical robot.

We describe a new method to cut a precise, high-quality femoral cavity in Revision Total Hip Replacement surgery (RTHR) using a surgical robot and an intra-operative C-arm fluoroscope. With respect to previous approaches, our method contains several new features. (1) We describe a novel checkerboard plate designed to correct the geometric distortion within fluoroscopic images. Unlike previous distortion correction devices, the plate does not completely obscure any part of the image, and the distortion correction algorithm works well even when there are some overlaid objects in the field of view. (2) Also included are a novel corkscrew fiducial object designed to be integrated with the robot end-effector, and a 6D pose estimation algorithm based on the two-dimensional (2D) projection of the corkscrew, used in robot-imager registration and imager co-registration. (3) In addition, we develop a cavity location algorithm, which utilizes image subtraction and 2D anatomy contour registration techniques. (4) Finally, we propose a progressive cut refinement strategy, which progressively improves the robot registration during the procedure. We have conducted several experiments, in both simulated and in vitro environments. The results indicate that our strategy is a promising method for precise orthopedic procedures like total hip replacement.

Computer-integrated revision total hip replacement surgery: concept and preliminary results.

This paper describes an ongoing project to develop a computer-integrated system to assist surgeons in revision total hip replacement (RTHR) surgery. In RTHR surgery, a failing orthopedic hip implant, typically cemented, is replaced with a new one by removing the old implant, removing the cement and fitting a new implant into an enlarged canal broached in the femur. RTHR surgery is a difficult procedure fraught with technical challenges and a high incidence of complications. The goals of the computer-based system are the significant reduction of cement removal labor and time, the elimination of cortical wall penetration and femur fracture, the improved positioning and fit of the new implant resulting from precise, high-quality canal milling and the reduction of bone sacrificed to fit the new implant. Our starting points are the ROBODOC system for primary hip replacement surgery and the manual RTHR surgical protocol. We first discuss the main difficulties of computer-integrated RTHR surgery and identify key issues and possible solutions. We then describe possible system architectures and protocols for preoperative planning and intraoperative execution. We present a summary of methods and preliminary results in CT image metal artifact removal, interactive cement cut-volume definition and cement machining, anatomy-based registration using fluoroscopic X-ray images and clinical trials using an extended RTHR version of ROBODOC. We conclude with a summary of lessons learned and a discussion of current and future work.

Anatomy-based registration of CT-scan and intraoperative X-ray images for guiding a surgical robot.

We describe new methods for rigid registration of a preoperative computed tomography (CT)-scan image to a set of intraoperative X-ray fluoroscopic images, for guiding a surgical robot to its trajectory planned from CT. Our goal is to perform the registration, i.e., compute a rotation and translation of one data set with respect to the other to within a prescribed accuracy, based upon bony anatomy only, without external fiducial markers. With respect to previous approaches, the following aspects are new: 1) we correct the geometric distortion in fluoroscopic images and calibrate them directly with respect to the robot by affixing to it a new calibration device designed as a radiolucent rod with embedded metallic markers, and by moving the device along two planes, while radiographs are being acquired at regular intervals; 2) the registration uses an algorithm for computing the best transformation between a set of lines in three space, the (intraoperative) X-ray paths, and a set of points on the surface of the bone (imaged preoperatively), in a statistically robust fashion, using the Cayley parameterization of a rotation; and 3) to find corresponding sets of points to the X-ray paths on the surfaces, our new approach consists of extracting the surface apparent contours for a given viewpoint, as a set of closed three-dimensional nonplanar curves, before registering the apparent contours to X-ray paths. Aside from algorithms, there are a number of major technical difficulties associated with engineering a clinically viable system using anatomy and image-based registration. To detect and solve them, we have so far conducted two experiments with the surgical robot in an operating room (OR), using CT and fluoroscopic image data of a cadaver bone, and attempting to faithfully simulate clinical conditions. Such experiments indicate that intraoperative X-ray-based registration is a promising alternative to marker-based registration for clinical use with our proposed method.

Safety considerations in a surgical robot.

This paper describes the safety features of the ROBODOC Surgical Assistant System, an image-driven robotic system which has been used to perform Total Hip Replacement surgery. These features include a dedicated processor for continuous monitoring of system status, shared data areas (dual-ported RAM), and external sensors (force-torque sensor, redundant positional encoders, and bone motion monitor).

Development of a surgical robot for cementless total hip arthroplasty.

The long-term success of cementless total hip arthroplasty (THA) may depend on bone ingrowth into the porous-fixation surfaces of the implant. The ingrowth process is facilitated when the surgeon achieves a satisfactory fit for the prosthesis. Clinically or roentgenographically visible failure and persistent thigh pain after cementless THA remain significant problems, both of which may be alleviated by more precise preparation of the femoral canal and selection of an appropriately sized prosthesis. The objective of this study was to obtain an exact fit for the prosthesis through the use of an image-directed surgical robot for femoral canal preparation.