Constantinos Nikou

An image overlay system for medical data visualization.

Abstract Image Overlay is a computer display technique which superimposes computer images over the user’s direct view of the real world. The images are transformed in real-time so they appear to the user to be an integral part of the surrounding environment. By using Image Overlay with three-dimensional medical images such as CT reconstructions, a surgeon can visualize the data ‘in-vivo’, exactly positioned within the patient’s anatomy, and potentially enhance the surgeon’s ability to perform a complex procedure. This paper describes prototype Image Overlay systems and initial experimental results from those systems.

Surgical navigation for total hip replacement with the use of hipnav

HipNav, an image-guided surgical navigation system, is presented. The system was developed to measure and guide the placement of prosthetic components in total hip replacement surgery (THR), it incorporates a 3-dimensional preoperative planner with a simulator and an intraoperative surgical navigator. Coupling optimized preoperative planning with accurate surgical navigation will assist the surgeon in properly orienting the components, minimizing the risk of impingement and dislocation. Intraoperatively, the system uses image-guided tools to assist in accurate placement of the acetabular cup. The acetabular implant is placed in the planned position with the aid of a simple “aim-and-shoot” interface. The actual measurements of version and abduction are also provided. The use of this new class of operative sensors has been incorporated into a regular surgical routine. There are few additional steps necessary, therefore, for the image-guided procedure, which does not add significantly to the total time of surgery. We expect that these tools will lead to less invasive and more accurate THR surgery and directly relate patient outcomes to measured surgical practice.

A Classification Proposal for Computer-Assisted Knee Systems

Computer-Assisted Surgery (CAS) combines various enabling technologies to help surgeons meet and exceed quality requirements in performing knee surgery. Emerging CAS systems for the knee already include applications for TKR, ACL reconstruction and tibial osteotomies. In this paper we propose a general scheme to classify computer-assisted knee systems currently in use and under development, with an emphasis on surgical navigation systems. A literature review and available commercialized product analyses allowed us to sort the different computer-assisted systems in several categories. We proposed a classification scheme relies upon medical criteria instead of solely technical criteria (such as localizer properties and computer specifics). New concepts in computer-assisted surgery can easily fit into this classification framework.

Augmented reality imaging technology for orthopaedic surgery

Augmented or hybrid reality is a display technique that combines the real world with the virtual world; it permits digital images or preoperative planning information to be combined with the surgeons view of the real world. This technique gives surgeons “x-ray vision” without the use of ionizing radiation, allowing them to visualize parts of the patients anatomy that are not typically exposed during a surgical procedure. Augmented reality can increase the surgeons view of unexposed bones and other tissues during surgery while using less invasive techniques. These visualization devices will also allow the surgeon to view preoperatively determined locations of incisions and real-time medical images with proper spatial alignment during surgery. Augmented reality will eventually enable less invasive and minimally invasive surgical techniques that are not technologically feasible at this time. In this article, the augmented reality technique is described and illustrated, showing examples of already existing medical systems that use this display technology. Possible orthopaedic applications of augmented reality are presented as well as current research and practical issues associated with making augmented reality a commonplace tool in surgical practice.

Description of Anatomic Coordinate Systems and Rationale for Use in an Image-Guided Total Hip Replacement System

Lowering the risks of a surgical procedure is extremely important, especially for high-volume procedures such as total hip replacement. Significant work has been done to study total hip replacement procedures and provide the surgeon with techniques and tools to achieve better patient outcomes. Computer-assisted intervention allows surgeons to “close the loop” in medical research, allowing the surgeon to preoperatively plan, interoperatively navigate, and postoperatively analyze medical procedures, then use the results to repeat or improve the quality of future procedures. In order to expedite the cycle of planning, execution, and analysis amoung multiple research groups, standards for description, measurement, and procedure are necessary. In this work, the authors preset the coordinate systems used in their suite of computer-based tools for planning, executing, and evaluating the total hip replacement procedure. Rationales for the choices of each system are given along with experimental data which support the definitions.

Surgical Navigation for THR: A Report on Clinical Trial Utilizing HipNav

Computer-assisted Total Hip Replacement (THR) surgery using the HipNav surgical navigational system was evaluated. This summary reports on the first 100 HipNav clinical trial patients and focuses on: 1) patient demographics, 2) post-operative clinical outcomes, 3) incision length measurements, 4) mechanical guide measures, and 5) functional pelvic tilt measurements. Results from this clinical trial have shown no system-related complications, an improvement in post-operative clinical outcomes, reductions in soft tissue dissection, an unreliability of traditional mechanical alignment guides, and a variability of pelvic orientation during functional activity.

Range of motion after total hip arthroplasty: experimental verification of the analytical simulator

Dislocation following total hip replacement surgery represents a significant cause of early failure, incurring additional medical costs. The causes of dislocation are multifactorial and are related to surgical approach, soft tissue tension, prosthetic design, and most important, orientation of components. This paper describes experimental verification of our analytical approach for predicting implant impingement and dislocation. Once fully developed and tested, this analytical methodology could be used as a preoperative simulation tool that will present surgeons with information about the “safe” range of motion and chance of dislocation based on selected component positions, allowing for the surgical plan to be optimized based on this criterion. Coupled with a computer-assisted clinical system for precise implant positioning, this approach could significantly reduce the postoperative risk of dislocation, maximize “safe” range of motion and minimize impingement.

Calibration Method for Determining the Physical Location of the Ultrasound Image Plane

This paper describes a calibration method for determining the physical location of the ultrasound (US) image plane relative to a rigidly attached 3D position sensor. A calibrated US probe can measure the 3D spatial location of anatomic structures relative to a global coordinate system. The calibration is performed by aiming the US probe at a calibration target containing a known point (1 mm diameter sphere) in physical space. This point is repeatedly collected at various locations in the US image plane to produce the calibration dataset. An idealized model of the collection process is used to eliminate outliers from the calibration dataset and also to examine the theoretical accuracy limits of this method. The results demonstrate accurate and robust calibration of the 3D spatial relationship between the US image plane and the 3D position sensor.

Precision freehand sculpting for unicondylar knee replacement: design and experimental validation.

Abstract Precision freehand sculpting (PFS), is a hand-held semi-active robotic technology for bone shaping that works within the surgical navigation framework. PFS can alternate between two control modes – one based on control of exposure of the cutting bur and another based on the control of the speed of the cutting bur. In this study we evaluate the performance of PFS in preparing the femoral bone surface for unicondylar knee replacement (UKR). The experiment is designed to prepare a synthetic bone for UKR. The implant was a modified commercial design that allows accurate measurement of the implant position after it is placed on the prepared bone surface. The distal and anterior-distal facets were cut with a 5 mm cylindrical bur using exposure control. The posterior facet and the post holes were cut using a 6-mm spherical bur using speed control. Three users cut five specimens each. The performance was evaluated in terms of the implant fit and the performance time. The average cut times for the first two cuts combined were 4:35 min, and for the posterior cut 3:26 min. The average distance from the planned implant position was 0.54 mm (SD 0.23 mm) and the average angular difference was 1.08° (SD 0.53°).

POP: Preoperative Planning and Simulation Software for Total Hip Replacement Surgery

Proper implant placement during total hip replacement (THR) surgery has been shown to reduce short and long term complication including dislocations, accelerated wear, and loosening of the implants. Correct implant orientation is the most important factor in preventing impingement, which is a major cause of dislocation and wear following total hip replacement surgery. However, proper implant orientation is also dependent upon patient-specific factors such as pelvic anatomy bone coverage and level of femoral osteotomy, and can affect leg lengths and offsets. This paper describes a preoperative planner for THR that enables the surgeon to determine the optimal placement of the femoral and acetabular components for THR taking all of these factors into account. Coupled with a computer-assisted clinical system for precise implant positioning, this approach could significantly improve patient outcomes and lower costs.