A virtual fluoroscopy system and its use for image guidance in unicompartmental knee surgery.

The C-arm fluoroscope is an indispensable intraoperative 2D imaging device for orthopaedic surgery. However, its frequent use in an operation presents a significant radiation hazard to the theatre staff and patient. A recent technique known as virtual fluoroscopy (VF) enhances the fluoroscope's capability for image guided surgery by tracking optically the position of the C-arm, surgical instruments and the patient. Virtuality is achieved by overlay of surgical instruments onto one or more previously captured fluoroscopic images. A key benefit of VF is that it reduces considerably the radiation hazard. This paper reports on a new VF technique for tracking and calibration of the fluoroscopic C-arm. Also reported is the use of our VF system to provide a new image guided technique for the accurate placement of the femoral component of unicompartmental knee prosthesis.

The development of an evaluation framework for the quantitative assessment of computer-assisted surgery and augmented reality accuracy performance.

The paper describes a framework for the quantitative assessment of errors within a computer assisted surgical system. The framework diagrammatically describes the registration process and simulates the error propagation chain based on the assumption that errors can be described through the use of a normal distribution model. The projection error associated with a fluoroscopic image intensifier is given as an example.

3D registration through pseudo x-ray image generation.

Registration of a pre operative plan with the intra operative position of the patient is still a largely unsolved problem. Current techniques generally require fiducials, either artificial or anatomic, to achieve the registration solution. Invariably these fiducials require implantation and/or direct digitisation. The technique described in this paper requires no digitisation or implantation of fiducials, but instead relies on the shape and form of the anatomy through a fully automated image comparison process. A pseudo image, generated from a virtual image intensifier's view of a CT dataset, is intra operatively compared with a real x-ray image. The principle is to align the virtual with the real image intensifier. The technique is an extension to the work undertaken by Domergue [1] and based on original ideas by Weese [4].

3D registration through pseudo x-ray image generation.

One of the less effective processes within current Computer Assisted Surgery systems, utilizing pre-operative planning, is the registration of the plan with the intra-operative position of the patient. The technique described in this paper requires no digitisation of anatomical features or fiducial markers but instead relies on image matching between pseudo and real x-ray images generated by a virtual and a real image intensifier respectively. The technique is an extension to the work undertaken by Weese [1].

A technique for very high accuracy image intensifier calibration.

Accurate characterisation of the image distortion within a fluoroscopic image intensifier is critical if it forms the vision component of an image guided surgical system. By considering non-linear dynamic distortion it is possible to greatly increase the accuracy of the image intensifier, although at the cost of some image quality.

Review of orthopaedic manipulator arms.

Trajectory planning and implementation forms a substantial part of current and future orthopaedic practice. This type of surgery is governed by a basic orthopaedic principle [1] which involves the placement of a surgical tool at a specific site within a region, via a trajectory which is planned from X-ray based 2D images and governed by 3D anatomical constraints. The accuracy and safety of procedures utilising the basic orthopaedic principle depends on the surgeon's judgement, experience, ability to integrate images, utilisation of intra-operative X-ray, knowledge of anatomical-biomechanical constraints and eye hand dexterity. The surgeon must remain as the responsible medical expert in charge of the overall system. At the same time the surgeon covets the accuracy offered by Computer Assisted Surgery including a manipulator. A summary of current inadequacies of manipulators indicates that the main drivers for future work are that accuracy is critical in close contact with the environment, safety concerns dictate manipulator geometry and technological limitations are many. In any effort to develop an optimal manipulator to guide surgical instruments and tools it is an obvious first step to review and categorise current manipulators. The aim of this paper is to review all aspects of manipulator design against the five main criteria of ergonomics; safety; accuracy; sterility and measurable benefits such as reduced operative time, reduced surgical trauma and improved clinical results.

A computer assisted orthopaedic surgical system for distal locking of intramedullary nails.

This paper presents a prototype system for computer assisted surgery, the purpose of which is to assist orthopaedic surgeons when performing distal locking of intramedullary nails. This system comprises three components, namely: an Intelligent Image Intensifier, a Trajectory Tactician and an Intelligent Trajectory Guide. The Intelligent Image Intensifier is an X-ray vision system that provides accurate X-ray images. Such images enable the Trajectory Tactician software to analyse the operation site and calculate the trajectory required for a screw to lock an intramedullary nail. This involves the capture of two X-ray images from which are extracted the projections of the nail's edge boundaries and its distal locking holes. Using an analytical mathematical model of the nail, the position and orientation of the nail is determined. The trajectory is then implemented by the surgeon using the Intelligent Trajectory Guide. Evaluation in the laboratory suggests that the system is capable of reliably inserting a locking screw into an intramedullary nail. The rapidity with which this computer assisted method achieves locking should benefit both patient and surgeon by reducing radiation dosage and the length of time required to lock a nail.