3D visualization and open planning platform in virtual fluoroscopy.

Typically virtual fluoroscopy systems display the tracked instruments as a projected shadow on a number of 2D x-ray images completely missing the depth information of the third dimension. This paper describes an extra tool for 3D reconstruction in virtual fluoroscopy which is useful to clarify the position of instruments or anatomy and can be used in planning and assessing surgical procedure without further x-ray images. Two examples are given: displaced subtrochanteric fracture and slipped upper femoral epiphysis is presented.

Factors affecting targeting using the computer assisted orthopaedic surgery system (CAOSS).

An advantage of CAOS over traditional surgery is improved precision of implant position and trajectories in 3D space. However, the implementation of these trajectories often adds an extra step to the operation that increases operative time and requires extra training. This paper reports a study of variation in time-to-task and learning curve in performing a standard task of targeting in 3D space using Hull's CAOSS. It shows that time-to-task can be reduced by replacing a 3D targeting task with multiple independent 2D targeting tasks whilst potentially reducing targeting error. Based on this better understanding of targeting a novel jig was developed for performing dynamic hip Screw (DHS) insertion using CAOSS that would provide improved targeting performance by the surgeon.

Stenting for bilateral congenital choanal atresia--a new technique.

We describe a new nasal stent for the treatment of bilateral congenital choanal atresia. The stent is made up of reinforced endotracheal tube mounted on a portex carrier tube. It potentially causes less internal crusting and stent blockage and is secured without sutures. It remains patent for at least 4 weeks. We have used the stent successfully in six patients between 1998 and 2004 at Leeds General Infirmary and present the data collected retrospectively. The current practice in the UK for treatment and stenting for congenital choanal atresia was investigated by a prospective internet based questionnaire sent to 18 consultant paediatric otolaryngologists of whom 12 (67%) responded. Their experience and results are reported. The literature has been reviewed.

Computer assisted orthopaedic surgical system for insertion of distal locking screws in intra-medullary nails: a valid and reliable navigation system.

The insertion of distal locking screws is a difficult task in intra-medullary (IM) nailing operations of long bones and contributes a significant proportion to the overall operating time. The current technique to insert these screws uses numerous fluoroscopic images and depends on the skills and expertise of the surgeon. The Computer Assisted Orthopaedic Surgical System (CAOSS) was developed to assist orthopaedic surgeons in these operations. The laboratory based test results for insertion of distal locking screws in IM nailing procedures are presented and discussed in terms of accuracy and as part of the validation process to introduce new CAOS procedures into clinical use. This study shows that CAOSS in IM nailing is robust and reliable. Positional accuracy was shown to be within 0.3 mm and angular accuracy within 0.2 degrees with femoral IM nail. CAOSS was also shown to be very reliable and accurate at different angles of distal screws in fluoroscopic image space.

Recovery of distal hole axis in intramedullary nail trajectory planning.

In intramedullary nail (IMN) surgical operations, one of the main efforts for surgeons is to find the axes of two distal holes. Two distal holes on an IMN, which are inside the intramedullary canal of a patient's femur, can only be seen in a lateral X-ray view. For the standard surgical procedure, the localization of the distal hole axes is a trial-and-error process which results in a long surgical time and large dose of X-ray exposure. In this paper, an algorithm to derive the three-dimensional position and orientation of the distal hole axis was developed. The algorithm first derives the nail axis through two X-ray images. Then the distal hole axis is calculated through projecting back the hole boundary on the X-ray image from a lateral view to three-dimensional space. A least-squares method is used to determine the centres of the front hole and the back hole through iteration. The algorithm has been tested with real data and it was robust.

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.

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.