Hip2Norm: an object-oriented cross-platform program for 3D analysis of hip joint morphology using 2D pelvic radiographs.

We developed an object-oriented cross-platform program to perform three-dimensional (3D) analysis of hip joint morphology using two-dimensional (2D) anteroposterior (AP) pelvic radiographs. Landmarks extracted from 2D AP pelvic radiographs and optionally an additional lateral pelvic X-ray were combined with a cone beam projection model to reconstruct 3D hip joints. Since individual pelvic orientation can vary considerably, a method for standardizing pelvic orientation was implemented to determine the absolute tilt/rotation. The evaluation of anatomically morphologic differences was achieved by reconstructing the projected acetabular rim and the measured hip parameters as if obtained in a standardized neutral orientation. The program had been successfully used to interactively objectify acetabular version in hips with femoro-acetabular impingement or developmental dysplasia. Hip(2)Norm is written in object-oriented programming language C++ using cross-platform software Qt (TrollTech, Oslo, Norway) for graphical user interface (GUI) and is transportable to any platform.

Range of motion in anterior femoroacetabular impingement.

The range of motion of normal hips and hips with femoroacetabular impingement relative to some specific anatomic reference landmarks is unknown. We therefore described: (1) the range of motion pattern relative to landmarks; (2) the location of the impingement zones in normal and impinging hips; and (3) the influence of surgical débridement on the range of motion. We used a previously developed and validated noninvasive 3-D CT-based method for kinematic hip analysis to compare the range of motion pattern, the location of impingement, and the effect of virtual surgical reconstruction in 28 hips with anterior femoroacetabular impingement and a control group of 33 normal hips. Hips with femoroacetabular impingement had decreased flexion, internal rotation, and abduction. Internal rotation decreased with increasing flexion and adduction. The calculated impingement zones were localized in the anterosuperior quadrant of the acetabulum and were similar in the two groups and in impingement subgroups. The average improvement of internal rotation was 5.4 degrees for pincer hips, 8.5 degrees for cam hips, and 15.7 degrees for mixed impingement. This method helps the surgeon quantify the severity of impingement and choose the appropriate treatment option; it provides a basis for future image-guided surgical reconstruction in femoroacetabular impingement with less invasive techniques.

[The foundations of computer assisted surgery]. / Grundlagen der computerassistierten Chirurgie.

Using navigation systems in general orthopaedic surgery and, in particular, knee replacement is becoming more and more accepted. This paper describes the basic technological concepts of modern computer assisted surgical systems. It explains the variation in currently available systems and outlines research activities that will potentially influence future products. In general, each navigation system is defined by three components: (1) the therapeutic object is the anatomical structure that is operated on using the navigation system, (2) the virtual object represents an image of the therapeutic object, with radiological images or computer generated models potentially being used, and (3) last but not least, the navigator acquires the spatial position and orientation of instruments and anatomy thus providing the necessary data to replay surgical action in real-time on the navigation system's screen.

Estimation of pelvic tilt on anteroposterior X-rays--a comparison of six parameters.

OBJECTIVE: To compare six different parameters described in literature for estimation of pelvic tilt on an anteroposterior pelvic radiograph and to create a simple nomogram for tilt correction of prosthetic cup version in total hip arthroplasty. DESIGN: Simultaneous anteroposterior and lateral pelvic radiographs are taken routinely in our institution and were analyzed prospectively. The different parameters (including three distances and three ratios) were measured and compared to the actual pelvic tilt on the lateral radiograph using simple linear regression analysis. PATIENTS: One hundred and four consecutive patients (41 men, 63 women with a mean age of 31.7 years, SD 9.2 years, range 15.7-59.1 years) were studied. RESULTS: The strongest correlation between pelvic tilt and one of the six parameters for both men and women was the distance between the upper border of the symphysis and the sacrococcygeal joint. The correlation coefficient was 0.68 for men (P<0.001) and 0.61 for women (P<0.001). Based on this linear correlation, a nomogram was created that enables fast, tilt-corrected cup version measurements in clinical routine use. CONCLUSION: This simple method for correcting variations in pelvic tilt on plain radiographs can potentially improve the radiologist's ability to diagnose and interpret malformations of the acetabulum (particularly acetabular retroversion and excessive acetabular overcoverage) and post-operative orientation of the prosthetic acetabulum.

Tilt and rotation correction of acetabular version on pelvic radiographs.

Anteroposterior pelvic radiographs are the gold standard of imaging for mechanical hip problems. However, correct interpretation is difficult because the projected morphologic features of the acetabulum and nearly all routinely used hip parameters depend on individual pelvic position, which can vary considerably during acquisition. We developed software that recreates the projected acetabular rim and the measured hip parameters as if obtained in a standardized orientation. The vertical and horizontal distances between two easy identifiable points were used as indicators of tilt and rotation. These points were the middle of the sacrococcygeal joint and the middle of the upper border of the symphyseal gap. Calibration of the indicators was achieved by means of serial pelvic radiographs of 20 cadaver pelves. Validation of tilt indicator in 100 patients and a theoretical error analysis revealed that for accurate tilt prediction an additional one-time lateral radiograph of the pelvis is mandatory. The computer-assisted method allows standardized evaluation of anatomic morphologic differences of femoral coverage (dysplasia, retroversion), making their clinical relevance for development of early osteoarthritis more valuable.

A semi-automatic orthopedic implant management tool for Computer Assisted planning, navigation and simulation: from XML implant database to unified implant access interface.

Nowadays, Computer Assisted Orthopedic planning and navigation systems have been recognized as an important tool that helps surgeons. Various systems have been developed so far, but most of them use non-standard formalisms and techniques. As a result there are no standard concepts for implant and tool management or data formats to store information for use in 3D planning and navigation systems. We addressed these limitations and developed a practical and generic solution which brings benefits for surgeons, implant manufacturers and CAS application developers. We developed a virtual implant database containing geometrical as well as calibration information for orthopedic implants and instruments with a focus on Trauma. This database has been successfully tested with various applications in client/server mode. Nevertheless, the implant information is not static because periodically manufacturers revise implants, resulting in the removal of some implants and addition of new ones. To ease the implant management in respect to implant life cycle, we developed an implant management tool which helps end-users to manage their implants. Currently, this tool allows the addition of new implants, modification of existing ones, deletion of obsolete implants, export of a given implant and also creation of backups. Our implant management system has been successfully tested in the laboratory and gave very promising results. It makes it possible to fill the current existing gap between CAS system, implant manufacturers, hospitals and surgeons.

New orthopaedic implant management tool for computer-assisted planning, navigation, and simulation: from implant CAD files to a standardized XML-based implant database.

Computer-Assisted Orthopaedic Surgery (CAOS) has made much progress over the last 10 years. Navigation systems have been recognized as important tools that help surgeons, and various such systems have been developed. A disadvantage of these systems is that they use non-standard formalisms and techniques. As a result, there are no standard concepts for implant and tool management or data formats to store information for use in 3D planning and navigation. We addressed these limitations and developed a practical and generic solution that offers benefits for surgeons, implant manufacturers, and CAS application developers. We developed a virtual implant database containing geometrical as well as calibration information for orthopedic implants and instruments, with a focus on trauma. This database has been successfully tested for various applications in the client/server mode. The implant information is not static, however, because manufacturers periodically revise their implants, resulting in the deletion of some implants and the introduction of new ones. Tracking these continuous changes and keeping CAS systems up to date is a tedious task if done manually. This leads to additional costs for system development, and some errors are inevitably generated due to the huge amount of information that has to be processed. To ease management with respect to implant life cycle, we developed a tool to assist end-users (surgeons, hospitals, CAS system providers, and implant manufacturers) in managing their implants. Our system can be used for pre-operative planning and intra-operative navigation, and also for any surgical simulation involving orthopedic implants. Currently, this tool allows addition of new implants, modification of existing ones, deletion of obsolete implants, export of a given implant, and also creation of backups. Our implant management system has been successfully tested in the laboratory with very promising results. It makes it possible to fill the current gap that exists between the CAS system and implant manufacturers, hospitals, and surgeons.

Computer-assisted pelvic surgery: an in vitro study of two registration protocols.

An in vitro study was done to test the accuracy and functionality of computer-assisted surgery in pelvic orthopaedic surgery. The study was done on two fresh hips from one cadaver. In each hip, 10 titanium marker screws were inserted through standard pelvic osteotomy incisions. After a computed tomography scan was obtained the data were introduced into the navigation system. For the accuracy measurements the location of the center of the spherical heads of the marker screws was determined relative to a reference base attached to the pelvis using a special pointer that corresponded to the spherical head of the screws. A randomized trial was done with two surgeons to test the accuracy of two different anatomy-based registration protocols. The deviation between the virtual position of the marker screws in the pelvis, calculated by the computer after each anatomy based registration, and the real position were compared for each registration. Accuracy is not only related to the distance of the computed tomography slices and the necessary computed tomography field of view but also depends on the location of the point on the pelvis.

Computer assisted screw insertion into real 3D rapid prototyping pelvis models.

OBJECTIVE: Show the use of computer navigation in exact screw positioning in the different pelvic bones. BACKGROUND: Computer assisted pedicle screw insertion in the spine is an established procedure. Screw fixation is also used in highly difficult pelvic and hip surgery (arthroplasty revision surgery and tumor surgery). DESIGN: Insert as long screws as possible with computer navigation into the different bones of the pelvis and compare these results with a non-computer controlled method. METHODS: The computer navigation was done with the system of Medivision (Oberdorf, Switzerland), the software was SurgiGATE 2.1. Optically controlled spine instruments and a special calibrated drill were used. The screw insertion with and without computer navigation took place in seven real rapid prototyping pelvis models matched by pairs. Three screws were inserted into the Os ileum, one into the Os pubis and one into the Os ischium. The length of the inserted screws were measured and compared using routine statistic methods. RESULTS: The mean screw length with vs. without computer navigation was 8.9 vs. 5.7 cm in the Os ileum (P=0.0001), 6.0 vs. 4.2 cm in the Os pubis (P=0.01) and 4.3 vs. 3.9 cm in the Os ischium (not significant). CONCLUSIONS: The use of computer navigation allows for the insertion of longer screws into the bones of the pelvis (more exact positioning), which requires a more precise original point of entry and direction of the drill (vector). RELEVANCE: The insertion of fixation screws in highly difficult pelvic and hip surgery (revision arthroplasty, tumor surgery) are another field for the use of computer navigation.

Frameless optical computer-aided tracking of a microscope for otorhinology and skull base surgery.

OBJECTIVES: To integrate a digitally controlled operating microscope without a laser autofocus system into a frameless optical computer-aided surgery system and to test the accuracy and usability of this system in otorhinological surgery. DESIGN: Experimental study and case series. SETTING: Department of Oto-Rhino-Laryngology, Head and Neck Surgery, Inselspital, and the Maurice E. Müller Institute for Biomechanics, University of Bern, Bern, Switzerland. PATIENTS: Eight computer-aided microscopic surgical procedures were performed between January and October 2000 on patients with various diseases of the anterior and lateral skull base. RESULTS: The practical accuracy of the navigated microscope on the lateral side of a cadaver skull was 2.27 +/- 0.25 mm and on the anterior side of the same skull was 2.07 +/- 0.35 mm. In all 8 cases of computer-aided microscopic surgery, no complications occurred. Clinical inaccuracy was 2 to 3 mm. CONCLUSION: Integration of a low-cost, non-laser autofocus microscope into our computer-aided surgery system was successfully performed and offers surgeons the ability to combine the precise optics of the operating microscope with the localization power of a computer-aided system.

A fast impingement detection algorithm for computer-aided orthopedic surgery.

OBJECTIVE: For simulation of computer-aided orthopedic interventions, the detection of impingement between parts of the patient's anatomy and/or implants is often of key importance. The impingement (collision) detection methods used in the existing literature seem to be unsuitable for two reasons. First, a polyhedral approximation of an anatomical model is not appropriate because medical images are quite irregular and are geometrically complex. Second, geometric and temporal coherences are not always available, because only the final results may be of interest. This article describes the development of a fast and accurate impingement detection algorithm for medical applications. MATERIALS AND METHODS: The presented algorithm takes implicit object models from reconstructions of anatomical CT data that represent complicated anatomical structures. To speed up the detection procedure, a lookup table and a linear transform are used so that searching for impingement between any two objects becomes a problem of calculating spatial indices and checking the lookup table. RESULTS: For any given transformation, the algorithm could perform impingement detection of two objects within 0.1 s on a 167 MHz Sun UltraSPARC1 workstation. Experimental results concerning accuracy, reliability and speed are given for a phantom and for a patient's data set. CONCLUSIONS: This algorithm provides a general-purpose impingement detection method in the sense that objects can be of any shape, and it can be extended to any number of objects in the scene.

Development of an opto-electronic positioning device for serial direct digital images of oral structures.

The aim of this study was to develop and test in vitro an opto-electronic positioning device for serial direct digital images of oral structures, i.e. to associate direct digital imaging with the principles of computer-aided surgery. This system registered positions of infrared light emitting diodes (LED) on carriers, establishing local coordinate systems. With LED markers attached on the sensor holder, the X-ray tube and a fix reference, the opto-electronic camera (Optotrak) registered the geometric source/detector relation. A specially designed tracking and guidance software was developed which enabled the operator to reposition the X-ray source. A graphical user interface guided the operator in aligning 2 circles to the reference axis, one indicating the origin of the beam, the other its tip. In addition, depth control was provided. An in vitro calibration was performed. A sensor holder/bite block carried the Sens-A-Ray sensor with a hair-cross. In front of the object a second hair-cross was fixed. A steel ball fixed to the center of the X-ray cone allowed to verify the alignment. The mean angulation error in the vertical plane was 0.06 degrees and 0.04 degrees in the horizontal one. Translation mean errors were small and ranged between -0.02 mm and 0.37 mm. The translation in the Z axis is negligible. This resulted in pairs of images suitable for digital subtraction. Although still in an experimental state, the results showed that opto-electronic navigation was useful to standardize projection geometry without any mechanical link and to achieve digital subtraction images based on direct digital imaging.

A pilot study on computer-assisted optimal contouring of orthopedic fixation devices.

Bending and shaping of longitudinal orthopedic fixation devices like rods and plates is often a difficult and time-consuming process to perform during surgery under sterile conditions. This study presents a novel device for implant contouring and introduces two strategies to obtain parameters necessary for the bending process. The first strategy is based on surgical navigation techniques as established within the framework of computer-assisted orthopedic surgery. Geometrical landmarks, e.g., the location of pedicle screws in a case of posterior spinal fixation, are collected with a three-dimensional pointing device. Subsequently, the final shape of the implant and the associated contouring parameters are calculated. The alternative strategy utilizes a flexible material intended to be used intra-operatively to enable the optimal shape of the implant to be modeled by hand. Contour parameters are calculated from a depth image of this model obtained using an object scanner. Bending of spinal rod systems is used to illustrate both strategies. A newly designed semi-automatic bending machine is proposed to impose the computed deformation on the implant material once parameters are obtained. Integrating the bending device into a system for computer-assisted surgery allows for the interactive control of the contouring process.

Computer assistance for pelvic osteotomies.

To assist surgeons performing pelvic osteotomies for the treatment of dysplastic hips, an image guided freehand navigation system has been developed. Preoperative computed tomographic scan images are presented in various ways to the surgeon together with real time display of the instruments and surgical action on the computer screen. The system supports the preoperative plan and provides optimized control of surgical action. The main focus of the image guidance has been placed on the execution of the different required cuts and the reorientation of the acetabular fragment. Special attention also has been given to the development of a sophisticated surgeon-machine interface. Fourteen surgeries have been performed with image guidance so far. The visualization aids provided by the system are able to help reduce potential risk and thus increase safety and accuracy for this difficult class of surgical interventions.

[Computer-assisted orthopedic surgery. From pedicle screw insertion to further applications]. / Computerassistierte Orthopädische Chirurgie (CAOS). Von der Pedikelschraubeninsertion zu weiteren Applikationen.

Computer assisted orthopaedic surgery is a new but rapidly evolving field. Based on previous research and development in the area of stereotactic neuronavigation a few groups have adapted these technologies for the image interactive insertion of pedicle screws. The present paper summarizes past and current work in the field of computer assisted orthopaedic surgery and describes the state of the art of research and future innovations, particularly in in vivo applications.

Accuracy of computer-assisted pedicle screw placement. An in vivo computed tomography analysis.

STUDY DESIGN: A computer-assisted planning and visualization system (the Orthopaedic Surgery Planning System) was tested for pedicle screw insertion in vivo. OBJECTIVES: To evaluate the system's applicability for regular intraoperative use and its accuracy for pedicle screw placement in vivo. SUMMARY OF BACKGROUND DATA: Pedicle screw placement poses considerable anatomic and biomechanical risks. The reported rates of screw misplacement with conventional insertion techniques are unacceptably high. It previously has been shown in vitro that computer assistance offers the potential to decrease the number of screws perforating the pedicular cortex. METHODS: The accuracy of 162 pedicle screws inserted with the Orthopaedic Surgery Planning System was assessed by means of postoperative computed tomography evaluation. Reconstructions of the horizontal, frontal, and sagittal planes were analyzed. Cortex perforations were graded in steps of 2 mm. RESULTS: The cortex was perforated in 2.7% of pedicles. Complete preoperative computed tomography scanning of the levels to be operated on is essential to allow for a precise image reconstruction. Initial difficulties in applying the system contribute to the malplacements. A learning curve for general handling of the Orthopaedic Surgery Planning System was observed. CONCLUSIONS: The system provides a safe and reproducible technique for pedicle screw insertion. Other applications in the field of spine surgery are under evaluation.

The first twelve cases of computer assisted periacetabular osteotomy.

Image guided freehand navigation of surgical instruments has been applied to the Bernese periacetabular osteotomy, a complex surgical technique for the treatment of dysplastic hips. This navigation system has been introduced into the operating room and has so far been used for 12 patients. Image data from computed tomography (CT) scans are presented in various ways to support the preoperative plan and to provide optimized control of surgical action. Special attention has been paid to the implementation of a sophisticated surgeon-machine interface. This paper describes the features of this novel surgical navigation system and its introduction into the clinical environment.

Computer-assisted Orthopaedic surgery (AOS): from pedicle screw insertion to further applications.

Computer assisted orthopaedic surgery is a new but rapidly evolving field. Based on previous research and development in the area of stereotactic neuronavigation a few groups have adapted these technologies for the image interactive insertion of pedicle screws. The present paper summarizes past and current work in the field of computer assisted orthopaedic surgery and describes the state of the art of research and future innovations, particularly in in vivo applications.

Clinical evaluation of a system for precision enhancement in spine surgery.

Most techniques in segmental spinal fixation surgery rely on the identification of predefined targets with the help of anatomical landmarks and on intraoperative use of image intensifiers. However, because there is no direct link between the image information, the accessible spinal anatomy, and the action of surgical instruments several potential problems and possible complications are still involved. A novel system for spinal surgery has been designed allowing for the real-time, intraoperative localization of surgical instruments in medical images. In practice this was achieved by combining image-guided stereotaxis with advanced optoelectronic position sensing techniques. Modules were developed for image data processing, surgical planning and simulation, and various intraoperative procedures. A detailed validation of the system was performed indicating an overall accuracy to be better than the slice distance of the spinal image used. In an in-vitro setting 20 pilot holes for pedicle screws were prepared in human cadaveric lumbar spines. An analysis in 77 histological cuts showed an ideal location in 70 and only minor cortex engagement in seven sections. In vivo the system has been successfully applied in three posterior low lumbar stabilizations with overall 15 transpedicular screws. RELEVANCE--:This article focuses on the clinical evaluation of a computer-assisted surgery system and its application to the operating theatre for transpedicular fixation of the spine. The given approach effectively keeps the surgeon 'in the loop' and requires only minor modifications of the established surgical techniques and associated instruments. The results of this study indicate that advanced computer-assisted techniques may significantly improve the accuracy and safety of surgical interventions of the spine. The proposed technique may in future be adapted to other applications in orthopaedic surgery.

Image-guided insertion of transpedicular screws. A laboratory set-up.

STUDY DESIGN: A computer-assisted system allowing precise preoperative planning and real-time intraoperative image localization of surgical instruments is tested in a laboratory setup. OBJECTIVES: The purpose of this study is to assess the applicability, functionality, and accuracy of this transpedicular spinal fixation technique. SUMMARY OF BACKGROUND DATA: Most techniques in transpedicular spinal fixation rely on the identification of predefined targets with the help of anatomic landmarks and on the intraoperative use of image intensifiers. Various studies report considerable screw misplacement rates which may lead to serious clinical sequelae such as permanent nerve damage. METHODS: The proposed system was tested in an in vitro setup drilling 20 pedicle pilot holes in lumbar vertebrae. The accuracy was assessed using precision cuts through the pedicles and simulation of a 6-mm pedicle screw insertion. RESULTS: An ideal screw position was found in 70 of 77 cuts, and in no case was an injury to the pedicular cortex observed. CONCLUSIONS: The presented technique provides a safe, accurate, and flexible basis for transpedicular screw placement in the spine. This approach should be further evaluated in clinical applications.