Учебники / Computer-Aided Otorhinolaryngology-Head and Neck Surgery Citardi 2002

naires is difficult, and the use of an existing and proven instrument such as SF36 is often preferable.

Klassen et al. used the SF-36 and two other questionnaires preoperatively and postoperatively in patients undergoing aesthetic surgery [27]. Their study suggested that patients undergoing aesthetic surgery began at a lower level of social and psychological functioning and had improvements in health status postoperatively. The study also demonstrated that general health status instruments offered a reliable, valid, and independent method of evaluating aesthetic plastic surgical interventions.

20.8SURGICAL APPLICATIONS

Citardi and Kokoska have reviewed developments in computer-aided surgery (CAS) techniques in craniomaxillofacial surgery [28]. While originally developed for stereotactic localization during neurosurgical procedures, CAS systems have an increasing role in craniomaxillofacial surgery due to their ability to provide insight into complex three-dimensional anatomic relationships. CAS provides an opportunity for three-dimensional image analysis that traditional plain radiographs and CT scans cannot produce.

The concept of CAS surgical navigation promotes a revolutionary approach to surgery. Preoperative data is currently uncoupled from the patient and the surgery and must be related by the surgeon to the actual anatomy. In the CAS surgical navigation paradigm, preoperative images, planning, simulation, and actual surgery are integrated. The software tools may be used not just in surgical planning but also intraoperatively. Further developments may create an unexpected impact on aesthetic and functional aspects of facial plastic and reconstructive surgery.

The heart of computer-aided surgery systems are the computer workstations that house the patient’s imaging data and facilitate data manipulation. The computer system allows stereotactic surgical navigation, so that the position of the patient and surgical instruments may be tracked in three-dimensional space in the operating room. Precise tracking is essential for accurate intraoperative information. Current technology relies on electromagnetic tracking (Visualization Technologies, Woburn, MA) or on optical tracking (CBYON, Palo Alto, CA; Zeiss/Linvatec-Hall, Surgical Largo, FL; Medtronic Surgical Navigation Technology, Louisville, CO). All systems noted above have been adapted to use in otorhinolaryngology–head and neck surgery.

Computer-aided surgery provides a potential advance over intraoperative C-arm fluoroscopy, which some surgeons have advocated for facial fracture reduction. Kokoska presented their cadaver experience on the use of computeraided surgery for the precise reduction of zygoma fractures. [29]. She reported an improved degree of accuracy of fracture reduction using CAS in this study.

Cephalometric analysis can be a useful guide during selected surgical procedures. However, it has important limitations because it relies on the two-dimen- sional analysis of three-dimensional structures. The usefulness of cephalometrics is based on the quantification of specific anatomical relationships by measuring the distance between points or the geometric angles between lines. Computeraided cephalometrics can now be performed on digitalized plain radiographs with specific software packages (Orthognathic Treatment Planner, Pacific Coast Software, Huntington Beach, CA) [28].

Computer-aided computed tomography (CT) based cephalometrics can provide both two-dimensional and three-dimensional volumetric information. This can provide more three-dimensional information than is now routinely applied during these cases. As computer-aided surgery develops, this provides an opportunity to improve the surgeon’s ability to perform the best possible reconstruction [28]. Indeed, in the area of cosmetic surgery, one might speculate that computer software could allow individualized modeling of precise implants, such as chin or malar implants, that could be specifically tailored to the patient to achieve the specific goals.

Computer-generated three-dimensional models and computer simulation of surgery (e.g., anticipated location of osteotomies) may facilitate more effective, less morbid surgery. Computer software for this kind of work has not yet been optimized but should be technically possible [28].

Computer-aided surgical navigation has been extensively developed for neurosurgical procedures, sinus surgery, and spine surgery. CAS navigation systems can follow the position of specific surgical instrumentation in the surgical field. Application of this technology to craniomaxillofacial surgery can be challenging because this sort of surgery was not considered in the development and design of most CAS systems. Intraoperative CAS remains a promising area of development.

Another area of ongoing development is ‘‘real-time’’ CTand MRI-guided surgical navigation. This approach is obviously expensive and logistically challenging, although technological advances may facilitate its application and reduce the cost.

The application of CAS surgical navigation technology to facial plastic surgery is still in its infancy. Nonetheless, Rosen suggests in his discussion on the application of advanced surgical technologies for plastic and reconstructive surgery that advances in computer animation techniques, virtual reality, and graphic interfaces may soon allow complex preoperative electronic modeling [30]. For example, in planning a reconstruction of a nasal defect with a midline forehead flap, a specialized helmet and electronic gloves may allow the surgeon to plan and simulate the ideal shape for the flap. The surgeon may actually be able to see and feel the reconstructed nose.

The limbs provide a simpler model for computer simulation, and so much

of the current work in computer simulation has focused on this area. In one report, a computer-generated model of a hip joint with muscle and tendon actuators was used to predict the outcome of hip arthroplasties (total hip joint replacements) [31].

Achieving a useful computer model will require taking human animation beyond simulating surface skin geometry but will require accurate computer depiction of the complex human system. Larrabee and Galt compared a twodimensional computer simulation of human skin to pigskin to analyze flap advancements [32]. Others have reported on the use of computer modeling to analyze Z-plasty, orthognathic surgery, and other plastic surgical procedures [31– 34]. Even these relatively simple constructs require fairly complex computer programs. Because the complexity of facial anatomy magnifies the challenges of surgical simulation, this work should be considered the early stages in this area.

Just as flight simulators are a proven means of training pilots, surgical simulators provide the opportunity for training experiences with decreased cost and increased safety. In addition, simulators may provide invaluable ‘‘planning’’ opportunities for complex cases. Moreover, as with flight simulators, simulation of infrequent but highly hazardous scenarios provides experience that would otherwise be unavailable. Furthermore, one can expect that as the systems become increasingly sophisticated, they may provide useful information intraoperatively.

20.9OFFICE AND OPERATING ROOM OF THE FUTURE

Miller and Mendelsohn have speculated about the potential office of the future [35]. Extrapolating today’s technology, they ‘‘let their imaginations wander . . .

into the realm of scientific speculation and science fiction’’ to envision incredible changes in the way computer technology affects both their personal and professional lives over the next 50 years. The authors see a critical turning point to be the secure storage and transfer of information that is accessible to anyone who is granted the authority. Wireless technology will allow unprecedented networking and communication between patients and physicians.

The authors describe ‘‘Mrs. Jones’’ and her decision to have a facelift in the year 2050. Her voice-activated personal digital assistant (PDA) scans the Internet; the ‘‘text-to-speech’’ option allows her to listen to the information while she is driving. She decides to proceed and asks her PDA to find a local facial plastic surgeon who has been in practice 10 years, performs primarily facelifts, has a ‘‘success’’ rate of greater than 95% and a limited complication rate. (The authors speculate that the governmental authorities will require this sort of information as part of a quality assurance and performance improvement plan.) She peruses a few websites and decides to schedule an appointment with your office. The details are all taken care of electronically, and she receives personalized

directions to your office via e-mail. Her chart has been completed electronically from her health database, and any additional necessary questions are also included in her e-mail. On the day of her consultation, you are running 20 minutes late and your office computer automatically informs your remaining patients via e-mail.

During your visit, you answer additional questions and also review the before and after holographic simulations. She decides to proceed. Her preoperative instructions are e-mailed to her, her postoperative medications are electronically sent to her pharmacy, and all financial transactions are completed electronically. Except for the day of surgery and the first postoperative visit, her remaining postoperative visits are handled via Web-based teleconference.

Will the future patient-physician interactions follow that vision? Today, nobody can answer that question; however, it is clear that computer-based technologies are forging dramatic changes in health care delivery. Additional changes can be expected.

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can be reviewed on the computer workstation. For instance, the Orthognathic Treatment Planner (OTP, Pacific Coast Software, Huntington Beach, CA) facilitates computer-based cephalometrics. Some of these programs also offer options for surgical planning, including predictions for final surgical results.

Several reports have focused on the accuracy and clinical utility of this type of software. When reviewing the literature, it is important to realize that the critical threshold is clinical significance. Experience has shown that the relative accuracy/inaccuracy of plain films, hand tracing, etc. are acceptable for current surgical applications. In this regard, traditional cephalometrics has an error margin that has been considered acceptable according to practical experience. If cephalometrics software packages produce results within this error margin, then it is considered acceptable.

Plain x-ray digitization can introduce extraneous image magnification and distortion; however, digitization procedures, using a specific protocols designed to reduce such errors, have been demonstrated to be accurate and reproducible for the vast majority of cephalometric parameters [9]. The predictive accuracy of the software has also been examined. The Quick Ceph Image (Orthodontic Processing, Coronado, CA) can calculate values of cephalometric parameters before or after orthognathic surgery. The predictive data produced by Quick Ceph and actual measurements after orthognathic surgery have been shown to be statistically equivalent for most parameters; for parameters in which statistically significant differences between predicted and actual values were noted, the magnitude of the differences was less than that commonly ascribed to traditional cephalometric tracings [9]. From a practical standpoint, Quick Ceph was equivalent to standard cephalometrics for these parameters. Most reports have emphasized that Quick Ceph, as well as Dentofacial Planner (Dentofacial Software, Toronto, Canada), provide good predictive data for a population of patients across a variety of parameters; however, some landmarks seem to possess a wide range of variation, and the software does a poor job of modeling soft-tissue changes after surgery [10].

Several factors contribute to the limitations of software applications for traditional cephalometrics. Interestingly, some of these issues reflect general issues with cephalometrics. Magnification and distortion of the original x-ray, during its initial acquisition as well as during digitization, may produce errors. Human errors in identifying landmarks may also influence cephalometric calculations. Software protocols usually have rounding functions. Although such rounding may seem insignificant for a given value, the rounding of multiple parameters may compromise accuracy. The software programs rely upon specific methods for modeling; if the premises for such methods are incorrect, the resultant models will be incorrect. Users of the software assume that the modeling approaches are reliable; however, this may not be true.

21.4LESSONS FROM TRADITIONAL CEPHALOMETRICS

Because of advanced imaging technologies (such as CT with model reconstruction), it may seem reasonable to downplay the significance of traditional cephalometrics; however, such a maneuver really dismisses the significance of cephalometrics. Despite its limitations, numerous surgeons have recognized the value of cephalometrics: cephalometrics provides a relatively objective means for quantitative analysis of the craniomaxillofacial skeleton. This information may guide the diagnosis of congential and acquired anomalies and assist surgical planning for the correction of these anomalies. Lastly cephalometrics can be used for the documentation of postoperative results. Even if traditional cephalometrics is eventually supplanted by other technologies, its objectives should influence its successor technologies.

The formal approaches for cephalometrics compensate for its intrinsic limitations. In many ways these standardized protocols resemble corresponding protocols for computed tomography (CT) scans for CAS systems. Furthermore, the cephalostat provides orientation for the craniomaxillofacial skeleton during plain x-ray acquisition. Although the cephalostat is not a frame used for CAS surgical navigation, the concepts for both are similar, since both the CAS frame and the cephalostat provide orientation.

21.5TOWARD A NEW UNDERSTANDING OF CEPHALOMETRICS

Traditional cephalometrics seeks to develop quantitative information about complex maxillomandibular anatomical relationships. The approach relies upon standardized plain films that are then analyzed in specific fashion. In this way, cephalometrics provides information about the occlusal relationships and the adjacent maxillomandibular facial skeleton. Surgeons can rely upon this knowledge for preoperative diagnosis and planning as well as postoperative monitoring of surgical outcomes.

As described above, traditional cephalometrics has intrinsic challenges that relate to image distortion and magnification during image acquisition as well as human errors. Importantly, cephalometrics relies upon two-dimensional representations of three-dimensional structures. The super-positioning of multiple structures on a single two-dimensional image may obscure image information. At the very least the image is difficult to comprehend, and at worst the image is incomplete.

Because CAS shares many of its objectives and basic premises with traditional cephalometrics, the application of CAS to cephalometrics is logical;

in fact, CAS-derived cephalometrics may offer critical advantages by merging CAS technologies and cephalometrics principles. Although the linkage of CAS and cephalometrics has not been formally recognized, CAS applications in craniomaxillofacial surgery have been reported numerous times over the previous 15 years. In these efforts, computer modeling has been used to create threedimensional models of various craniomaxillofacial deformities and then these models were used for surgical planning. These approaches all rely upon highresolution CT scans that provide excellent three-dimensional anatomical data, but the entire process has been qualitative, rather than quantitative.

CAS-based cephalometrics should seek to apply traditional cephalometrics’ emphasis upon a systematic, quantitative analysis of image data. Although it is not yet a recognized discipline, the goal of CAS-based cephalometrics is a com- puter-based system for the quantitative assessment of CT image data.

What are the advantages of this approach? Stated simply, CT scans offer more precise anatomical data than corresponding plain films. For this reason, CT has emerged as the preferred imaging modality for preoperative planning for craniomaxillofacial surgery. In a sense, traditional cephalometrics needs an ‘‘update’’ to recognize this fact. It also should be noted that while CT scans provide an excellent understanding of anatomical relationships, the surgeon still must make a mental extrapolation from surgical plan to implementation. Computerbased modeling may simplify surgical planning, and CAS surgical navigation for craniomaxillofacial surgery, which is still developmental, may provide direct intraoperative guidance. It is reasonable to make this entire process quantitative by applying principles learned from traditional cephalometrics.

CAS surgical navigation workstations already contain a variety of software tools that may be applied to CAS cephalometrics. Obviously, the specific details for these tools differ among the various CAS systems; however, most systems have some or all of these features. Even systems in which these tools are not readily apparent may have the capability of offering these tools, but the software interfaces used in the clinical applications are not offered in these particular systems.

CAS software tools facilitate a variety of functions:

Image review: CT data in the three orthogonal planes (namely axial, coronal, and sagittal planes) through a given point may be reviewed (Figure 21.1). Users can use the scroll buttons to sequentially review contiguous images.

Coordinate systems: Points within the imaging volume are assigned x,y,z coordinates (Figure 21.1). Such coordinates may be used to identify precisely and reproducibly a point within the image data set volume.

3D modeling: Three-dimensional models can be constructed from the raw