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

FIGURE 24.6 The photo summarizes the experimental setup for the sequential reduction of the frontozygomaticomaxillary fracture. The cadaver head was placed in a modified Mayfield head holder (D). The dynamic reference frame was secured directly to the skull. For probe calibration, the tracking probe or ‘‘localizer’’ (A) was placed in the calibration divot as shown. Registration was performed using bone-anchored fiducial screws (C), which were place prior to the CT scan. The probe and DRF (B) are from the StealthStation (Medtronic Surgical Navigation Technologies, Jacksonville, FL).

for fracture tracking during operative reduction as well as the confirmation of optimal fragment reduction. In addition, this project also served as a proof of concept for real-time CAS guidance during actual fracture reduction.

In this cadaveric study, frontozygomaticomaxillary fractures were created by blunt blows to the malar eminence. After a postfracture CT, operative reduction was performed under CAS guidance with StealthStation 2.6.4 (Medtronic Surgical Navigation, Louisville, CO). Again, the SBR points served as a reference

system for CAS-derived measurements, and the point of maximal curvature on the malar eminence was selected to represent fragment position. As in the clinical study, the distance-measurement tools provided information about malar projection and position before, during, and after reduction. The StealthStation also includes a surgical guidance mode that tracks positioning of a surgical probe/instrument relative to planned trajectory. This surgical guidance mode was used during the reduction.

Analysis of the coordinate measurements at these intervals of fracture reduction (prereduction, intermediate reduction, and final reduction) confirmed that the surgical guidance mode can be used to direct and confirm the adequacy of fracture reduction. In addition, this study model closely simulated the actual intraoperative process, where sequential reduction is frequently done to find the ‘‘bestfit’’ result. In this project, the sequential reduction was performed with CAS guidance, which was felt to reduce the complexity of this task.

24.3.3Pre-Operative Virtual Modeling and Simulation

Potentially, a computer workstation that has specific software for preoperative CT image manipulation could support the modeling of specific surgical maneuvers (i.e., implant placement and anticipated osteotomies for facial bone advancement or reduction) [7]. In this way, preoperative surgical plans could potentially be tested prior to entry into the operating room. Although this strategy has not been conclusively validated, these computer-based simulations should facilitate more effective and more efficient surgery with lower overall morbidity. The resultant shorter operative times would yield cost savings. Patient satisfaction should also improve. Surgical simulation could also introduce another teaching modality, which would allow trainees the opportunity to test and observe the results of surgical maneuvers without any patient morbidity. Unfortunately, the computer systems for this type of work has not been full developed. At least, such technology should be technically possible.

Preoperative virtual modeling and simulation can be directly applied during the actual procedure through the surgical navigation features of CAS. For example, after the surgical simulation has been performed on a computer workstation, the intraoperative position of fragments can be compared to this preoperative simulation [8]. Light-emitting diode (LED) markers, which can be tracked by an overhead camera array, permit intraoperative navigation, and permit comparisons between planned positions (from the preoperative simulation) and the positions in the operating field. In this report, the LED markers were attached to the patient’s skull base (as a frame of reference) and a mobile, osteotomized bone fragment. Through surgical navigation, the surgeons monitored the position of this fragment relative to a preoperative surgical plan that was stored in the CAS computer. In this way, the optimal position of the osteomized fragment (deter-

metrics is discussed in Chapter 21.) After bone fragment repositioning, repeat measurements can be obtained. These measurements can be compared to the contralateral side for the confirmation of symmetry. Alternatively, such measurements can be compared to normative data as such data become available. Experience with this approach is limited; however, it has been applied with some success to orbitomaxillozygomatic fracture reduction [5].

24.4Limitations of the Current Technology

Despite the impressive advances in preoperative imaging and surgical techniques, the operative repair of complex facial fractures is still less than optimal. Reduction of the fracture requires the positioning of the fragment or fragments in a precise, three-dimensional arrangement. Although preoperative CT scans facilitate the recognition of fracture patterns and secondary deformities, the scans themselves do not directly guide the operative reduction and fixation. Instead, the surgeon must extrapolate information from the preoperative images and intraoperative findings. The actual reduction is usually just an approximation that hopefully will restore function and cosmesis. Clearly, better methods must be sought. CAS may provide a means for better intraoperative reductions; however, the current systems really have not been optimized for these applications.

A variety of deficiencies in current CAS technology have been identified:

As already stated, commercially available CAS systems have been designed for neurosurgery, spine surgery, and rhinologic surgery, but not craniomaxillofacial surgery. Current reports on CAS for facial fracture reduction and related procedures typically describe a prototype system or an adaptation of a commercially available system.

Although CAS availability has improved considerably, it is still relatively expensive, especially when one considers that any hardware and software purchased now will shortly be obsolete. From a cost and marketing perspective, the ideal CAS system would contain software that is specific for use in other subspecialty applications (i.e., sinus surgery and neurosurgery) but also contain software that is particular to craniomaxillofacial surgery. The LED array or reference frame could be designed specifically for each subspecialty so that the designs accommodate the incisions, anatomy, patient positioning, and other issues that are considerations in specific procedures. In this way, the core CAS platform would be used by multiple surgical disciplines; this platform would then support various modules that would be optimized for specific applications.

Recent improvements have simplified CAS systems for routine use; nonetheless, CAS is still relatively complicated. Even surgeons who are familiar with computers and CAS may have difficulty with CAS applications for computer-aided reduction of facial fractures.

tion, an aspect absent in other subspecialty applications. If accuracy of the system is dependent on absolute patient immobility, then it is unlikely to be optimal for reconstruction of traumatic facial deformities.

Registration for CAS surgical navigation currently uses a variety of strategies, including anatomical fiducial points, bone-anchored fiducial points, external fiducial points, contour mapping, and fiducial headset reference frames. None of these alternatives are well suited for registration of the severely (or even moderately) traumatized head. New strategies for registration are needed.

Anatomical data, which can be directly applied in CAS measurements and ultimately fracture reduction, may not be readily available. Normative information regarding orbital volume and/or cross-sectional area or area would be useful in repositioning bone fragments and the intraoperative evaluation of fracture reduction of complex orbital fractures. Similarly, information about the relative angles of the orbital walls would also be helpful.

CAS instrumentation for facial fracture reduction is nonexistent, since the optimal way to use CAS for this purpose has not yet been defined. As a result, surgeons must use instruments designed for other procedures if they wish to use CAS during facial fracture reduction.

The use of current CAS systems often requires a considerable time commitment, since the introduction of additional hardware typically requires additional time for its appropriate use. For instance, surgical navigation requires specific tracking devices and patient positioning. Furthermore, the various measurements that the CAS software package supports must actually be performed. All of these steps take time. Of course, new technology may ultimately increase efficiency; however, this has not happened yet in CAS for facial fracture reduction. These somewhat timeconsuming aspects of CAS may serve as a deterrent for any surgeon considering the use of CAS. On the other hand, greater efficiency can be anticipated as improved strategies for CAS are developed and implemented.

24.5FUTURE DEVELOPMENTS

The use of CAS for facial fracture reduction is currently in its initial stages. Most craniomaxillofacial surgeons would welcome a method of intraoperative tracking and/or imaging of the craniomaxillofacial skeleton and overlying soft tissues. After additional refinement and innovation, CAS may meet the demanding criteria set by these surgeons, who are seeking a better alternative for their patients.

Obviously, further rapid developments in CAS can be anticipated. Rapid enhancements in microprocessor computing power, data storage capacity, net-

work bandwidth, and image displays will like drive this growth. In addition, more surgeons are gaining experience with this technology in their clinical practices; this familiarity will likely encourage further technological adaptations. Collaborative efforts among surgical specialists, who share common and divergent interests and experiences, will also drive specific CAS adaptations.

The role of computers in the workplace will likely undergo substantial revision and modification. Standard CAS systems use a cathode ray tube (CRT) or liquid crystal display (LCD) computer monitor for the presentation of information for use by the operating surgeon. In this approach, the computer workstation tower is intrinsically separate from the actual operation. As an alternative to this arrangement, new display technologies, including integrated head-mounted displays worn by the surgical team, may create an ‘‘augmented reality,’’ in which the surgeon can directly access all information [17,18].

As the systems grow more powerful (and more complicated), the design of the user interface becomes more important. In these matters, the practical operation of both the software and hardware must be facilitated. In most work environments, the presentation of the computer in the workplace has not been a major concern. In the typical office setting, this lackadaisical design philosophy has generated some problems; however, those issues are minor when they are compared with the introduction of computer systems in more complex work settings (such as the operating room). In the latter case, the computer can actually be disruptive to the performance of the requisite tasks. As a result, the integration of the computer workstation into the work environment is of paramount importance. In this regard, head-mounted displays for the surgical team—if implemented appropriately—may be an important advance.

Ergonomic designs that enhance usability are desirable in all computer systems; however, they are especially important for CAS systems for facial fracture reduction. Surgeons who have used these systems have universally commented that the systems are so cumbersome that they are almost unusable. The use of CAS for facial fracture reduction by surgeons other than those self-described ‘‘early adopters’’ will require substantial and meaningful changes in CAS system design.

The ways in which surgeons use preoperative images (i.e., CT scans) will likely be substantially updated. The standard use of preoperative images is ‘‘uncoupled’’ from the actual surgery; the surgeon must relate remote preoperative imaging data and the actual intraoperative anatomy. In contrast, in CAS surgical navigation, the surgeon utilizes a CAS system that integrates preoperative images, planning, simulation, and actual surgery; in this way, all aspects of the procedure are ‘‘coupled’’ [19].

Although CAS holds considerable promise, it would be foolish to assume that other alternatives would not be explored. For instance, intraoperative CT scans would permit direct assessment of operative reductions. In this regard, the

intraoperative CT scanner would be analogous to intraoperative fluoroscopy. In fact, one report has noted that direct intraoperative CT scan confirmation of postreduction relationships is of value in cases of facial fracture reduction [20]. Despite this favorable report, it is unlikely that intraoperative CT scans will become the standard for immediate confirmation of adequate reduction, since intraoperative CT scanners are expensive, cumbersome devices. Obviously, these scanners are expensive, even when compared with CAS. All intraoperative CT scanners require laborious, impractical patient positioning. They also require additional radiation exposure for the patient and staff. Because of the risk of radiationinduced cataracts at relatively low levels of exposure, it has long been considered reasonable to minimize radiation exposure to the orbits. It should also be noted that intraoperative CT scanners provide only static images. In contract, CAS surgical navigation provides dynamic point localizations. In theory, the integration of active virtual modeling with real-time surgical navigation would permit the construction of virtual three-dimensional models of the operative reduction during the actual procedure. Computer-aided design (CAD) and computer-aided manufacturing (CAM) software, which has gained widespread use for its industrial applications, may guide the design of software for the real-time construction of detailed three-dimensional models.

It is important that surgeons with an interest in CAS and its extended applications (including facial fracture reduction) continue to test new systems; their feedback will provide guidance to the CAS engineering teams at the CAS companies. Meaningful progress will require collaboration among surgeons and engineers, who together will mold technological advances into practical, powerful CAS systems. As these new platforms are introduced, further clinical evaluation of CAS systems will be necessary to confirm that CAS implementation improves the functional and cosmetic results of the operative repair of facial fractures and decreases the morbidity of these procedures.

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