gms | German Medical Science

Introduction: Frontal sinus fractures remain a relatively rare event. This is mainly attributed to strength of the frontal bone, the strongest facial bone, which requires up to 500 to 1500 lbs of force to fracture. Such forces are typically only generated by motor vehicle collisions and assaults [1]. The incidence of frontal sinus fractures ranges from 10–15 percent of all facial fractures and they often occur in combination with other facial fractures such as orbital walls and nasal bones [2] . Diagnosis can be made clinically in cases where the frontal table is severely involved, however, computed tomographic (CT) scanning has become the gold standard for both diagnosis and planning of surgery [3]. Fracture type, comminution, degree of posterior table fracture, naso-frontal duct injury, neurologic status, and cerebrospinal fluid leak all influence patient management and have lead to constant debate amongst surgeons [4]. As a result, multiple classification systems have been developed to aid in treatment of these rare bony fractures.

Uniquely the frontal bone has both an anterior and posterior table, which in addition to the naso-frontal duct, are variably involved in the pattern injury. Most commonly, in two out of three cases, both the anterior and posterior tables are involved. Second most commonly, in one out of three, the anterior table alone is involved, while isolated posterior wall fractures are extremely rare [5]. Fracture of the anterior wall poses mostly a cosmetic concern, while involvement of the posterior wall alone may lead to liquorrhoe. The involvement of the naso-frontal duct is another important factor in determining treatment of frontal sinus factures, since chronic obstruction may lead mucocele formation. There are multiple techniques and theories on how to surgically approach the frontal sinus. Various incision patterns including supraorbital and Killian-type incisions have been described but are fraught with poor cosmetic outcomes and high complication rates, including forehead dysaesthesias from injury to the supra-orbital and -trochlear nerves. For these reasons, most surgeons choose either a bi-coronal incision or, rarely, direct access in cases of severe lacerations overlying the fracture. Once the frontal bone is exposed, again several techniques exist to gain access to the frontal sinus. It has recently been shown that surgical planning and using computer-aided design/computer-aided manufacturing (CAD/CAM) technology for craniofacial reconstruction allows for surgically efficient and highly predictable outcomes in both bony and soft tissue reconstructions [6]. This investigation describes the uses of this novel technique to gain access to the frontal sinus in eight cases.

Methods: Computer-aided surgery involves several distinct phases: planning, modeling, surgery, and evaluation. Planning begins with a high-resolution computed tomographic (CT) scan of the patient’s craniofacial skeleton according to standard scanning protocols, which are usually part of any trauma- or pre-craniofacial surgery work-up. These images are then forwarded to the modeling company (Medical Modeling, Inc, Golden, CO) where the scans are converted into three-dimensional reconstructions of the cranio-maxillofacial skeleton. A Web meeting between biomedical engineers from the modeling company and the surgical team is then held. During this interactive meeting the surgeons can precisely outline where the borders of the frontal sinus are located. Real-time cephalometric, volumetric, and linear analysis can be extrapolated as bony segments are being virtually manipulated. The goal is to create a cutting guide for the surgeon that allows for safe and rapid access to the entire frontal sinus while maximizing the size of the available bone segments and minimizing further fracture dislocation. Further and most importantly, in cases of minimal or no fracture of the anterior table of the frontal sinus, the guide allows widest access to the sinus with minimal risk to injure the brain.

The modeling phase involves stereolithographic manufacturing of the planned components. This includes the generation of a model of the native craniofacial skeleton for intraoperative reference and to augment the education of residents, surgeons, and the patient. Together with the model, cutting guides that precisely match those created during the planning phase are produced. These cutting guides facilitate the osteotomy process and provide seamless transition between the frontal bone and bone of the anterior table. The precision and speed to perform these osteotomies, which has to follow the often complex anatomical pattern of the frontal sinus, are greatly improved by this technique. During the surgical phase, the cutting guide is placed and secured to the craniofacial skeleton with screws into the frontal bone. These are designed not to interfere with the placement of osteosynthesis plates. This use of guidance technology, which integrates between the preoperative scan and the desired reconstruction, helps to guarantee bony repositioning. In the evaluation phase, a postoperative CT is obtained. This is superimposed against the virtual treatment plan, and analysis is completed by the biomedical engineer. Deviation of the actual results compared with the virtual plan is measured in all planes and color coded for ease of viewing. This clearly identifies areas of success and error and allows correction in future operations.

Results: Eight patients sustaining frontal sinus fractures were treated with the aid of medical modeling: 37.5% (n=3) had isolated anterior table fractures, 50% (n=4) had combined anterior and posterior table fractures, and 12.5% (n=1) sustainedisolated posterior table fractures. A computer-aided, precise cutting guide was designed preoperatively as described above, and allowed to perfectly outline and then cut the anterior table of the frontal sinus at its junction to the surrounding frontal bone, thereby protecting the brain while maximizing the size of the bone pieces as well as enhancing stable fixation (Figure 1 [Fig. 1]). Fracture type, sex, age, operative times, post-operative fracture alignment (evaluated via 3D-CT), and complications were recorded.

Conclusion: Frontal sinus surgery remains challenging in both diagnosis and indication for treatment. Given the wide range of fracture patterns and possible complications, the main questions, which untreated fractures may lead to early or late onset complications and further by which means fractures should be addressed if surgical intervention is opted, remain. One of the largest studies by Rodriguez et al. concluded that patients without radiographic evidence of naso-frontal outflow tract involvement may be observed, whereas those with naso-frontal outflow tract injury with obstruction must be treated by either obliteration or cranialization. Furthermore they stated that there is no role for obliteration with fat or osteoneogenesis [7]. Whenever the posterior wall is fractured in isolation, the anterior table should be cut as close as possible to the surrounding frontal bone to gain widest access possible. In 1955, Bergara and Itoiz described how to use plain radiographs to outline the dimensions of the frontal sinus before creating burr holes and out-fracturing the anterior table downward like a trap door while maintaining its inferior periosteal attachments [8].

Endoscopic-assisted reduction of frontal bone fracture has been advocated but is mostly of value for minimally displaced low anterior table fractures [9], [10]. We found that employing the outlined medical modeling aided method, the time needed for exposure of the frontal sinus was significantly shortened while precision and safety are greatly improved. Computer-aided surgical approaches initially seems too expensive for many indications, however it may shorten operative times and can thus be more cost-efficient in the long run. Virtual surgical planning and model design provide the ability to visualize the oftentimes complex operation and enhance outcomes by providing safe and precise access to the frontal sinus.