TNOA Journal of Ophthalmic Science and Research

REVIEW ARTICLE
Year
: 2021  |  Volume : 59  |  Issue : 3  |  Page : 233--240

Navigation-guided surgery in orbital trauma


Priti Udhay 
 Department of Oculoplasty and Aesthetics, DRR Eye Care and Oculoplasty Hospital, Chennai, Tamil Nadu, India

Correspondence Address:
Dr. Priti Udhay
DRR Eye Care and Oculoplasty Hospital, Chennai, Tamil Nadu
India

Abstract

There are times in an orbital surgeon's life when experience and instincts seem inadequate and there is a need for some extra guidance and technical support. High-velocity injuries with shattered orbits are one such instance. In these cases, the entire orbit is disrupted and there are no bony landmarks to guide placement of implants and restoration of volume. Orbital walls have complex curvatures and it is extremely difficult to reestablish and symmetrize this complex three-dimensional (3D) anatomy. Inadequate reductions and poor implant placements are common causes of postoperative persistent enophthalmos. Intraoperative navigation guidance has greatly aided in accurate localization of bony landmarks, in planning complex reconstructions and verifying adequate reconstruction and symmetry, and in planning patient-specific or customized 3D-printed implants. It has brought in a revolution in the treatment of orbital trauma in current times.



How to cite this article:
Udhay P. Navigation-guided surgery in orbital trauma.TNOA J Ophthalmic Sci Res 2021;59:233-240


How to cite this URL:
Udhay P. Navigation-guided surgery in orbital trauma. TNOA J Ophthalmic Sci Res [serial online] 2021 [cited 2021 Oct 22 ];59:233-240
Available from: https://www.tnoajosr.com/text.asp?2021/59/3/233/325719


Full Text



 Introduction



Till recent times and even today in many cases, surgery for secondary orbital reconstruction was planned on a three-dimensional (3D) skull model created using stereolithographic (STL) technology and patient's (computerized tomography [CT]) scans. The planned surgical procedure was performed on these models. Orbital implants were precontoured on these models and used intraoperatively[1],[2],[3] [Figure 1]. However, lack of intraoperative guidance made many of these surgeries difficult and also verification of correct implant placement was not possible.{Figure 1}

Intraoperative navigation and computer-assisted surgery (CAS) were first used in the field of neurosurgery to localize intracranial tumors. It was later widely used by ENT surgeons for skull base surgeries. Its use in cranio-maxillo-facial (CMF) surgery started in Europe in the late 1990s.[4],[5],[6] In oculoplasty, it is now used for orbital reconstructions, optic canal decompressions, orbital decompressions, orbital tumor/foreign body localization, and in endoscopic and lacrimal surgeries.

In trauma, intraoperative image-guided navigation system is a useful tool to guide the surgeon in the identification of bony landmarks especially in cases where the anatomy is distorted; in planning complex reconstructions and verifying adequate reconstruction and symmetry; and in planning patient-specific or customized 3D printed implants.

In complex trauma with massive comminution and distorted anatomy, achieving symmetry with the other unaffected orbit is very challenging and also vital to avoid diplopia and give a good cosmetic outcome. Navigation guidance helps in achieving precise and predictable results in complex orbital reconstructions.

 Methods



A systematic review of the use of navigation guidance in orbitofacial trauma was done with the use of data sources such as PubMed, Ovid, MEDLINE, and Scopus using keywords such as “Navigation surgery, posttraumatic orbital reconstruction, computer-assisted orbital surgery and image-guided orbital surgery (IGOS).” A total of 148 abstracts were reviewed and 24 full-text articles were taken for reference. The inclusion criteria were clinically controlled trials and case reports involving navigation-guided surgery with a minimum of two or more patients being included. The exclusion criteria were articles with no objective endpoint of the surgical outcomes. The abstracts of relevant articles were studied. After perusal of the abstracts, the chosen articles were reviewed in details. As per the inclusion criteria, the search was augmented by a search of the bibliographies of the included articles and a manual search of the relevant journals.

Principle of intraoperative navigation

Intraoperative navigation has its origins from stereotaxy. Stereotaxy, a popular tool in neurosurgery, involves the use of external reference markers for the localization of internal surgical landmarks. This has paved way to the current generation of equipment used for intraoperative navigation.

The principle by which intraoperative navigation works is very similar to that of a common global positioning system (GPS) or “GPS” that is used in cars. The GPS network involves (1) A digitized Map stored online (2) A Satellite (3) A Network Tower or towers which are plotted on a map with their locations and (4) The mobile GPS tracker mounted on the car [Figure 2]a. The position of the car on the digitized map is shown when the satellite is able to process the information of the car relative to the nearest tower.{Figure 2}

A similar process occurs in the navigation system within the operating room. For better clarity, the patients CT scan is analogous to the digitized map, the infrared camera on the navigation machine to the satellite, the fixed patient tracker to the tower, and the mobile hand-held pointer which surgeon uses to the sensor in the car [Figure 2]b Therefore, the signal emitted by the infrared camera locates the position of the hand-held pointer in relation to the tracker on the preoperative CT scan of the patient.

Two types of navigation technologies are available-

Electromagnetic navigation, where an emitter fixed to the operating table, emits electro-magnetic field around the surgical site and the position of the navigation probe within this field is detected. However, as this technology utilizes an electro-magnetic field, most ferromagnetic surgical instruments create disturbances, and titanium instruments are neededOptical guided navigation systems where infrared cameras emit beams which reflect the position of the navigation probe using optical sensors.

Procedure

The armamentarium for intraoperative navigation includes the following components:

The navigation platform which contains the display panel with touch screen and the operating softwareThe patient tracker which is fixed on the patient's skull (optical system) or scalp (electromagnetic system)The handheld pointer.

Preoperative steps

Importing digital images and communication in medicine (DICOM) dataSelection of procedure-Here CMF softwareRegistration planningProcedure planning

The Intra-operative steps which include

System setupValidation and calibration of the toolsPatient registrationNavigation verification and activation.

Steps in detail

While using navigation, the patient's bony landmarks can be seen in real-time on the patient's preoperative CT scan images on the navigation platform. Most navigation platforms allow the use of different imaging modalities such as CT, (magnetic resonance imaging [MRI]), CT and MRI angiographies, (CT Dacryocystography), fluoroscopy, and the C-arm imaging systems. In orbital trauma, CT scan is the imaging modality of choice. When surgery is planned using navigation guidance, the CT scans should be taken using a specific protocol. For intraoperative navigation, contiguous thin sections (<1 mm) are obtained from the hard palate to the vertex (for orbital fractures) and the whole face (for pan facial fractures) with zero gantry tilt and head in neutral position. The cuts are continuous, without gap or overlap. Axial, reformatted coronal, sagittal, and 3D images are utilized for navigation. The (DICOM) images are then uploaded on the navigation platform where preoperative image analysis is followed by treatment planning.

The four-panel window of the navigation platform screen includes the chosen scans in different planes-sagittal, coronal, axial, and 3D reconstructed. The first step in virtual planning is auto segmentation of the orbit. Various softwares in the navigation platform are then used for virtual planning. In trauma, the CMF software is used and treatment planning is typically performed by mirroring the normal bony orbit onto the affected side [Figure 3]a. The mirrored image is used as a template intraoperatively for reconstruction. In case of bilateral trauma, the contours of the auto segmented orbits can be virtually drawn or age and race matched algorithms from standard CT datasets may be used. This virtual plan gives real-time guidance during surgery.{Figure 3}

Intraoperative tracking can be performed using optical guidance (BrainLab®, Stryker, Medtronic Stealth system) or electromagnetic guidance (Fusion®, Medtronic Stealth, BrainLab®). Tracking of the patient's head is achieved with the dynamic reference frame fixed to the forehead with a plaster in case of electromagnetic tracking. For optical navigation, a skull post/reference array with tracker is fixed with screw to the skull bone. These tracking devices can be placed at a convenient location where it does not interfere with the surgical field and cause intraoperative navigation disruptions. The limitation of optical navigation is “line of sight interference” which means that the area between the infra-red camera on the navigation platform and the tracker on the patient should be free of personnel to avoid disruption in navigation. Pros and cons of each system are explained in [Table 1].{Table 1}

Registration is the most important step and accurate registration is the key to success in the procedure. Registration in simple words is to tell the computer which patient's anatomy you are correlating with the CT scan on the navigation platform. This can be performed using either soft tissue surface anatomy (surface tracking-Medtronic Stealth system, Stryker Nav 3 system, Brainlab) or the skeletal bony landmarks (BrainLab, Stryker Nav3) with or without markers. Markers used maybe invasive or noninvasive. The choice of registration method depends upon the surgical site as well the possibility of soft tissue movement during surgery. Most craniofacial surgeons prefer bony registration as craniofacial surgeries involve major soft tissue movement. The distribution of the bony points should cover a large area and should be far from each other. Dental splints are another option. However, there is a possibility of slight movement of the splint during surgery which will affect the accuracy of navigation and also as we move away from the splint the accuracy reduces. Hence for craniofacial surgery, these splints are combined with bony screws in the periorbital area. Oculoplastic surgeons prefer soft tissue registration without markers using pointer or Laser scanning (Z scanning in Brainlab) as oculoplastic surgeries do not involve movement of soft tissue of forehead and midface. Soft tissue registration is more accurate as 200 points are obtained during registration as compared to 4–5 points in bony registration. Registration error in periorbital area is around 1 mm which is acceptable; irrespective of the registration method. However, posttraumatic edema can result in a significant error when registering to an initial CT scan where tissues are edematous. Hence it is important to obtain CT scan just prior to surgery.[6],[7],[8] Once the registration is complete, the instruments are validated and the accuracy is verified by placing the pointer on known bony landmarks such as the orbital rim, and canthi. When using CAS, surgical steps are performed according to standard procedures and navigation gives real-time guidance during surgery.

Reconstruction of complex orbital wall defects may benefit from preoperative virtual insertion of STL image of the precontoured implants [Figure 3]b. Some complex reconstructions may require customized implants for the reconstruction of orbital walls. This can be made by transferring virtual preoperative planning into 3D printing software to make customized implants or patient-specific implants (PSI).[9] PSI allows correction and reconstruction without additional osteotomies or bone grafts [Figure 4].{Figure 4}

Navigation in orbital fractures and reconstruction

Complex orbital and orbitofacial fractures are a real challenge even in primary trauma.

Displaced and comminuted (zygomaticomaxillary complex [ZMC]) fractures are often difficult to repair, due to incomplete visualization of the entire zygoma through small incisions and also because the reduction of zygomatic prominence and the arch is usually performed with the soft tissue drape intact. Moreover, the assessment of reduction involves a comparison with the contra-lateral side for symmetry which is usually performed by mere “eye-balling.” Inadequate primary repair can result in an inadequate anterior projection of the body of zygoma and increase in the facial width resulting from outward bowing of the zygomatic arch. A good ZMC repair is key to successful orbital trauma management and significantly contributes to the normal functioning and aesthetics of the midface [Figure 5]a and [Figure 5]b. Computer-assisted planning and intraoperative navigation guidance is a useful tool in achieving this [Figure 5]c, [Figure 5]d, [Figure 5]e, [Figure 5]f, [Figure 5]g, [Figure 5]h, [Figure 5]i, [Figure 5]j, [Figure 5]k, [Figure 5]l, [Figure 5]m, [Figure 5]n.[10],[11],[12],[13],[14],[15],[16],[17],[18],[19],[20],[21],[22]{Figure 5}

Likewise, complex reconstructions involving more than two orbital walls may benefit by the use of intraoperative navigation. Restoration of the normal S-curve of the orbital floor and the medial wall bulge requires special contoured implants. This reconstruction may not be possible with sheet implants and persistence enophthalmos is a common problem in these cases.[23] The reconstruction of orbital wall curvatures can be planned preoperatively and checked intraoperatively by navigation guidance. In floor fractures, it is important for the surgeon to identify the posterior shelf of intact bone for proper placement of the implant. Its identification is difficult during surgery because of displaced orbital contents, intraoperative bleeding, poor lighting, and surgeons apprehension in dissecting too far posteriorly for fear of injuring the optic nerve. This leads to inadequate reconstruction of the posterior orbit and residual enophthalmos. For good results and adequate volume restoration, it is imperative that the floor implant should rest on the posterior shelf of bone and intraoperative navigation can help identify this structure [Figure 5]b: [Figure 5]k.

Often in large fractures involving floor and medial wall the entire inferomedial strut is comminuted and displaced. In these cases, accurately placing the transition area between floor and medial wall of the precontoured titanium implant can be impossible without intraoperative navigation assistance [Figure 6]. Navigation-assisted mirroring, measuring, and simulating helps to predictably restore the difficult-to-match posteromedial bulge, identify the posterior shelf and also symmetrically restore the inferomedial strut and achieve successful orbital reconstruction.{Figure 6}

Virtual insertion of the anatomically preformed titanium mesh can also be done which allows preoperative selection of the correct implant size, trimming of implant if needed and the correct 3D positioning of the implant. Navigation helps visualize the actual surgical outcome during surgery in relation to the preoperative plan. With this technique, insufficient orbital reconstruction can be identified and corrected during surgery, thereby reducing the need for secondary procedures [Figure 7]. It also helps avoid unnecessary surgical manipulation and dangerous dissection close to optic nerve.{Figure 7}

Delayed reconstructions are challenging due to malunion, nonunion, bony resorption, scarring of soft tissue envelope, presence of bony callouses, and scars. As a result of remodeling, no obvious fracture edges are seen that can serve as a landmark for correction. Navigation has almost become indispensable in the management of secondary deformities of the ZOC as it helps in the accurate positioning of the sites of osteotomy and facilitates removal of bony callouses which may impede proper reduction[24],[25] [Figure 8].{Figure 8}

The accuracy of navigation was demonstrated by Hongbu et al. who noted maximum deviation of <2 mm when comparing postoperative CT scans with the preoperative planning. They also reported an accurate match between intraoperative anatomy and preoperative CT scans with an error of <1 mm. This degree of precision was acceptable especially when natural asymmetry is considered.[16]

It is important to note that diplopia correction does not always accompany enophthalmos correction as the soft tissue envelope of the globe with preexisting scars in extraocular muscles and periorbita may play an important role.

 Discussion



Accuracy and precision in orbital surgery have undergone a revolution in recent times. This is especially true in orbital and orbitofacial trauma. Restoration of the complex anatomy of orbital walls which are not straight but curved in different ways, and symmetrizing the orbital rim and walls with the other side is not only challenging but impossible without adequate preoperative planning using latest technology and improved vastly with intraoperative navigation guidance. Intraoperative navigation is known by various terms such as computer-assisted navigation surgery and IGOS. Bony restoration is the foundation on which soft tissue restoration depends and adequate reconstruction of both bone and soft tissue is needed for aesthetic and functional outcome [Figure 6]. Maximizing outcomes and minimizing complications can be achieved by using 3D printing and navigation technology.

In orbital trauma, the rims are repaired first, then the orbital walls [Figure 8]. Paying attention to the bony landmarks, contours and using great caution to avoid damage to the vital structures, through precise intraoperative localization techniques and intraoperative verification should be the goal standard in orbital surgery, whenever and wherever possible. There is great value in preoperative analysis of the DICOM data, virtual surgery followed by intraoperative replication of treatment planning.[23]

A study by Markiewicz et al.,[20] using navigation in 23 patients for reconstruction of posttraumatic and postablative orbital defects, concluded that navigation was effective in establishing normal orbital volume and globe projection.

Bly et al.[17] have published a large series of 113 cases analyzing results with and without navigation guidance in unilateral complex orbital trauma. They concluded improved outcomes in postoperative diplopia and orbital volume with the use of navigation. Need for revision surgery was reduced from 20% in nonnavigation group to 4% in navigation group (P = 0.03). Similar results were seen in 15 patients by Bell and Markiewicz.[1]

The future of orbital and orbitofacial navigation surgery includes not only intraoperative navigation but intraoperative imaging, to ensure accuracy of reduction of orbital fracture fragments and confirm implant placement, posttreatment image analysis to verify and ensure high quality and good outcomes. The limitations of navigation guidance are inaccuracy in bilateral trauma cases and inadequate soft tissue guidance. It is definitely not a substitute to proper surgical technique and expertise. Another major limitation is that it assumes orbital and facial symmetry. Studies have shown that there are measurable differences in orbital volumes between the two-sided for any given individual.[13] However, in most, the difference is small with no significant effect on facial appearance and function. Controversy regarding the additional cost of investment, additional time incurred in preoperative planning, and intraoperative navigation setup and execution may also be justified with better outcomes and minimizing the need for revision surgery. Although probably not necessary for routine use in small orbital blow-out fractures, its use in shattered orbits due to high-velocity injury resulting in severe disruption of internal and external orbit; shows promise.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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