Cervical Three-Dimensional Navigation to Facilitate Minimally Invasive Spine Surgery

24 Cervical Three-Dimensional Navigation to Facilitate Minimally Invasive Spine Surgery

Maziyar A. Kalani, Iain H. Kalfas, and Michael P. Steinmetz

Summary

As three-dimensional spinal navigation becomes more pervasive, its role in cervical spine surgery continues to evolve. Although the indications for performing surgery in the cervical spine remain dependent on the patient-specific pathology and complaints, surgical navigation acts as a powerful adjunct in helping address challenging anatomy and pathology. This technology may be applied to anterior and posterior approaches, from the craniocervical down to the cervicothoracic junction; it may be applied to degenerative and bony pathology and to intradural cysts and tumors. Although computed tomography (CT) imaging is the standard data set used for spinal navigation, magnetic resonance imaging (MRI) and ultrasonography may play a greater role in its future. In this chapter, we discuss the role of navigation in facilitating cervical spine surgery, including our experience, pearls, and pitfall avoidance.

Keywords: cervical spine surgery intraoperative computed tomography surgical navigation minimally invasive spine surgery transarticular screw craniocervical junction atlantoaxial instability cervical spine deformity

24.1 Introduction

The presence of the spinal cord, nerve roots, carotid and vertebral arteries as well as small bony fixation points in the cervical spine provide an opportunity for exploring the use of spinal navigation to facilitate the safety and effectiveness of instrumentation. A very well-known risk in instrumenting the upper cervical spine is that of vertebral artery injury during transarticular screw placement; a major vascular complication rate is reported to be as high as 4.1%, resulting in a movement away from this biomechanically favorable screw toward the potentially safer C1 lateral mass and C2 pars/pedicle instrumentation.1 In addition to critical neural and vascular structures, the other remaining challenges to cervical spine surgery include appropriate localization, particularly in the lower cervical spine, and maintenance of alignment in order to prevent iatrogenic deformity during instrumentation. Although these issues may be addressed with larger incisions, the use of image guidance and navigation may mitigate the need for further invasion of soft tissue. Herein, we discuss the role of navigation in facilitating cervical spine surgery, highlighting the relative indications and contraindications, complication avoidance as well as tips and tricks to aid spine surgeons.

Similar to cranial navigation, spinal navigation relies on frameless stereotaxy. Indeed the first case of frameless stereotactic spinal navigation was performed at the Cleveland Clinic in 1994.²^,³ The first reported feasibility study for the use of three-dimensional fluoroscopic-based stereotactic navigation in the cervical spine was reported by Holly and Foley, where screws were placed at C1–C2 (transarticular), C3–C6 (lateral mass), and C7 (pedicle) with 97.6% accuracy with only one of 42 screws demonstrating a cortical breech (C7 pedicle screw).⁴ Since then, numerous cadaveric and clinical feasibility studies have reported lower rates of misplaced instrumentation in the cervical spine for translaminar, transarticular, lateral mass, and transpedicular screws with overall lower blood loss.⁵^,⁶^,⁷^,⁸^,⁹ The rate of poor screw placement was 12.5 to 17.9% higher without the use of three-dimensional navigation.¹⁰^,¹¹^,¹² A similar study demonstrated the safety and feasibility of using three-dimensional computer-assisted navigation in the instrumentation of pediatric cervical spines.¹³^14,15

Anterior cervical corpectomy may be performed with shorter operative time and reduced morbidity when assisted by three-dimensional navigation.¹⁴^,¹⁵ Moreover, computer-assisted navigation has facilitated both anterior and posterior approaches for minimally invasive foraminotomies.¹⁶^,¹⁷^,¹⁸ Often, patients’ body habitus may make localization of lower cervical foraminotomies challenging. The use of image guidance not only eases correct level surgery, but also helps delineate the boundaries of decompression, allowing for a safe and efficacious operation to be performed at the intended level.

Traumatic injuries to the cervical spine may distort normal anatomy significantly. Anatomic consideration and reduced room for error in hardware placement make traumatic cervical spine injuries an area where navigation is highly used. Three-dimensional navigation has been used to treat hangman’s fractures,¹⁹^,²⁰ Jefferson-variant fractures,²¹ atlantoaxial instability,²²^,²³ as well as uncomplicated injuries to the subaxial spine.²²^,²³

Adult degenerative cervical deformity is an interesting area of potential application of three-dimensional navigation. There is little description of its use in the literature so far; although it may not help facilitate minimally invasive surgery due to challenges such as spinal cord and vascular considerations, it has ample uses in open cervical deformity correction such as placement of instrumentation or osteotomy planning.

Three-dimensional navigation is of particular utility in the craniocervical junction. Frameless stereotaxis has successfully facilitated the decompression of anterior transcervical, transoral, and transnasal odontoidectomy,²⁴^,²⁵²⁶^,²⁷ as well as resection of malignancies of the craniocervical junction.²⁸

Beyond utilizing three-dimensional navigation for bony decompression and arthrodesis, image guidance may be utilized for fenestration of intradural arachnoid cysts,²⁹^,³⁰^,³¹ and intra- and extramedullary tumors.³²^,³³^,³⁴^,³⁵

24.2 Indications

The decision whether to use three-dimensional navigation for cervical spine surgery dovetails with the indications for surgical intervention. Indications typically include decompression of the spinal cord and/or nerve roots, correction of deformity, stabilization of instability causing mechanical pain, and, in the case of malignancy and infection, for diagnostic purposes. There is no absolute indication for the use of this technology; relative indications include revision surgery or irradiation where the anatomy is distorted, presence of trauma, and as an adjunct for en bloc resection or complex osteotomies in deformity correction.

24.3 Contraindications

Relative contraindications include a lack of static structure to affix the reference array, inability to fixate the head using a three-point holder, patient habitus resulting in poor image acquisition, and lack of appropriate surgical table which may result in poor resolution images.

24.4 Preoperative Planning

In order to prepare for operative intervention, standard preoperative imaging is obtained to aid in the surgical plan. Magnetic resonance imaging (MRI) and computed tomography (CT) scans are helpful in determining the pathology as well as normal anatomy with respect to the pathology. Standing upright radiographs may be useful in better understanding alignment and stability; dynamic noninvasive imaging with MRI and CT may be considered to give further insight into the specific patient’s complaints. Other preoperative ancillaries may include choice of specific instrumentation, use of autograft versus allograft, incorporation of intraoperative neurophysiologic monitoring, patient positioning, and necessity of an approach surgeon (for transnasal or high-risk anterior cervical approaches).

Surgical table selection is particularly important for cervical three-dimensional navigation assisted surgery. Careful selection of the appropriate bed will allow for ease of workflow while acquiring the necessary intraoperative imaging; certain table designs and radiolucent head holder dimensions may hinder the ability to acquire intraoperative cone-beam CT for three-dimensional navigation (Fig. 24.1). Both the standard surgical table with the pedestal at the caudal end as well as a carbon frame table allow for appropriate positioning of the intraoperative O-arm CT (Medtronic, Dublin, Ireland) to acquire imaging and provide for appropriate maintenance of alignment and deformity correction. Alternatively, the Airo CT scanner system (Brainlab, Munich, Germany) has an integrated surgical bed to which a radiolucent three-point cranial fixation may be attached.

Fig. 24.1 Standard surgical bed with bolsters is shown with a radiolucent three-pin head holder. Rigid fixation of the reference array to the radiolucent head holder is demonstrated.

In the cervical spine, three-dimensional navigation can be helpful for the planning and placement of transarticular C1–C2 screws, C1 lateral mass screws, C2 translaminar screws, C2 pars/pedicle screws, lateral mass screws, and C7 pedicle screws. In addition, it can also be used for occipital screw placement and for localization of pathology, for example, for cervical foraminotomies. Navigation is especially useful for localization of the correct level in the lower cervical spine due to the shoulder blade artifact seen with fluoroscopy during conventional surgical techniques.

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