Navigation in Non-Instrumented Spine Surgery

Tubular Minimally Invasive Spine Microdiscectomy Surgery

Tubular minimally invasive spine (MIS) microdiscectomy surgical techniques are utilized for degenerative disk disease and herniation throughout the spinal cord for numerous approaches including cervical, lumbar, far lateral lumbar, transthoracic, and thoracolumbar discectomy. Notably, it has been demonstrated that tubular MIS microdiscectomy in the cervical and lumbar spine results in diminished blood loss, reduced postoperative pain, and shorter hospital stays compared with the traditional open techniques. The procedure involves percutaneous localization of the anatomical segment and focus of interest, typically under fluoroscopic guidance, followed by serial dilation of the paraspinal musculature and soft tissues and insertion of a tubular port or retractor over the dilators and through which the surgical decompression is performed. Radiographic localization is essential not only for identifying the appropriate level of the pathology but also for the anatomical localization of the bony elements to optimize the bony exposure, both for adequate decompressive access as well as to limit and avoid iatrogenic instability from overly aggressive bony resection. In this regard, the 3D anatomical representation afforded by iCT-based spinal navigation is far superior to 2D-fluoroscopic guidance.

Navigated Cervical and Lumbar MIS Surgery

The use of spinal navigation, such as with iCT, has been effective in both cervical and lumbar MIS discectomy and offers improved real-time visualization of the operative anatomy. Disk herniation in the cervical and lumbar spine represents the vast majority of symptomatic disk herniation cases.

In the cervical spine, spinal navigation technology has proven efficacious and highly valuable in performing posterior cervical foraminotomy (PCF), unilateral laminotomy for bilateral decompression (ULBD), and posterior facet joint fusion (PFJF).

PCF, typically utilized for unilateral cervical radiculopathy, was initially developed as an open procedure; however, the tubular, minimally invasive approach often used today offers similar efficacy while reducing blood loss, postoperative analgesic use, and length of hospital stay. This tubular MIS approach involves the placement of a small paramedian incision on the localized level and side of pathology, dilation, and ultimately placement of a tubular retractor through which the lateral aspect of the lamina and medial portion facet joint are removed to complete the foraminotomy. In PCF, 3D intraoperative navigation is often used successfully to identify the precise location of the primary incision and docking site to perform the foraminotomy with the highest degree of safety. Often, both the ipsi- and contralateral foramina can be accessed using this procedural approach, for patients with bilateral radiculopathy, and improved visualization of the contralateral side using intraoperative 3D navigation can prepare the surgeon for optimal positioning and docking for this procedure.

ULBD, a unilateral approach for bilateral decompression of the spinal cord, was initially developed in lumbar spine procedures but has since been utilized effectively as an MIS procedure in all levels of the spine column. Of note, it is a particularly useful procedure in patients with cervical spondylotic myelopathy. In ULBD, intraoperative spinal navigation is used to determine the precise entry point for the placement of a 2 to 3-mm incision at the affected level. After the incision and placement of a tubular retractor, the ipsilateral lamina is accessed and drilled away and the retractor is realigned, and, using an “over-the-top” approach, the spinal cord is safely bypassed to perform the contralateral laminotomy. Navigation is used successfully to guide both the trajectory and extent of the laminotomy. The MIS tubular ULBD is equally in efficacy to its open counterpart and reduces exposure, blood loss, muscle manipulation, and removal of bone, making it an often-preferred approach in some elderly or obese patients.

The PFJF is a procedure aimed at treating cervical spondylotic radiculopathy and myelopathy by percutaneously placing bilateral cervical facet joint cages from a posterior approach, as opposed to the more traditional lateral mass fusion. Spinal navigation is critical in this procedure, as it allows the surgeon to identify the medial and lateral aspects of the facet and safely enter the facet joint without injuring the nerve root. Finally, a cage is placed in the facet joint and secured to the inferior articulating facet, thereby stabilizing the joint space and allowing for the introduction of graft material into the joint. This approach may be similarly efficacious to lateral screw fixation as a successful indirect decompression and fusion method for single-level radiculopathy with high rates of radiographic fusion and similar postoperative cervical segmental stability.

Lumbar MIS Surgery

An estimated 95% of herniated disks occur in the lumbar spine at either L4–L5 or L5–S1; thus, non-instrumented spinal navigation may offer the most significant epidemiological benefit in the treatment of lumbar spine disease.

Navigated Lumbar Far-Lateral MIS Discectomy

Extraforaminal or far-lateral lumbar disk herniations (FLDH), first described by Abdullah et al., in 1974, represent 0.3% to 11% of lumbar disk herniations and pose a significant challenge to the spine surgeon. The proportion of patients presenting preoperatively with symptoms of sensory dysesthesia has been observed to be greater with FLDH than with other types of disk herniations and the dysesthesia is often significantly more severe. This is thought to be related to the direct compression of the dorsal root ganglion (DRG) by the disk fragment.

Foley et al. developed a tubular MIS approach based upon a modification of the earlier Wiltse paramedian approach to reduce approach-related muscle trauma with improved postoperative pain. The technique involves the early identification of the exiting nerve inferior to the rostral pedicle, followed by visualization and resection of the disk herniation. However, this technique involves dissection and manipulation of the exiting nerve root and DRG and may contribute to painful postoperative dysesthesia, potentially leading to poor postoperative outcomes, as has been suggested by cadaveric dissection studies. An alternate technique in which the Kambin triangle (formed by the exiting nerve, the lateral border of the traversing nerve root, and the superior endplate of the caudal vertebral body) is targeted for direct access to the disk has been proposed. While this latter approach presumes a fixed relationship of the exiting nerve root to the disk space and traversing nerve root, it has been shown that this relationship may be quite variable with as many as 83% of patients having a reduced or non-identifiable Kambin triangle. Thus, a challenge of the tubular MIS approach for FLDH surgery is the early identification of the exiting nerve root. A second major challenge is the proper anatomical localization of the bony elements and the disk space lateral to the spine given the paucity of familiar osseous landmarks such as the spinous process and lamina, through which a surgical corridor of safety may be negotiated. While fluoroscopy has been used in MIS surgery as the standard imaging modality for localization, it has the drawbacks of 2D anatomical representation, which is less accurate, and increased radiation exposure to the surgeon and operating room staff. We recently demonstrated the utility of iCT navigational guidance for accurate bony anatomical localization in combination with Electromyography stimulation for early localization of the exiting nerve in the MIS tubular, microscopic paramedian approach for resection of far lateral disk herniations.

Transthoracic MIS Discectomy

Thoracic central disk herniations may be calcified and present with myelopathy, often requiring an anterior transthoracic approach for surgical intervention. However, this approach is fraught with complexities including the precise localization of the level of the pathology of interest. Wrong-level thoracic spine surgery is not uncommon and may result in significant neurological morbidity and litigation. Localization is challenging in part because of the similarity of thoracic vertebral segments and their remoteness from fixed identifiable landmarks such as the skull base or the sacrum.

The surgical technique for transthoracic approaches for central disk herniations may be divided into two parts: The approach technique involving the transthoracic/retropleural exposure and the decompressive technique involving the removal of the rib head and pedicle, creation of a trough in the adjacent vertebral bodies extending to the contralateral pedicle, and, finally, decompression of the central canal by removal of the centrally herniated disk material. The 3D anatomical representation of iCT spinal navigation offers superior localization and guidance in these two critical portions of this surgical approach compared with fluoroscopic guidance.

In our technique for the procedure, we percutaneously place a pedicle marker consisting of aneurysm endovascular coils at the level of interest, following which we obtain a CT or post-myelogram CT scan of the thoracic spine to confirm the relationship between the marker and the level of interest. The patient is then taken to the operating room, and, following induction with provision for potential lung isolation, positioned in the lateral decubitus position and secured in place rigidly with 3-inch tape to minimize motion. The posterior and lateral torso is prepared and draped widely in the standard surgical fashion. A DRA is mounted either into the iliac crest or sutured to the flat of the back and an iCT scan is obtained with auto-registration on the Brainlab Curve navigation system. The scan may be autofused with the post-myelogram CT scan or high-resolution MRI scan. The pedicle marker is localized and used to plan the skin incision. A mini-open incision (4–6 cm) is created and a thoracotomy is performed with rib resection if required, with a retropleural approach to obviate the need for a chest tube. An expandable MIS retractor (NuVasive or Globus) is inserted over dilators for visualization of the anatomy of interest. We use a navigable ultrasonic bone scalpel (Misonix) to remove the rib head and to create the trough in the vertebral bodies of the segments adjacent to the disk at the level of pathology. The neural foramen is used to identify the canal and, using a navigable high-speed drill with a coarse 5 mm diamond burr, the pedicle is drilled back to reveal the spinal canal. The remainder of the posterior wall of the vertebral body is then removed with the decompression extending from pedicle to pedicle and exposing the posterior longitudinal ligament (PLL) craniad and caudad to the disk space. The PLL is divided and the disk material removed by peeling it away from the spinal cord. iCT navigational guidance is a very useful adjunct in the confirmatory localization of the surgical level as well as anatomical localization of critical structures such as the rib head, pedicle, and spinal canal during the decompressive phase of the procedure. This is achieved while minimizing radiation exposure to the surgeon and OR staff from fluoroscopic guidance.

MIS Lateral Approach for Central Thoracolumbar Microdiscectomy

Like central thoracic disk herniations, large central disk herniations at the thoracolumbar junction (T11–T12, T12–L1) and in the upper lumbar spine (L1–L2, L2–L3) may represent a management dilemma for the spine surgeon. Given the high density of neural elements located in this anatomical region (conus medullaris, upper cauda equina), the presenting symptoms in patients with upper lumbar disk herniations tend to be more varied than the clear-cut lumbosacral radiculopathy with which patients experiencing lower lumbar disk herniations present. Additionally, given the bony anatomical characteristics in this region with more narrow, sagitally oriented facet joints, smaller spinal canal and shorter width of the pars interarticularis, decompressive procedures geared toward the removal of central and large paracentral herniated disk fragments in the upper lumbar spine tend to be destabilizing with twice as many patients than at lower lumbar levels requiring additional fusion procedures. Not surprisingly, the outcomes following surgical intervention for upper lumbar disk herniations tend to be less favorable than are those for lower lumbar disk pathologies.

We recently described a minimally invasive, lateral retroperitoneal, transpsoas, direct transforaminal approach to central and paracentral disk herniation at L1–L2. The approach combines the principles of the extreme or direct lateral retroperitoneal, transpsoas approach targeting the anterior third of the disk space and the posterior, transforaminal approach through the neural foramen utilized in percutaneous endoscopic lumbar discectomy (PELD) with iCT navigational assistance playing a crucial role in the feasibility of the approach.

Endoscopic Applications

The field of spine surgery has seen a resurgence in the utilization of endoscopic approaches in the last decade. Percutaneous endoscopic approaches to the lumbar, thoracolumbar, and thoracic spine utilize a posterolateral, percutaneous trajectory under fluoroscopic guidance to gain access to the spinal canal through a transforaminal approach. As with other MIS approaches, accurate anatomical localization and targeting are critical to the success of the approach. iCT navigational assistance allows for more precise anatomical localization without the increased radiation exposure to the OR staff and surgeon while also increasing the comfort level of the surgeon. However, the challenge here is how to perform the mounting of the DRA and registration in an awake patient given that in most MIS navigated spine cases, the DRA is mounted into the iliac crest. We utilize a technique in which the DRA is either sutured to the skin under local anesthetic or affixed in place with Ioban. The patient is asked to hold their breath during the scan. The accuracy is confirmed by touching the navigation probe to the skin. A trajectory is then planned for access to the neural foramen of interest. Under local anesthetic, the skin is incised and a navigated Jamshidi needle is inserted along the plotted trajectory and docked on the lateral facet at the foramen. A guide wire is inserted through the Jamshidi needle which is removed and over the guide wire are inserted, serial dilators for the endoscopic tools and endoscope (Joimax). A foraminoplasty is performed with a rimming drill, a port is placed and the endoscope is inserted through this. The endoscope itself may be rendered navigable by attaching a DRA.

Tumor Resection Surgery

Perhaps, the greatest progress and widespread adaption of spinal navigation technology in non-instrumented spine cases has been in the field of spinal oncology with the resection of metastatic and primary spinal tumors.