
==== Front
J Neurosurg Case Lessons
J Neurosurg Case Lessons
J Neurosurg Case Lessons
Journal of Neurosurgery: Case Lessons
2694-1902
American Association of Neurological Surgeons

39250836
10.3171/CASE2415
CASE2415
PainPainSpineSpineLumbarLumbarTraumaTraumaTechniqueTechniqueSurgical-TechniqueSurgical TechniqueCase Lesson
Minimally invasive robot-assisted direct pars repair: illustrative cases
Stewart Jeffrey J MD 1
Zhao David Y MD 1
Pivazyan Gnel MD 1
Gensler Ryan BS 2
Voyadzis Jean-Marc MD 1
1 Department of Neurosurgery, MedStar Georgetown University Hospital, Washington, DC
2 Georgetown University School of Medicine, Washington, DC
Correspondence David Y. Zhao: MedStar Georgetown University Hospital, Washington, DC. dyz@georgetown.edu.
INCLUDE WHEN CITING Published September 9, 2024; DOI: 10.3171/CASE2415.

Disclosures Dr. Pivazyan reported funds from Stryker/K2M paid to MedStar Health Research Institute outside the submitted work. Dr. Voyadzis reported being a consultant for Globus outside the submitted work.

09 9 2024
09 9 2024
8 11 CASE241512 1 2024
30 5 2024
© 2024 the authors
2024
the authors
https://creativecommons.org/licenses/by-nc-nd/4.0/ CC BY-NC-ND 4.0 (http://creativecommons.org/licenses/by-nc-nd/4.0/)

BACKGROUND

Robot-assisted techniques are increasingly integrated into the field of spine surgery, with the potential benefits of increased accuracy and reduced radiation exposure. The objective of this study was to describe the technique of minimally invasive robot-assisted direct pars repair with 2 case illustrations.

OBSERVATIONS

An 18-year-old male and a 42-year-old male, both with bilateral L5 spondylolysis, underwent successful minimally invasive L5 direct pars repairs with robotic assistance after conservative measures failed, and their cases are presented herein.

LESSONS

A robot-assisted direct pars repair is a safe and effective technique for treating bilateral lumbar spondylolysis. The integration of robot-assisted techniques in spine surgery has the potential to improve outcomes, decrease surgical time, and reduce the amount of radiation exposure to operating room staff.

https://thejns.org/doi/10.3171/CASE2415

direct pars repair
pars screws
robot-assisted surgery
robotic spine surgery
case report
ABBREVIATIONS

AP = anteroposterior
CT = computed tomography
EMG = electromyography
FDA = Food and Drug Administration
LSO = lumbar-sacral orthosis
MIS = minimally invasive surgery
MRI = magnetic resonance imaging.
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pmcRobot-assisted lumbar spine instrumentation positively impacts patient outcomes with improved screw accuracy and lower rates of perioperative complications.1 Shared-control robotic systems have also shown great potential in reducing radiation exposure and enhancing accessibility via minimally invasive corridors,2 thereby decreasing infection rates, blood loss, postoperative pain, and hospital stays.3–5

The integration of robotics into spine surgery furthers technological advancements made in spinal navigation, and the field has grown rapidly, as evidenced by a number of publications on this topic alone within the last decade.1, 6–8 Since the Food and Drug Administration (FDA) approval of the first device in the United States in 2004, a multitude of spinal robotic devices have become available on the market.6 As the use of robotics gains favor, its applications will naturally encompass a wider spectrum of instrumentation techniques and spinal pathologies.

Lumbar isthmic spondylolysis occurs at L5 in 95% of cases and is estimated to be prevalent in 3%–7% of the general adult population.7, 9–14 Repetitive stress on the pars interarticularis can lead to microfractures and subsequent osseous defects. In adolescents, especially those participating in certain sports involving repetitive hyperextension, the actual incidence is much higher.11, 12 Patients typically present with progressive axial back pain, with or without radiculopathy. If symptoms are refractory to conservative therapy, surgery may be indicated for pain reduction, return to physical activity, and the prevention of progression to spondylolisthesis.9, 14 A number of surgical treatment options have been utilized, including direct pars repair with Buck’s lag screw technique, segmental fusion, and various other wiring or screw-hook stabilization techniques.10, 13 Minimally invasive techniques for direct pars repair have been described by our group and others,9, 12, 15–17 with the potential advantages of decreased postoperative pain, reduced surgical site infections and blood loss, and earlier mobilization.3–5

We report our experience with minimally invasive robot-assisted lumbar direct pars repair, describe technical nuances, and assess the advantages afforded by minimally invasive surgery (MIS) with robotic assistance.

Illustrative Cases

Surgical Technique

A preoperative thin-cut computed tomography (CT) scan is obtained and uploaded to the Excelsius robot’s workstation (ExcelsiusGPS, Globus Medical). Buck’s technique, consisting of a single lag screw placement through the pars defect, is utilized, as it is uniquely suited for MIS or percutaneous screw applications. Screw trajectories are planned from medial to lateral and caudad to cephalad, with a starting point at the inferior aspect of the lamina and an endpoint at the pedicle of the index level through the pars defect (Fig. 1). Appropriate screw sizes (Zyfuse, Globus) are also determined based on sagittal, coronal, axial, and three-dimensional reconstructions using the planning software and workstation. An optimal single sacral midline skin incision for unilateral or bilateral screw placement is planned using the software. Standard pedicle screws are also planned at the adjacent levels to add additional reference points to improve navigation accuracy. FIG. 1. Preoperative planning of the pars screw trajectory in the axial (A) and sagittal (B) planes. The trajectory of the pars screws (blue) intersects in the midline, enabling the use of a midline incision as opposed to the 4 traditional pedicle screws (gray) utilized in a posterolateral fusion (C).

Upon induction of general anesthesia and intubation, the patient is positioned prone on a flat Jackson table with gel rolls to facilitate the caudad-to-cephalad trajectory of screw placement. Somatosensory evoked potentials are monitored, and electromyography (EMG) is performed. Antibiotics are given for perioperative infection prophylaxis, and all pressure points are padded. The first 2-cm midline incision is made after local anesthetic infiltration over the L4 spinous process, to which the navigation reference array is clamped. This same incision is later used for pars decortication as described below. Anteroposterior (AP) and lateral radiographs are obtained and then merged with the preoperative CT for registration. The accuracy of patient registration is confirmed. Navigation is then performed to mark the planned second caudal 2-cm midline incision for screw placement (Fig. 2). The incision is made after local anesthetic infiltration, and the underlying fascia is opened with electrocautery. The robotic arm is then brought in to guide screw placement. A pilot hole is created with navigated robot assistance at the inferior aspect of the lamina using a high-speed drill, followed by the insertion of a navigated drill through the pars defect and into the L5 pedicles bilaterally (Fig. 3). A series of dilators are placed through the tubular retractor of the robotic arm, and a K-wire is advanced through the tract (Fig. 4A). The exact same steps are repeated utilizing the same caudad midline incision for bilateral repair. FIG. 2. The patient is positioned prone on a flat Jackson table with gel rolls. The first 2-cm midline incision is made over the L4 spinous process to which the navigation reference array is clamped. The workstation is placed at the patient’s feet. Navigation is then performed to mark the second planned 2-cm midline incision more caudally for screw placement, pictured here. Cephalad is at the bottom of the image, and caudad is at the top.

FIG. 3. Use of intraoperative navigation to create pilot holes and place K-wires prior to decorticating.

FIG. 4. Intraoperative fluoroscopy demonstrating placement of K-wires (A), decorticating the fracture surfaces (B), and placement and compression of pars screws on the left (CandD) and on the right (EandF).

The L4 spinous process navigation clamp is removed. A series of tubular dilators are placed through this incision and docked onto the pars defect on one side using fluoroscopy. This is followed by the tubular retractor, which is connected to the table-mounted flexible arm. The placement of the dilators and tubular retractor could also be performed with navigation, avoiding fluoroscopy, by placing the reference clamp through a separate spinous process incision more cephalad or onto the iliac crest.

After the clearance of soft tissue, the pars defect is exposed, and all fibrous tissue is vigorously removed with curettes and rongeurs down to the bone. The defect is then decorticated with a high-speed drill (Fig. 4B) and prepared for fusion by placing bone grafting materials. Care is taken not to damage the visualized K-wire.

From the caudad incision, a cannulated lag screw is then advanced over the K-wire and subsequently compressed after placement confirmation with AP and lateral fluoroscopy (Fig. 4C and D). The implant design of the lag screw allows for compression of up to 10 mm to optimize the fusion potential across the pars defect. Similar steps are performed on the contralateral side (Fig. 4E and F). Triggered EMG screw stimulation of the screws is performed to evaluate for cortical breach and screw malposition. The working channel is removed, and both wounds are closed in the standard fashion. A long-acting local anesthetic (Exparel, Pacira Pharmaceuticals) is injected into the muscular and subcutaneous tissues prior to skin closure.

Patients are deemed to be good candidates for minimally invasive direct pars repair if there is no evidence of disc degeneration, disc herniation, or malalignment at the index level. All patients are counseled on the possibility of segmental fusion and that this robotic technique is a non–FDA-approved application.

Case 1

An 18-year-old male presented with severe progressive axial low-back pain accompanied by worsening bilateral leg paresthesias. He reported that his low-back pain was far greater than his leg symptoms. He was otherwise healthy and an avid martial arts competitor without a significant past medical or surgical history. On examination, bilateral lower-extremity motor strength, sensation, and reflexes were intact and symmetric. Imaging studies, including dynamic radiography and CT (Fig. 5) of the lumbar spine, demonstrated a bilateral L5 pars defect, or spondylolysis, without associated spondylolisthesis or significant disc degeneration. There was no significant stenosis or facet arthropathy at any level on magnetic resonance imaging (MRI). FIG. 5. Case 1. Standing dynamic radiographs of the lumbar spine in flexion (A) and extension (B), which demonstrate no evidence of dynamic instability. Preoperative CT of the lumbar spine with an axial section through the L5 pars (D) and sagittal sections through the left (C) and right (E) L5 pars. Postoperative CT of the lumbar spine with axial sections through the L5 pars (G) and sagittal sections through the left (F) and right (H) L5 pars, demonstrating intact hardware and fusion across the defect.

After unsuccessful initial conservative treatment including bracing, physical therapy, and pain management strategies consisting of targeted pars steroid injections, he underwent a bilateral minimally invasive robot-assisted direct L5 pars repair with two 5 × 40–mm lag screws.

Postoperatively, he wore a lumbar-sacral orthosis (LSO) brace continuously for 6 weeks and an external bone stimulator for 6 months. At the 9-month follow-up, he endorsed significant improvement with a reported 75% reduction in his chronic low-back pain. Follow-up imaging studies, consisting of CT, demonstrated an intact appearance of the instrumentation and fusion across the pars defect (Fig. 5).

Case 2

A 42-year-old healthy and active male presented with a 6-year history of progressive low-back pain. He reported that the pain radiated into his groin and hips but denied radicular leg symptoms. He had been previously managed conservatively with pain medication, injections, bracing, and physical therapy, which were no longer effective. On examination, bilateral lower-extremity motor strength, sensation, and reflexes were intact and symmetric. CT of the lumbar spine demonstrated a bilateral L5 pars defect, or spondylolysis, without significant disc degeneration. MRI and dynamic radiography of the lumbar spine did not demonstrate any significant stenosis or facet arthropathy at any level or any associated spondylolisthesis.

After conservative management had failed, the patient underwent a bilateral minimally invasive robot-assisted direct L5 pars repair with two 5 × 40–mm lag screws. Postoperatively, he also wore an LSO brace continuously for 6 weeks. At the 9-month follow-up, he reported significant improvement in his chronic pain and discontinued opioid use. Follow-up CT demonstrated intact instrumentation and a robust fusion across the pars defect.

Patient Informed Consent

The necessary patient informed consent was obtained in this study.

Discussion

Observations

A number of studies have reported on the safety and efficacy of minimally invasive direct pars repair using Buck’s technique.10, 13 These muscle-sparing approaches decrease postoperative pain, limit surgical site infections and blood loss with smaller incisions, and reduce the hospital stay. The addition of spinal navigation to these less invasive techniques can dramatically reduce reliance on fluoroscopy and improve accuracy.9, 18 Fracture morphology assessed on CT can inform the choice of technique for pars repair. The use of navigation and robotics is advantageous in optimizing the screw trajectory orthogonal to the defect for optimal fixation, thereby decreasing the potential need for revision.1, 6, 9, 18, 19

The benefits afforded by robotic assistance are high screw accuracy and reduced radiation exposure. A number of studies have validated the accuracy of robot-assisted lumbar spine instrumentation.1, 2, 8, 20 In a cadaveric study using the same robotic navigation platform, Vaccaro et al. found significantly decreased radiation exposure with robotic assistance compared to that with freehand thoracolumbar screw instrumentation.20 The cases presented here illustrate that the tenets of MIS are further enhanced by robotic assistance. Using planning software, tracing the screw trajectory back to the skin allowed for the creation of a 2-cm midline incision, and small paramedian stab openings through the fascia avoided extensive paraspinal muscular dissection with the use of dilators. With these strategies, blood loss becomes negligible, and postoperative pain is mitigated. Execution of a preplanned, navigated screw trajectory assisted by the robotic arm resulted in accurate placement. In their minimally invasive direct pars repair case series, Ghobrial et al. demonstrated the safety and feasibility of this approach in 9 young patients with good clinical and radiographic outcomes.12 Screw insertion under robotic navigation additionally reduced our need for fluoroscopy. A single AP and a lateral image were required for registration, after which only confirmatory images were essential. This is in contrast to fluoroscopy-guided pars repair, which requires repeated AP and lateral images.

We describe 2 cases of patients who underwent minimally invasive direct pars repairs with robotic assistance. Both patients had uneventful postoperative courses and improved considerably after surgery. In both cases described, preoperative CT was used for intraoperative navigated screw tract preparation and the use of K-wires. Screw tract preparation was performed first before pars defect exposure to minimize navigation imprecision from manipulation of the patient, consistent with our technique of robot-assisted pedicle screws. Screws were placed last after pars defect decortication to optimize exposure and preparation of the pars defect. Another approach with an alternative workflow can utilize intraoperative CT. Here, the pars defect can be exposed and prepared first, followed byintraoperative CT and navigated screw placement with robotic assistance second.

Lessons

The use of robotics in spine surgery can be applied safely and accurately to nontraditional methods of screw fixation. Even though the planning software was designed for the placement of robot-assisted navigated pedicle screws, there were no technological complications referable to an alternative method of screw fixation during planning, registration, navigation, and execution. Thus, pedicle screws were used in the planning process to allow for a successful and accurate registration (Fig. 2). Future iterations of the software will allow for direct pars screw planning. When planning alternative methods of screw fixation, the degrees of freedom and subsequent envisaged movements of the robotic arm with respect to the patient must be taken into consideration.

While the use of robots in spine surgery is becoming increasingly prevalent, the upfront cost to a hospital or healthcare system is significant, ranging from $500,000 to $1,000,000 for one robot.21 This substantial investment can be recouped by increasing operating room efficiency and decreasing operating room time after an initial learning curve.21 In addition, minimally invasive and robotic spine surgery can significantly decrease surgical site infections compared to those with open surgery.3–5, 21

There are several limitations to this study, including its retrospective nature, lack of a control group, and small number of patients. Furthermore, the relatively high cost of obtaining and implementing a robotic system may limit its external validity, as many smaller hospitals and hospital systems may not be capable of making such a substantial investment.

Minimally invasive robot-assisted direct pars repair is a safe and effective technique for treating bilateral pars defects. Pars screws allow the surgeon to employ a single midline incision rather than the 4 separate paramedian incisions used for robot-assisted pedicle screws. The use of robotic systems in spine surgery offers many potential benefits, including improved screw accuracy, lower rates of complications, shorter operative time, and decreased radiation exposure for both the operating room staff and the patient. The significant upfront cost of the robot can be recouped quickly through the savings the robot provides the hospital.

Disclosures

Dr. Pivazyan reported funds from Stryker/K2M paid to MedStar Health Research Institute outside the submitted work. Dr. Voyadzis reported being a consultant for Globus outside the submitted work.

Author Contributions

Conception and design: Zhao, Stewart, Voyadzis. Acquisition of data: Zhao, Stewart, Gensler. Analysis and interpretation of data: Zhao, Stewart, Pivazyan, Voyadzis. Drafting the article: Zhao, Stewart, Gensler. Critically revising the article: Zhao, Stewart, Pivazyan, Voyadzis. Reviewed submitted version of manuscript: Zhao, Stewart, Pivazyan, Voyadzis. Approved the final version of the manuscript on behalf of all authors: Zhao. Statistical analysis: Zhao. Study supervision: Voyadzis.

Correspondence

David Y. Zhao: MedStar Georgetown University Hospital, Washington, DC. dyz@georgetown.edu.
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