Change in study design [Randomization not feasible]

Computer-based navigation systems were first introduced to spine surgery in 1995 and while they have been long established as standards in certain cranial procedures, they have not been similarly adopted in spine surgery. Designed to overcome some of the limitations of navigation-based technologies, robot-guided surgical systems have become commercially available to surgeons worldwide.These systems are rapidly challenging the gold standards.

The aim is to conduct a prospective randomized controlled trial. The randomized variable will be the screw placement technique used. One arm will be treated with lumbar fusion using robotic guidance (RG), one arm will receive the same procedure but with a free hand technique (FH) and the third arm will use navigation (NV) (CT or Fluoroscopy-assisted). Intraoperative screw revisions and revision surgery for screw malposition as well as clinical patient-reported outcomes to identify any such differences between these methods of screw insertion will be assessed.

A decade ago, minimally invasive surgery (MIS) was considered a promising development in spine surgery, yet the value of the pioneering technologies was questionable. With the growing number of experienced MIS surgeons, the influx of evidence in favour of MIS is rapidly increasing. This makes a compelling argument towards MIS offering distinct clinical benefits over open approaches in terms of blood loss, length of stay, rehabilitation, cost-effectiveness and perioperative patient comfort. Due to the limited or inexistent line-of-sight in MIS procedures, surgeons need to rely on imaging, navigation, and guidance technologies to operate in a safe and efficient manner. Therefore, a plethora of new and ever improving navigational systems have been developed. These systems allow a consistent level of safety and accuracy, on par with results achieved by very experienced free hand surgeons, with a reasonably short learning curve.

Computer-based navigation systems were first introduced to spine surgery in 1995 and while they have been long established as standards in certain cranial procedures, they have not been similarly adopted in spine surgery. Designed to overcome some of the limitations of navigation-based technologies, robot-guided surgery has become commercially available to surgeons worldwide, like SpineAssist® (Mazor Robotics Ltd. Caesarea, Israel) and the recently launched ROSA™ Spine (Zimmer-Biomet, Warsaw, Indiana, USA). These systems are rapidly challenging the gold standards.

SpineAssist®, and its upgraded version, the Renaissance®, provides a stable drilling platform and restricts the surgeon's natural full range of motion to 2 degrees of freedom (up/down motion and yaw in the cannula). The system's guidance unit moves into the trajectory based on exact preoperative planning of pedicle screws, while accounting for changes in intervertebral relationships such as due to distraction, cage insertion or changes between the supine patient position in the preoperative CT and the prone patient on the operating table. Published evidence on robot-guided screw placement has demonstrated high levels of accuracy with most reports ranging around 98% of screws placed within the pedicle or with a cortical encroachment of less than 2 mm.

Although the reliability and accuracy of robot-guided spine surgery have been established, the actual benefits for the patient in terms of clinical outcomes and revision surgeries remain unknown.

The investigators recently conducted a cohort study that showed some evidence that robotic guidance lowers the rate of intraoperative screw revisions and implant related reoperations compared to free hand procedures, while achieving comparable clinical outcomes. Now, these factors, among others, have to be assessed on a higher level of evidence. This would be, to date, the first randomized controlled trial comparing clinical patient reported outcomes of robotic guided (RG) pedicle screw placement vs. navigated (NV) vs. free hand (FH) pedicle screw placement.

The investigator's aim is to conduct a prospective randomized controlled trial. The randomized variable will be the screw placement technique used. One arm will be treated with lumbar fusion using robotic guidance (RG), one arm will receive the same procedure but with a free hand technique (FH) and the third arm will use navigation (NV) (CT or Fluoroscopy-assisted).

Inclusion Criteria:

• Informed Consent
• Lumbar single level discopathy or Spondylolisthesis of Meyerding Grade 1 or 2
• Body Mass Index >19 and <33
• American Society of Anesthesiologists Scale 1 or 2

Exclusion Criteria:

• Severe Scoliosis (Coronal Cobb's >30 degrees / Schwab classification sagittal modifier + or ++)