This retrospective chart review was exempt from the Italian Ethics Committee. Data were collected from 3 surgeons at a single site. Patients who were included in the analysis were at between 21 and 85 years of age and required surgery that includes screws to be inserted in cervical, thoracic, lumbar spine or sacrum. Demographic data (including age, gender, BMI and diagnosis), operative data (including set up time, screw insertion time, operative time, blood loss, radiation time), preoperative/postoperative computerized tomography (CT) scans, and complication rates of 127 patients treated with lumbosacral pedicle screws through a minimally invasive robotic assisted technique were analyzed. The methods for this publication are similar to those described in a previously published manuscript by the same principal investigators [17].
The surgical technique employed in this study utilized a robotic positioning system (ExcelsiusGPS®, Globus Medical, Inc., Audubon, PA, USA) (Fig. 1) in which patient radiographs may be uploaded and registered through one of three modalities: preoperative CT, intraoperative CT, or fluoroscopy. For this study, only the preoperative CT workflow was used. In this workflow, a CT scan is taken prior to the surgery, and screw placement planning can be performed. In the operating room (OR), fluoroscopy is used to “merge” the CT and plan to the patient’s positioning on the surgical table. The robotic system uses a dynamic reference base and positioning camera to track the position of instrumentation in real time and 3-dimensional (3D) space, while the rigid robotic arm guides the surgeon to the planned screw trajectory.
2.1 Surgical Technique
Once the patient was placed on the table, the dynamic reference base was then placed by making a small incision and anchoring the base to the posterior superior iliac. An attachment to the C-arm was used while fluoroscopy shots were taken in view of the robotic system’s positioning camera to merge the patient positioning to the preoperative CT scan. Anterior-posterior and lateral shots were taken to ensure registration of each targeted vertebral level. To confirm successful registration, landmark checks were performed with tracked instruments.
The robotic arm was controlled by the surgeon through a foot pedal, which when pressed caused the arm to move to the preplanned screw trajectory. Through the guide tube attached to the robotic arm, stab incisions were made using a scalpel. Navigated instruments were passed through the guide tube to maintain the planned trajectory, and screws were inserted with these instruments. This process was repeated for all screws. Based on the surgeons’ discretion, 81/127 (63.8 %) patients underwent a laminectomy and/or discectomy. Once the screws were placed, rods were placed and held in place with locking caps. Implant position was confirmed with fluoroscopy.
2.2 Accuracy and Screw Offset
Postoperative CT scans were used to perform a Gertzbein and Robbins System (GRS) evaluation of pedicle screw accuracy. In this scale, screws were graded as A (no breach), B (breach of less than 2 mm), C (breach of less than 4 mm), D (breach of less than 6 mm), or E (breach of more than 6 mm). Screws graded to have a less than 2 mm breach (Grade A or B) were considered clinically acceptable, while those screws with a greater than 2 mm breach were considered inaccurate, as in other studies [17–21]. The number of A- and B-graded screws as a percentage of the total screws implanted is presented as an accuracy percentage. Further accuracy analysis utilized postoperative CT scans and the preoperative screw plan trajectories to compare the plan to final placement (Fig. 2). Screw tip, tail, and angulation offsets were measured using software designed for this purpose. Visualizations of planned screws were removed during image overlay to remove potential bias. Screw tip deviation was measured as the difference from planned and final placement at the end, or exit point, of the screw. Screw tail deviation was measured as the difference from the planned and final placement at the head, or entry point, of the screw. These values were 2-dimensional translational measurements, in millimeters, on a screw-centric coordinate system, with the longitudinal axis along the screw being excluded. The 3D angle between the tip and tail vector of the planned trajectory and the vector of the final screw placement was reported as the angular deviation in degrees. Rates of return to OR, screw malposition, and screw repositioning were collected. Patient blood loss was collected for the total surgery time, and during use of the robot system specifically. Blood loss of less than 25cc was reported as no blood loss. Radiation time was collected and similarly broken out by surgery total and during use of the robotic system. Total operative time and time to place screws was collected.
2.3 Statistical Analysis
Statistical analysis was performed using SPSS Statistics Version 25 software (IBM Corp., Armonk, NY, USA). Data were presented as mean ± standard deviation. Pearson correlation coefficients were calculated for the relationship between body mass index (BMI) and screw offset [22]. The level of statistical significance was set to p < 0.05 for all statistical analysis.