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Choi et al. Mini-invasive Surg 2021;5:43 https://dx.doi.org/10.20517/2574-1225.2021.73 Page 5 of 14

For patients opting for robot-assisted pedicle screw insertions, a 3rd generation floor mounted robot
(ExcelsiusGPS, Globus Medical, Inc. Audubon, PA, USA) was utilised. Similar to the CT navigation system,
a dynamic reference base and surveillance markers were placed, and the image coordinate system was
obtained from a portable intraoperative CT. From there, pedicle screw trajectory planning was performed.
A surgeon-controlled foot pedal was then used to activate and position the robot arm to the planned pedicle
trajectory. Small stab incisions were used, and guide holes were created and tapped. Pedicle screws were
then inserted by the surgeon under assistance from the robotic arm.

After the insertion of the pedicle screws, a rod was passed percutaneously and secured the pedicle screw
head using torque-limiting locking caps. Intraoperative fluoroscopy was then utilised to verify the pedicle
screw, interbody spacer, and rod position.

Outcomes
CT scans were routinely obtained 6 months postoperatively to assess fusion and hardware placement and
[32]
integrity. Screw accuracy was evaluated using the technique seen by Spitz et al. , where screw breaches
[32]
were graded based upon the magnitude and direction of the breach; A = 0-2 mm, B = 2-4 mm, C ≥ 4 mm .
Lumbar lordosis (L1-S1) was obtained by preoperative and 6 months follow-up anteroposterior and lateral
radiographs . All radiographic outcome measures were reviewed by an independent orthopaedic fellow
[33]
(Mehul Sakar).

Visual Analog Pain Scale (VAS) for the legs and/or back was recorded preoperatively and at 6 months
follow-up.

Statistics
Data were presented as mean ± SD (range). Statistical analysis included descriptive statistics, and two-tailed
paired t-test or Mann-Whitney U test (if non-normally distributed) was used. A P value of < 0.05 was
defined as statistically significant. Data distributions were evaluated using the Shapiro-Wilks test.

RESULTS
Patient characteristics and results are presented in Table 1. Thirty-five patients (17 males and 18 females)
with a mean age at surgery of 69 years (46-87 years) were included in this study. All patients were followed
up for a minimum of 6 months after surgery. The mean body mass index (BMI) was 31.9 (22.0-50.9), and
26% of the cohort had a history of smoking whilst 17% had diabetes. Most of the patients had no previous
lumbar spine surgery (83%), and those that did had either a laminectomy (9%), microdiscectomy (5%), or
PLIF (3%).

Surgical data are presented in [Table 2]. The primary indication for surgery in our cohort included
spondylolisthesis (46%), degenerative disc disease (44%), stenosis (5%), and scoliosis (5%). A total of 51
lumbar intervertebral disc levels were operated on, with 23 patients undergoing single-level surgery, 8
undergoing two-level fusions, and 4 undergoing three-level fusions. The most common spinal level treated
was L4/5 (22 patients), followed by L5/S1 (21 patients), L3/4 (15 patients), and L2/3 (2 patients). The mean
total operative time was 152.2 ± 54.8 min (80-320 min), and the mean length of hospitalization was 5.3 ± 1.7
days (3-9 days).

A total of 169 pedicle screws were placed; 72 screws using fluoroscopy, 10 screws with CT navigation, and
87 with robot assistance. Different techniques were used for pedicle screws placement in part due to the
surgeon transitioning from navigation use to robot-assisted technique. Also, fluoroscopic guided