This study was approved by the Ethics Committee of the Hebei General Hospital before data collection and analysis. It was a prospective study. Patients with lumbar degenerative disease who underwent robot-assisted PELIF or fluoroscopy-guided minimally invasive transforaminal lumbar interbody fusion (MIS-TLIF) from December 2017 to February 2020 were enrolled. The patients were divided into two groups according to the pedicle screw implantation method: the robot-assisted under regional anaesthesia (group RE-RO) and fluoroscopy-guided under general anaesthesia (group GE-FLU) groups.
The inclusion criteria were as follows: 1. scheduled 1- or 2-level PELIF or MIS-TILF surgery with either robot-assisted or fluoroscopy-guided percutaneous pedicle screw placement as the internal fixation technique; and 2. postoperative computed tomography (CT) scans taken before discharge with images meeting the measurement requirements. The exclusion criteria were as follows: 1. patients with a degree of lumbar spondylolisthesis or lumbar spondylolysis of II or higher; and 2. patients with infection, tumours or scoliosis of the spine.
All procedures were performed by the same senior spine surgeon who had performed more than 20 cases of robot-assisted surgery. The patients’ CT data of the lumbar vertebrae (continuous scanning, ≤1-mm cuts) were copied from the inspection equipment and input into the robotic surgical plan workstation (Mazor Renaissance Surgical Technologies, Caesarea, Israel) for preoperative planning. During surgery, the patient was placed in a comfortable prone position on the operating table, with oxygen inhalation and ECG and vital sign monitoring. Dexmedetomidine (4 µg/ml) was pumped at a rate of 3-8 ml/h. The administration of epidural anaesthesia was performed using the loss-of-resistance technique though the interlaminar space of the operated segments (Fig 1). The anaesthetic drug for the injection was a mixture of 0.5% lidocaine and 0.25% ropivacaine. The dose was 10 ml. In this anaesthetic state, patients had hypoesthesia rather than loss of sensation in the operative region and lower extremities. Motion of the lower limbs persisted. The surgical procedure was performed as follows. First, the working platform was installed. The Hover-T frame platform was used for all operations in this group. After local infiltration anaesthesia (1% lidocaine), three needles were inserted into the spinous process of the upper lumbar spine and bilateral posterior superior iliac spines to fix the frame (Fig 2). After image acquisition, registration, and robot motion, local infiltration anaesthesia was administered to the skin and around the facet joints before incision and drilling (Fig 3). To minimize deviations caused by spine movement, drilling was carried out in a painless state. Otherwise, additional local anaesthesia was administered, as pedicle screw insertion could aggravate the patient’s pain. It was essential to increase the speed of drug pumping in advance. Details of the robot-assisted procedure have been described in previous articles [8,15]. After screw (Minimally Invasive Spinal System; WEGORTHO Paedic Device CO., LTD; Weihai, China) placement, decompression and interbody fusion were performed (Fig 4).
The pedicle screw placement procedures were completed by two senior spine surgeons who both had performed more than 50 cases of fluoroscopy-guided pedicle screw insertion. After general anaesthesia, the patient was placed in a prone position. A C-arm was used to locate the targeted vertebral pedicles and plan the screw route. A puncture needle was inserted through a 1.5-cm incision with fluoroscopy guidance. After a final fluoroscopy check on AP and lateral views, the puncture needle was replaced with a spacer. Screw (Minimally Invasive Spinal System; WEGORTHO Paedic Device CO., LTD; Weihai, China) placement was performed after decompression and interbody fusion.
The primary outcome measures were screw accuracy and the incidence of FJV. All patients underwent thin-slice CT scans (≤1.2-mm slices) of the lumbar spine postoperatively. Screw accuracy was evaluated using the Gertzbein and Robbins criteria : grade A: completely within the pedicle, grade B: < 2 mm cortical breach, grade C: 2-4 mm cortical breach, grade D: 4-6 mm cortical breach, and grade E: > 6 mm cortical breach. Screw grades A and B were considered clinically acceptable [17-19]. Differences in the screw accuracy grades between the two groups and the proportions of clinically acceptable screws were assessed as the accuracy comparison parameters. FJV was evaluated only for the upper pedicle screws because of the related clinical significance using the Babu classification system : grade 0: the screw does not violate the facet joint, grade 1: the screw violates the lateral facet, grade 2: the screw penetrates the articular facet by 1 mm, and grade 3: the screw lies within the articular facet surface. Differences in violation grades and the percentages of violating screws (grades 1, 2, and 3) were assessed as the FJV comparison parameters. The data were measured independently by two spinal graduate students using a Picture Archiving and Communication System (PACS) (Neusoft Medical image diagnostic reporting system; Neusoft Co., Ltd., Shenyang, China) who were not aware of the purpose of the study in advance. If there was a discrepancy between the results, the worse result was adopted.
As secondary outcome measures, we compared the X-ray exposure and intraoperative adverse events related to the screw placement procedure as well as to anaesthesia. X-ray exposure measurements were determined by the fluoroscopy time for each screw (sum of exposure times of screw implantation and rod connecting procedures/number of screws inserted).
Fisher’s exact test and Pearson's chi-squared test were used for group comparisons of sex and screw location as well as the percentages of clinically acceptable screws and facet violation screws. Two-sample t tests were used for group comparisons of age, body mass index (BMI) and fluoroscopy time for each screw. The Mann-Whitney U test was used for group comparisons of accuracy and FJV grades. The statistical significance of these parameters was set at P < 0.05, and statistical analyses were performed using IBM SPSS Statistics for Windows, version 23.0 (IBM Corp, Armonk, NY, USA).