Over time, doctors have increasingly favored minimally invasive surgery. While ensuring clinical results, minimally invasive procedures minimize surgical trauma and ease patient suffering. Various minimally invasive techniques have been applied in the clinic and have benefitted many patients. In recent years, the clinic has widely used minimally invasive oblique lateral spinal fusion surgery via OLIF. This procedure uses extraperitoneal blood vessels and the psoas muscle space for entry, allows the implantation of a larger fusion cage, increases the bone contact surface, and thus increases the fusion rate. This approach also allows complete opening of the intervertebral space, expansion of the intervertebral foramen area, and restoration of the spinal canal volume to achieve indirect decompression [2, 11]. OLIF is widely used because of its ability to provide indirect decompression and its minimal invasiveness; it also helps restore the sagittal curve and coronal balance. It can be applied to treat various lumbar degenerative diseases, especially lumbar spondylolisthesis . Because of the lack of an ideal effect and the insufficient rotational stability achieved with a fusion cage alone, bilateral pedicle screw fixation is still the gold standard .
However, in conventional OLIF, the patient usually needs to be in the lateral position for cage placement and then transitioned to the prone position for pedicle screw placement. In this study, single-position OLIF significantly reduced the intraoperative blood loss and shortened the operation time compared with conventional OLIF. Single-position OLIF does not require repositioning, which helps save operative time. Additionally, because the operation time is reduced, the intraoperative blood loss and anesthesia time are reduced, which helps decrease the risk of infection and anesthesia decannulation. Although no patients with anesthesia decannulation and infection were observed in this study, patients may benefit from the close attention of anesthesiologists and strict compliance with routine aseptic procedures.
In addition, the VAS score and ODI in this study were significantly lower after the operation than before the operation. The lumbar and lower limb symptoms were significantly improved. Similarly, IDH and LL on imaging were considerably enhanced compared with those before operation. Loss of the LL angle and changes in the IDH are closely related to the development of DLS. Therefore, it has important clinical significance to study the changes in the LL and IDH in DLS patients. The loss of LL is a key cause of low back pain in patients , and the restoration of the IDH at the affected segment improves the compression of the nerve root at the corresponding segment. In this study, both OLIF and PLIF can significantly restore lumbar lordosis and intervertebral space height. There was no significant difference in the VAS, ODI, IDH, and LL between the two groups at the last follow-up. In short, single-position OLIF has clinical efficacy, high safety, and feasibility that are similar to those of conventional OLIF. Similar results have been obtained in other studies [6, 15].
The two groups of patients inevitably had different degrees of complications. Vascular injury, which is mainly the injury of vertebral segmental vessels and iliac vessels, is a common complication of OLIF . The risk of vascular injury by the OLIF technique is mainly related to the process of incision exposure, separation of psoas muscle and vascular sheath, and deep clearance of intervertebral space . Endplate injury mostly occurs in patients with osteoporosis . Improper operations during surgery, such as directly using a sharp reamer to remove the nucleus pulposus or the following the wrong direction during intervertebral disc cleaning, can cause endplate damage. For patients with intraoperative endplate injury, screw fixation is necessary . Among our patients who underwent single-position OLIF, three patients (11.11%) had transient leg weakness during follow-up, and four patients (8.62%) in the conventional OLIF group had transient leg weakness during follow-up. The numbers were within the normal range (6.1-60.3%) [11, 19, 20]. Postoperative thigh numbness and hip flexion weakness may be caused by retraction of the psoas muscle and associated sensory nerves . These symptoms are mostly transient, and postoperative rehabilitation exercises can facilitate recovery in a short period.
Pedicle screw misplacement is a common complication in spinal surgery. This study used “freehand” screw placement. According to reports, the displacement rate of “freehand” pedicle screw placement is 1.5-14.3% [22-24]. Although the development of robotic technology (computer navigation technology) has helped to improve accuracy [25, 26], sometimes hospitals do not have computer technology navigation technology and often still perform “freehand” operations.
The single-position OLIF may be a new technology worthy of recommendation. Recently, Kotani et al.  found that single-position OLIF can provide a comparable fusion rate, segmental radiologic alignment, and symptomatic adjacent segment degeneration to MIS-TLIF surgery. Pham et al.  presented a novel technical report on the recommended workflow of simultaneous robotic single-position OLIF and demonstrated the ’feasibility of placement of sacroiliac fixation in the lateral decubitus position. In addition, Diaz-Aguila et al.  found that robot-assisted OLIF can reduce the operative time while ensuring accurate and timely screen placement with minimal complications. As medical technology continues to develop, minimally invasive, robot-assisted surgical treatment will be increasingly used. We expect to see more reports on robot-assisted treatments for lumbar degenerative disease. In short, single-position OLIF serves as a safe, minimally invasive and effective surgical modality that saves valuable operating room time and is worth popularizing.
Although OLIF has advantages over conventional surgery in terms of the operative duration, there is no need for a significant learning curve to adapt to this technology. However, we believe that surgeons should pay attention to the following factors. First, surgeons must have sufficient experience with OLIF combined with "freehand" placement of PPSF. Second, the patient's position is significant. On the one hand, being too close to the bed will affect the fluoroscopy. On the other hand, being too far away from the bed will limit the puncture angle of PPSF. According to our experience, the average time required to insert each percutaneous pedicle screw on the patient's right side was significantly longer than that required to insert each screw on the left side. This difference may occur because it is easier to apply force while inserting the percutaneous pedicle screw from the left side. Therefore, the patient's position should be as close as possible to the side of the operating bed so as not to block the operating bed when the nail is placed on the right side. In our opinion, the ideal position is from the edge of the bed to a quarter of the width of the bed.
There are some limitations to our study. First, because the single-position OLIF method has not yet been popularized, the sample size of our study is small, and larger sample size is needed to confirm its safety and efficacy. Second, the survey subjects were limited to LDS patients treated at Lanzhou University Second Hospital. There may be differences among medical institutions due to differences in medical equipment. Third, surgeons may have varying experiences with OLIF techniques.