The occurrence of lumbar degenerative diseases is on the rise in the global society with the advancement of the society and the phenomenon of aging population of the society . Obviously, as the incidence increases, it seriously affects the quality of life of patients and is a major source of chronic disability [22–24].Therefore, lumbar fusion is becoming increasingly common as an adjunct in the surgical treatment of lumbar degenerative diseases . Interbody fusion is an effective treatment for a variety of spinal conditions, including degenerative disc disease, spinal stenosis, lumbar slippage, degenerative scoliosis, traumatic changes, infections, and tumors. However, with the development of interbody fusion, the frequency and complications of the procedure have increased [4, 21]. Our goal is to reduce complications and increase the success of the procedure. In between, a number of minimally invasive interbody fusions have emerged, and for many surgeons, minimally invasive surgical approaches have become a safe alternative to traditional open techniques.
In this study, we report the safety and efficacy of OLIF compared to the PLIF technique in treating degenerative lumbar spondylosis, which has the advantages of shorter operative time, more temporary hospital stays, less bleeding, and lower incidence of postoperative low back pain. We found that the back VAS score, ODI score, and JOA score were lower in the OLIF group than in the PLIF group 7 days after surgery. Furthermore, intraoperative bleeding was lower, the incision was smaller, and the operative time was shorter in the OLIF group. This may be related to the entry route of the OLIF procedure, where the disc is entered through the natural gap between the abdominal aorta and the anterior border of the psoas major muscle in the abdomen, with a smaller incision, preserving the posterior structures of the spine and reducing the risk of damage to the surrounding tissues [26, 27]. PLIF is a classic and effective surgical procedure for treating lumbar degenerative spine disease and is suitable for most patients with lumbar degenerative disease. The stability of the posterior column structures in the three columns of the spine is compromised due to an extensive dissection of the paravertebral tissue during the procedure. As a result, the incidence of intraoperative complications associated with PLIF is higher than with OLIF, and the short-term effects of PLIF are slightly lower than those of OLIF; in particular, postoperative symptoms may worsen in the short term, or they may not be relieved. Compared to PLIF, the OLIF group did not have a dissection of the paravertebral muscles of the back, as well as damage to the back muscles, avoiding posterior scar tissue, thus reducing bleeding, shortening the operative time, and effectively reducing the incidence of postoperative low back pain . This resulted in a better back VAS score in the OLIF group than in the PLIF group in the early postoperative period. Also, leg VAS scores were lower in the OLIF group than in the PLIF group 7 days after surgery, which may be due to the avoidance of direct stimulation and nerve roots pulling during the OLIF procedure.
In previous analyses, it has been found that the occurrence and progression of degenerative lumbar spine disease are strongly associated with loss of lumbar curvature and intervertebral space height. Indirect decompression is achieved through the OLIF procedure by inserting a larger area and volume fusion in the vertebral body's lateral aspect, increasing the lumbar lordotic angle and gap height, and pulling on the ligaments. According to Sato  et al., there was a significant improvement in the intervertebral space's size after OLIF compared to preoperatively. In the present study, the immediate postoperative intervertebral space height was significantly higher than the preoperative space height in both groups, and the OLIF group had a statistically significant difference in postoperative intervertebral space height compared to the PLIF group. The loss of the lumbar lordotic angle is a fundamental cause of lower back pain. It is crucial to restore the lumbar lordotic angel and the lumbar lordotic angel of the surgical segment for symptom recovery and prevent degeneration of the adjacent phases . It has been shown  that OLIF surgery has a significant improvement in lumbar lordotic at the surgical stage. In the present study, both the OLIF and PLIF groups showed a substantial recovery of lumbar lordotic angle and operative segmental lordotic angle, with a statistically significant difference between the OLIF and PLIF groups in the immediate postoperative period, which may be related to the insertion of a larger fusion device. At the final follow-up, there was a statistically significant difference between the lumbar lordostic and the operative segmental lordotic angle between the two groups and the preoperative period, but not between the two groups. This means that the OLIF group achieved the same surgical results as the PLIF group.No fusion was observed in any of the patients by CT and X-ray at the final follow-up. In the OLIF group, four patients found fusion subsidence, and the loss of vertebral space was less than 25%, which is considered mild , and all patients with subsidence had no clinical symptoms during the follow-up. Osseous fusion was obtained in both groups at the final follow-up, with no difference in infusion rate. We believe that the more extensive fusion apparatus used in the OLIF procedure increases the contact area with the last plate, which contributes to a higher fusion rate and a lower settling rate .
Intraoperative complications of OLIF include vascular injury, nerve injury, ureteral injury, and cerebrospinal fluid leakage [9, 32, 33], which did not occur in the present study. Postoperative complications included transient thigh and groin sensory deficits and hip flexor weakness, fusion settling, pseudarthrosis, and postoperative infection [32, 34, 35], none of which were serious complications in the present study.