Preserving the soft tissue envelope and understanding the anatomy and biology of the posterior spinal musculature are key concepts in minimally invasive spine surgery . Based on this concept, the minimally invasive treatment of DLSS is applied. Many scholars have reported that MISTLIF through bilateral decompression via unilateral approach has achieved good results in the treatment of DLSS [14–16]. OLIF is a minimally invasive anterior retroperitoneal approach surgery, which has been very popular in recent years. In OLIF surgery, the surgeon reaches the operative segment through the anatomical space between the abdominal aorta and the psoas muscle via the retroperitoneal space and preserves the integrity of the posterior structure of the spine. In this study, OLIF shows more advantages in the treatment of single-segment lumbar spinal stenosis than MISTLIF.
OLIF had less bleeding and less postoperative drainage than MISTLIF. The possible reasons are as follows: 1) The OLIF passes through the retroperitoneal approach to the disc, with few peripheral vessels, which are easily protected under direct vision. 2) MISTLIF needs to open the spinal canal, which can easily damage the venous plexus and cause bleeding; especially when contralateral decompression is performed, effective hemostasis is difficult. 3) Bony structural damage is avoided since laminectomy is not required in OLIF. The decrease in the incidence of iatrogenic disturbance to the surrounding tissues and nerves ultimately yields better outcomes in surgical bleeding . The shorter postoperative hospital stay and bedtime in the OLIF group were closely related to less intraoperative injury and less postoperative drainage, which was controversial in previous studies [18–19]. Pain caused by injury to paravertebral muscles and articular processes in the MISTLIF group was also responsible for increased postoperative hospital stay and bedtime. However, the times of fluoroscopy were significantly increased in the OLIF group than those in the MISTLIF group. Possible reasons are as follows: 1) Repeated fluoroscopy is required to determine the orientation and location of the cage during the OLIF procedure. 2) Spine surgeons are familiar with posterior surgery and unfamiliar with lateral surgery. Therefore, the lack of OLIF surgical experience is also the reason for the increase in fluoroscopy times. In contrast to previous reports [20–21], the intraoperative time in the OLIF group was longer than in the MISTLIF group. The possible reasons are as follows: 1) The time of repositioning and disinfection in the OLIF procedure was also included in the intraoperative time in our study. 2) The repeated intraoperative fluoroscopy, surgeon’s expertise, and repertoire were the other related reasons. Higher cost in the OLIF group is mainly related to high-value medical consumables (Cage and artificial bone). This shortcoming may limit the widespread use of OLIF in the treatment of DLSS.
The most important treatment of DLSS is decompression by increasing the area of the spinal canal. OLIF is an indirect decompression procedure, whereas MISTLIF is a direct decompression procedure. In our study, both achieved effective decompression. In this study, although the preoperative PISH in the OLIF group was smaller than that in the MISTLIF group, the postoperative PISH was found significantly larger in the OLIF group. The effective increment and maintenance of IFH and IFA in the OLIF group were closely related to the increment of PISH. The possible reasons are as follows: 1) The cage, which was inserted into the disc gap through the Kambin triangle in the MISTLIF procedure, is smaller than that in the OLIF procedure. It is reported that the triangle between the exiting and traversing nerve roots above the superior margin of the inferior pedicle is narrow. The triangle area is from 1.83 cm2 to 2.19 cm2 . If the cage was large in the MISTLIF procedure, the never roots were easy to injure. Thus the cage was confined by the anatomy of the Kambin triangle and the PISH in the MISTLIF group was not larger enough. 2) In MISTILF surgery, only one side of the facet joints was resected while the contralateral side was usually preserved, so the intervertebral space may not be effectively expanded, especially for patients with facet osteophytosis . Although there was no significant increase in PISH, IFH, and IFA in the MISTLIF group, the postoperative spinal canal area was significantly larger than that in the OLIF group, reflecting the advantage of direct decompression.
Postoperative pain relief and lumbar function recovery were the key focus of both the surgeons and patients. In our study, VAS and ODI scores were significantly decreased, especially in the first 6 months. The symptoms were further improved over time in the follow-up periods and reached a steady state. However, the lumbar VAS and ODI scores at 1 month and 6 months after operation in the OLIF group were significantly lower than those in the MISTLIF group, which was consistent with Kim's report . The reasons are as follows: 1) The paraspinal muscles are not separated from the bony structure, and there is no damage to the posterior branch of the nerve, which reduces the denervation or fatty degeneration of the paraspinal muscles, thereby reducing the incidence of lower back pain in the OLIF group [5, 25]. 2) There was little iatrogenic damage to nerves and tissues around the spinal canal in the OLIF group . Although there was no significant difference in VAS and ODI scores of the lower extremity, we found that there were more patients with transient thigh flexion weakness in the OLIF group. This was likely due to genitofemoral nerve disturbance during the procedure, in which the disturbance is usually temporary and reversible. Both the surgeon's skill and the patient's mental health influence the clinical outcome. The quality of life of patients with lumbar spinal stenosis is closely related to their emotional status . It is reported that anxiety status after spinal surgery could lead to poor clinical outcomes . Pain is considered a psychosomatic factor that connects both the physical and psychological domains . Thus the relief of postoperative pain also affects the psychological status. In our study, the HADS scores on the postoperative day 3 and PTD in the OLIF group decreased significantly compared with those in the MISTLIF group. This may be related to the lower lumbar VAS scores after operation in the OLIF group. In addition to pain, other factors may also affect the psychological state of patients after surgery, such as early getting out of bed, drainage, etc . Shorter bedtime and hospital stay after operation, less intraoperative blood loss, and postoperative drainage in the OLIF group would be other reasons.
This study also has some limitations. First, it is a retrospective cohort study, a double-blind randomized control trial needs to be performed. Second, the surgeons and patients had a different understanding of prognosis and treatment, which may affect the evaluation of results and cause bias. Third, the small sample size and short follow-up period may have affected the strength of the statistical analysis. Although OLIF could acquire good indirect decompression efficacy, it is still necessary to extend the follow-up period to confirm this conclusion because the spinal canal could remodel during long-term follow-up after surgery . A high-quality study of a large sample size and long-term follow-up period is still needed to compare the results of OLIF and MISTLIF.