This study describes the application of oblique lateral interbody fusion in lumbar spinal surgeries.

Lumbar spine diseases often cause lower back pain, lower extremity pain, numbness, and paresthesia. In severe cases, intermittent claudication may occur, affecting the quality of life of patients. Surgery is often required when conservative treatment fails, or when patients' symptoms become unbearable. Surgical treatments include laminectomy and discectomy, as well as interbody fusion. The main purpose of laminectomy and discectomy is to relieve nerve compression; however, recurrence is common due to spinal instability. Interbody fusion improves stability while relieving nerve compression and significantly reduces the risk of recurrence compared to non-fusion surgery. Nonetheless, conventionally posterior intervertebral fusion requires separation of the muscles to expose the operated segment, which causes more trauma to the patient. In contrast, the oblique lateral interbody fusion (OLIF) technique achieves spinal fusion with minimal trauma to the patients and shortens the recovery time. This article introduces procedures of stand-alone OLIF surgery performed in the lumbar spine, providing a reference for other spine surgeons.

Lumbar spine disorders are a global economic concern, with affected patients experiencing lower quality of life¹. The treatment of lumbar spine diseases can be divided into two categories: conservative and surgical treatment. Conservative treatment includes rest, oral nonsteroidal drugs, massage, and physical therapy. For instance, studies have shown that estrogen can be used to delay degeneration of the intervertebral disc, thus providing a basis for its treatment of lumbar spine disease^2,3. For patients who have failed in conservative treatment, surgery is typically required to treat lumbar spine diseases. Among the surgical methods used for this cohort, interbody fusion is generally preferred.

Briefly, the techniques reported consist of anterior lumbar interbody fusion (ALIF), direct lateral interbody fusion (DLIF), extreme lateral interbody fusion (XLIF), oblique lateral interbody fusion (OLIF), posterior lumbar interbody fusion (PLIF), and transforaminal lumbar interbody fusion (TLIF)^4,5. Among these surgical approaches, OLIF has its unique advantages. In comparison with DLIF and XLIF, OLIF has been shown to reduce the incidence of postoperative hip flexion weakness and thigh numbness^6,7. Moreover, compared with ALIF, surgeries with OLIF have a lower risk of both postoperative retrograde ejaculation and damage of blood vessels anterior to the vertebral body⁸. Nonetheless, it is worth mentioning that PLIF and TLIF techniques exhibit a good operative field, which could reduce damage to important structures; the placement of pedicle screws used by these methods could reduce the probability of non-fusion of the interbody cage. Nonetheless, compared with OLIF, PLIF and TLIF require intraoperative muscle dissociation and stretching the muscle for an extended period of time, which could result in increased intraoperative blood loss, slow wound healing, and prolonged patient recovery time^9,10,11.

By harnessing the OLIF approach, the intervertebral site can be accessed through the space between the anterior border of the psoas muscle and the major abdominal vessels. The surgery is performed by removing the diseased disc and implanting an interbody cage. Because of the reduced damage to muscle, OLIF can minimize intraoperative blood loss and operation time, shortening patients' postoperative recovery. In addition, earlier studies have shown that the placement of interbody cages can boost restoration of the disc height and patients' physiological curvature of the spine^{6,12,13,14,15,16}. In the present study, the surgical procedures of stand-alone OLIF for the treatment of L4-5 lumbar diseases are introduced in detail.

This study has been approved by the Ethics Committee of the Third Hospital of Hebei Medical University. The patients signed informed consent, consented to be filmed, and allowed the investigators to use their surgical data.

1. Patient selection

1. Select patients based on the following inclusion criteria.
   1. Select patients for whom conservative treatment time was longer than 3 months and to which the patients responded poorly.
   2. Select patients whose symptoms and signs were consistent with the imaging findings.
   3. Select patients whose magnetic resonance imaging (MRI) of the lumbar spine shows a width greater than 1 cm between the psoas muscle and the anterior border of the vertebral artery.
   4. Select patients with no significant variants on abdominal vascular examination.
2. Apply the following exclusion criteria.
   1. Exclude patients with spinal canal infection and tumor complications.
   2. Exclude patients with spinal stenosis due to severe facet joint hyperplasia and prolapse of the nucleus pulposus.
   3. Exclude patients with severe lumbar spondylolisthesis greater than grade III.
   4. Exclude patients with a history of abdominal surgery.

2. Preoperative preparation

1. Instruct the patient to undergo lumbar computed tomography (CT), lumbar MRI, and lumbar X-ray examination. Perform cardiovascular and cerebrovascular, and abdominal vascular examinations to identify and better manage risk factors to ensure safety of the operation^17,18.
2. Advise the patient on skin preparation of the surgical site preoperatively, with a fasting requirement of 12 h before the surgery.
3. On the day of the operation, after the administration of general anesthesia with endotracheal intubation, place the patient on the operating table in a right-sided lateral decubitus position.
4. Insert a cushion beneath the right abdomen, which is slightly tilted backward depending on the target intervertebral disc, in order to obtain adequate access to the physiologic OLIF corridor between the psoas muscle and the vena cava anteriorly.
5. Choose the left abdomen of the patient as the surgical area.
6. Ensure that the patient remains in the correct position for the surgery. Secure the patient with tape and confirm the operation stage.

3. Starting the operation

1. Place a square locator on the left abdomen of the patient. Ensure the upper and lower edges of the locator correspond to the upper and lower vertebral bodies of the diseased intervertebral disc, and the anterior and posterior edges correspond to the anterior and posterior edges of the diseased intervertebral disc.
2. Confirm the projection of the target segment on the patient's skin with X-ray fluoroscopy. Mark the surgical site (Figure 1).
3. After identifying the surgical site, disinfect the incision area, lay sheets, and prepare surgical instruments.
4. Make a 4-5 cm skin incision parallel to the external oblique muscle fibers. Separate the aponeurosis of the external oblique muscle, the transverse abdominis, and the transverse abdominal fascia bluntly with fingers (Figure 2).
5. Use long-handled forceps to clamp the peanut-like gauze mass to expose the surgical intervertebral space between the abdominal vascular sheath and the psoas major muscle.
6. After completing exposure of the target intervertebral space, insert Kirschner wire and perform intraoperative X-ray examinations to confirm that the exposed segment is the surgical segment (Figure 3A).
7. After completing identification of the intervertebral space, insert the dilation tubes successively for expansion. Confirm the position of the expansion channel by intraoperative X-ray (Figure 3B).
8. Attach the retractor to the operating table using the universal arm and operating table clips. Ensure that the channel does not move during the surgery, and then place the working light.
9. Use a long-handled sharp knife to remove the annulus fibrosus, and long-handled nucleus pulposus forceps to remove the diseased disc tissue (Figure 3C).
10. Clean the intervertebral space with a scraper and curette to clear the residual disc tissue in the surgical segment.
11. After cleaning the intervertebral space, use a spreader to open a collapsed intervertebral space.
12. Use a bone rasp to remove the cartilage layer on the surface of the endplate until the bony surface bleeds.
13. Place an appropriately sized intervertebral exploration device into the disc. Perform intraoperative X-ray fluoroscopies to determine the appropriate fusion device size (Figure 3D,E).
14. After determining the appropriate device size, add allogeneic bone to the interbody cage of the same size and implant the cage under X-ray fluoroscopy (Figure 3F,G).
15. After placing the interbody cage, suture the wound layer by layer. Use No. 10, No. 4, and No. 1 thread to suture the muscle, fascia, and surgical incision, respectively (Figure 3H). Compress the surgical incision with gauze.
16. Prescribe an anti-inflammatory (cefazolin) once a day for 3 days to prevent infection after the patient returns to the ward. Use antithrombotic drugs (low-molecular weight heparin sodium) to prevent deep vein thrombosis of the lower limbs on the 2nd postoperative day, once a day for 3 days.

4. Postoperative care

1. Instruct the patient to rest in bed. Perform deep vein color Doppler on the third postoperative day.
2. Instruct the patient to walk on the ground with the assistance of a lumbar brace, usually within 3 days post-operation if the deep vein color Doppler shows no deep vein thrombosis in the lower extremities.
3. Change the antithrombotic medication to twice daily if an intramuscular vein thrombosis is present on a deep vein ultrasound of the lower extremities.
4. Contact Vascular Surgery for treatment if the deep vein ultrasound of the lower extremities shows a deep vein thrombosis. Perform the lower-extremity rehabilitation exercise as reported previously^19,20.

Studies from other groups have shown that, compared to other methods, OLIF surgery has the advantages of a shorter operative time and less intraoperative blood loss (Table 1). Importantly, patients who undergo OLIF surgery recover faster than the commonly used TLIF surgery group^12,21,22. Our research group has monitored 42 patients with degenerative lumbar spondylolisthesis (DLS) undergoing OLIF surgery for more than 1 year. The results have shown improvements in visual analog scale (VAS) scores in patients with DLS treated with OLIF compared to preoperative VAS scores, and significant improvements in ventral and dorsal disc heights in OLIF patients as well as segmental lordotic angle and lumbar lordotic angle compared with preoperative outcomes¹⁶ (Figure 4). Similar to results published from previous groups, the intervertebral disc height and the intervertebral foramen height of the patients in the OLIF group were higher than those in the TLIF group^12,21.

In a previous study of 56 patients who underwent OLIF, one patient developed a psoas major abscess and intervertebral space infection, and one patient developed cage subsidence at the end follow-up¹⁶. In a study by Hung et al., 5 of 21 patients treated with OLIF developed cage subsidence²². Sheng treated 38 patients with OLIF and found that two patients had postoperative hip flexion weakness and one patient had postoperative sensory disturbance, but both resolved within 6 months²¹. In a study by Li et al, where 35 patients were treated with OLIF, one patient had postoperative ileus and one patient had postoperative thigh and numbness, but these symptoms resolved within a short time¹².

Figure 1: Selection of the patient's surgical stage and positioning. (A) Preoperative X-ray positioning. (B) The localizer is used to estimate the skin projection point before surgery. Please click here to view a larger version of this figure.

Figure 2: Intraoperative blunt dissection of abdominal muscles to expose the target intervertebral disc. (A,B) Images show the surgeon dissecting the muscle bluntly with the fingers. Please click here to view a larger version of this figure.

Figure 3: OLIF intraoperative procedures. (A) Intraoperative fluoroscopy to clarify the surgical segment. (B) Working channel. (C) Removal of the target intervertebral disc. (D,E) Intraoperative lumbar vertebrae fluoroscopy to clarify the size of the cage. (F,G) X-ray examination after interbody cage placement. (H) Suture surgical incision. Please click here to view a larger version of this figure.

Figure 4: Representative results from a previous study of 42 patients with OLIF. (A) Patients with OLIF had improved postoperative VAS scores compared to preoperative. Lower back pain decreased immediately after OLIF. Compared with preoperative, the postoperative VAS significantly scores decreased (p < 0.05). The visual analog scale (VAS) ranges from 0 to 10, with 0 being no pain and 10 being the most severe pain. (B,C) The postoperative imaging results of OLIF patients were significantly improved compared with before surgery. (B) The mean postoperative ventral disc height and dorsal disc height increased significantly compared with preoperative (p < 0.05). (C) A significant postoperative increase was also observed in the mean operative segmental lordotic angle and the whole lumbar lordotic angle (p < 0.05). Radiological and clinical parameters were all compared using the independent-sample t-test. p < 0.05 was considered statistically significant. This figure has been modified from Huo et al.¹⁶. Please click here to view a larger version of this figure.

Table 1: Comparison of OLIF and TLIF treatment effects.

Since formally introduced by Silvestre in 2012²³, OLIF has gradually attracted the attention of spine surgeons due to the various advantages over other methods used in treating lumbar spine diseases^{6,12,13,16,21,22}. OLIF significantly improved patients' disc height and lordotic angle, which may be due to the more complete clearance of the diseased disc and the larger intervertebral fusion placement compared to the traditional posterior surgery, which facilitated the restoration of the physiological curvature of the spine^12,16,21. Long-term postoperative follow-up of OLIF patients showed no significant difference in clinical symptom relief compared to posterior TLIF surgery, but significantly reduced operative time and intraoperative bleeding in patients⁶. Furthermore, OLIF can be used as a potential approach to treat lumbar infectious diseases, as this method can thoroughly remove lesions and achieve good therapeutic effects^24,25. As a minimally invasive interbody fusion, OLIF causes less intraoperative trauma to patients and significantly relieves symptoms. Hence, OLIF can be considered a safer alternative to other surgical techniques. Nonetheless, despite the numerous advantages of OLIF, a full understanding of OLIF-related risks and additional care, which are critical to the surgery success, are highlighted below.

First, the selection criteria of patients should be reviewed carefully. For patients with a history of abdominal surgery, abdominal scar tissues can increase the complexity of performing another surgery. Hence, adequate preoperative examination is highly recommended. Preoperative MRI examination can determine the size of the OLIF working corridor, as a smaller corridor would increase the difficulty of surgery and affect the prognosis of patients^26,27. Our study confirmed that when the anterior edge of the left psoas muscle exceeds the anterior edge of the surgical segment, it increases the risk of lumbar plexus injury (LPI) associated with OLIF surgery²⁷. It has also been suggested that a gap width less than 1 cm between the psoas muscle and the anterior vertebral artery is not suitable for OLIF²⁸. Preoperative abdominal vascular examination can determine whether there is variation in the abdominal great vessels¹⁸, as well as the blood vessels of the patient's vertebral body segments, which can provide a reference for selecting appropriate size of the interbody cage used in OLIF.

Another important category is patients with obesity. The accumulation of abdominal fat in obese patients may affect the surgical field of vision. Compared with the traditional posterior approach, OLIF places greater demands on the surgical skills of surgeons. In a study of 238 patients undergoing OLIF surgeries, obese patients with OLIF at stage L5-S1 required a longer operative time than non-obese patients (273.75 ± 90.07 min vs. 223.55 ± 57.93 min), and the complication rate of surgical approach-related sequelae in obese patients was higher than that in non-obese patients²⁹. Therefore, surgeons should fully understand the related risks for obese patients and strengthen the nursing care for these patients following OLIF surgery. Our study has shown that systematic postoperative lower extremity exercise can promote the recovery of patients after OLIF surgery³⁰. Thus, we think lower-limb exercises may benefit patients with obesity after OLIF surgery.

On that note, special care for all patients requiring surgery at the L5-S1 level should be considered. This is advised because the L5-S1 level is affected by the iliac vessels and iliac crest, so it is challenging for some spine surgeons to perform OLIF at L5-S1. The risk of vascular injury in L5-S1 is higher in OLIF than that in ALIF³¹. In recent years, with the development of related techniques and the invention of special traction devices, OLIF surgery in the L5-S1 level has been gradually increasing³².

Separately, during OLIF surgery, surgeons should minimize the duration of surgery and reduce traction on the psoas muscles. This is due to the fact that patients undergoing OLIF have a certain likelihood of experiencing intraoperative dural tear, symptoms of dysuria, numbness in the front of the thigh, and retrograde ejaculation after surgery³³. Because OLIF surgery goes through the abdomen, some patients may experience postoperative abdominal distension due to intraoperative pulling of the intestinal canal. Therefore, OLIF surgery should be performed in a cautious manner to reduce damage to the blood vessels, nerves, related tissues, and to achieve better surgical effects.

Patients with stand-alone OLIF may have a certain probability of cage sedimentation. Previous studies have shown that the occurrence of cage sedimentation ranges from 2.9% to 10%^34,35. In addition, due to postmenopausal osteoporosis, some elderly female patients have poor interbody fusion ability, and the interbody cage in some patients may not fuse or even shift in the intervertebral space²⁵. Hence, OLIF surgery-assisted posterior percutaneous screw placement is needed in such cases. This post-OLIF surgical approach can improve the interbody fusion rate, decrease the pressure of the interbody cage on the upper and lower endplates, and reduce complications associated with non-fusion^36,37.

It is worth noting that due to the right decubitus position for OLIF patients, accurate disc positioning is required. Compared with the prone position, OLIF patients have greater spinal flexibility. The patient's target disc needs to be precisely located during OLIF surgery. In addition, the interbody cage inserted during OLIF surgery is larger, and thus multiple fluoroscopies are needed to adjust and optimize the position of the cage to achieve better radiological outcomes³⁸. Although the development of intraoperative 3D navigation techniques can assist surgeons in careful positioning of the interbody cage, the consequence of radiation exposure from intraoperative imaging in OLIF patients still requires further study³⁰.

It is worth noting that, in addition to the advantages and the considerations we need to take into account above, OLIF surgery also has disadvantages. To start with, compared with the traditional posterior approach, there is a tendency to damage abdominal blood vessels, the lumbar plexus, and other structures during OLIF surgery. In addition, as a minimally invasive surgery, the surgical field of OLIF is more limited than that of posterior surgery. Therefore, it is necessary to maintain a good surgical field during the operation for the smooth progress of OLIF surgery. However, stand-alone OLIF has a higher incidence of cage subsidence compared to posterior screw-assisted fixation of OLIF, and this is an important factor in postoperative revision.

The authors declare that there are no conflicts of interest in this study.

None.