Abstract
Purpose
This study aimed to evaluate the effectiveness of microscope-assisted modified lateral lumbar interbody fusion (micro-XOLIF) and to compare its impact on lumbar sagittal plane imaging parameters with extreme lateral interbody fusion (XLIF).
Methods
We retrospectively collected the data of patients who underwent XLIF and micro-XOLIF in our hospital. We compared general data, medical records, and imaging parameters of both groups, including lumbar sagittal balance and postoperative intervertebral height. We evaluated operative efficacy through complications, and the Visual Analogue Scale (VAS) and the Oswestry Disability Index (ODI) at each follow-up time.
Results
There was no significant difference in general data between the two groups. In the micro-XOLIF group, cages were predominantly placed in the anterior part of the intervertebral space, showing notable improvement in anterior intervertebral height and segmental lordosis. Postoperative ODI and VAS scores decreased significantly in both groups. VAS score of micro-XOLIF group was lower than that of XLIF group 3 days after operation, but there was no significant difference in ODI and VAS scores between the two groups in other time periods. The incidence of vertebral collapse and neurological complications in micro-XOLIF group was also lower than that in XLIF group.
Conclusions
Microscope-assisted modified lateral lumbar interbody fusion, utilizing a simple retractor, reduces the equipment needs for lateral lumbar fusion, aids in identifying crucial anatomical structures, and diminishes risks associated with lateral surgery and nerve-related complications. Additionally, micro-XOLIF effectively restores lumbar lordosis and reduces vertebral collapse rates through anterior cage placement.
Keywords: Microscope, XOLIF, Segmental lordosis, Minimally invasive surgery
Introduction
Extreme lateral interbody fusion (XLIF) emerged as a transformative technique in spinal surgery following its first report by Brazilian doctor Pimenta Luiz in 2001. NuVasive, an American company, further advanced this field in 2003 by introducing a minimally invasive channel, specialized cage, and intraoperative neuromonitoring system specifically for lumbar lateral fusion. The technique gained prominence with its publication in The Spine Journal in 2006 [1]. Distinguished by its psoas approach, XLIF mitigates posterior muscle injury and preserves posterior column stability better than posterior surgery. It also reduces complications such as macrovascular injury and retrograde ejaculation, commonly associated with anterior lumbar interbody fusion [2].
Despite its advantages, XLIF is not without risks, particularly concerning the psoas major muscle and lumbar plexus injury [3]. Efforts to mitigate these risks have included the development of specialized instruments and intraoperative nerve detection tools. However, these solutions are limited by false negatives and high costs, leaving the risk of lumbar plexus nerve injury via the psoas major muscle as an unresolved issue. To address this, our group previously refined the XLIF approach to a modified lateral lumbar interbody fusion (XOLIF). This modified technique involves separating the psoas major muscle in its first third and performing intervertebral operations through a channel tilted similarly to the oblique Lumbar Interbody Fusion (OLIF) technique. This approach not only reduces the likelihood of iliac vascular injury but also minimizes traction and stimulation of the lumbar plexus nerve during surgery [4].
Subsequent follow-ups, however, revealed residual issues, including a minor incidence of lumbar plexus and sympathetic nerve injuries. These complications, while often resolving over time, impacted early postoperative outcomes. Additionally, while XLIF can correct lumbar scoliosis to an extent, the imbalance in the lumbar spine’s sagittal plane can lead to chronic pain and postoperative degenerative joint disease, contributing to post-XLIF low back pain [5, 6]. Furthermore, lateral lumbar interbody fusion (LLIF) relied on indirect decompression through large cage implantation. However too high a cage may cause the intervertebral space to overstretch, leading to subsidence and necessitating revision surgeries in some cases [7].
To overcome these challenges of postoperative complications, difficult operation and high requirements of surgical equipment, our group further evolved the XOLIF method into micro-XOLIF. This advanced technique involves relocating the surgical incision posteriorly, splitting the tendinous anterior edge of the psoas major muscle towards the lateral side of the vertebral body, and placing the cage vertically in the anterior part of the intervertebral space. Enhanced with microscope assistance, this approach significantly reduces the risk of nerve, vascular, and peritoneal injuries. The current study aims to evaluate the prognosis and complications of patients undergoing micro-XOLIF, compare its advantages over traditional XLIF, and assess its impact on sagittal balance improvement.
Methods
Study population
We conducted a retrospective analysis of medical records, imaging data, and follow-up information of patients who underwent XLIF and micro-XOLIF from December 2018 to December 2022. The inclusion criteria were: (1) patients undergoing single-segment surgery for lumbar degenerative diseases; (2) a minimum follow-up duration of one year. The exclusion criteria included: (1) patients with incomplete follow-up data; (2) those with a previous history of spinal surgery; (3) patients diagnosed with spinal tumors, infections, or fractures.
Description of surgery
Micro-XOLIF procedure
Under general anesthesia, the patient took the right lateral position, with a lumbar bridge established to widen the intervertebral space. A longitudinal incision approximately 4 cm in length was made anterior to the midpoint of the target disc on the left abdomen. This incision penetrated the skin, subcutaneous tissue, and then the abdominal wall muscle layer. Utilizing microscopic assistance, the fascia of the abdominal external oblique muscle was incised, followed by blunt dissection through the muscle fibers of the external oblique, internal oblique, and transverse abdominal muscles to enter the retroperitoneal space.
A deep retractor was employed to expose the surgical field. Peritoneal tissue and retroperitoneal fat anterior to the psoas major muscle were bluntly dissected. Abdominal organs, the vascular sheath, ureter, and peritoneum were ventrally retracted, and the psoas muscle group was separated bluntly to access the intervertebral space at the aponeurosis tendinous portion of the anterior edge of the psoas major muscle. Another retractor was used to retract posteriorly, exposing the target intervertebral disc. After inserting the positioning needle, the “C” arm X-ray machine confirmed the surgical segment.
The lateral side of the vertebral body and intervertebral disc were fully exposed. The annulus fibrosus was incised, diseased intervertebral disc material removed, and the endplate scraped clean. The intervertebral space was successively expanded using implant trial molds. The space was irrigated with normal saline and an angled (6°), 18 mm wide, 45–50 mm long, and 12–14 mm high cage filled with allogeneic bone and BMP-2 was implanted. The muscle, subcutaneous tissue, and skin were sutured in layers with silk thread. Microscopic assistance facilitated the intraoperative imaging of micro-XOLIF, as shown in Fig. 1. Figure 2 presents schematic diagrams of four types of lateral lumbar interbody fusion.
Fig. 1.
Intraoperative images of Micro-XOLIF a, Body surface marking of the vertebral body. b, X-ray localization of the anterior and posterior edges of the vertebral body. c, Lumbar transverse fascia and extraperitoneal fat visualized under a microscope. d, Genitofemoral nerve observed under a microscope. e, Surface of the psoas muscle as seen through the microscope. f, Lumbar plexus nerves piercing through the psoas muscle, visible under microscopic examination. g, Hemostasis process conducted under microscopic guidance. h, Microscopic view illustrating the relationship between the psoas muscle and the iliac vessels. i, Tendinous anterior margin of the psoas muscle. j, Sympathetic nerves located on the side of the lumbar spine. k, Use of the microscope in conjunction with a deep abdominal retractor. l, Removal of the intervertebral disc. m, X-ray image showing the trial mold inserted into the intervertebral space. n, X-ray depiction of the cage placed within the intervertebral space. o, Microscopic view of the cage in relation to the psoas muscle and iliac vessels. (“a” means Anterior and “p” means Posterior)
Fig. 2.
Schematic diagram of lateral lumbar interbody fusion. a, Oblique Lumbar Interbody Fusion (OLIF). b, Anteroinferior Psoas Technique (AIP). c, Microscope -Assisted Modified Lateral Lumbar Interbody Fusion (Micro-XOLIF). d, Extreme Lateral Interbody Fusion (XLIF). e, Position of Incision on Body Surface: (a) OLIF, (b) AIP, (c) Micro-XOLIF, (d) XLIF
Clinical data and radiographic evaluation
Data collection
We compiled comprehensive medical records, imaging, and follow-up data for all patients. This included demographic details (age, sex, BMI), surgical specifics (operation length, blood loss), and both intraoperative and postoperative complications. Pain assessments were conducted using the Visual Analogue Scale (VAS) for low back and leg pain and the Oswestry Disability Index (ODI) for disability, recorded preoperatively, and at 3 days, 3 months, 6 months, and 12 months postoperatively [8].
Imaging data
Imaging assessments encompassed anterior and lateral lumbar X-rays, CT scans, and MRIs conducted before and after the operation. We evaluated several parameters: Anterior Disk Height (ADH) is defined as the distance between the anterior end of the inferior and superior endplates. Posterior Disk Height (PDH) is defined as the distance between the posterior end of the inferior and superior endplates. Foraminal height (FH) is defined as the distance between the inferior edge of the superior pedicle and the upper edge of the inferior pedicle. Segmental lordosis (SL) is defined as the Cobb angle between the superior endplate of the lower vertebral body and the inferior endplate of the superior vertebral body. Lumbar lordosis (LL) is defined as the Cobb angle between the upper endplate of L1 and S1 vertebrae. Center point ratio (CPR) is defined as the distance between the midpoint of cage and the posterior edge of the superior endplate of the lower vertebral body, divided by the entire length of the upper endplate of the lower vertebral body [9, 10]. CPR means the position of cage in the intervertebral space relative to the lower endplate, and when the CPR is greater than 50%, the cage is located in the anterior part of the intervertebral space. Vertebral collapse is defined as a collapse depth of more than 2 mm [11, 12]. (Fig. 3) All data points were measured three times to obtain an average value.
Fig. 3.
Measurement methods for lumbar spine imaging data. a, LL, Lumbar Lordosis, the angle between the upper endplate of L1 and S1; ADH, Anterior disk height, the height of the anterior edge of the intervertebral space of the fusion segment; PDH, Posterior disk height, the height of the posterior edge of the intervertebral space of the fusion segment; FH, Foraminal height, the distance between the inferior edge of the superior pedicle and the upper edge of the inferior pedicle b, SL, Segmental Lordosis, the angle between the lower endplate of the superior vertebral body and the superior endplate of the inferior vertebral body; Vertebral collapse is defined as endplate collapse exceeding 2 mm c, cage CPR, center point ratio, CPR = a/b*100%
Data analysis
We utilized SPSS software (version 26.0; SPSS, Inc., Chicago, IL, USA) for all data analyses. Measurement data were expressed as (x̅±s). When the data were normally distributed, the two groups were compared using the two-independent sample t-test; the comparisons at different time points within the same group were performed using one-way analysis of variance. When the data were non-normally distributed, the rank sum test was used for comparison. The count data were compared using the X2 test or Fisher’s exact test. The Mann-whitney U test was used to compare the rank data between the two groups, and the Friedman test for multiple related data was used to compare the data within the same group. P < 0.05 indicated that the difference was statistically significant.
Results
A total of 174 patients were included in this study, including 48 patients in micro-XOLIF group and 126 patients in XLIF group. There was no significant difference in sex, age, BMI, bone quality and other general data between the two groups (Table 1). The average surgery length for the micro-XOLIF group was 88.10 ± 11.34 min, marginally longer than the XLIF group, though the difference was not statistically significant. Similarly, average intraoperative blood loss was slightly lower in the micro-XOLIF group (65.25 ± 16.28 ml) compared to the XLIF group (68.71 ± 9.23 ml), but this difference also did not reach statistical significance. There were no significant differences between the two groups in terms of the proportion of surgical segments and the use of internal fixation. Notably, the micro-XOLIF group demonstrated a lower incidence of intraoperative complications, including peritoneal injury, lumbar plexus nerve injury, sympathetic nerve injury, and psoas major muscle weakness. Additionally, the occurrence of postoperative cage displacement was less frequent in the micro-XOLIF group (Table 2). The comparison of VAS and ODI scores between the XLIF and micro-XOLIF groups is detailed in Table 3. Initially, there were no significant differences in preoperative VAS and ODI scores between the two groups.
Table 1.
General information
| Values | XLIF | Micro-XOLIF | P |
|---|---|---|---|
| Gender(male/female) | 54/72 | 21/27 | 0.915# |
| Age (year) | 58.66 ± 10.99 | 58.81 ± 12.27 | 0.936$ |
| BMI (kg/m2) | 26.16 ± 2.43 | 26.57 ± 3.70 | 0.400$ |
| Bone quality | 0.921# | ||
| Normal | 55 | 20 | |
| Osteopenia | 38 | 16 | |
| Osteoporosis | 33 | 12 |
#Pearson Chi-square test; $Two independent samples t-test; BMI body mass index
Table 2.
Surgery-related data
| Values | XLIF | Micro-XOLIF | P |
|---|---|---|---|
| Operation time (min) | 86.24 ± 10.25 | 88.10 ± 11.34 | 0.403* |
| Bleeding volume (ml) | 68.71 ± 9.23 | 65.25 ± 16.28 | 0.193* |
| Surgical segment | 0.973& | ||
| L1-2 | 2 | 1 | |
| L2-3 | 19 | 7 | |
| L3-4 | 27 | 12 | |
| L4-5 | 76 | 28 | |
| L5-1 | 2 | 0 | |
| Internal fixation mode | 0.850# | ||
| Stand Alone | 10 | 2 | |
| Cage with Fin device | 44 | 18 | |
| Lateral plating | 16 | 6 | |
| Posterior internal fixation | 56 | 22 | |
| Complication | |||
| Sympathetic nerve injury | 2(1.59%) | 0 | 1 |
| Pain and numbness in front of the thigh | 12(9.52%) | 1(2.08%) | 0.116 |
| Transient iliopsoas weakness | 5(3.97%) | 1(2.08%) | 1 |
| Genitofemoral nerve injury | 1(0.795%) | 0 | 1 |
| Macrovascular injury | 0 | 0 | 1 |
| Peritoneal injury | 2(1.59%) | 0 | 1 |
| Cage displacement | 6(4.76%) | 2(4.17%) | 1 |
*Mann-Whitney U test; &Fisher’s exact test; #Pearson Chi-square test
Table 3.
Clinical effect in perioperative period
| Vaules | Group | Preoperative | 3 Days Postoperatively | 3 Months Postoperatively | 12 Months Postoperatively | P |
|---|---|---|---|---|---|---|
| VAS | XLIF | 6.30 ± 0.99 | 2.57 ± 0.79 | 1.64 ± 0.73 | 1.21 ± 0.64 | <0.001¥ |
| Micro-XOLIF | 6.23 ± 1.04 | 2.08 ± 1.35 | 1.52 ± 0.74 | 1.15 ± 0.65 | <0.001¥ | |
| P | 0.671 | 0.004 | 0.362 | 0.578 | ||
| ODI | XLIF | 52.85 ± 7.15 | 18.78 ± 4.41 | 14.79 ± 2.91 | 13.26 ± 2.66 | <0.001¥ |
| Micro-XOLIF | 53.83 ± 9.61 | 18.42 ± 5.64 | 14.21 ± 3.34 | 13.04 ± 3.04 | <0.001¥ | |
| P | 0.464 | 0.656 | 0.264 | 0.640 |
¥repeated measure ANOVA
At 3 days postoperatively, the VAS score in the XLIF group (2.57 ± 0.79) was significantly higher than that in the XOLIF group (2.08 ± 1.35) (P < 0.05), but there was no significant difference in ODI score between the two groups. The scores of VAS and ODI in XLIF group were 1.64 ± 0.73 and 14.79 ± 2.91 at 3 months after surgery, and 1.21 ± 0.64, 13.26 ± 2.66 at 12 months after surgery. The scores of VAS and ODI in micro-XOLIF group were 1.52 ± 0.74, 14.21 ± 3.34 at 3 months after surgery, and 1.15 ± 0.65, 13.04 ± 3.04 at 12 months after surgery. There was no significant difference in VAS and ODI scores between the two groups at 3 and 12 months after surgery. The scores of VAS and ODI decreased gradually at each follow-up time in both groups.
Table 4 showed the comparison of DH, FH, SL, LL, CPR, and vertebral body collapse in each follow-up period between XLIF and micro-XOLIF groups. There was no significant difference in the preoperative DH, FH, SL, and LL between the two groups. Postoperative CPR in the micro-XOLIF group was significantly higher than that in the XLIF group, with all cages positioned in the anterior part of intervertebral space. Both groups showed significant postoperative increases in ADH, PDH, FH, SL, and LL compared to their preoperative values (P < 0.05). ADH and SL in micro-XOLIF group were higher than those in XLIF group at 3 days after surgery. ADH, PDH, FH, SL and LL in both groups at 12 months after surgery were lower than those at 3 days after surgery. At 12 months after surgery, there were still significant differences in ADH and SL between the two groups, with the micro-XOLIF group exhibiting a lower rate of vertebral collapse (P < 0.05). There was no significant difference in PDH, FH and LL between the two groups at 3 days and 12 months after surgery. Figure 4 showed the images of a patient undergoing micro-XOLIF before and after surgery.
Table 4.
Perioperative imaging index
| Vaules | Group | Preoperative | 3 Days Postoperatively | 12 Months Postoperatively | P |
|---|---|---|---|---|---|
| ADH (mm) | XLIF | 12.36 ± 2.28 | 15.14 ± 2.32 | 13.84 ± 2.04 | ＜0.001¥ |
| Micro-XOLIF | 12.31 ± 2.04 | 16.24 ± 2.02 | 14.82 ± 1.69 | ＜0.001¥ | |
| P | 0.677 | <0.001 | <0.001 | ||
| PDH (mm) | XLIF | 6.12 ± 1.29 | 8.68 ± 1.13 | 7.58 ± 1.07 | ＜0.001¥ |
| Micro-XOLIF | 5.96 ± 1.37 | 8.77 ± 1.20 | 7.70 ± 1.15 | ＜0.001¥ | |
| P | 0.097 | 0.272 | 0.133 | ||
| FH (mm) | XLIF | 16.97 ± 1.81 | 20.98 ± 1.48 | 19.46 ± 1.42 | ＜0.001¥ |
| Micro-XOLIF | 16.85 ± 1.74 | 21.05 ± 1.25 | 19.52 ± 1.42 | ＜0.001¥ | |
| P | 0.103 | 0.307 | 0.339 | ||
| SL (°) | XLIF | 8.00 ± 1.83 | 10.87 ± 1.45 | 9.54 ± 1.53 | ＜0.001¥ |
| Micro-XOLIF | 8.18 ± 2.37 | 11.19 ± 1.79 | 9.92 ± 1.91 | ＜0.001¥ | |
| P | 0.128 | 0.001 | <0.001 | ||
| LL (°) | XLIF | 42.44 ± 11.53 | 49.48 ± 8.37 | 46.67 ± 8.57 | ＜0.001¥ |
| Micro-XOLIF | 41.95 ± 10.19 | 49.55 ± 5.16 | 46.96 ± 5.01 | ＜0.001¥ | |
| P | 0.109 | 0.762 | 0.159 | ||
| CPR | XLIF | - | 47.57 ± 7.22 | - | |
| Micro-XOLIF | - | 61.64 ± 10.63 | - | ||
| P | <0.001$ | ||||
| Vertebral body collapse | XLIF | - | - | 4 | |
| Micro-XOLIF | - | - | 27 | ||
| P | 0.044# |
¥repeated measure ANOVA; $Two independent samples t-test; #Pearson Chi-square test
Fig. 4.
A case of micro-XOLIF because of low back pain a and b, Preoperative anterior and lateral X-ray c and d, Preoperative sagittal MRI and CT e, Preoperative axial MRI of operative segments f, Postoperative axial CT of operative segments g and h, Postoperative anterior and lateral X-ray i and j, Postoperative sagittal MRI and CT k, Sagittal CT one year after operation
Discussion
Lumbar fusion is a common operation for treating lumbar degenerative diseases. Traditional surgical methods, particularly posterior lumbar surgery, often involve extensive peeling of paraspinal muscles, leading to excessive muscle injury and denervation. In the long term, this can result in muscle fat infiltration, atrophy, and residual low back pain in some patients, thereby affecting the overall surgical outcomes [13]. The anterior lumbar surgery bypasses the retroperitoneal space through the iliac vascular space to the anterior lumbar spine, posing a complex surgical approach and increased risk of peritoneal and iliac vascular injuries [14]. XLIF offers a middle ground by passing through the psoas major muscle to the lumbar spine’s lateral side, thus avoiding direct contact with iliac vessels and reducing the risk of vascular injury. However, this technique can stimulate the lumbar plexus nerve while passing through the psoas major muscle, leading to postoperative complications such as psoas major muscle weakness and anterior thigh numbness, which can impact the procedure’s widespread adoption [15].
To mitigate the risk of lumbar plexus injury and other complications after XLIF, as well as to minimize contact with iliac vessels, our group proposed the concept of XOLIF [4]. This technique, based on XLIF, advances the incision point and utilizes a double-leaf retractor to create a surgical channel through the anterior 1/3 of the psoas major muscle. It allows for the vertical insertion of the cage using a specially designed inclined handle. Postoperative follow-up has demonstrated significantly improved VAS and ODI scores after XOLIF, highlighting its advantages in reducing the risk of lumbar plexus and vascular injuries.
While XOLIF minimized the injury to the psoas major muscle and the disturbance and traction of the lumbar plexus nerve, there were still a few cases of injury of the lumbar plexus nerve and sympathetic trunk. Anatomical variability, such as the twisting and deformation of the femoral and genitofemoral nerves in some individuals, contributes to these problems [16]. Such anatomical differences can position the lumbar plexus more anteriorly, increasing the risk of nerve injury during XLIF procedures. Acknowledging these issues, there has been a growing emphasis on the importance of LLIF under direct vision. Some surgeons have adopted air-assisted endoscopy to perform XLIF surgery, seeking to minimize nerve and vessel injuries [17]. However, endoscopy brings its own set of limitations, including issues like lens staining, occlusion, interference with surgical instruments, and a restricted field of view.
To address these limitations and build on the concept of direct vision from XOLIF, our approach evolved to incorporate microscope-assisted surgery, resulting in the development of micro-XOLIF. This technique replaces the double-blade spreader with two simple gastrointestinal retractors, simplifying the equipment requirements and enhancing the adaptability under microscopic observation. Unlike the oblique channel approach of OLIF or XOLIF, micro-XOLIF employs a vertical approach through the tendinous anterior edge of the psoas major muscle. This approach aligns more closely with the XLIF methodology, facilitating the use of a microscope and enabling more precise vertical placement of the cage.
During the surgical approach, the microscope enables the surgeon to clearly distinguish the peritoneum and the transversalis fascia, significantly reducing the risk of intraoperative peritoneal injury [18] (Fig. 1c). Iliac vessels and ureters, which run anterior to the psoas major muscle, are particularly vulnerable during surgery. The microscope facilitates a more controlled surgical approach, minimizing direct contact and potential injury to these key tissues (Fig. 1h). A critical advantage of microscopic assistance is the improved ability to identify and thus preserve vital nerves. The genitofemoral nerve and sympathetic nerve on the psoas muscle surface can be distinctly visualized, reducing the incidence of postoperative complications like limb temperature differences, thigh and perineum numbness, and potential infertility issues (Fig. 1d). Even though micro-XOLIF aims to avoid the typical pathways of the lumbar plexus, the variability in lumbar plexus anatomy necessitates careful navigation, made possible by microscopic observation (Fig. 1f). In traditional XLIF, the depth and narrowness of the incision site, combined with the location of the sympathetic chain in the anterior third of the vertebral body, make it challenging to identify and preserve the sympathetic chain. The microscope is important in this regard, allowing for clear identification and reducing the risk of complications like altered skin temperature, anhidrosis, sensory abnormalities, and neurogenic pain [19, 20] (Fig. 1j). Microscopic surgery also aids in the direct observation of the anterior longitudinal ligament, enabling surgeons to accurately judge the position of the lumbar spine’s anterior edge and thereby reducing reliance on fluoroscopy (Fig. 1i). Additionally, it allows for precise positioning of the cage within the intervertebral space, a critical aspect of the procedure (Fig. 1o).
In our study, we observed a vertebral collapse rate of 8.3% in the micro-XOLIF group, which is notably lower than that in the traditional XLIF group. This reduced rate is significant, as it directly correlates with the effectiveness of the procedure. Various studies have pointed out that cage subsidence can lead to a loss of the indirect decompression effect [21]. The lateral approach, utilized in both XLIF and micro-XOLIF, aims to achieve indirect decompression by restoring normal intervertebral height through cage insertion. However, if this decompression is compromised, additional direct decompression may be required to alleviate persistent pain [22]. Therefore, maintaining a low collapse rate is crucial for the long-term success of the procedure and to avoid the need for further surgical intervention. Anatomical studies have shown that the density of the epiphyseal ring is greater than that in the central part of the vertebral body. The lumbar endplate’s epiphyseal ring, particularly those located at the front and sides, is capable of withstanding higher pressures [23–25]. Codman et al. [26] have indicated that the stability provided by the cage is significantly enhanced when it is positioned on the epiphyseal ring. They found that the pressure required for cage subsidence is threefold higher when placed on the epiphyseal ring compared to a central endplate location. The anterior approach in micro-XOLIF allows for the strategic placement of the cage in the anterior part of the vertebral endplate. This positioning enables the cage to span both the anterior and bilateral epiphyseal rings, thereby providing stronger and more stable support.
Previous studies have underscored the importance of the fusion cage’s anterior positioning in extending the anterior column, which proves beneficial for correcting the sagittal plane of the lumbar spine [27, 28]. In our study, the micro-XOLIF group demonstrated significantly higher postoperative SL and ADH compared to the traditional XLIF group. This suggests a more effective restoration of the lumbar spine’s natural curvature. Although there was a slight reduction in sagittal anterior protrusion during the postoperative follow-up, the overall loss of intervertebral height and lordosis was lesser in the micro-XOLIF group. This advantage is attributed to the strong support provided by the placement of the cage over the epiphyseal rings. The correction of the lumbar spine’s sagittal curvature is vital for the success of spinal fusion surgery. Effective restoration of lumbar lordosis has been shown to improve functional outcomes in patients and reduce postoperative complications [29, 30]. Research by Matsumoto et al. [31] highlights that proper restoration of SL and LL is crucial for maintaining sagittal balance and minimizing the risk of adjacent segmental degeneration. The recovery of lumbar lordosis plays a pivotal role, not only in the short-term therapeutic effects but also in preventing long-term complications following surgery. Despite these positive outcomes, it’s important to note that all surgeries in this study were single-segment, which means the improvements in the overall lumbar spine lordosis, while present, were somewhat limited.
Minimally invasive anterior column release (ACR) has been noted for its ability to achieve significant correction in the sagittal plane of a single spinal segment by releasing the anterior longitudinal ligament. A concern with the anterior placement of the cage is the potential for cage prolapse from the anterior lumbar spine. However, it’s noteworthy that in both micro-XOLIF and ACR techniques, complications involving cage prolapse from the anterior lumbar spine have not been observed [32–34]. However, ACR comes with heightened risks, particularly concerning macrovascular and peritoneal structural injuries [35]. When compared to ACR, micro-XOLIF offers several distinct advantages. Notably, micro-XOLIF is capable of restoring the lordosis of the lumbar spine to a significant degree. Furthermore, it minimizes damage to the anterior longitudinal ligament, thereby preserving spinal stability. Additionally, micro-XOLIF reduces the risk of injury to vital structures such as blood vessels, peritoneum, and organs located anterior to the vertebral body. This makes micro-XOLIF a safer and more conservative option for correcting lumbar spine deformities while maintaining the structural integrity and stability of the spine.
One significant limitation of our study is its retrospective case-control design, not a randomized controlled trial. This limits the ability to draw definitive causal inferences from the data. Additionally, the relatively small sample size included in this study may lead to results that are not universally applicable or could be considered incidental. Secondly, in the measurement of imaging parameters, the position and angle of lumbar vertebrae at different follow-up time points are difficult to be completely consistent, and there may be some artificial measurement errors. Furthermore, the follow-up period for patients included in this study was limited to one year. While this duration allowed for an assessment of early postoperative efficacy and immediate intraoperative as well as postoperative complications, it was not sufficient to observe long-term complications such as adjacent segment degeneration.
Conclusions
Microscope-assisted modified lateral lumbar interbody fusion, utilizing simple retractors, can reduce the complexity and variety of instruments typically required for lumbar lateral interbody fusion. And it can identify important tissue structures such as large vessels, nerves and ureter under microscope, reducing the risk of operation and neurological complications. Furthermore, through the anterior cage, micro-XOLIF can better restore lumbar lordosis and reduce the rate of vertebral collapse.
Acknowledgements
Not applicable.
Clinical trial number
Not applicable.
Abbreviations
- CT
Computed tomography
- VAS
Visual analog scale
- ODI
Oswestry Disability Index
- ADH
Anterior disk height
- PDH
Posterior disk height
- FH
Foraminal height
- SL
Segmental lordosis
- LL
Lumbar lordosis
- CPR
Center point ratio
- LLIF
Lateral lumbar interbody fusion
- XLIF
Extreme lateral interbody fusion
- OLIF
Oblique Lumbar Interbody Fusion
- XOLIF
Modified lateral lumbar interbody fusion
- micro-XOLIF
microscope-assisted modified lateral lumbar interbody fusion
Authors’ contributions
WZ had the idea for the study. WJW and HW selected studies for inclusion and abstracted data. HYW did the statistical analyses and interpreted the data. WJW and JLA wrote the first draft. JQL, WZ and YPS critically revised the paper for important intellectual content. All authors approved the final draft.
Funding
S&T Program of Hebei(22377708D); Hebei Provincial Government funded Provincial Medical Talent Project in 2022.
Data availability
The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request.
Declarations
Ethics approval and consent to participate
This research does not involve any content that violates any personal rights of the subjects. The participation in the study was voluntary and written informed consent was obtained from the participants for the use of their retrospective data. This study conforms to the provisions of the Declaration of Helsinki and has been reviewed and approved by the Medical Ethics Committee of the third Hospital of Hebei Medical University (K2022-085-1). All protocols are carried out in accordance with relevant guidelines and regulations.
Consent for publication
Not applicable.
Competing interests
The authors declare no competing interests.
Footnotes
Publisher’s Note
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Weijian Wang and Jilong An these authors contributed equally to this work and should be considered co-first authors.
References
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Data Availability Statement
The datasets used and/or analysed during the current study are available from the corresponding author on reasonable request.