Oblique Lateral Interbody Fusion Combined with Lateral Plate VS. Combined with Posterior Pedicle Screw Fixation in Lumbar Degenerative Diseases

Background The oblique lateral interbody fusion (OLIF) is a minimally invasive indirect decompression technique for the treatment of degenerative spinal disease. OLIF with posterior pedicle screws xation frequently is performed, whereas it requires much more surgery time and blood loss. The purpose of this study was to compare the oblique lateral interbody fusion (OLIF) combined with lateral plate (LP) vs. OLIF combined with posterior pedicle screw (PS) xation for the treatment of lumbar degenerative diseases. Methods The clinical data of 53 patients with lumbar degenerative diseases who underwent OLIF from to 2020 were retrospectively analyzed(cid:0)24 in OLIF combined with lateral plate (OLIF+LP) group and 29 in OLIF combined with pedicle screw (OLIF+PS) group. All patients completed a minimum 1-year follow-up. The duration of operation, blood loss, fusion rate and complications were recorded. The visual analog scale (VAS) score, Oswestry Disability Index (ODI), disc height (DH), foraminal height (FH) and cross-sectional area (CSA) were also evaluated.


Background
Lumbar degenerative disease is a common and debilitating ailment, causing pain and disability in elderly patients and burdening our healthcare system. The prevalence of low-back pain due to lumbar spondylosis is estimated at 3.6% worldwide [1]. Meantime, the rates of lumbar spine surgery have increased steadily over time [2]. Posterior lumbar interbody fusion (PLIF) and transforaminal lumbar interbody fusion (TLIF) have widely used as a gold treatment for lumbar degenerative disease. However, extensive dissection of the paraspinal muscles as well as multi dus atrophy was the common criticism for the posterior surgery [3]. Many complications such as peri-operative bleeding, dural tear, nerve root injury and postoperative low back pain were reported [4]. It has been suggested that the perioperative complications rate of minimally invasive transforaminal lumbar interbody fusion (MI-TLIF) was still 15.6%, and the most common complication was durotomy (5.1%) [5].
Oblique lateral lumbar interbody fusion (OLIF) was rst reported in 2012 by Silvestre, which using the natural space between the left lateral border of the abdominal aorta and the anterior medial border of the left psoas muscle, to avoiding the morbidity of traditional posterior surgery [6]. Moreover, minimally invasive OLIF technique can also signi cantly improve the coronal and sagittal balance of adult degenerative scoliosis (ADS) [7]. Excellent clinical results of this minimal invasive surgery has been already con rmed for treatment of ADS [8].
OLIF has mostly combined with supplemental posterior pedicle screw xation (OLIF+PS) for the treatment of lumbar spine disease [9]. Zeng et al suggested that the rate of complications was lower with the usage of combined pedicle screw xation [10]. Ohtori et al used posterior pedicle screws in all their patients who underwent OLIF and reported good outcomes [11]. However, these procedures need two different incisions, adding more surgical risks and economic expense. To our knowledge, few studies have reported about OLIF combined with lateral plate instrumentation (OLIF+LP). The purpose of this study is to compare the clinical and radiographic e cacy of OLIF+LP and OLIF+PS for the treatment of lumbar degenerative disease.

Methods
This retrospective study was approved by the Ethics Committee of the authors' a liated institutions, and all the patients signed an informed consent document. From January 2020 to September 2020, 53 patients who underwent single-segmental OLIF surgery were identi ed and included in this study. The inclusion criteria were the presence of single-segmental lumbar degenerative diseases as follows: (1) lumbar degenerative disc diseases; (2) degenerative spondylolisthesis with Meyerding grade I; (3) failure to >6 months of conservative treatment. The exclusion criteria were as follows: (1) severe osteoporosis (T score<2.5); (2) multi-segmental degenerative lumbar spine diseases; (3) follow-up < 6 months; (4) severe lumbar degenerative spondylolisthesis (more than Meyerding grade II); (5) severe lumbar spinal canal stenosis which required direct posterior decompression. They were randomly grouped according to the order of admission, there were 24 patients in OLIF+LP group, and 29 patients in OLIF+PS group. The surgical manipulations of all the patients were completed by the same surgical team. The characteristics of the patients are shown in Table 1. There was no difference in demographic characteristics between the two groups. All the patients were followed up at least 12 months.

Surgical procedure
The general technique of OLIF has been previously described [12]. After general anesthesia, the patient was positioned in a lateral decubitus manner with left hip on the top. A standard X-ray was made to identify the targeting vertebral levels. A skin incision of 3-4cm in length was made and retroperitoneal space was accessed by blunt dissection along the retroperitoneal fat tissue. The psoas muscle was dissected with the index nger and retracted posteriorly, and the peritoneal sac was mobilized anteriorly.
After discectomy, vertebral endplates were prepared, and then inserted the intervertebral cage lled with demineralized bone matrix (DBM).
In OLIF+LP group, after conventional OLIF procedure, lateral plate xation system was placed at the lateral part of vertebrae. The screws were usually inserted upward and downward along the endplate so that segmental vessels would be spared (Fig 1). In the OLIF+PS group, after the general OLIF procedure, the patient was placed in the prone position to undergoing posterior bilateral pedicle screw xation via Wiltse approach, and the posterolateral fusion was not performed. All the patients were allowed to ambulate by Boston brace on the second postoperative day. The Boston brace was recommended for 3 months.

Radiographic assessment
The routine X-ray, computed tomography (CT) and MRI were allowed for all the patients. As shown in the Fig 2, the radiological parameters, such as disk height (DH), foraminal height (FH), and cross-sectional area (CSA) were measured according to the methods reported by Sato [13]. All the imaging examinations were read independently by two experience physicians. The calculated intra-class correlation coe cients were all >0.85 for all variables. The Bridwell interbody fusion grading system was used for evaluation of fusion rate [14]. Grades I and II were considered as successful. Cage subsidence was de ned as a cage sinking into an adjacent vertebral body by >2 mm according to the CT scans [15].

Clinical assessment
A standardized and validated questionnaires that included the VAS score for back pain intensity and the ODI score were allowed for all the patients. A 10-point VAS was used, which 1= least pain and 10=worst pain. Clinical data were obtained on preoperative, 7 days, 3 months, and 12 months after operation. Surgical characteristics and complications were also recorded.

Statistical analysis
Statistical analysis was performed using SPSS 18.0 for Windows (IBM, Armonk, NY, USA). Continuous data are presented as means ± standard deviation, and were analyzed using the Student t test. The level of signi cance was set at P <0.05.

Clinical evaluation
The mean operative time was 75.41±11.53 min (range 53-110 min) in OLIF+LP group, and 127.05±5.62 min (range 93-210 min) in the OLIF+PS group, the difference was statistically signi cant (P<0.01). The mean intraoperative blood loss was 89.81±9.62 ml in the OLIF+PS group, much more than OLIF+LP group (39.55±5.32, P<0.01). There was no signi cant difference either in VAS or ODI scores pre-operative between two groups. As shown in the Fig3, the VAS and ODI scores were both improved signi cantly after the surgery in the two groups. However, the OLIF+LP group suffered less back pain both at 7 days (3.05±0.67 VS 4.55±0.39, P<0.01) and 3 months after surgery (2.35±0.67 VS 3.25±0.37, P<0.05) than OLIF+PS group; Interestingly, this difference was disappeared at one year after surgery. Similarly, the difference on ODI scores between the two groups had statistical signi cant only at 7 days after surgery (17.36±2.76 VS 22.80±6.02, P<0.01). The clinical outcomes are summarized in Table 2.

Radiographic evaluation
As shown in the Table 3, the DH, FH, and CSA were 8.96±1.23 mm, 16.18±3.49 mm and 88.95±14.79 mm 2 respectively before the surgery in the OLIF+LP group, and they were all increased signi cantly after the surgery (P<0.05). Similarly, these three radiographic parameters were all improved signi cantly after operation in the OLIF+PS group. There was no signi cant difference on these three parameters at any follow-up period between two groups. The rate of cage subsidence was 8.33% (2/24) in the OLIF+LP group, which is similar to the OLIF+PS group (2/29, 6.90%). There was no cage retropulsion in both of groups during the follow-up. The fusion rate was 91.67% (22/24)

Complications
The total complication rate was 13.21% (7/53) in this retrospective study. In the OLIF+LP group, two cases of L4/5 end-plate injury were noticed intraoperatively. Two patients with lumbosacral injury were recorded in the OLIF+LP group. These patients had hip exion weakness. Fortunately, they had both recovered within 2 months postoperative. In the OLIF+PS group, one patient with leg weakness and two patients with end-plate injury were recorded. No major vessel injuries or nerve root injuries occurred during the surgery. No intervertebral space infections, cerebrospinal uid leakage, vertebral body fracture or instrument failure occurred during the follow-up.

Discussion
The lateral spinal xation system was an internal xation system tailored for lateral and anterior surgical approaches. It increased the immediate stability after OLIF, and theoretically increased the fusion rate after surgery. Moreover, single lateral incision can avoid the muscle injury of posterior structures, decrease the potential risk of nerve damage and shorten the operation time. In this retrospective study, the post-operative radiograpgic parameters such as DH FH and CSH were all improved than before in both of the groups. Undoubtedly, the clinical symptoms alleviated in all of the patients. However, the patients in OLIF+LP group had lower VAS and ODI scores after surgery than the OLIF+PS group, the destruction of posterior longitudinal complex during the pedicle screw xation in the OLIF+PS group may be the main cause.
OLIF was reported as an relatively safe procedure through the transpsoas approach, allowing for psoas preservation, and avoids the vascular injury [6]. It has been found to result in about 30.0% average increase in the neural foramen area and a 30.2% median increase in the cross-sectional area of the dural sac [12][13]. However, the occurrence of complications is inevitable, and the complications rate uctuates from 3.7% to 66.7% [16]. In a study directed by Abe, intraoperative complications were reported as 44.5%, while only 4.7% of postoperative complications occured. The most common complication was the endplate fracture followed by the transitory weakness of the psoas muscle and transient neurological symptoms. Zeng et al reported that the endplate damage, cage sedimentation and shifting were the three most common complications of OLIF [10]. In their study, the complication rate was 36.26% in the standalone group, much higher than that in OLIF combined pedicle screw group (29.86%). Up to date, the pedicle screw instrumentation was commonly applied for stabilization after OLIF because they were considered as the standard method of xation to providing the best bio-mechanical stability of the spine [17]. However, the selection between unilateral pedicle screw (UPS) and bilateral pedicle screw (BPS) xation still remain controversial in lumbar spine surgery. Wen et al compared the clinical and radiological outcomes of BPS and UPS xation among the patients who underwent OLIF, they suggested that the OLIF combined with UPS xation is an effective and reliable option for single-level lumbar diseases [18].
Obviously, posterior pedicle screw xation decreases the incidence of sedimentation, but the increased cost, prolonged operation time, and greater damage to the posterior muscle tissue should be taken into consideration. Blizzard et al rst reported the lateral position technique for percutaneous pedicle screw placement following LLIF or OLIF, however, the 2.8% rate of re-operation for malpositioned screws is slightly higher [19]. Lateral pedicle screw instrumentation after anterior lumbar interbody fusin (ALIF) or lateral lumbar interbody fusion (LLIF) has been previously reported to avoiding the disadvantages of posterior pedicle screw xation [20][21]. In a retrospective study of 65 lumbar DDD patients, Xie et al reported that OLIF combined with lateral pedicle screw xation is a safe and effective surgical method with less operation time and less blood loss [22]. Liu et al suggested the OLIF with supplemental anterolateral screw instrumentation can achieve good clinical result with about 95% fusion rate [23]. Moreover, the combination of OLIF and lateral screw instrumentation was also reported as an effective and safe option for the treatment of degenerative spine deformity [24]. However, there was few report about the usage of lateral plate instrumentation combined with OLIF. In the current study, the oblique lateral spinal system was used with OLIF procedure, it was a very convenient and safe method realizing one-stage intervertebral fusion and instrumentation through a single small incision.
A major concern is that the lateral instrumentation may not be strong enough to maintain the spinal stability, preventing the interbody cages from subsidence and promoting fusion. The biomechanical strength of lateral plate xation system should be considered. Compared with the stand-alone OLIF condition, lateral plate instrumentation signi cantly decreased the lateral bending and axial rotation ROM without changing on exion-extension ROM [25]. The cage combined with a lateral plate was not statistically different from that with bilateral pedicle screws in lateral bending. In another biomenchanical study, the two-hole lateral plate and bilateral pedicle screw xation both signi cantly limit ROM in all loading planes, and they are both recommended with laterally placed cages for the treatment of two-level lumbar spine disease [26]. In a three dimensional nite element study, Liu et al suggested the lateral plate and screws can not provide su cient biomechanical stability for multilevel lateral interbody fusion [27].
On the other hand, in an cadaveric biomechanical study, Lai et al suggested that unilateral pedicle screw and lateral plate may both provide su cient biomechanical stability for multilevel LLIF [28]. In present study, we apply the lateral plate instrumentation only to the one-segmental lumbar degenerative disease, the grade II or more serious lumbar spondylisthesis patients were excluded. No instrumentation failure case occurred in our study.
The complication of lateral plate xation is another concern. The vertebral body fractures have been reported in the patients who underwent LLIF combined with lateral pedicle screw or lateral plate xation [29][30]. The reason might be that a fracture propagated through the screw hole from the xed-angle anterolateral plate, resulting the coronal plane fracture especially in osteoporotic cases. The coronal plane vertebral fracture also occurred in osteoporotic patients who underwent XLIF combined with XLP lateral instrumentation, the unilateral pedicle screw instrumentation does not prevent this complication . In present study, there was none complication related to the lateral plate xation system. Several factors as follows may be able to explained it. Firstly, all patients admitted were single-segmental lumbar degenerative disease; Secondly, the cages used by OLIF were much larger, which located in the II-III area of the vertebral body, and the stress distribution of the whole vertebral body is even. Thirdly, the spine brace is advised for the rst three months after surgery.

Limitations
The present study had some limitations. Firstly, We performed a retrospective study with a small sample size, and the duration of follow-up was short. Secondly, our study only included patients with singlesegmental lumbar degenerative disease, whether it suitable for the multilevel lumbar degenerative disease is unknown. Further random control trials with large samples are needed to verify its pros and cons.

Conclusion
OLIF+LP xation seems to be a valuable surgical option for single-segmental lumbar degenerative disease, it can achieve much better clinical outcomes than OLIF+PS group.

Declarations
Ethics approval and consent to participate This study had been approved by Ethics Committee of the authors' a liated institutions, and the informed consent to participate in the study should be obtained from all the patients.

Consent for publication
All patients provided written informed consent to use their clinical data for publication purposes.

Availability of data and material
The datasets used and/or analyzed during the current study are availabe from the corresponding author on reasonable request.  Table 2 Comparison of the VAS and ODI score between the groups.