The lateral spinal fixation system (PIVOX) was an internal fixation 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 CSA, FH and DH were all significantly improved after the OLIF + LP surgery. Also, the ODI and VAS scores of the patients both decreased significantly than before. No major vascular and nerve damage, vertebral body fracture or instrument failure had occurred.
OLIF was first reported in 2012 as an relatively safe procedure, allowing for psoas preservation, and avoids the lumbar plexus [5]. It has been found to result in a 30.2% median increase in the cross-sectional area of the dural sac and a 30.0% average increase in the neural foramen area [12–13]. However, the occurrence of complications is inevitable, the incidence of complications after surgery fluctuates was reported from 3.7–66.7% [16]. In a study directed by Abe et al, intraoperative complications were reported in 44.5% of the cases, while only 4.7% of postoperative complications occured [7]. The most common complication was the endplate fracture followed by the transitory weakness of the psoas muscle and transient neurological symptoms. Zeng et al also reported that the endplate damage and cage sedimentation were the most common complications of OLIF [10]. In their study, the complication rate in the OLIF stand-alone group was 36.26%, much higher than the OLIF combined pedicle screw group (29.86%). Up to date, the pedicle screws and rod systems were usually applied for stabilization after OLIF because they were considered as the standard method of instrumentation to provide the most rigid fixation of the spine [17].
Lateral pedicle screw instrumentation after anterior lumbar interbody fusin (ALIF) or lateral lumbar interbody fusion (LLIF) has been previously reported to avoid posterior pedicle screw fixation [18–19]. In a retrospective study of 65 lumbar DDD patients, Xie et al reported that the lateral pedicle screw combined OLIF is a safe and effective surgical option with less blood loss and less operative time [20]. Also, Liu et al suggested the OLIF with supplemental anterolateral screw and rod instrumentation can achieve good clinical result, and about 95% fusion rate was reported in their study [21]. Wang et al reported a combination of OLIF and lateral instrumentation for the treatment of moderate degenerative spine deformity,it can correct both coronal and sagittal deformity and improve the quality of life [22]. However, there was few report about the usage of lateral plate fixation system in OLIF. In the current study, the PIVOX oblique lateral spinal system was used in the OLIF procedure, which was a very convenient and safe method of fixation, realizing one-stage intervertebral fusion and instrumentation through a single small incision.
A major concern regarding the use of anterolateral instrumentation is that the construct may not be strong enough to maintain stability, prevent the interbody cages from subsidence and promote fusion. The biomechanical strength of lateral plate fixation system should be considered. Forge et al reported that compared with the stand-alone condition, lateral plate instrumentation significantly decreased lateral bending and axial rotation ROM, though not altering the ROM in flexion-extension [23]. The cage supplemented with a lateral plate was not statistically different from bilateral pedicle screws in lateral bending. In another biomenchanical study, it was reported that the two-hole lateral plate and bilateral pedicle screw fixation both significantly limit ROM in all loading planes relative to the stand-alone condition,and they are recommended when used in two-level lumbar fusion with laterally placed cages [24]. Bilateral pedicle screw rod fixation can provide the greatest reduction in ROM and may be a preferable fusion construct when rigid, motion-eliminating stabilization is required. Guo et al suggested that the ilateral pedicle screws model provided the best biomechanical stability for OLIF; the stand-alone model could not provide sufficient stability [25]. In a three dimensional finite element study, Liu et al suggested the lateral plate and screws can not provide the favorable biomechanical stability for the multilevel lateral interbody fusion [26]. However, In an cadaveric biomechanical study, Lai et al suggested that less invasive adjunctive fixation methods such as unilateral pedicle screw and lateral plate may provide sufficient biomechanical stability for multilevel LLIF [27]. In present study, we apply the lateral plate fixation system only to the one-segmental lumbar degenerative disease patients, and the grade II or more serious lumbar spondylisthesis patients were excluded. No instrumentation failure case occurred in our study .
The difference between lateral plate fixation and anterolateral screw rod fixation also needs to be mentioned. The lateral plates system and the anterolateral screw system can both significantly reduce the ROM, compared with the stand-alone lateral interbody fusion construct. However, which one can support the better stability was unknown. One problem of lateral pedicle screw fixation is that it dose not conform to the inherent curvature of lumbar spine, and the long rod may be interfere with adjacent segmental degeneration. Moreover, the rod is much higher than the side of vertebral body, and the psoas muscle can not fully return to the original position after the surgery, also it may cause twisting injury of the lumbar plexus and ureter. Like the anterior cervical plate, the lumbar lateral plate system can fit the side of vertebral body more easily, and make less interference to the psoas muscle. Furthermore, the length of plate was much shorter than rod, it can decreased the rate of ASD theoretically. However, as we known there was few studies about the application of lateral plate fixation on the OLIF surgery, the long-term efficacy should be further confirmed.
Recent reports address vertebral body fractures on the patients who received supplemental lateral plating or pedicle screw fixation during the LLIF [28–29]. The reason might be that a fracture propagated through the screw hole from the fixed-angle anterolateral plate, resulting the coronal plane fracture pattern as the cage subsided 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 [30]. Brier-Jones et al speculate that violation of the epiphyseal ring or subchondral bone by plate-anchoring screws may contribute to the coronal vertebral body fractures [31]. Kepler et al suggested that vertebral fractures occur when compressive forces are unevenly distributed by a subsided cage into the bone surrounding plate-anchoring screws [28]. In present study, there was none complication related to the lateral plate fixation 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 first 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, the absence of control group was another drawback of this study. Thirdly, OLIF-LP surgery only conducted in the single-segmental lumbar spine disease in our study, whether it suitable for the multi-segmental lumbar degenerative disease is unknown. Further random control trials with large samples are needed to verify its pros and cons.