The lateral spinal fixation system 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 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 fixation 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 . 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 fluctuates from 3.7% to 66.7% . 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 . In their study, the complication rate was 36.26% in the stand-alone 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 fixation to providing the best bio-mechanical stability of the spine . However, the selection between unilateral pedicle screw (UPS) and bilateral pedicle screw (BPS) fixation still remain controversial in lumbar spine surgery. Wen et al compared the clinical and radiological outcomes of BPS and UPS fixation among the patients who underwent OLIF, they suggested that the OLIF combined with UPS fixation is an effective and reliable option for single-level lumbar diseases .
Obviously, posterior pedicle screw fixation 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 first 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 . 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 fixation [20-21]. In a retrospective study of 65 lumbar DDD patients, Xie et al reported that OLIF combined with lateral pedicle screw fixation is a safe and effective surgical method with less operation time and less blood loss . Liu et al suggested the OLIF with supplemental anterolateral screw instrumentation can achieve good clinical result with about 95% fusion rate . 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 . 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 fixation system should be considered. Compared with the stand-alone OLIF condition, lateral plate instrumentation significantly decreased the lateral bending and axial rotation ROM without changing on flexion-extension ROM . 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 fixation both significantly limit ROM in all loading planes, and they are both recommended with laterally placed cages for the treatment of two-level lumbar spine disease . In a three dimensional finite element study, Liu et al suggested the lateral plate and screws can not provide sufficient biomechanical stability for multilevel lateral interbody fusion . On the other hand, in an cadaveric biomechanical study, Lai et al suggested that unilateral pedicle screw and lateral plate may both provide sufficient biomechanical stability for multilevel LLIF . 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 fixation is another concern. The vertebral body fractures have been reported in the patients who underwent LLIF combined with lateral pedicle screw or lateral plate fixation [29-30]. The reason might be that a fracture propagated through the screw hole from the fixed-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 . 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 . Kepler et al suggested that the unbalanced distribution of compressive stress is another important factor leading to vertebral fractures . 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.
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 single-segmental 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.