Main finding
Our meta-analysis comprehensively and systematically reviewed the currently available literature and found that (1) unilateral pedicle screw fixation compared with bilateral pedicle screw fixation significantly reduced total blood loss, operation time, and increase the cage migration and (2) unilateral pedicle screw fixation had no benefit on VAS, JOA, ODI, SF-36, and complications compared with bilateral pedicle screw fixation for lumbar degenerative diseases patients.
Two relevant meta-analyses about unilateral pedicle screw fixation and bilateral pedicle screw fixation have been published. Although the main finding of our meta-analysis was consistent with most of the outcomes of previous meta-analyses, differences between ours and the previous ones should be noted. First, these previous meta-analyses included no more than six trials and 399 patients. In comparison, our current meta-analysis included 12 RCTs involving 808 patients. With the added statistical power of at least 409 cases, our current meta-analysis was the latest and the most comprehensive one, which generally concurs and further reinforces earlier results of previous meta-analyses. Second, we only included RCTs and thus the selection bias was avoided. Third, we performed subgroup analysis and sensitivity analysis to increase the robustness of our meta-analysis.
We identify the fusion rate as the main outcome. The results showed that unilateral pedicle screw fixation has a similar fusion rate with bilateral pedicle screw fixation at the final follow-up. There is a heated discussion about the biomechanics stability of unilateral pedicle screw fixation. Han et al. [
21] conducted a meta-analysis and they found that there was significantly a higher fusion rate in the bilateral group than in the unilateral group. A major concern about this meta-analysis was that they mixed RCTs with non-RCTs. Xiao et al. [
6] found that there was no statistically significant difference in terms of the fusion rate. However, only eight RCTs involving 545 patients were included. Chen et al. [
22] performed a biomechanical study and found that unilateral fixation with cage implantation was sufficient to maintain the stability of the lumbar spine. The reason may be that unilateral pedicle screw fixation with cage fusion provides enough biomechanical stability for intervertebral fusion. It was probably considered as a two-point fusion in the unilateral screw fixation, while it was a three-point fusion in the bilateral screw fixation. That means that two-point fusion has a similar fusion rate when compared with three-point fusion.
We then compared unilateral and bilateral groups in terms of the clinical and functional outcomes (VAS, JOA, ODI, and SF-36). The ODI was used to assess a patient’s disability during the activities of daily living. The results showed that unilateral pedicle screw fixation has similar outcomes with bilateral pedicle screw fixation. Lin et al. [
23] found that when patients in the unilateral pedicle fixation group are compared with the bilateral pedicle screw fixation group on the VAS, ODI scores demonstrated no significant differences. Xiao et al. [
6] drawn a similar conclusion with our results. They found that unilateral pedicle screw fixation with cage fusion achieves a similar VAS, ODI, and SF-36 scores with bilateral pedicle screw fixation.
Operation time, blood loss, and the length of hospital stay were took for evaluating surgical trauma and economic costs in this study. The results showed that unilateral pedicle screw fixation was associated with a reduction of the operation time and blood loss than bilateral pedicle screw fixation. No significant difference was found for the length of hospital stay. Since unilateral pedicle screw fixation only needs dissection on one side of the soft tissue and paravertebral muscles and insertion on the side of the pedicle screw, it can accordingly reduce the operation time and blood loss as compared with bilateral pedicle screw fixation [
24]. Moreover, lesser soft tissue dissection may allow for early functional recovery. In theory, unilateral pedicle screw fixation may be related with the short length of hospital stay. In the current meta-analysis, we found no significant difference between the two groups in terms of the length of hospital stay.
There was no significant difference between the occurrence of complication. There was no significant heterogeneity between the included studies. Eliades et al. [
5] found that bilateral pedicle screw fixation increases the stability of the spine, and it also increases the implant costs and the incidence of neurologic complications. And, unilateral pedicle screw fixation was associated with an increase of the cage migration than bilateral pedicle screw fixation. Many studies have reported that unilateral fixation is not stable enough to prevent fusion cage migration [
11]. The reason may be that unilateral screw fixation inherently results in asymmetry. Therefore, the cage should be inserted obliquely into the disk space, and the cage of the anterior part should cross the midline of the vertebral body to support the contralateral anterior column.
The current study had several limitations. (1) Patients with different phases of follow-up were included. There was marked heterogeneity among the included studies in terms of total blood loss, length of hospital stay, and JOA. (2) The type of operation (including TLIF and MID-TLIF) and surgical segments varied between studies. (3) Blinding of the participant was unclear and this bias could not be avoided. (4) Some data for comparisons were not originally available but were calculated by estimation, leading to other bias.