The current study shows that PCBT technique led to smaller incisions and shorter hospital stay, yet equivalent clinical outcomes compared with traditional PPSF surgery. The average incision length of PCBT was only 7.17±0.72 cm, significantly shorter than that of the PPSF group (14.74±1.35 cm). This advantage would lead to less muscular damage, which was correlated with better recovery after surgery (Marengo et al. 2018). In our study, this may be associated with the obviously shorter period of hospital stay in the PCBT group (9.92±7.53 days vs. 13.85±7.53 days in the PPSF group), although this difference between groups was no longer significant after adjustment. Nonetheless, it should also be noted that PCBT technique in our study had longer surgery time and more X-ray exposures. This was different from the clinical data reported by Nicola Marengo et al(Marengo et al. 2018) in which CBT technique provided less Radiation DAP, blood loss, and Surgical time compared to PS procedure in posterior lumbar interbody fusion. The possible explanation for the result in our study may be that there is no previous experience for surgeons to conduct this totally new technique and it still needs time and experience to master the whole procedure.
In this study the average pain intensity VAS scores and ODI were significantly improved after surgery and at the last follow-up in both groups. There was no significant difference between groups in the short- and long-term improvement with or without adjustment, suggesting that PCBT technique yielded equivalent clinical outcomes to the PPSF approach. Hironobu Sakaura et al. (Sakaura et al. 2018) also reported similarly equal outcomes among patients with 2-level degenerative lumbar spondylolisthesis: The mean JOA scores recovery rate (54.4%, from 12.3 points before surgery to 21.1 points at the latest follow-up) in the CBT group was comparable with that of PS group (51.8%, from 12.8 points to 20.4 points). From a small clinical case series study, Yiren Chen et al.(Chen et al. 2018) reported that CBT fixation for degenerative lumbar disease showed a decrease of 27 from the baseline ODI at six to eight months, which is comparable to changes from the baseline ODI reported in three large clinical trials following traditional pedicle screw fixation. Likewise, Shiyuan Shi et al. found no significant difference in the improvement of VAS scores after surgery between CBT group and traditional PS group in the treatment of elderly patients with lumbar spinal tuberculosis(Shi et al. 2018). However, in a prospective cohort of 40 patients with monosegmental degenerative disease, Nicola Marengo et al. reported that CBT-PLIF technique provided significantly better clinical scores (ODI and VAS) compared to PS-PLIF technique, and this significant difference is still present one year after surgery(Marengo et al. 2018).
Regarding radiographic outcomes, before adjustment we found no significant difference in either the postoperative restoration or the maintenance till the latest follow-up of both VWA and sagittal index between the two groups (p > 0.05). Notably, after adjustment for all the possible confounders including BMI, fracture level, fracture type and follow-up period, patients underwent PCBT technique had significantly better postoperative restoration in VWA compared with PPSF group (p < 0.05). Although more follow-up studies in larger patient populations are needed, this result suggests that PCBT fixation may be superior to traditional PPSF technique in intraoperatively promoting the recovery of the height of the compressed vertebra. Since Santoni et al. (Santoni et al. 2009) firstly reported that the cortical bone trajectory (CBT) screw technique demonstrated a 30% increase in uniaxial yield pull-out load relative to the traditional pedicle screws, several biomechanical and morphometric studies comparing the properties of CBT fixation with traditional pedicle screws technique have been performed. Calvert et al.(Calvert et al. 2015) conducted a biomechanical study in 10 fresh frozen human lumbar spines and demonstrated that CBT screws provided stiffness in flexion, extension, lateral bending and axial rotation tests similar to that provided by traditional pedicle screws in cases of rescue screw constructs. Baluch et al. (Baluch et al. 2014) also performed a human cadaveric study on 17 vertebral levels (T11-L5) and then performed quantitative CT scans to compare the fixation strength of cortical screws under physiological loads with traditional pedicle screws. They found that the force necessary to displace CBT screws were significantly greater than the traditional screws. Matsukawa et al. (Matsukawa et al. 2014b) measured the insertional torque of CBT intraoperatively in 48 patients and demonstrated that the insertional torque of CBT screws was 2.01 times higher than that of the traditional screw technique, suggesting an advantage for CBT screws. However, it should be noted that there is still a lack of comprehensive and robust evidence for CBT screws in directly evaluating the comparative biomechanical performance to PS fixation in traumatic vertebral fractures.
Screw loosening is a very common complication for PS fixation, and the rate of screw loosening has been estimated to exceed 60% in patients with osteoporosis (Delgado-Fernandez et al. 2017). The internal fixation of CBT technology can increase the bone screw interface strength as it allows the screw to be fully in contact with the cortical bone. Therefore, CBT screws were conceived as an alternative method to traditional pedicle screw fixation, particularly for stabilization of lower lumbar segments with definitive osteoporosis (Sansur et al. 2016). The equivalent or superior biomechanical properties of CBT screws may be associated with the lower rate of screw loosening reported in the few clinical studies. Gonchar et al.(Delgado-Fernandez et al. 2017) reported a retrospective comparative study of 100 CBT versus 63 traditional pedicle screws in patients who had spinal deformity, degenerative disease, osteoporotic vertebral collapse or trauma. There was one case (1%) of screw loosening in the CBT group versus 16 cases (25%) in the traditional pedicle group. They (Phan et al. 2015) also conducted a prospective comparative study of 30 CBT and 30 traditional pedicle screws patients undergoing posterior lumbar interbody fusion surgery, and reported a similarly high screw loosening rate in the traditional pedicle fixation group (six cases vs. one case). In a retrospective study of 12 patients with single-level lumbar spondylolisthesis who underwent posterior or transforaminal lumbar interbody fusion surgery using CBT screws (Mizuno et al. 2014), no loose screws were detected after the 20-month follow-up. In our study, while no case of screw loosening was detected in the PCBT group, there was one case occurred in the PPSF group.
Moreover, the incidence of pedicle screws misplacement was reported to range from 21 to 40% in despite of the introduction of navigation equipment (Laine et al. 2000; Gertzbein and Robbins 1990; Weinstein et al. 1988). This would lead to a series of serious complications, such as neurological injury, cerebrospinal fluid leakage and abdominal artery injury (Ouchida et al. 2020; Zhao et al. 2018). At this point, CBT technique may significantly decrease the risk of neurovascular injury, as the trajectory of lumbar CBT screws is placed with medial to lateral angulation, which allows the insertion to depart from the nerve roots, dural sac and anterior vascular structures(Phan et al. 2015). This may well explain the lower rate of neurovascular damage of CBT patients currently reported in clinical studies. In a retrospective comparative study of 16 CBT versus 19 traditional PS screws in patients undergoing open posterior lumbar interbody fusions, Okudaira et al.(Phan et al. 2015) reported that while no complications were noted in the CBT group, there was one case of deep infection and permanent neural damage in the traditional pedicle screw group. Hironobu Sakaura et al(Sakaura et al. 2018) designed a comparative study consisted of 22 patients with 2-level DS underwent 2-level PLIF with CBT screw fixation (CBT group, mean follow-up 39 months) and a historical control group of 20 patients who underwent 2-level PLIF using traditional PS fixation (PS group, mean follow-up 35 months). They found that the incidence of intraoperative and early postoperative complications (including dural laceration, symptomatic hematoma and misplacement of screws) was higher in the PS group than in the CBT group, though no significant difference between the groups was found. In this comparative study, while no complications were noted in the PCBT group, there was 1 case with cerebrospinal fluid leakage in the traditional PPSF group. This indicates that PCBT is a safe technique with insignificantly fewer complications compared with traditional PPSF instrumentation.
To the best of our knowledge, we are the first to apply this minimally invasive PCBT technique in the surgical treatment of patients with lumbar fractures. Its application values are as follows. Firstly, it reduces the number of incisions, significantly shortens the incision length and minimizes soft tissue injury. These can contribute to a shorter period of hospital stay and consequently reduce the medical costs. Secondly, we find that this technique is feasible as PCBT screws can be successfully inserted under intraoperative fluoroscopy in a similar way to traditional PPSF technique. The surgery time and X-ray exposure times of PCBT were also comparable to those of PPSF fixation. Finally, it provides clinical data for the treatment of lumbar fractures and demonstrates that PCBT technique can yield equivalent or superior clinical outcomes compared with traditional PPSF fixation. Therefore, it can be considered as an alternative method to traditional PPSF fixation with fewer complications, particularly for the treatment of osteoporotic fractures.
However, our study also has some shortcomings. All of the enrolled patients were only followed up for less than 2 years, thus, the long-term clinical results of PCBT fixation were still uncertain. Therefore, the application of this new approach should be conducted with caution. Also, the number of enrolled patients was limited, and in the future large longitudinal studies should be designed to further testify the safety and feasibility of this new approach. Only patients more than 45 years old were reviewed for this retrospective study, therefore, it is still unclear whether this technique can have similarly inspiring outcomes among younger patients.