Known as microinvasive technologies, PVP and PKP, is considered as the "gold standard" for the treatment of osteoporotic VCFs [5, 6, 15]. However, PVP and PKP may no longer be applicable when VCFs accompanied with severe high-energy trauma. Some special reasons are as follows: 1. High-energy trauma may cause spinal canal stenosis due to the vertebral posterior wall fracture. Symptoms of neurological impairment usually require spinal decompression [16, 17]. 2. Internal fixation must be performed to restore spinal stability because of the three-column fracture. 3. Delayed neurological symptoms caused by the injured vertebral wedging may require anterior column resection and reconstruction [18, 19]. However, osteoporosis significantly reduces the internal fixation stability in HVCFs patients with a failure rate up to 12% [20].
Recently, PMMA-augmented cannulated pedicle screw has been considered as an optional technique for broad application prospects [21, 22]. Some researchers recommended this type of pedicle screw for lumbar spondylolisthesis with osteoporosis [23, 24]. Meanwhile, Sawakami et al. [25], Park et al. [26] and Cho et al. [27] have achieved satisfactorily clinical efficacy in pseudoarthrosis following VCFs and Kummell’s disease. But few studies concentrated on the clinical outcome of PMMA-augmented cannulated pedicle screw in HVCFs. Previously, in vitro study showed that CICPS could significantly improve the biomechanical stability of pedicle screws, and preliminary clinical application suggested that CICPS had satisfactory reliability and safety in osteoporotic patients with lumbar spondylolisthesis and thoracolumbar VCF (AO Type A) [8–10, 28]. This clinical study confirmed that CICPS can also obtain satisfactory effect in patients with HVCFs.
In current study, the VAS and ODI score significantly improved after operation immediately and at the last follow-up compared with those before operation. Additionally, there are no significant differences between VAS and ODI scores immediately after operation and at the final follow-up more than 6 months. The results indicate that satisfactory mid-term clinical outcomes can be achieved in this group. Singh V et al. [29] did a systematic analysis for PMMA-augmented cannulated pedicle screw. The published studies showed the average VAS score before operation was 8.4 (range 8-9.2) compared to 2.3 (range 1.42-4.8) at the last follow up. The average improvement ODI for assessment of functional recovery was 42.1. In this study, VAS score before operation was 8.3 compared with 2.2 at last follow-up and ODI improved from 30.5 to 75.5. Therefore, the results obtained in our series are similar to those of previous studies.
PMMA leakage is a focus point to surgeons because neurological or spinal cord damage may cause by the situation [12, 18, 30]. Traditionally, PMMA is injected into the preset nail tunnel using a PVP device during laddering period, and then the screw is inserted into the nail tunnel [25]. The challenges of this procedure lie in uncontrollable diffusion of PMMA during the screw insertion process. Even if PMMA is removed immediately when the spinal canal leakage occurs, these surgical procedures will lead to the time window of PMMA injection being exceeded. Therefore, we chose to further investigate CICPS instead of traditional injection method. The advantage is that screws are left in situ and monitored by intraoperative X-ray during PMMA injection, which can reduce the leakage risk due to pressurised cement injection. Moreover, compared with common screws, the design of side holes located at the screw rod can also play an important role to avoid PMMA leakage [8–10].
CICPSs were used in 18 patients with HVCFs and osteoporosis. 3 screws in 2 patients (3/40, 7.5%) were observed PMMA leakage, but without any neurological symptom. Wuisman et al. [31] reported four out of 49 screws (8.2%) had PMMA leakage into spinal canal using traditional technique and removed PMMA by laminectomy and dura manipulation. Janssen et al. [32] reported that the incidence of asymptomatic PMMA leakage was 66.7% and that of symptoms was 5.5%, in 1.2% of which needed to remove the PMMA and screws. Martı´n-Ferna´ndez et al. [33] observed a 62.3% incidence of PMMA leakage in 313 patients. 1.55% of the cases had symptoms such as radicular pain of lower limbs and transient sensorimotor deficit. In brief, PMMA leakage presented no symptoms or only mild symptoms in most studies and the leakage rate showed a big difference, the reason of which might be related to the small sample size or different screw design in different studies.
In our series, the loss of kyphosis cobb angle increased significantly comparing these indexes at the date of post-operation with that of last follow-up. While there is no significant differences in the vertebral height and no screw loosening was observed. The reason for this phenomenon can be explained by physiological progress. Studies have shown that kyphosis progressed an average 7 degree over 15 years in healthy women, especially between age of 50 and 59 [34, 35]. In thoracolumbar burst fracture following internal fixation without PMMA augmentation, progressive kyphosis was also observed [36]. Therefore, trauma-related disc apoptosis or osteoporosis process [37–39] may play important roles in kyphosis progression spite of PMMA augmentation or not. Besides high-energy fractures are often accompanied by loss of sagittal balance of the spine, which may be another reason for the continued loss of Cobb angle of the spine compared to the postoperative correction angle. From a biomechanical perspective, postoperative stress concentration in the the upper vertebra of the uppermost fixed vertebra may also lead to progressive loss of Cobb angle and even fracture.
In one study of Huang et al [30], they observed the clinical outcomes of traditional PMMA augmentation technology in 28 cases of Kummell’s disease. The operation time, blood loss and hospitalization time were 115.9±10.0 minutes, 214.3±17.5 ml and 7.6±1.3 days respectively. While in this study, the corresponding data were 165 ± 23 minutes, 206 ± 75 ml and 12.5 ± 3.5 days. Furthermore, 3 patients had asymptomatic PMMA leakage, one developed a urinary tract infection, one contracted pneumonia, and one experienced delayed wound healing. There was no screw loosening at the final follow-up. Comparing these data with our findings, we cannot draw any better conclusions by comparing these data with our findings. However, the absolute values of the data between CICPS and the traditional PMMA augmentation technology only have small differences, which may be related to the technical proficiency of surgeons and postoperative management procedures.
This study also has several limitations. Firstly, this study is not a randomized controlled study, contributing to a low level of evidence. Secondly, the sample size is small and the follow-up time is short, thus a study with more patients and longer follow-up duration is required to further confirm our results. Thirdly, since the safety and effectiveness of CICPS have been biomechanically evaluated before [8], only clinical evaluation was performed in this study. Finally, standard application protocol of CICPS should be developed to avoid the catastrophic consequences from excessive application, and it will be our future research focus.