The accuracy of pedicle screw insertion is especially crucial because of the severe consequences followed by malposition including neurological and vascular injuries, revision surgery, and spinal instability.[13, 16] Meanwhile, the proximal FJV has been regarded as an independent risk factor for ASD, finally resulting in higher reoperation rate and diminished improvement in quality of life.[3, 4] Thus, the safety of pedicle screw placement has increasingly drawn attention from spinal surgeons. With the application of robotic guidance systems, higher rate of intra-pedicular accuracy and lower rate of proximal FJV in RA technique than those in percutaneous fluoroscopy-guided and freehand techniques have been reported in recent years.[5, 7-9, 13, 14, 16-19] However, the rates of intra-pedicular accuracy and proximal FJV were quite different in previously published studies, and compared with the Mazor RA techniques, the studies on TINAVI systems are rare. Furthermore, the risk factors that affected the outcomes of pedicle screw placement remain controversial and no consensus has been reached in clinical research. Here, we evaluated the safety of pedicle screw placement with TINAVI RA techniques in terms of the intra-pedicular accuracy and proximal FJV, and analyzed the risk factors associated with the two issues in screw implantation.
Many studies have concluded that RA technique showed improvement of intra-pedicular accuracy at the rates of 86.16-98.2% than conventional techniques. [8, 16-18, 24, 25] However, the previously published studies also showed that the RA technique performed no clear advantage in terms of intra-pedicular accuracy rates of 78.8-93.7% over the conventional techniques. [5, 9, 13, 26] Hyun et al.[9] conducted a RCT of Mazor robotic-guided versus freehand surgery, and found that all screws were optimal positions in RA group and 98.6% screws were graded as optimal positions, showing no remarkable difference. Kim et al.[13] also concluded that the intra-pedicular rate of 93.7% in the Mazor robotic-guided group was significantly similar to that of 91.9% in the freehand group. In the current study, we found that the optimal (grade A) and clinically acceptable (grade A+B) screw position were 85.8% and 93.4%, respectively, indicating promising results. Moreover, the main direction of screw deviations in pedicle was lateral, followed by medial and inferior breaches. The results might be explained as follows. First, based on the intraoperative 3D images where the anatomical structures, especially the abnormal and degenerative parts were clearly displayed, the RA system could automatically identify the optimal entry point and trajectory direction for the safety of the pedicle cortex. Then the implantation procedure was automatically performed according to the preplanned satisfactory trajectory in order to ensure the intra-pedicular accuracy. Second, the robot can repeat complex tasks precisely, thereby avoiding the limitation of human manual errors. Third, RA technique can minimize the resistance from the soft tissues around the spine compared to freehand method. After the guidewire was inserted under the guidance of a robotic arm, the screws were placed through the guiding tube into the pedicle. In contrast, the selection of entry point and the adjustment of trajectory would be biased due to the pulling and blocking of the paravertebral muscles in freehand surgery, leading to higher risk of screw malposition. Fourth, the RA insertion has a short learning curve because of the automatic procedures and the precision of implantation. Previous studies reported that the surgical outcomes from the initial experience to practiced experience showed no remarkable difference.[27, 28] Thus, surgical skills are relatively less demanding, thereby indicating that RA technique may prevent malposition by reducing unnecessary manual mistakes. Fifth, due to the precise insertion of RA technique, the rate of medial penetrations was greatly reduced, avoiding the relevant severe complications, such as spinal cord and nerve root injuries.
The importance of proximal facet joint protection has been increasingly realized in recent years and the violation might lead to the spinal instability in adjacent segments and reduce the load-bearing ability, eventually resulting in the radiographic ASD.[3, 29] The studies regarding the superiority of RA versus conventional freehand techniques remained controversial. On the one hand, Some studies revealed that the RA pedicle screw placement was associated with significantly fewer FJV (0.00%-2.84%) than the conventional trajectory freehand implantation (15.85-100.00%).[2, 13, 14, 16, 18, 30-33] On the other hand, in a prospective RCT conducted by Hyun et al.[9], no remarkably statistical difference was noted regarding the rates of proximal FJV between the RA and freehand techniques (0.00% vs 0.71%). In a similar study, Archavlis et al.[14] also reported that the rate of f proximal FJV in the RA group was similar to that in the freehand group (5% vs 6%). In the present study, we found that the proximal FJV was 23.2%, which was lower than that in freehand method but relatively higher than that in RA method from most of the previous published studies. Moreover, majority of the proximal FJV resulted from the screw head, followed by the screw shaft. The results might be attributed to the fact that the reduction of proximal FJV might result from the precision of pedicle screw placement. With the 3D images, the anatomical landmarks on the vertebra with hypoplastic or degenerative diseases can be displayed clearly with RA method. The RA system can identify the optimal entry point and trajectory and insert screws more accurately for the safety of facet joint by enlarging the distance between the facet and screws. Moreover, the advantages of muscle resistance and the short learning curve via RA method are also beneficial to facet protection. Furthermore, we found that the proximal FJV in the current study was higher than other trials. The results might be interpreted as that majority of pedicle screws were inserted in thoracolumbar levels with the patients diagnosed of vertebral fractures. However, we concluded in the current study that the FJVs in the thoracolumbar levels were remarkably higher than those in the lumbosacral levels due to the thinner diameter of pedicle in the thoracolumbar segments. Thus, the overall rate of FJV may be affected by the higher rate of thoracolumbar FJV.
The factors that affected the intra-pedicular accuracy and proximal FJV were also explored with univariate and multivariate analyses. As for the pedicle screw placement accuracy, our multivariate regression analysis demonstrated that lumbosacral instrumentation was 0.227 times likely to breach the cortex because of a larger diameter of pedicle in the lower lumbar segments. Thus, the occurrence of screw deviation causing severe penetration in lumbosacral segments might decrease than that in thoracolumbar segments. Moreover, we also found that the facet angle ≥45° and the depth of surgical field ≥4.5cm are the protective factors in pedicle screw placement, which might result from the fact that in the lumbosacral levels, the facet angle was larger and the mean distance from the entry point to the skin was further than those in the thoracolumbar levels. Because of the higher rate of accuracy in lumbosacral instrumentation,
The distance from entry point to screw ≥4.5cm was less likely to breach the cortex. Moreover, we also found that the male patients suffered from less screw penetration.
In terms of the independent factors that affected the cranial FJV, our multivariate analysis showed that the L5 insertion was 2.02 times more likely to breach the facet. Tian et al.[34] identified an increasing trend of proximal FJV rates ranging from 1.5%, 7.4%, 17.6%, 30.9% to 42.6% with the levels of vertebrae dropping from L1 to L5. Besides, Moshirfar et al.[35] inserted the screws with freehand method, and it was found that the proximal FJV in the L5 level (48%) was significantly higher than that of other levels. In L5 segment, the ideal entry point was deviated to the outside with the increasement of valgus angle. Meanwhile, the articular surface of the facet joint also shifted to the lateral and coronal planes, blocking the insertion trajectory and ultimately increasing proximal FJV.[22, 31] Moreover, patients with facet angle ≥45° were 1.89 times more likely have a proximal FJV than patients with facet angle <45°. When the facet angle increases, the surface of facet joint gradually deviates to the coronal position, thereby blocking the trajectory of screws.[29] Another explanation might be that the facet angle in the lower lumbar is larger than that in the upper lumbar, and the lumbar lordosis is mainly manifested in the lower lumbar. Thus, there is more overlap between the facet joints and the pedicle direction, which also blocks the pathway of screws.[19]
There are some potential limitations in the current study. First, no control group was included in the study and only the data of RA technique was reported without comparative results. Although we compared the outcomes with those from previously published literatures, yet the higher biases appeared. Second, the overall intra-pedicular accuracy and proximal FJV consisted of thoracic and lumbar segments. The results may be affected due to the different anatomical characteristics. Third, we only reported the radiographic results in a short-term follow-up period. Nevertheless, the postoperative short-term outcomes are crucial for a novel technique regarding the accuracy of pedicle screw placement. Continued assessment of safety and accuracy of screw placement in long-term follow-up using TINAVI RA technique is needed in the future work.