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BACKGROUND: The angle of screw placement in anterior cervical discectomy and fusion plays a crucial role in determining the stability of the internal fixation system. OBJECTIVE: To predict the impact of different screw placement angles on the stress experienced by the internal fixation system in anterior cervical discectomy and fusion utilizing finite element analysis, with the ultimate goal of identifying the optimal screw placement angle. METHODS: A three-dimensional reconstruction method was employed to establish a mechanical model of the cervical spine, enabling the simulation of three distinct working conditions: scoliosis, uprightness, and forward flexion. In SolidWorks 2017, the anterior cervical plate and screw models were built according to different placement angles of the screws, with a as the inward offset, b as the ideal position, c as the outward offset, d as the downward offset, and e as the upward offset. The stress distribution of internal fixation system at different screw placement angles was observed, and the stress and displacement were recorded. RESULTS AND CONCLUSION: (1) By constructing a finite element model of the entire cervical spine and incorporating an anterior titanium plate, it was found that the biomechanical changes in the spine did not significantly differ based on the various angles of screw insertion on the titanium plate under the same working conditions. (2) However, microscopic analysis revealed that the outward offset (c) screw position exhibited the most effective resistance against side bending, while the downward offset (d) screw demonstrated optimal load-bearing capacity in the upright condition. Additionally, the outward deviation (c) screw displayed superior anti-bending effects in the reverse buckling condition. (3) The fixation effect of the internal fixation device remained relatively stable across different motion conditions. Although there was a 10% variation in the internal fixation effect under the three working conditions when the screw was placed inward, outward, downward, or upward, the displacement changes were minimal. These findings suggest that the requirements of load bearing, bending resistance, and flexion resistance could be simultaneously met without a specific optimal screw location in clinical practice. (4) The placement direction of titanium plate screw in anterior cervical disc-resection and fusion has little effect on the mechanical stability of the cervical spine. The screw angles in different directions have little influence on the stability of the internal fixation device in the lateral, upright, and forward flexion movements of the cervical spine. There is no need to pursue the direction of screw placement in clinical operations. [ABSTRACT FROM AUTHOR]

BACKGROUND: Atlantoaxial dislocation, because of its high difficulty and high risk of surgery, has been regarded as the “surgical restricted area” by the international orthopedic community. However, with the rapid development of intelligent digitization in orthopedics, robot-assisted navigation screw placement technology has been widely used in clinical practice, which significantly reduces the difficulty and risk of surgery and improves the safety of surgery. However, there are few reports on the application of this technique in the treatment of atlantoaxial dislocation. OBJECTIVE: To explore the application value of robot-assisted pedicle screw internal fixation in the treatment of atlantoaxial dislocation. METHODS: The medical records of five patients with atlantoaxial dislocation treated with C1-C2 pedicle screw fixation under robot-assisted navigation in Zhuhai Hospital of Guangdong Provincial Hospital of Chinese Medicine from October 2021 to July 2022 were retrospectively analyzed. Operation time, length of neck incision, blood loss, postoperative drainage volume, and length of hospital stay were recorded. Attention should be paid to cerebrospinal fluid leakage, vertebral artery injury, nerve injury, operative area infection and other complications. The visual analog scale score of neck pain, the spinal cord injury grade of the American Spinal Injury Association, the cervical spine score of the Japanese Orthopaedic Association, and the imaging indicators were collected before surgery and at the last follow-up. Screw placement accuracy was assessed. RESULTS AND CONCLUSION: (1) Five patients were successfully completed surgery, without vascular, nerve injury or other complications, and were followed up for 12-20 months. (2) A total of 20 cervical pedicle screws were placed in 5 patients, including 9 type A screws, 10 type B screws, and 1 type C screw. The accuracy of screw placement was 95%. (3) At the last follow-up, the visual analog scale score was (0.80±0.71) points, which was significantly lower than that before operation (4.00±2.83) points; the Japanese Orthopaedic Association score was (14.80±0.84) points, which was significantly higher than that before operation (8.00±0.71) points. Anterior atlantodental interval decreased from (7.86±3.25) mm to (2.82±0.93) mm; space available of the spinal cord increased from (6.74±1.99) mm to (12.10±3.51) mm; cervicomedullary angle increased from (133.32±13.55)° to (153.44±9.53)°; clivus-canal angle increased from (128.02±9.92)° to (143.25±12.99)°. The results of the last follow-up indexes were improved compared with those before operation, and the differences were significant (all P < 0.05). (4) Postoperative imaging follow-up showed that all patients had bone fusion in the bone graft area, and no internal fixation loosening, fracture or pull-out occurred. (5) This method can avoid relying on the doctor’s experience and hand feeling, ensure the accuracy of upper cervical screw placement, reduce the risk of surgery, and obtain satisfactory results in mid-term follow-up. [ABSTRACT FROM AUTHOR]

BACKGROUND: Orthopedic robots have been widely used in clinical practice, and relevant reports have shown that they have many advantages such as minimal trauma and short surgical time. However, there is currently no clear report on how accurate they are. OBJECTIVE: To evaluate the accuracy of robot-assisted sacroiliac screw insertion. METHODS: A total of 131 patients with sacroiliac joint fracture and dislocation and sacral fracture admitted to the Department of Trauma Surgery, Gansu Provincial Hospital from January 2020 to April 2023 were retrospectively collected, including 131 S1 screws and 46 S2 screws, totaling 177 screws. They were divided into two groups based on whether robot-assisted navigation was performed. There were 63 cases of sacroiliac screws inserted under robot-assisted navigation (observation group), with 36 males and 27 females, aged 19-72 years, with a mean age of (45.3±17.6) years. Among them, 39 cases were fixed with only S1 screws, while 24 cases were fixed with S1S2 screws, resulting in a total of 87 sacroiliac screws. Under C-arm fluoroscopy, 68 cases of sacroiliac screws were inserted with bare hands (control group), including 41 males and 27 females, aged 23-67 years, with a mean age of (42.6±21.3) years. Among them, 46 cases were fixed with simple S1 screws, while 22 cases were fixed with S1S2 screws, resulting in a total of 90 sacroiliac screws. A postoperative CT scan was performed to evaluate the number of S1 screws, S2 screws, total screw level, and calculate accuracy based on the method introduced by SMITH et al. RESULTS AND CONCLUSION: (1) In the observation group, 62 S1 screws were accurately placed (62/63), with an accuracy rate of 98%. 24 S2 screws were accurately placed (24/24), with an accuracy rate of 100%. The total number of screws accurately placed was 86 (86/87), with an accuracy rate of 99%. (2) In the control group, 58 S1 screws were accurately inserted (58/68), with an accuracy rate of 85%. 19 S2 screws were accurately inserted (19/22), with an accuracy rate of 86%. The total number of screws accurately inserted was 77 (77/90), with an accuracy rate of 86%. (3) There was a statistically significant difference in the accuracy of the S1 screw, S2 screw, and total screw between the two groups (P < 0.05). It is suggested that the placement of sacroiliac screws under robot navigation has higher accuracy compared to manual placement under C-arm fluoroscopy, but still has a lower error rate in placement. [ABSTRACT FROM AUTHOR]

BACKGROUND: Because of its excellent biomechanical advantages, pedicle screw of subaxial cervical spine is widely used in various cervical spine diseases caused by trauma, tumors and deformities. How to improve the accuracy of nail placement and reduce postoperative complications has been hotspots in the research of the placement technology of the pedicle screw of subaxial cervical spine. OBJECTIVE: To review relevant domestic and foreign articles, to review the related anatomical characteristics of the placement technology of the pedicle screw of subaxial cervical spine, the biomechanical characteristics of pedicle screw of subaxial cervical spine and the research on the screw placement technology in and outside China, and to analyze the advantages and disadvantages of each placement technology. METHODS: Relevant articles in PubMed, Web of Science, CNKI, Wanfang and other databases were searched using “cervical, pedicle” in English, and “cervical vertebrae, pedicle” in Chinese as search terms. Related Chinese articles published from January 2015 to December 2020 and related English articles published in the past 5 years were searched. Finally, 52 articles were included, including 22 Chinese articles and 30 English articles. RESULTS AND CONCLUSION: (1) Regarding the thickness and strength of the cortex, the inner wall of the pedicle was higher than that of the outer wall. The abduction angle of the pedicle gradually decreased from C3-C7. The shape of the pedicle was similar to an ellipsoid. The distance between the upper edge of the pedicle and the upper nerve root gradually increased from C3-C7, and the distance between the lower edge of the pedicle and the inferior nerve root gradually decreased from C3-C7. The anterior lateral wall of the pedicle was close to the vertebral artery; and the anterior medial wall of the pedicle was close to the epidural sinus. (2) The penetrating force of the inner wall of the pedicle was greater than the other three side walls. In terms of direct extraction force, pedicle screws were superior to intervertebral foraminal screws and lateral mass screws. In terms of fatigue extraction force, pedicle screws and intervertebral foraminal screws were better than lateral mass screws. (3) At present, screw placement in posterior route pedicle on subaxial cervical spine mainly included freehand screw placement, computer-assisted screw placement, 3D printing guide-assisted screw placement, and surgical robot-assisted screw placement. However, various screw placement techniques have certain drawbacks. In the future, freehand screw placement technology will still be the mainstream of the subaxial cervical pedicle placement technology. With the improvement of technical level and the support of artificial auxiliary equipment, artificial intelligence assisted screw placement technology will become the future development direction. [ABSTRACT FROM AUTHOR]

BACKGROUND: In the surgical treatment of spinal deformities and tumors, the firm and stable fixation of the lumbosacral junction is a task that must be completed in the operation, and it is a relatively great challenge. The incidence rate of postoperative complications (such as pseudarthrosis, failure of internal fixation and loosening) is high. The mechanical strength of the bone tissue in the sacrum is low, and the high load in the lumbar vertebrae and pelvis increases the risk of internal fixation pullout, which further leads to the loosening of the instrument. Although there are some of the most effective surgical techniques, the complexity of surgical techniques often leads to unsatisfactory clinical results OBJECTIVE: To summarize the latest research progress on the sacropelvic fixation and clinical applications of the S2 alar iliac (S2AI) screws, and provide a reference for clinical treatment. METHODS: The computer was used to search articles published from 2005 to 2020 in CNKI, Wanfang, and PubMed. The search terms were “S2 alar iliac screw, S2AI, iliac screw, sacropelvic fixation, alar iliac screw” in English and Chinese. Relevant articles were consulted, and finally 43 articles were included for analysis. RESULTS AND CONCLUSION: (1) Sacral pelvic fixation, such as ilium and S2AI screw, was added to the lower end of long segmental fixation of the spine to solve the above-mentioned related complications. (2) S2AI screw placement technique plays an important role in stabilizing sacroiliac joint. Because of its unique screw placement method, it avoids screw dislocation, reduces postoperative sacroiliac joint pain and reduces the risk of reoperation. (3) As a new technology of spinal and pelvic fixation, S2AI screw has many advantages and clinical significance, but due to the complex and diverse structure of sacroiliac joint and individual differences of patients, there are still related problems in clinical application of S2AI screw. [ABSTRACT FROM AUTHOR]

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BACKGROUND: With the development of three-dimensional (3D) printing technology, it has been widely used in spinal surgery. However, whether 3D printing-assisted surgery for lumbar spondylolisthesis has an advantage over traditional surgery is still controversial. OBJECTIVE: To compare the clinical efficacy and safety of 3D printing-assisted versus conventional surgery for the treatment of lumbar spondylolisthesis using system evaluation. METHODS: Randomized controlled trials about 3D printing technology for lumbar spondylolisthesis in CNKI, Wanfang database, CBM, VIP, PubMed, Cochrane Library, Embase, and Web of Science were searched via computer from inception to November 16, 2019. The retrieved literatures were screened according to predefined inclusion and exclusion criteria, and quality evaluation was performed. Then, the available data were extracted and analyzed with the Stata 11.0 software. RESULTS AND CONCLUSION: (1) Six randomized controlled trials including 394 cases were included. Among them, 201 cases were assigned to the 3D printing-assisted group and 193 cases to the conventional group. (2) Meta-analysis results showed that the 3D printing-assisted group proved significantly superior to the conventional group regrading the operation time [WMD=-38.17, 95%CI(-43.93, -32.41), P=0.00], intraoperative blood loss [WMD=-61.61, 95%CI(-69.19, -54.03), P=0.00], the frequency of fluoroscopy [WMD=-4.89, 95%CI(-6.38, -3.41), P=0.00] and the screw placement accuracy [OR=3.89, 95%CI(2.43, 6.25), P=0.00]. (3) However, in terms of the postoperative visual analogue scale scores [WMD=-0.47, 95%CI(-1.21, 0.27), P=0.215], Oswestry disability index [WMD=-1.41, 95%CI(-2.87, 0.05), P=0.058], Japanese Orthopaedic Association scores [WMD=1.02, 95%CI(-0.68, 2.72), P=0.240] and the rate of complications [OR=0.37, 95%CI(0.12, 1.11), P=0.075], no statistically significant differences were found between the two groups. (4) In conclusion, the application of 3D printing technology in the surgical treatment of lumbar spondylolisthesis has the advantage of shortening the operation time, reducing intraoperative blood loss and frequency of fluoroscopy and improving the accuracy of the screw placement. [ABSTRACT FROM AUTHOR]

BACKGROUND: The bone trabecula of the vertebral body cannot be fully recovered, and the mechanical stability of the sagittal position of the spinal column is affected. The anti-bending force and the anti-torsion force of the short-segment fixation of fractured vertebra are obviously increased. The bearing load of various activities such as flexion, extension, and rotation of the vertebral body is increased. The stability of the injured vertebra is better maintained, and favorable conditions are created for fracture healing. OBJECTIVE: To compare the early- and mid-term follow-up results of trans-injured and cross-injured vertebra pedicle screw fixation in the treatment of thoracolumbar fractures. METHODS: Eighty-eight patients with thoracolumbar vertebrae fracture treated in Affiliated Hospital of Qinghai University from April 2017 to April 2018 were divided into trans-injured vertebra group and cross-injured vertebra group according to the treatment plan. All patients signed the informed consent. This study was approved by the Hospital Ethics Committee. Intraoperative blood loss, operation time, postoperative bed rest time, postoperative site infection, and subcutaneous hematoma were analyzed in both groups. Visual analogue scale score, Oswestry Disability Index, anterior edge height ratio and kyphosis Cobb angle were compared before surgery, 6 and 12 months after surgery between the two groups. RESULTS AND CONCLUSION: (1) The operation time was longer and intraoperative blood loss was higher in the trans-injured group than those in the cross-injured group, but the postoperative bed rest time was shorter in the trans-injured group than that in the cross-injured group (P < 0.05). (2) There was no significant difference in visual analogue scale score, Oswestry Disability Index, anterior edge height ratio and kyphosis Cobb angle between the two groups preoperatively and 2 weeks after the operation (P > 0.05). (3) At 6 and 12 months after surgery, visual analogue scale score and Oswestry Disability Index were lower in the trans-injured group than in the cross-injured group; anterior edge height ratio was larger in the trans-injured group than in the cross-injured group; kyphosis Cobb angle was smaller in the trans-injured group than in the cross-injured group (all P < 0.05). (4) Incidence of complications was higher in the cross-injured group (30%) than in the trans-injured group (7%) (P=0.001 ). (5) The treatment of thoracolumbar fracture with trans-injured pedicle screw can not only effectively restore and maintain the injured vertebral height and kyphosis Cobb angle, restore the physiological height and curvature of vertebral body, but also the incidence of postoperative complications is low, which can effectively improve the prognosis of patients and improve the quality of life of patients. [ABSTRACT FROM AUTHOR]

BACKGROUND: Traditional fluoroscopy-guided pedicle screw fixation is not highly accurate and can lead to serious surgical complications. To reduce surgical complications and improve the success rate of surgery, robotic assistive technology emerges as the times require. OBJECTIVE: To compare the difference of robot-assisted and fluoroscopy-guided pedicle screw placement using meta-analysis. METHODS: The study included clinical controlled trials on robot-assisted and fluoroscopy-guided pedicle screw placement published in and outside China from December 2008 to December 2018. The retrieval was performed in the online databases include Embase, PubMed, Central, CNKI, CQVIP, Wanfang, and CBM. Keywords used for search were robot assisted, fluoroscopy guided, conventional, freehand, pedicle screw in English and Chinese. After the data were extracted, statistical software Review Manager 5.3 was used for data-analysis. RESULTS AND CONCLUSION: (1) Based on the above search strategy, 1 615 studies were retrieved, and 13 were included. (2) Statistical analysis found that placement accuracy in the robot-assisted group was better than that of the fluoroscopy group [95%CI(1.55, 4.06), P=0.000 2]. Radiation intensity in the fluoroscopy group was lower than that in the robot-assisted group [95%CI(0.42, 0.82), P < 0.001], and the difference was statistically significant. (3) However, the incidence of complications [95%CI(0.23, 4.65), P=0.96] and revised surgery [95%CI(0.03, 3.17), P=0.33] were not statistically significant between the robot-assisted group and the fluoroscopy group. Intraoperative fluoroscopy time was similar between the two groups [95%CI(-38.55, 78.26), P=0.51]. Postoperative back pain [95%CI(-0.58, 0.38), P=0.68], leg pain score [95%CI(-0.20, 0.19), P=0.94] and operation time [95%CI(-6.33, 53.02), P=0.12] were also similar between the two groups, and the differences were not statistically significant. (4) Compared with fluoroscopy, robot-assisted technique has higher pedicle screw placement accuracy, especially under percutaneous conditions. Inevitably, the intraoperative radiation intensity is also more than conventional fluoroscopy. [ABSTRACT FROM AUTHOR]

Objective: To compare the effectiveness of O-arm navigation and ultrasound volume navigation (UVN) in guiding screw placement during minimally invasive transforaminal lumbar interbody fusion (MIS-TLIF) surgery., Methods: Sixty patients who underwent MIS-TLIF surgery for lumbar disc herniation between June 2022 and June 2023 and met the selection criteria were included in the study. They were randomly assigned to group A (screw placement guided by UVN during MIS-TLIF) or group B (screw placement guided by O-arm navigation during MIS-TLIF), with 30 cases in each group. There was no significant difference in baseline data, including gender, age, body mass index, and surgical segment, between the two groups ( P >0.05). Intraoperative data, including average single screw placement time, total radiation dose, and average single screw effective radiation dose, were recorded and calculated. Postoperatively, X-ray film and CT scans were performed at 10 days to evaluate screw placement accuracy and assess facet joint violation. Pearson correlation and Spearman correlation analyses were used to observe the relationship between the studied parameters (average single screw placement time and screw placement accuracy grading) and BMI., Results: The average single screw placement time in group B was significantly shorter than that in group A, and the total radiation dose of single segment and multi-segment and the average single screw effective radiation dose in group B were significantly higher than those in group A ( P <0.05). There was no significant difference in the total radiation dose between single segment and multiple segments in group B ( P >0.05), while the total radiation dose of multiple segments was significantly higher than that of single segment in group A ( P <0.05). No significant difference was found in the accuracy of screw implantation between the two groups ( P >0.05). In both groups, the grade 1 and grade 2 screws broke through the outer wall of the pedicle, and no screw broke through the inner wall of the pedicle. There was no significant difference in the rate of facet joint violation between the two groups ( P >0.05). In group A, both the average single screw placement time and screw placement accuracy grading were positively correlated with BMI ( r =0.677, P <0.001; r =0.222, P =0.012), while in group B, neither of them was correlated with BMI ( r =0.224, P =0.233; r =0.034, P =0.697)., Conclusion: UVN-guided screw placement in MIS-TLIF surgery demonstrates comparable efficiency, visualization, and accuracy to O-arm navigation, while significantly reducing radiation exposure. However, it may be influenced by factors such as obesity, which poses certain limitations.

Objective: To compare the effectiveness and screw planting accuracy of percutaneous reduction and internal fixation with robot and traditional fluoroscopy-assisted in the treatment of single-level thoracolumbar fractures without neurological symptoms., Methods: The clinical data of 58 patients with single-level thoracolumbar fractures without neurological symptoms between December 2016 and January 2018 were retrospectively analysed. According to different surgical methods, the patients were divided into group A (28 cases underwent robot-assisted percutaneous reduction and internal fixation) and group B (30 cases underwent fluoroscopy-assisted percutaneous reduction and internal fixation). There was no neurological symptoms, other fractures or organ injuries in the two groups. There was no significant difference in general data of age, gender, fracture location, AO classification, time from injury to surgery, and preoperative vertebral anterior height ratio, sagittal Cobb angle, visual analogue scale (VAS) score, and Oswestry disability index (ODI) score between the two groups ( P >0.05). The screw placement time, operation time, intraoperative blood loss, intraoperative fluoroscopy frequency, hospitalization time, operation cost, postoperative complications, VAS score, ODI score, anterior vertebral height ratio, and sagittal Cobb angle before operation, at 3 days, 6 months after operation, and at last follow-up were recorded and compared between the two groups. The accuracy of the pedicle screw placement was evaluated by Neo's criteria., Results: The screw placement time, operation time, and intraoperative fluoroscopy frequency of group A were significantly less than those of group B, and the operation cost was significantly higher than that of group B ( P <0.05). But there was no significant difference in intraoperative blood loss and hospitalization time between the two groups ( P >0.05). Both groups were followed up 12-24 months, with an average of 15.2 months. The accuracy rate of screw placement in groups A and B was 93.75% (150/160) and 84.71% (144/170), respectively, and the difference was significant ( χ 2 =5.820, P =0.008). Except for 1 case of postoperative superficial infection in group A and wound healing after dressing change, there was no complication such as neurovascular injury, screw loosening and fracture in both groups, and there was no significant difference in the incidence of complications between the two groups ( χ 2 =0.625, P =0.547). The anterior vertebral height ratio, sagittal Cobb angle, VAS score, and ODI score of the two groups were significantly improved ( P <0.05); there was no significant difference between the two groups at all time points after operation ( P >0.05)., Conclusion: The spinal robot and traditional fluoroscopy-assisted percutaneous reduction and internal fixation can both achieve satisfactory effectiveness in the treatment of single-level thoracolumbar fractures without neurological symptoms. However, the former has higher accuracy, fewer fluoroscopy times, shorter time of screw placement, and lower technical requirements for the operator. It has wide application potential.

Objective: To investigate the anatomical characters of the sustentaculum tali (ST), accurate entry point and direction for the placement of ST screw from posterior subtalar joint facet to the constant fragment (CF) in calcaneal fractures., Methods: A total of 100 patients with calcaneal fractures performed ankle CT scans were enrolled between January 2016 and April 2016. According to the inclusion criteria, the clinical data of 33 patients were analyzed, including 18 males and 15 females, with a median age of 41.0 years (range, 18-60 years). There were 16 cases on left side and 17 cases on the right side. Three-dimensional (3D) calcaneal model was reconstructed by Mimics 17.0 software, and the ST anatomical references were measured, including the length of upper and lower edge, the length and height of the midline, the horizontal angle between the midline and foot plantar surface. The parameters of the optimal entry point position (P' point) and placement angle of the ST screw were determined. The length of ST screw was also measured. The differences between males and females or left and right sides were compared., Results: The length of upper edge of the ST was (16.60±2.23) mm, lower edge (20.65±2.90) mm, midline (20.56±2.62) mm, and the height of midline was (9.61±1.36) mm. The horizontal angle between the midline and foot plantar surface was (23.43±3.36)°. The vertical distance from P' point to the lowest point of the tarsal sinus was (3.09±1.65) mm, while the horizontal distance was (14.29±2.75) mm. The distance from P' point to the apex of the lateral talus, subchondral bone of subtalar joint, calcaneocuboid joint was (11.41±3.22), (6.59±2.22), (34.58±3.75) mm, respectively. The horizontal angle between the ST screw and foot plantar surface was (-1.17±2.07)°. The anteversion angle of ST screw was (16.18±2.05)° and the length was (41.64 ± 3.09) mm. There were significant differences in the length of upper and lower edge, the length and height of the midline, the distance from P' point to the apex of the lateral talus, subchondral bone of subtalar joint, and calcaneocuboid joint, and the anteversion angle and length of the ST screw between males and females ( P <0.05). There was no significant difference in above all parameters between left and right sides ( P >0.05)., Conclusion: After appropriate reduction of the calcaneal fractures, the entry point of ST screw was recommended at about 14 mm posterior and about 3 mm upper related to the foot horizontal line through the lowest tarsal sinus point; and the direction of ST screw placement was about 17° anteversion for males and 15° anteversion for females.

Objective: To investigate the skill and evaluate the accuracy for application of guide combined with probing the internal wall of pedicle screw trajectory for subaxial cervical pedicle screw placement., Methods: Subaxial cervical pedicle screw was inserted in 11 patients by the guide combined with probing the internal wall of pedicle screw trajectory from January 2014 to October 2016, including 7 males and 4 females with an average age of 48.1 years(ranged 32 to 63 years). There were 4 cases with cervical spondylotic myelopathy, 4 with fracture and dislocation of cervical vertebrae, 1 with cervical cord injury without fracture and dislocation, and 2 with atlantoaxialfracture and dislocation. The target pedicle's diameter, optimal entry point, sagittal angle and cross-sectional angle were measured by CT before operation. During operation, the pedicle screw inserted angle was controlled by a guide with a self-designed protractor and probed the internal wall of pedicle screw trajectory as medial safety margin of insertion screw. The accuracy of cervical pedicle screw was evaluated by CT with classification of four grades and assessed whether there was injury of spine cord or vertebral artery postoperatively., Results: Seventy-one cervical pedicle screws were placed among 11 patients, and no one had been found with clinical manifestations of injury of spine cord (or nerve root) or vertebral artery after operation. According to postoperative CT scan for evaluating the grade of screw position, 52 screws were in grade 0, 13 in grade 1, 4 in grade 2, 2 in grade 3, and 91% (65/71) located in good position. In total, 6 screws were incorreted in placement, and 4 cases of them broke medial wall and 2 cases broke lateral wall., Conclusions: The method of probing the internal wall of pedicle screw trajectory for subaxial cervical pedicle screw placement is safe and reliable, but the studying curve is long. Probing the internal wall of pedicle screw trajectory and controlling the insertion angle by guide with a protractor are key points of this technology., Competing Interests: The authors of this article and the planning committee members and staff have no relevant financial relationships with commercial interests to disclose.