[3D printing navigation template assisted pedicle screw placement for the treatment of typeâ ¡old odontoid fractures].

OBJECTIVE: To compare the safety and clinical efficacy of freehand and 3D printing navigation template assisted screw placement in patients with old odontoid fractures of typeⅡ. METHODS: Total of 38 patients with old odontoid fractures of typeⅡwere treated from November 2018 to December 2022, all of which presented as chronic neck pain. According to the different methods of screw insertion into the pedicle, the patients were divided into a navigation template group and a freehand group. In the navigation template group, there were 17 patients including 9 males and 8 females with an average age of (51.30±13.20) years old, disease duration was (22.18±7.59) months. In the freehand group, there 21 patients including 7 males and 14 females with an average age of (49.46±11.92) years old, disease duration was (19.52±9.17) months. The intraoperative blood loss, operation time, and postoperative drainage output were recorded and compared between two groups. The accuracy of screw placement was evaluated by CT scan. Before operation and 1 year after operation, cervical pain was assessed by visual analogue scale(VAS), neurological changes were evaluated by the Japanese Orthopaedic Association (JOA) score, and the degree of spinal cord injury was assessed by the American Spinal Injury Association (ASIA) injury scale. RESULTS: All patients were followed up for (25.31±1.21) months. The operation time of template group (112.00±20.48) min had significantly shorter than that of the freehand group(124.29±15.24) min(P<0.05), while there were no significant differences between two groups in terms of intraoperative blood loss, postoperative drainage, and hospital stay(P>0.05). At 1 year after operation, in template group and freehand group, the VAS [(2.88±0.86), (2.90±0.83)] and JOA [(14.94±1.82), (14.62±2.19)] improved with preoperative [VAS(4.71±0.92), (4.86±0.79) and JOA (12.18±2.30), (11.95±2.31)](P<0.05), with no significant difference between two groups (P>0.05). No significant improvement was observed in ASIA grading in either group at 1 year after operation(P>0.05), and there was no significant difference between two groups(P>0.05). The template group had significantly better accuracy of screw placement in the pedicle of the axis than the freehand group (P<0.05), while no significant difference was observed between two groups in the accuracy of screw placement in the pedicle of the atlas (P>0.05). CONCLUSION: In the treatment of typeⅡold odontoid fractures with posterior pedicle screw fixation, 3D printing navigation template screw placement can significantly shorten the operation time, achieve similar clinical efficacy as free-hand screw placement, and significantly improve the accuracy of screw placement in the pedicle of the axis.

Biomechanical evaluation of reinsertion and revision screws in the subaxial cervical vertebrae.

BACKGROUND: This study aimed to evaluate the biomechanical effects of reinserted or revised subaxial cervical vertebral screws. METHODS: The first part aimed to gauge the maximum insertional torque (MIT) of 30 subaxial cervical vertebrae outfitted with 4.0-mm titanium screws. A reinsertion group was created wherein a screw was wholly removed and replaced along the same trajectory to test its maximum pullout strength (MPOS). A control group was also implemented. The second part involved implanting 4.0-mm titanium screws into 20 subaxial cervical vertebrae, testing them to failure, and then reinserting 4.5-mm revision screws along the same path to determine and compare the MIT and MPOS between the test and revision groups. RESULTS: Part I findings: No significant difference was observed in the initial insertion's maximum insertion torque (MIT) and maximum pull-out strength (MPOS) between the control and reinsertion groups. However, the MIT of the reinsertion group was substantially decreased compared to the first insertion. Moderate to high correlations were observed between the MIT and MPOS in both groups, as well as between the MIT of the first and second screw in the reinsertion group. Part II, the MIT and MPOS of the screw in the test group showed a strong correlation, while a modest correlation was observed for the revision screw used in failed cervical vertebrae screw. Additionally, the MPOS of the screw in the test group was significantly higher than that of the revision screw group. CONCLUSION: This study suggests that reinsertion of subaxial cervical vertebrae screws along the same trajectory is a viable option that does not significantly affect fixation stability. However, the use of 4.5-mm revision screws is inadequate for failed fixation cases with 4.0-mm cervical vertebral screws.

A Novel Method to Improve the Accuracy and Stability of the 3D Guide Template Technique Applied in Upper Cervical Spine Surgery.

AIM: To evaluate the safety and accuracy of C1 and C2 pedicle screw placement using a three-dimensional (3D)-printed double template and compare them with those of the conventional method in a clinical study. MATERIAL AND METHODS: DICOM format data from 60 cases with C1-C2 instability were obtained after computed tomography (CT) was performed. A total of 32 cases underwent surgery via the free-hand technique, whereas 28 cases underwent surgery via a 3D-printed "pointing-drilling" guide template. The ideal trajectory of the C1 and C2 pedicle screws was designed using a baseplate as a separate complementary template for the corresponding posterior C1-C2 anatomical surface, after which the "pointingdrilling" guide template was materialized using a 3D printing machine. The 3D-printed "pointing-drilling" guide template, which was sterilized with low-temperature plasma, was used to locate the starting point and determine the drill trajectory during surgery. The positions of the screws in the axial and sagittal planes of the CT scan were observed and categorized into four grades, after which the operative time, fluoroscopy time, and intraoperative bleeding in the two groups were compared. RESULTS: No significant difference (p > 0.05) in each screw classification grade was observed between the free-hand and "pointingdrilling" template groups; however, a significant difference was observed (p=0.048) between these two groups. A significant difference (p < 0.05) in fluoroscopy times was observed between the free-hand and "pointing-drilling" template groups. Conversely, no significant differences were observed in bleeding (p=0.491) and operative time (p=0.309) between the free-hand and "pointingdrilling" template groups. CONCLUSION: The 3D-printed "pointing-drilling" guide template technique promoted more secure C1 and C2 pedicle screw placement compared with the free-hand technique in clinics.

Biomechanical Properties of Novel Lateral Hole Pedicle Screws and Solid Pedicle Screws: A Comparative Study in the Beagle Dogs.

OBJECTIVE: Although pedicle screws are widely used to reconstruct the stability of the spine, screw loosening is a common complication after spine surgery. The main objective of this study was to investigate whether the application of the hollow lateral hole structure had the potential to improve the stability of the pedicle screw by comparing the biomechanical properties of the novel lateral hole pedicle screws (LHPSs) with those of the solid pedicle screws (SPSs) in beagle dogs. METHODS: The cancellous bone of the distal femur, proximal femur, distal tibia, and proximal tibia were chosen as implantation sites in beagle dogs. In each of 12 dogs, four LHPSs, and four SPSs were implanted into both lower limbs. At 1, 2, and 3 months after surgery, four dogs were randomly sampled and sacrificed. The LHPS group and SPS group were subdivided into four subgroups according to the length of their duration of implantation (0, 1, 2, 3 months). The biomechanical properties of both pedicle screws were evaluated by pull-out and the cyclic bending tests. RESULTS: The results of the study showed that no significant difference was found between LHPSs (276.62 ± 50.11 N) and SPSs (282.47 ± 42.98 N) in pull-out tests at time 0 (P > 0.05). At the same time point after implantations, LHPSs exhibited significantly higher maximal pullout strength than SPSs (month 1: 360.51 ± 25.63 vs 325.87 ± 28.11 N; month 2: 416.59 ± 23.78 vs 362.12 ± 29.27 N; month 3: 447.05 ± 38.26 vs 376.63 ± 32.36 N) (P < 0.05). Moreover, compared with SPSs, LHPSs withstood more loading cycles (month 2: 592 ± 21 vs 534 ± 48 times; month 3: 596 ± 10 vs 543 ± 59 times), and exhibiting less displacement before loosening at month 2 (1.70 ± 0.17 vs 1.96 ± 0.10 mm) and 3 (1.69 ± 0.19 vs 1.92 ± 0.14 mm) (P < 0.05), but no significant difference in time 0 and month 1 (P > 0.05). CONCLUSIONS: The pedicle screw with the hollow lateral hole structure could allow bone to grow into the inner architecture, which improved biomechanical properties by extending the contact area between screw and bone tissue after implantation into the cancellous bone. It indicated that LHPS could reduce loosening of the pedicle screws in long term after surgery.

Clinical characteristic and surgical treatment of traumatic lumbar spondylolisthesis: A series of 28 patients.

OBJECTIVE: To explore the clinical characteristics and the short-term efficacy of posterior operation for traumatic lumbar spondylolisthesis. METHODS: All 28 patients (between January 2013 and June 2018) were treated with lumbar pedicle screw fixation combined with posterior intervertebral fusion. The clinical data and imaging materials of these patients were retrospectively analyzed. RESULTS: The mean follow-up period was 24.3 months (12-36 months). The average VAS score and JOA score were significantly improved after surgery, and the difference was statistically significant (P<0.05).The last follow-up X-ray showed that 16 cases were degree 0 and 12 cases were degree I according to Meyerding grading, which were statistically improved compared with preoperative. Postoperative CT indicated lumbar internal fixation well, and the lumbar fusion rate was 100%. The Frankel grading of neurological function was significantly improved compared with preoperative. CONCLUSION: Acute traumatic lumbar spondylolisthesis is caused by severe trauma and mostly occurred at L4/L5 and L5/S1 level. Early posterior reduction, decompression and intervertebral fusion can achieve satisfactory clinical and radiological outcome.

[Clinical and radiological results of thoracic and lumbar fracture and dislocation treated with posterior transforaminal decompression and interbody fusion].

OBJECTIVE: To evaluate the clinical and radiological results of patients with thoracic and lumbar fracture and dislocation treated by posterior transforaminal decompression and interbody fusion. METHODS: From June 2010 to June 2017, posterior transforaminal decompression, interbody fusion combined with pedicle screw fixation were performed in 21 patients with thoracic and lumbar fracture and dislocation. Their clinical and radiological data were collected and retrospectively analyzed, including 15 males and 6 females, aged from 25 to 58 years with an average of 45 years old. According to the criterion of American Spinal Injury(ASIA), preoperative neurological function was graded A in 3 cases, B in 7 cases, C in 6 cases, D in 4 cases and E in 1 case. Operative time and intraoperative blood loss and correlative complications were recorded. And VAS score, ODI and Cobb angle were evaluated before and after surgery. The improvement of neurological function was also analyzed at the final follow-up. Intervertebral bony fusion was observed during the follow-up by CT three-dimensional reconstruction. RESULTS: The operative time was 150 to 240 min with an average of (192±47) min. The intraoperative blood loss was 380 to 750 ml with an average of(603±120) ml. Dura sac tearing and cerebral fluid leakage occurred in 3 cases and were repaired during operation; superficial wound infection occurred in 1 case, and got healing after dressing change. The postoperative follow-up duration was 24 to 45 months with an average of(37.0±9.5) months. VAS score was improved from preoperative 8.9±0.4 to immediately postoperative 4.2±1.3(P<0.05). At the final follow-up, VAS score decreased further to 3.6±0.8. ODI was decreased from preoperative (95.30±3.52)% to (32.51±6.30)% at the final follow-up (P<0.05). Cobb angle was corrected from preoperative (21.2±8.8)° to immediately postoperative(2.3±3.1)° (P<0.05). At the final follow-up, Cobb angle was (3.2±2.5)°, showing no significant difference with immediately postoperative value. The neurological function was grade A in 3 cases, B in 3 cases, C in 5 cases, D in 6 cases and E in 4 cases at the final follow-up. All the patients got solid intervertebral bone fusion in 8 to 13 months after operation, with an average fusion time of (10.3±2.5) months. CONCLUSIONS: For the patients with thoracic and lumbar fracture and dislocation mainly involving intervertebral disc and endplate plane, posterior transforaminal decompression and interbody fusion not only is less invasive, but also can effectively reconstruct spinal three column and obtain good biomechanical stability. And, it is beneficial for the good recovery of neurological function.

Optimal Entry Point and Trajectory for Anterior C1 Lateral Mass Screw.

STUDY DESIGN: A radiographic analysis of the anatomy of the C1 lateral mass using computed tomography (CT) scans and Mimics software. OBJECTIVE: To define the anatomy of the C1 lateral mass and make recommendations for optimal entry point and trajectory for anterior C1 lateral mass screws. SUMMARY OF BACKGROUND DATA: Although various posterior insertion angles and entry points for screw insertion have been proposed for posterior C1 lateral mass screws, no large series have been performed to assess the ideal entry point and optimal trajectory for anterior C1 lateral mass screw placement. MATERIALS AND METHODS: The C1 lateral mass was evaluated using CT scans and a 3-dimensional imaging application (Mimics software). Measuring the space available for the anterior C1 lateral mass screw (SAS) at different camber angles from 0 to 30 degrees (5-degree intervals) was performed to identify the ideal camber angle of insertion. Measuring the range of sagittal angles was performed to calculate the ideal sagittal angle. Other measurements involving the height of the C1 lateral mass were also made. RESULTS: The optimal screw entry point was found to be located on the anterior surface of the atlas 12.88 mm (±1.10 mm) lateral to the center of the anterior tubercle. This optimal entry point was found to be 6.81 mm (±0.59 mm) superior to the anterior edge of the atlas inferior articulating process. The mean ideal camber angle was 20.92 degrees laterally and the mean ideal sagittal angle was 5.80 degrees downward. CONCLUSIONS: These measurements define the optimal entry point and trajectory for anterior C1 lateral mass screws and facilitate anterior C1 lateral mass screw placement. A thorough understanding of the local anatomy may decrease the risk of injury to the spinal cord, vertebral artery, and internal carotid artery. Delineating the anatomy in each case with preoperative 3D CT evaluation is recommended.

A comparative study on the accuracy of pedicle screw placement assisted by personalized rapid prototyping template between pre- and post-operation in patients with relatively normal mid-upper thoracic spine.

PURPOSE: The aim of this study was to assess the accuracy of rapid prototyping drill template technique for placing pedicle screws in the mid-upper thoracic vertebrae in clinics. METHODS: 151 consecutive patients underwent thoracic instrumentation and fusion for a total of 582 pedicle screws placed in the mid-upper thoracic vertebrae. Using computer software, the authors constructed drill templates that fit onto the posterior elements of the mid-upper thoracic vertebrae with drill guides designed to instrument the pedicles. The start point and three dimensional location of the planned and inserted screws were measured and compared. RESULTS: Grading of the CT scans revealed 559 (96.1 %) out of 582 screws completely within the desired pedicle. The direction of pedicle violation included 5 medial, 2 airball, and 16 lateral. The paired t test suggested that these results were statistically significant in more than half of the locations (T1-left-TA(P = 0.024), T2-left-SA(P = 0.031), T3-left-SA(P = 0.014), T4-left-TA(P = 0.004), T5-left-TA(P = 0.034), T7-left-TA(P = 0.000). T1-right-TA(P = 0.049), T2-right-TA(P = 0.044), T3-right-TA(P = 0.014), T5-right-TA(P = 0.013)). The paired t-test suggested that these results were statistically significant at several locations (T4-left-Δy(P = 0.041), T5-left-Δx(P = 0.016), T3-right-Δy(P = 0.015)). CONCLUSION: Use of a rapid prototyping drill template to assist in the placement of mid and upper thoracic pedicle screws may lead to increased accuracy. This patient specific technology must be combined with an understanding of the patients' anatomy and carefully secured to the posterior elements intraoperatively to avoid nerve or vascular complications.

Conservative and Operative Treatment in Extension Teardrop Fractures of the Axis.

STUDY DESIGN: A retrospective case series describing teardrop fracture of the axis. OBJECT: The purpose of the study was to clarify the clinical features, the mechanism of injury, and the potential instability of extension teardrop fractures of the axis, so as to emphasize the importance of recognizing this injury as a separate entity. SUMMARY OF BACKGROUND DATA: Teardrop fractures of the axis are rare spinal fractures, comprising only a small percentage of all injuries of the cervical spine. The stability of this fracture pattern has been a matter of debate leading to controversy regarding treatment strategies and the need for stabilization. METHODS: We retrospectively reviewed data collected from 16 patients to document the mechanism of injury, neurological deficit, treatment and clinical outcome, and imaging findings. RESULTS: Extension teardrop fractures accounted for approximately 8.9% of the upper cervical spinal injuries and 12.7% of axis fractures at the authors' institution over the same period. Six patients (4 males and 2 females) underwent surgery (4 by an anterior approach, 2 by a posterior approach). Ten cases underwent Halo-vest immobilization for a period between 6 and 12 weeks. At final follow-up, 14 cases achieved excellent results, whereas 2 patients complained of mild residual neck pain. Maximum cranial-caudal dimensions of the fragments were between 5 and 24 mm (average, 12.9 mm), and the transverse dimensions were between 5 and 22 mm (average, 11.1 mm). Fragment displacement ranged from 1 to 9 mm (average, 3.5 mm), whereas fragment rotation ranged from 10 to 52 degrees (average, 24.4 degrees) in the sagittal plane. CONCLUSIONS: Most patients with an extension teardrop fracture of the axis can be treated conservatively. On the basis of this case series, the authors suggest that large fragment size, displacement or angulation, intervertebral disk injury, neurologic deficit, or signs of instability are reasonable indications for surgical treatment.

Deviation analysis of atlantoaxial pedicle screws assisted by a drill template.

Although C1-C2 pedicle screw fixation provides an excellent fusion rate and rigid fixation, this technique has a potential risk. It is essential to develop an accurate screwing method to avoid this neurovascular injury. To develop and validate the accuracy of a novel navigational template for C1-C2 pedicle screw placement in cadaveric specimens, computed tomography scans with 1-mm-wide cuts were obtained of 32 cadaveric cervical specimens. The authors developed 64 three-dimensional full-scale templates that were created by computer modeling with a rapid prototyping technique from the computed tomography data. Drill templates were constructed with a custom trajectory for each level and side. The drill templates were used to guide the establishment of a pilot hole for screw placement. The average distances between ideal and actual entry points of the C1 pedicle screws in the x, y, and z axes were 0.16±0.46 mm, 0.11±0.52 mm, and -0.01±0.54 mm, respectively, on the left side and 0.11±0.49 mm, 0.01±0.56 mm, and -0.09±0.59 mm, respectively, on the right side. The average distances between ideal and actual entry points of the C2 pedicle screws in the x, y, and z axes were 0.05±0.54 mm, 0.20±0.59 mm, and -0.06±0.58 mm, respectively, on the left side and 0.17±0.55 mm, 0.1±0.58 mm, and -0.01±0.49 mm, respectively, on the right side. Factors related to human error and imprecision are responsible for most malpositioning of instrumentation. The rapid prototyping drill template for C1-C2 screw placement is described to minimize human error, although it introduces error related to computer software and variation in manufacturing.

Unstable Jefferson fractures: Results of transoral osteosynthesis.

BACKGROUND: Majority of C1 fractures can be effectively treated conservatively by immobilization or traction unless there is an injury to the transverse ligament. Conservative treatment usually involves a long period of immobilization in a halo-vest. Surgical intervention generally involves fusion, eliminating the motion of the upper cervical spine. We describe the treatment of unstable Jefferson fractures designed to avoid these problems of both conservative and invasive methods. MATERIALS AND METHODS: A retrospective review of 12 patients with unstable Jefferson fractures treated with transoral osteosynthesis of C1 between July 2008 and December 2011 was performed. A steel plate and C1 lateral mass screw fixation were used to repair the unstable Jefferson fractures. Our study group included eight males and four females with an average age of 33 years (range 23-62 years). RESULTS: Patients were followed up for an average of 16 months after surgery. Range of motion of the cervical spine was by and large physiologic: Average flexion 35° (range 28-40°), average extension 42° (range 30-48°). Lateral bending to the right and left averaged 30° and 28° respectively (range 12-36° and 14-32° respectively). The average postoperative rotation of the atlantoaxial joint, evaluated by functional computed tomography scan was 60° (range 35-72°). Total average lateral displacement of the lateral masses was 7.0 mm before surgery (range 5-12 mm), which improved to 3.5 mm after surgery (range 1-6.5 mm). The total average difference of the atlanto-dens interval in flexion and extension after surgery was 1.0 mm (range 1-3 mm). CONCLUSIONS: Transoral osteosynthesis of the anterior ring using C1 lateral mass screws is a viable option for treating unstable Jefferson fractures, which allows maintenance of rotation at the C1-C2 joint and restoration of congruency of the atlanto-occipital and atlantoaxial joints.

Deviation analysis of C1-C2 transarticular screw placement assisted by a novel rapid prototyping drill template: a cadaveric study.

STUDY DESIGN: Cadaveric study. OBJECTIVE: The aim of this study was to develop and validate the accuracy of a novel navigational template for C1-C2 transarticular screw (C1C2TAS) placement in cadaveric specimens. SUMMARY OF BACKGROUND DATA: Currently, C1C2TASs are primarily positioned using a free-hand technique or under fluoroscopic guidance. Screw placement is challenging owing to the small size of the C2 isthmus, which places technical demands on the surgeon. Screw insertion carries a potential risk of neurovascular injury, magnifying the importance of using a precise technique for screw insertion. MATERIALS AND METHODS: Computed tomography (CT) scans with 0.625-mm wide cuts were obtained from the 32 cadaveric cervical specimens. The CT data were imported into a computer navigation system. We developed 32 three-dimensional drill templates, which were created by computer modeling using a rapid prototyping technique based on the CT data. We constructed drill templates using a custom trajectory for each level and side based on specimen anatomy. The drill templates were used to guide establishment of a pilot hole for screw placement. The entry point and angular direction of the intended screw positions and inserted screw positions were measured by comparing postoperative and preoperative images after the coordinate axes were synchronized. RESULTS: The average displacement of the entry point of the left and right C1C2TAS in the x-, y-, and z-axis was 0.13±0.90 mm, 0.50±1.50 mm, and -0.22±0.71 mm on the left, and 0.21±1.03 mm, 0.46±1.55 mm, and -0.29±0.58 mm on the right. There was no statistically significant difference in entry point and direction between the intended and actual screw trajectory. CONCLUSIONS: The small deviations seen are likely due to human error in the form of small variations in the surgical technique and use of software to design the prototype. This technology improves the safety profile of this fixation technique and should be further studied in clinical applications.

Function-preserving reduction and fixation of unstable Jefferson fractures using a C1 posterior limited construct.

STUDY DESIGN: This is a retrospective, clinical, and radiologic study of posterior reduction and fusion of the C1 arch in the treatment of unstable Jefferson fractures. OBJECTIVE: The aim of the study was to describe a new motion-preserving surgical technique in the treatment of unstable Jefferson fracture. SUMMARY OF BACKGROUND DATA: The management of unstable Jefferson fractures remains controversial. The majority of C1 fractures can be effectively treated nonoperatively with external immobilization unless there is an injury to the transverse atlantal ligament (TAL). Conservative treatment usually involves immobilization for a long time in Halo vest, whereas surgical intervention generally involves C1-C2 fusion, eliminating the range of motion of the upper cervical spine. We propose a novel method for the treatment of unstable Jefferson fractures without restricting the range of motion. METHODS: A retrospective review of 12 patients with unstable C1 fractures between April 2008 and October 2011 was performed. They were treated by inserting bilateral posterior C1 pedicle screws or lateral mass screws interconnected by a transversal rod to achieve internal fixation. There were 8 men and 4 women, with an average age of 35.6 years (range, 20-60 y). Presenting symptoms included neck pain, stiffness, and decreased range of motion but none had neurological injury. Seven patients had bilateral posterior arch fractures associated with unilateral anterior arch fractures (posterior 3/4 Jefferson fracture, Landells type II), and 5 had unilateral anterior and posterior arch fractures (half-ring Jefferson fracture, Landells type II). Seven patients had intact TAL, and 5 patients had fractures and avulsion of the attachment of TAL (Dickman type II). RESULTS: A total of 24 screws were inserted. Five cases had screws placed in the lateral mass: 3 because of posterior arch breakage, and 2 because the height of the posterior arch at the entry point was <4 mm. The remaining 7 cases had pedicle screw fixation. One patient had venous plexus injury during exposure of lower margin of the posterior arch; however, successful hemostasis was achieved with Gelfoam. Postoperative x-ray and computed tomography scan showed partial breach of the transverse foramen caused by a screw in 1 case, and breach of the inner cortex of the pedicle caused by screw displacement in 1 case; however, no spinal cord injury or vertebral artery injury was found. The remaining screws were in good position. Patients were followed up for 6-40 months (average, 22 mo). All cases had recovery of range of motion of the cervical spine to the preinjury level by 3-6 months after surgery, with resolution of pain. At 6 months follow-up, plain radiographs and computed tomography scans revealed satisfactory cervical alignment, no implant failure, and satisfactory bony fusion of the fractures; no C1-C2 instability was observed on the flexion-extension radiographs. CONCLUSIONS: C1 posterior limited construct is a valid technique and a feasible method for treating unstable Jefferson fractures, which allows preservation of the function of the craniocervical junction, without significant morbidity.

[A novel computer-assisted drill template for atlantoaxial pedicle screw placement:a cadaveric experimental study].

OBJECTIVE: To validate the accuracy of atlanto-axial pedicle screw placement with a rapid prototyping drill guide template and analyze the factors of screw deviations. METHODS: Computed tomography (CT) scan was performed in 16 cervical specimens. And three-dimension cervical vertebrae was reconstructed by Mimics software. The ideal trajectory for atlanto-axial pedicle screws was designed with a complementary basal template for posterior surface of atlanto-axial corresponding anatomical structure. Then drill guide template was materialized in a rapid prototyping machine. These templates were used during operation. The entry point and ideal and actual trajectories were measured after matching the positions of preoperative and postoperative specimens at designated coordinate axis. RESULTS: The average displacement of entry point of left and right C1 pedicle screw in x, y, z axis was (0.14 ± 0.59),(0.31 ± 1.32), (0.27 ± 0.68), (0.23 ± 0.55), (0.43 ± 1.21) and (0.30 ± 0.72) mm. And the average displacement of entry point of left and right C2 pedicle screw in m, n, p axis was (0.25 ± 0.85), (0.52 ± 1.52), (-0.27 ± 0.67), (0.44 ± 0.87), (0.38 ± 1.48), (-0.14 ± 0.62) mm.No statistically significant difference existed (P > 0.05) in deviation of entry point and between ideal and actual trajectories. CONCLUSION: Both human handling and inherent hardware and software factors are main reasons for a deviation of C1-C2 pedicle screw placement assisted by a rapid prototyping drill guide template.Ease of operation and individualized design are the advantages of drill guide template so as to greatly improve the precision of screw placement and reduce screw deviation.

Accuracy and complications associated with the freehand C-1 lateral mass screw fixation technique: a radiographic and clinical assessment.

OBJECT: The aims of this study were to evaluate a large series of posterior C-1 lateral mass screws (LMSs) to determine accuracy based on CT scanning findings and to assess the perioperative complication rate related to errant screw placement. METHODS: Accuracy of screw placement was evaluated using postoperative CT scans obtained in 196 patients with atlantoaxial instability. Radiographic analysis included measurement of preoperative and postoperative CT scans to evaluate relevant anatomy and classify accuracy of instrumentation placement. Screws were graded using the following definitions: Type I, screw threads completely within the bone (ideal); Type II, less than half the diameter of the screw violates the surrounding cortex (safe); and Type III, clear violation of transverse foramen or spinal canal (unacceptable). RESULTS: A total of 390 C-1 LMSs were placed, but 32 screws (8.2%) were excluded from accuracy measurements because of a lack of postoperative CT scans; patients in these cases were still included in the assessment of potential clinical complications based on clinical records. Of the 358 evaluable screws with postoperative CT scanning, 85.5% of screws (Type I) were rated as being in the ideal position, 11.7% of screws (Type II) were rated as occupying a safe position, and 10 screws (2.8%) were unacceptable (Type III). Overall, 97.2% of screws were rated Type I or II. Of the 10 screws that were unacceptable on postoperative CT scans, there were no known associated neurological or vertebral artery (VA) injuries. Seven unacceptable screws erred medially into the spinal canal, and 2 patients underwent revision surgery for medial screws. In 2 patients, unilateral C-1 LMSs penetrated the C-1 anterior cortex by approximately 4 mm. Neither patient with anterior C-1 penetration had evidence of internal carotid artery or hypoglossal nerve injury. Computed tomography scanning showed partial entry of C-1 LMSs into the VA foramen of C-1 in 10 cases; no occlusion, associated aneurysm, or fistula of the VA was found. Two patients complained of postoperative occipital neuralgia. This was transient in one patient and resolved by 2 months after surgery. The second patient developed persistent neuralgia, which remained 2 years after surgery, necessitating referral to the pain service. CONCLUSIONS: The technique for freehand C-1 LMS fixation appears to be safe and effective without intraoperative fluoroscopy guidance. Preoperative planning and determination of the ideal screw insertion point, the ideal trajectory, and screw length are the most important considerations. In addition, fewer malpositioned screws were inserted as the study progressed, suggesting a learning curve to the technique.