Cervical Pedicle Screw Research Articles

Morphometric analysis of typical cervical vertebral pedicle - An osteological study

Background: Successful placement of cervical pedicle screws requires accurate identification of entry point, trajectory and appropriate size of implant. Studies and guidelines regarding the direction of pedicle screw insertion and pedicle dimensions in Indian population are very limited and hence the objective of our study was to do Morphometric analysis of Typical Cervical Vertebral pedicle (C3 to C6) Materials and Methods: Osteological study of the pedicle was performed in 100 typical (C3-C6) dry bone specimens. The vertebral pedicles were evaluated by measuring its height, width, length, lateral mass + pedicle length, total pedicle axis length and transverse pedicle angle. Results: In our study, the mean pedicle length of C3, C4, C5, C6 was 6.04, 5.48, 5.30, and 5.92 respectively. The mean pedicle height in our study ranged from 5.05 mm (C3) to 5.86 mm (C6). The Range of Mean pedicle width was from 4.79 to 5.16 mm. The mean lateral mass + pedilce length ranged from 11.17 to 13.18 mm while the mean total pedicle axis length ranged from 27.05 to 30.04 mm. Conclusions: We found that there were high individual variations. The pedicle dimensions were relatively smaller in Indians compared to previous studies in other population. This mandates preoperative CT evaluation of pedicle and smaller size pedicle screws customized according to pedicle dimensions of Indians.

Cervical Pedicle Screw Placement Using Medial Funnel Technique.

ObjectiveCervical pedicle screw (CPS) placement is very challenging due to high risk of neurovascular complications. We devised a new technique (medial funnel technique) to improve the accuracy and feasibility of CPS placement.MethodsWe reviewed 28 consecutive patients undergoing CPS instrumentation using the medial funnel technique. Their mean age was 51.4 years (range, 30–81 years). Preoperative diagnosis included degenerative disease (n=5), trauma (n=22), and infection (n=1). Screw perforations were graded with the following criteria: grade 0 having no perforation, grade 1 having <25%, grade 2 having 25%–50% and grade 3 having >50% of screw diameter. Grades 0 and 1 were considered as correct position. The degree of perforation was determined by 2 junior neurosurgeons and 1 senior neurosurgeon.ResultsA total of 88 CPSs were inserted. The rate of correct placement was 94.3%; grade 0, 54 screws; grade 1, 29 screws; grade 2, 4 screws; and grade 3, 1 screw. No neurovascular complications or failure of instrumentation occurred. In perforated screws (34 screws), lateral perforations were 4 and medial perforations were 30.ConclusionWe performed CPS insertion using medial funnel technique and achieved 94.3% (83 of 88) of correct placement. And it can decrease lateral perforation.

Application of guide combined with probing the internal wall of pedicle screw trajectory for subaxial cervical pedicle screw placement

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. 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. 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. 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.

In vitro study of accuracy of subaxial cervical pedicle screw insertion using calipers based on the gravity line.

ObjectThere is a high probability of iatrogenic perforation of the vertebral pedicle wall during the application of subaxial cervical pedicle screw (CPS). The goal of this study was to evaluate the accuracy of CPS insertion at C3-C7 in vitro using novel calipers based on the gravity line.MethodsNine cadaveric cervical spines underwent computed tomography scanning and preoperative design. A lateral fluoroscopic view was taken to measure the intra-operative sagittal angle by C-arm with hanging cross structured K-wires. By referring to the gravity line, caliper A was used to locate the entry point, while caliper B was employed to guide the screw insertion. Postoperative CT scans were performed to assess the accuracy of the screw placements, according to the Neo classification.ResultsOverall, 78 (88.6%) of the 88 pedicle screw placements were classified as grade 0 (correct position), 4 (4.5%) were grade 1 (non-critical perforation), 4 (4.5%) were grade 2 (critical perforation), and 2 (2.3%) were grade 3 (critical perforation).ConclusionsUsing our novel calipers and referring to the gravity line was helpful for locating and guiding individual cervical pedicle screw insertions.

Characteristics of regional bone quality in cervical vertebrae considering BMD: Determining a safe trajectory for cervical pedicle screw fixation.

This study aimed to report the mechanical strength and characteristics of the lateral mass and pedicle considering BMD for the safe insertion of pedicle screws in the subaxial cervical level. We evaluated BMD and Hounsfield unit (HU) values of cortical bones at the lateral mass and pedicle of C3-7 from CT images in 99 patients. Patients were divided into three groups (Group A, T-score ≥ -1; Group B, -2.5 < T-score < -1.0; Group C, T-score ≤ -2.5). The HU numbers of cortical bone in the vertebral canal (medial wall of the lateral mass; cHU), posterior wall of the transverse foramen (fHU), and medial wall, lateral wall, and trabecular area of the pedicle (mHU, lHU, and pHU, respectively) were measured on the CT images in the middle of the pedicle. A mechanical study was also performed to measure cortical bone strength using 10 fresh cadavers. The cHU and mHU values in Group C were higher than lHU and fHU in Groups A and B, and there was a wide gap between the pHU value and other areas. The penetrating force also had a close correlation with HU number. The mean penetrating force of the medial wall of the lateral mass and the posterior wall of the transverse foramen were 210.08 ± 110.46 and 50.51 ± 46.09 N, respectively. The cortical bones in the vertebral canal and medial wall of the pedicle were stronger than the lateral wall and the trabecular area. The cHU and mHU in the osteoporotic group were higher than fHU and pHU in the normal group. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:217-223, 2018.

Application of a novel 3D drill template for cervical pedicle screw tunnel design: a cadaveric study.

To develop and validate the efficacy and accuracy of a three-dimensional (3D) computed tomography (CT) reconstructive rapid prototyping drill template for cervical pedicle screw placement. CT thin-layer scans were obtained from 12 adult cadaveric cervical specimens and reconstructed. The ideal screw channels were chosen by analyzing the cross sections of the reconstructed 3D images. The navigation templates were designed and printed based on the optimal screw channels. The pedicle screws were placed on the cadaver specimens under template guidance, and the cadaver specimens were scanned and reconstructed. The pre- and post-operative models were compared. Entry point and exit point data of these two models were collected and compared using the Chi-square test. A total of 164 cervical pedicle screws were placed; among them, six punctured the cortical bone of the vertebral pedicle reaching an accuracy of 96.3%. Among the outside screws, all of the deviation distances were <2mm. The Chi-square test results showed that when a deviation of 1.2mm was used as a standard for the entry point, there was no difference between the two groups (χ 2=1.346, p=0.248); when a deviation of 2.2mm was used as a standard for the exit point, there was no difference between the two groups (χ 2=3.250, p=0.061). The 3D CT reconstructive rapid prototyping drill template combined with the screw tunnel design based on 3D cutting technique can help facilitate accurate cervical pedicle screw insertion.

Widening of the safe trajectory range during subaxial cervical pedicle screw placement: advantages of a curved pedicle probe and laterally located starting point without creating a funnel-shaped hole.

OBJECTIVE The small diameter of cervical pedicles and a large transverse cervical pedicle angle are challenges that have led spinal surgeons to investigate how they could achieve a wider safety trajectory and reduce the insertion angle during cervical pedicle screw (CPS) placement. In this paper, the authors detail the advantages of using a curved pedicle probe and a laterally located entry point for overcoming these challenges. METHODS From March 2012 to May 2016, the authors performed posterior cervical fusions using CPSs on 119 consecutive patients. The lateral mass screw conversion and the CPS breach rate were analyzed. Using preoperative CT, it was determined that θlat is similar to the anatomical pedicle angle, and θmed is the minimally acceptable medial angle. The actual insertion medial angle (θins) was determined by postoperative CT. To identify how much of the medial angle on θins could be reduced from the anatomical pedicle angle (θlat), and how much closer to θmed, (θins-θmed) / (θlat-θmed) was calculated. To verify shifting of the entry point and widening of the trajectory, the mean df/Df (i.e., shifted facet point/planned facet point) values were analyzed. RESULTS The total number of planed CPSs was 759, the conversion rate was 4.61% (35/759), and the accuracy rate was 95.9% (694/724). The authors could calculate that θins could be expected near the 90%, 80%, 80%, 80%, and 110% value of θlat on C-3, C-4, C-5, C-6, and C-7 levels, respectively, with the (θins-θmed) / (θlat-θmed) equation. The mean df/Df values were 0.64, 0.62, 0.63, 0.63, and 1.24 on the C3-7 levels, respectively. CONCLUSIONS Through the use of a curved pedicle probe and a laterally located starting point, the planned and laterally located entry point medial shift was made during CPS placement. The entry point shift yielded a wider, safe trajectory and reduced the burden of making a large medial angle, similar to an anatomical cervical pedicle lateral angle, for safe CPS placement without creating a funnel-shaped hole.

Advance in screws fixation in posterior route pedicle on lower cervical spine

With the continuously exploration, in recent years, further understanding of anatomical characteristics of the cervical pedicle brings great breakthrough in cervical pedicle screw implantation. In addition, pedicle screw implantation in cervical spine is considered as a technique with high safety and reliability, which can be widely used in cervical trauma fracture, cervical instability, degenerative, inflammatory, benign or malignant tumor, deformity and other neck diseases. Because of the tremendous differences between upper cervical spine (C1, C2) and lower cervical spine (C3-7) in anatomical morphology, cervical pedicle screw implantation in C1 and C2 differs from in lower cervical spine. Due to the similar structure of C3-7, pedicle screw implantation methods are based on the same principle and sharing a few points in common. The pedicle screw technique can be classified in two groups according to the practice methods: navigation technology and manual placement of cervical pedicle screw. Navigation nailing is considered as reliable, easy handing, and with clear operative vision, however, with disadvantages as complex procedures, highly cost operation equipment, and risk in navigation draft. Therefore, manual placement of pedicle screw is more reasonable and practical comparing with the former. In this study, it analyzed anatomical characteristics of lower cervical pedicle and the measurement of pedicle structure, discussed technique of manual placement of pedicle screw in lower cervical spine and biomechanical study of pedicle screw, and summed up the comparison of the advantages and disadvantages of current representative manual placement technology.

Cervical vertebral body fracture with ankylosing spondylitis treated with cervical pedicle screw: A fracture body overlapping reduction technique

We describe a patient with ankylosing spondylitis (AS) with cervical spinal fracture treated with cervical pedicle screw placement (CPS) through a single posterior approach.A 43-year-old male patient with AS visited our emergency centre due to paralysis following a trauma. Coronal reconstructed cervical spine computed tomography (CT) scan showed a C5 oblique fracture, and the bilateral pedicles were separated superiorly and inferiorly. The sagittal reconstructed CT image revealed bamboo spine and C5 vertebrae body fracture. Hyperextension between the fractured segments of the C5 body was noted because the fracture gap was anteriorly open. Magnetic resonance imaging (MRI) showed cord compression and injury at the C4–5 level.CPS was performed at the C3–6 levels. Because the left and right pedicles were displaced superiorly and inferiorly, dual compressions between the left C5 and left C6 pedicle screws and between the right C5 and right C4 pedicle screws were performed. Decompression at the C4 and C5 levels was performed after identifying good alignment. This posterior fusion surgery was performed for two hours. After surgery, the radiograph showed complete reduction and fracture gap apposition. The patient was rehabilitated, and his muscle strength improved. Postoperative CT and X-rays revealed complete fracture site fusion and correct CPS position.Considering increased morbidity of long-level or -duration surgery, our fracture body overlapping technique using CPS and posterior only approach seems to be a possible and good surgical method in traumatic cervical fracture with AS.

Coronal Multiplane Reconstructed Computed Tomography Image Determining Lateral Vertebral Notch-Referred Pedicle Screw Entry Point in Subaxial Cervical Spine: A Preclinical Study.

To evaluate feasibility of computed tomography (CT) coronal multiplane reconstruction image (CMRI) to determine subaxial cervical pedicle screw (PS) entry point and guide lateral vertebral notch (LVN)-referred technique for subaxial cervical PS insertion. Cervical CT scans were performed in 40 volunteers. PS entry point was determined by quantitating PS entry point related to LVN on CMRI. Pedicle mediolateral angle (α) and cephalocaudad angle (β) were also measured to guide the trajectory of PS insertion. Based on these quantitations, 12 human cadaveric subaxial cervical pedicles were inserted with PS referring to LVN. Cortical integrity of each pedicle was evaluated after dissecting the cadaveric vertebrae one by one and confirmed by radiography and CT. The cortical penetration and PS position were classified into 4 grades: 0 (excellent position), I(goodposition), II (fair position), and III (poor position). On CT CMRI, PS entry point was consistently located approximately 2.2 mm medial to LVN from C3 to C7 and approximately 1.4 mm lower to LVN from C3 to C6, but 1.2 mm higher at C7. Bilateral α angle and β angle showed substantial decrease from cranial to caudal. Cortical integrity of PS positions was excellent and good in 88.33%, fair in 8.33%, and poor in 3.33%. CMRI is reliable for determining subaxial cervical PS entry point. LVN is a consistent landmark for the notch-referred technique, which is a practical and easy to master technique for subaxial cervical spine PS insertion.

A Novel Patient-Specific Drill Guide Template for Pedicle Screw Insertion into the Subaxial Cervical Spine Utilizing Stereolithographic Modelling: An In Vitro Study.

Study DesignCadaveric study.PurposeThe purpose of this study was to assess the accuracy and feasibility of cervical pedicle screw (CPS) insertion into the subaxial cervical spine placed using a patient-specific drill guide template constructed from a stereolithographic model.Overview of LiteratureCPS fixation is an invaluable tool for posterior cervical fixation because of its biomechanical advantages. The major drawback is its narrow corridor that allows very little clearance for neural and vascular injuries.MethodsFifty subaxial pedicles of the cervical vertebrae from five cadavers were scanned into thin slices using computed tomography (CT). Digital imaging and communications in medicine images of the cadaver spine were digitally processed and printed to scale as a three-dimensional (3D) model. Drill guide templates were manually moulded over the 3D-printed models incorporating pins inserted in the pedicles. The drill guide templates were used for precise placement of the drill holes in the pedicles of cadaveric specimens for pedicle screw fixation.ResultsThe instrumented cadaveric spines were subjected to CT to assess the accuracy of our pedicle placement by an external observer. Our patient-specific drill guide template had an accuracy of 94%.ConclusionsThe use of a patient-specific drill guide constructed using stereolithography improved the accuracy of CPS placement in a cadaveric model.

Novel Landmark for Cervical Pedicle Screw Insertion Point from Computed Tomography-Based Study.

Study DesignCross-sectional study.PurposeThe purpose of this study was to evaluate a novel landmark for the cervical pedicle screw insertion point.Overview of LiteratureTo improve the accuracy of pedicle screw placement, several studies have employed the lateral mass, lateral vertical notch, and/or inferior articular process as landmarks; however, we often encounter patients in whom we cannot identify accurate insertion points for pedicle screws using these landmarks because of degenerative changes in the facet joints. The superomedial edge of the lamina is less affected by degenerative changes, and we hypothesized that it could be a new landmark for identifying an accurate cervical pedicle screw insertion point.MethodsA total of 327 consecutive patients, who had undergone neck computed tomographic scanning for determination of neck disease in our institute, were included in the study. At first, the line was drawn parallel to the superior border of the pedicle in the sagittal plane and parallel to the vertical body in the coronal plane. The line was moved downward in 1-mm increments to the inferior border of the pedicle. We determined whether the line passing through the superomedial edge of the lamina (termed the “N-line”) was located between the superior and inferior borders of the pedicle in the sagittal plane.ResultsThe percentages of N-lines located between the superior and inferior borders of the pedicle were 100% at C3, 100% at C4, 99% at C5, 96% at C6, and 97% at C7. The lower cervical spine has the higher N-line location.ConclusionsThe N-line was frequently located at the level of the pedicle of each cervical spine in the sagittal plane. The superomedial edge of the lamina could be a new landmark for the insertion point of the cervical pedicle screw.

Clinical research on the accuracy of cervical pedicle screws

Objective To evaluate the clinical effect of a self-developed technique of manual placement of pedicle screw in cervical spine based on anatomical research. Methods Data of 105 patients who had cervical pedicle screw placement within seven years (from April 2007 to April 2013, and April 2013 to April 2016) were retrospectively analyzed, including 60 male and 45 female, aged from 20 to 76 years (51.7±14.5 years). Five main types of spinal injury were included: traumatic spinal injury (61 cases), degenerative cervical injury (19 cases including 12 ossification of posterior longitudinal ligament and 7 cervical spondylosis), cervical cancer (16 cases including 9 schwannoma, 4 meningioma, and 3 cases of cervical vertebral tumor), cervical deformity (6 cases including 3 kyphosis and 3 congenital malformation), and intervertebral space infection (3 cases). All the patients had X-ray, CT scan and MRI imaging pre-operatively, and X-ray and CT scan were also performed post-operatively to assess the accuracy of the position of screws. The accuracy of pedicle screws placement and screw leaning degree were analyzed according to the Lee standard. Grade 0: no penetration; Grade I: pedicle penetration within 25% of the pedical screw diameter; Grade II: pedicle penetration between 25% to 50% of the pedical screw diameter; Grade III: pedicle penetration beyond 50% of the pedical screw diameter. Grade II and III were considered as misplacement. In patients of Grade II and/or III, complications of blood vessels and nerve injury, etc. were observed. American spinal injury association (ASIA) was used to classify spinal injury among patients with trauma, while Japanese Orthopaedic Association Scores (JOA) was used to evaluate neural function improvement within patients without trauma. Results A total of 510 screws were placed by manual placement in 105 patients. Among 99 valid patients (6 without post-operative CT scan were excluded) with 497 screws (including 201 in upper cervical spine, and 296 in lower cervical spine), the results were shown as following: (1) Screw placement accuracy: 486 screws of Grade 0, 8 screws of Grade I, 3 screws of grade II, and 0 screws of Grade III. (2) 11 screws were penetrated pedical cortex with 8 of Grade I and 3 of Grade II (2 penetrated into cortical paries medialis and 1 penetrated into paries lateralis, but no screw penetrated into upper or inferior border). The accuracy of screw placement was 97.79% (Grade 0), the total misplacement rate was 0.6% (Grade II and III). According to post-operative follow up in 12 to 30 months (average 20.6±5.2 months), no complication of spinal, nerve root, or vascular injury was found. No screw loosening or fracture occurred, and all bones were healed properly. Follow up in the 6 months after operation showed that patients with trauma had significantly improvement in ASIA grading, while patients without trauma had better JOA scores. Conclusion Based on the study, the technique of manual placement of pedicle screw in cervical spine is considered to be safe and reliable. Considering its wide indication, it’s a technique worthy of clinical application. Key words: Cervical vertebrae; Spinal fusion; Bone screws; Tomography, X-ray computed

36 - Subaxial cervical pedicle screw fixation: safe zone for screw placement—a systematic review

BACKGROUND CONTEXT: The use of pedicle screw fixation in the cervical spine has been considered an unacceptable risk for intraoperative neurovascular (nerves and blood vessels) injuries due to the proximity of the cervical neurovascular structures to the pedicle.

Minimally invasive cervical pedicle screw fixation via the posterolateral approach for metastatic cervical spinal tumors.

Background To avoid lateral misplacement of midcervical pedicle screws, we developed a method for Minimally Invasive Cervical Pedicle Screw (MICEPS) fixation via a posterolateral approach. This intramuscular approach allows for horizontal pedicle screw insertion and reduced intraoperative bleeding. We reviewed our initial experience with MICEPS fixation for patients with cervical metastases. Methods This study included 18 consecutive patients who received cervical spinal surgery for metastatic tumor. We treated 12 patients with conventional cervical pedicle screw fixation, and 6 patients with the MICEPS fixation technique. Average follow-up was 14 months (range 3 to 34). We inserted 117 pedicle screws using the navigation system. Average fusion area was 4.9 vertebrae (range 3 to 8). Alpha-angles between a line perpendicular to the posterior cortex of the vertebral body and the screw trajectory in the transverse plane were also measured. Results The average surgical time was 250 min (range 151 to 420 min) with the conventional pedicle screw fixation and 234 min (range 154 to 300 min) with the MICEPS fixation. The average total blood loss was 780 mL (range, 180-1430 mL) in the conventional pedicle screw fixation group and 180 mL (range, 70-400 mL) in the MICEPS fixation group. At the level of midcervical (C3-5), average alpha-angles was 52 degrees (range 43 to 62) in MICEPS fixation group, and 39 degrees (range 19 to 55) in conventional cervical pedicle screw group. Conclusions The MICEPS fixation technique uses an intramuscular approach, which is minimally invasive and reduces intraoperative bleeding. Intramuscular approach allows for horizontal pedicle screw insertion, and reduced critical screw deviation.

Efficacy and safety of a digital navigation template combined with cervical pedicle screw implantation: study protocol for a prospective, single-center, self-controlled, clinical trial

Background and objectives: Cervical pedicle screw fixation is a reliable method for the treatment of traumatic and non-traumatic cervical instability and cervical disc removal and fixation; however, the operation risks and the failure rate of screw insertion are still high. At present, the digital navigation template with digital computer technology, used in the department of orthopedics, has the advantages of accurate screw insertion and a small error in the screw insertion depth. This trial aims to observe the clinical efficacy and safety of the digital navigation template combined with cervical pedicle screw implantation. Design: This is a prospective, single-center, self-controlled, clinical trial. Methods: Thirty-two patients with cervical spondylosis will be recruited from the Harrison International Peace Hospital, Hebei Province, China. Before surgery, a three-dimensional (3D) navigation model of the cervical vertebrae will be designed by 3D reconstruction. The navigation template will be generated by 3D printing. The cervical pedicle screws will be implanted according to preoperatively designed models and the screw positions will be observed by computerized tomography (CT) after surgery. The patients will be followed up for 40 months. Outcome measures: The primary outcome measure is the excellent and good rate of screw position 40 months after implantation. The secondary outcome measures include the Visual Analog Scale score, American Spinal Injury Association classification, cervical X-ray and CT images before implantation and 40 months after implantation, and the incidence of adverse reactions 40 months after implantation. Discussion: We will verify a high success rate of cervical pedicle screw implantation using the digital navigation template. The operation is simple and quick, with good efficacy and safety. Ethics and dissemination: The protocols have been approved by the Ethics Committee of the Harrison International Peace Hospital in China (approval number: 20120630). The study protocol has been conducted in accordance with the Declaration of Helsinki, formulated by the World Medical Association. Written informed consent will be obtained from all participants. The recruitment of subjects will begin in December 2017. Samples and data will be collected from December 2017 to April 2019. Outcome measures will be analyzed in October 2020. This trial will be completed in November 2020. The results of the trial will be reported in a scientific conference or disseminated in a peer-reviewed journal. Trial registration: This trial has been registered in the Chinese Clinical Trial Registry (registration number: ChiCTR-ONC-17013481).

頚椎椎弓根スクリュー (CPS) 刺入精度の変遷

Objective : Cervical pedicle screw (CPS) may be the best anchor system for posterior cervical segmental fixation, but may carry high surgery-related risks such as neurovascular injury. The purpose of this study was to evaluate the accuracy of CPS placement by using various techniques such as a free-hand, computer navigation system.

Easy method to simplify “freehand” subaxial cervical pedicle screw insertion

Study Design:Technical note.Objectives:The objective of this study is to check out safety and rationality of standardized and fast tricks to select trajectory of subaxial cervical pedicle screw (SCPS) insertion, based on simple angles to bony landmarks.Materials and Methods:Stage 1 – Computed tomography (CT)-morphometric analysis of C3–C7 vertebrae of ten patients with cervical degenerative diseases. Stage 2 – SCPS insertion in 6 cadavers, according to the developed technique (59 pedicle screws). Stage 3 – SCPS insertion in 6 patients, according to the developed technique (32 pedicle screws).Results:CT-morphometric analysis showed that the average length of C3–C7 pedicle channels was 32 mm, the average angle between a pedicle axis and an axis of contralateral lamina - 180°, the average angle between a pedicle axis and plane of a posterior surface of a lateral mass amounted to 90° and the coordinates of an optimal entry point – 2 mm from a lateral edge and 2 mm from an upper edge of the lateral mass posterior surface. During the cadaveric study, 39 screws had a satisfactory position (66.1%), 7 screws permissible (11.9%), and 13 screws unacceptable (22%). During the clinical study, 26 screws (81.25%) had satisfactory position, 4 (12.5%) had permissible position, and 2 (6.25%) unacceptable position.Conclusion:Developed and clinically approved a method for simplicity SCPS insertion is relatively safe and cheap. No doubt, it requires further investigation, but the results of primary analysis allow us to recommend it to wide practical application.

Perforations and angulations of 324 cervical medial cortical pedicle screws: a possible guide to avoid lateral perforations with use of pedicle screws in lower cervical spine

Background ContextMore than half of the perforations reported with usage of cervical pedicle screws (CPS) are lateral perforations, endangering the vertebral artery. The medial cortical pedicle screw (MCPS) technique with partial drilling of the medial cortex shifts the trajectory of pedicle screws medially, decreasing the lateral perforations. PurposeTo evaluate the decrease in lateral perforations of CPS with use of MCPS technique, in relation to medial angulation. Study Design/SettingRetrospective analysis and technical report of the MCPS technique and its safety. Patient SampleA total of 58 patients operated on between December 2011 and May 2015 with insertion of pedicle screws from C3 to C7 were included in the study. Outcome MeasuresAxial reconstructed computed tomography (CT) scan images of the inserted screws were evaluated for placement, perforations, and transverse plane angulations using the Surgimap software (Surgimap Spine 1.1.2.271 Intl. 2009 Nemaris LLC). The angulations of screws were analyzed by the type and level of placement through unpaired t test and analysis of variance test. MethodsA total of 58 patients operated on between December 2011 and May 2015 with insertion of pedicle screws from C3 to C7 were included in the study. There were 49 males and 9 females. Thirty-seven patients had cervical trauma, 17 had cervical spondylotic myelopathy, two had tumors, and two had ankylosing spondylitis. The average age was 49 years (range 18 to 80 years). The screws were inserted using the MCPS technique. All patients underwent postoperative CT scans with GE Optima CT540 16 slice CT scanner (GE Healthcare Chalfont St. Giles, Buckinghamshire, UK). Axial reconstructed images along the axis of the inserted screws were evaluated for placement and perforations. Further, all the screws were evaluated for transverse plane angulations using the Surgimap software. The angulations of screw were analyzed by the type and level of placement through unpaired t test and analysis of variance test. No funds were received by any of the authors for the purpose of the present study. ResultsA total of 324 screws were assessed with postoperative CT scans. Two hundred fifty-six were found to be placed within the pedicle and 68 (20.98%) screws were found to have perforations. Forty screws (12.34%) had grade I medial perforations, 14 screws (4.32%) had grade I lateral perforations, 10 screws (3.08%) had grade II medial perforations, and 4 screws (1.23%) had grade IIlateral perforations. The average angulation of the nonperforated screws (n=256) was 28.6° (43°–17°), that of laterally perforated screws was 20.33° (13°–24°), and that of the medially perforated screws was 34.94° (45°–20°). On statistical analysis with each series, the 99% CI range for the in-screw angles was 27.91° to 29.34°; for the laterally perforated screw series, it was 18.42° to 22.23°; and that for the medially perforated screw series was 32.97° to 36.9°. ConclusionsThe MCPS technique represents a shift in the concept of placement of CPS from the cancellous core to the medial cortex, avoiding screw deflection laterally by the thick proximal medial cortex. The present study shows that the lateral perforations can be consistently avoided, with a medial angulation of more than 27.91°, which is the primary concern with the use of pedicle screws in lower cervical spine. Further, the MCPS technique reduces the lateral perforations at a lesser insertion angle, which is technically desirable.

Accuracy of a dynamic surgical guidance probe for screw insertion in the cervical spine: a cadaveric study.

A fresh frozen cadaver study was conducted. To report the cortical breach rate using the dynamic surgical guidance (DSG) probe versus traditional freehand technique for cervical lateral mass, cervical pedicle and cervical laminar screws. Nine male fresh frozen cadaveric torsos were utilized for this study. Each investigator was assigned three specimens that were randomized by fixation point, side and order of technique for establishing a screw pilot hole. The technique for screw hole preparation utilized was either a DSG probe in the "on" mode or in the "off" mode using a freehand technique popularized by Lenke et al. Levels instrumented included C1 lateral mass, C2 pedicle screws and lamina screws, and C6-T1 pedicle screws. Fluoroscopy and other navigational assistance were not used for screw hole preparation or screw insertion. All specimens were CT imaged following insertion of all screws. A senior radiologist evaluated all scans and determined that a misplaced screw was a breach of ≥2mm. A total of 104 drillings were performed, 52 with DSG and 52 without DSG There were 68 total pedicle drillings, 34 in each group. There were 18 drillings in the lamina and lateral mass. There was no significant difference between surgeons or between the left and right side. All breaches were in the pedicle, and none in the lamina or lateral mass. The breach rate for PG "on" was 6/68=8.96% (95% CI 3.69, 19.12%). The breach rate for PG "off" was 20/68=29.41% (95% CI 19.30, 41.87%). Of the 20 pedicle breaches in the non-DSG group, 7 were lateral and superior, 8 were lateral, 4 medial and 1 inferior. Of the six pedicle breaches in the DSG group, two were lateral/superior, two were lateral and two were medial in the pedicle. The dynamic surgical guidance probe is a safe tool to assist the surgeon with screw placement in the cervical spine. Additionally, the DSG potentially avoids the cumulative risks associated with fluoroscopy and provides real-time feedback to the surgeon allowing correction at the time of breach. Level of evidence Level IV.