Posterior C1 Lateral Mass Screws Research Articles

Predisposing Factors of Fracture Nonunion After Posterior C1 Lateral Mass Screws Combined with C2 Pedicle/Laminar Screw Fixation for Type II Odontoid Fracture.

The aim of this study was to explore the predisposing factors for fracture nonunion after a lateral screw was combined with C2 pedicle/laminar screw for a type II odontoid fracture and hopefully provide references in decision making and surgical planning for spinal surgeons. This is a retrospective study. By retrieving the medical records from January 2010 to July 2015 in our hospital, 117 type II odontoid fracture patients were reviewed. According to the occurrence of fracture union at the final follow-up, patients were divided into 2 groups: union and nonunion. To investigate the predisposing factors for fracture nonunion, 3 categorized factors were analyzed statistically: patient characteristics-age, sex, body mass index, preoperative Japanese Orthopaedic Association (JOA) scores, duration, comorbidity, and complicated injuries; surgical variables-surgery time, blood loss, C2 fixation manner, vertebral artery injury, bone source for fusion between the posterior arch of C1 and the laminae and spinous process of C2; radiographic parameters-preoperative and immediate postoperative data of C0-2 curvature, C2-7 curvature, C2-7 sagittal vertical axis, C7 slope, fracture classification, congenital hypoplastic vertebral artery, and the separation and displacement of the odontoid fracture. Other variables including JOA and visual analog scale scores for neck pain, neck stiffness, and patient satisfaction at final follow-up were recorded and compared between the 2 groups. Postoperative fracture nonunion was detected in 76 of 117 patients (65%) at final follow-up. There was no statistically significant difference between the 2 groups in patient characteristics of sex, body mass index, JOA score, comorbidity, and complicated injuries. The mean age at operation was younger in the union group than in the nonunion group, and the mean duration was shorter in the union group than in the nonunion group. There was no difference in surgical variables of surgery time, blood loss, C2 fixation manner, vertebral artery injury, bone source for fusion between the posterior arch of C1 and the laminae and spinous process of C2. There was no difference in radiographic parameters of fracture classification, congenital hypoplastic vertebral artery, preoperative and immediate postoperative C0-2 curvature, C2-7 curvature, C2-7 SVA, and C7 slope. No difference was found in preoperative and immediate postoperative displacement of the odontoid fracture or immediate postoperative separation of the odontoid fracture, while the preoperative separation of the odontoid fracture was shorter in the union group than in the nonunion group. The logistic regression analysis revealed that advanced age (>45 years), long duration (>2 months), and preoperative separation of the odontoid fracture (>4 mm) were independently associated with the postoperative fracture nonunion. There were no differences between the 2 groups in JOA, neck pain, neck stiffness, and patient satisfaction at final follow-up. Advanced age, long duration, and preoperative separation of odontoid fracture >4 mm are predisposing factors for fracture nonunion after posterior C1 lateral screw combined with C2 pedicle/laminar screw fixation for type II odontoid fracture. Our findings did not demonstrate any evidence of lower functional outcome and patients satisfaction for those patients who had odontoid nonunion.

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

A radiographic analysis of the anatomy of the C1 lateral mass using computed tomography (CT) scans and Mimics software. To define the anatomy of the C1 lateral mass and make recommendations for optimal entry point and trajectory for anterior C1 lateral mass screws. 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. 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. 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. 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.

An anatomic study to determine the optimal entry point, medial angles, and effective length for safe fixation using posterior C1 lateral mass screws.

Anatomic study of the C1 lateral mass using fine-cut computed tomographic scans and Mimics software. To investigate the optimal entry point, medial angles, and effective length for safe fixation using posterior C1 lateral mass screws. Placing posterior C1 lateral mass screws is technically demanding, and a misplaced screw can result in injury to the vertebral artery, spinal cord, or internal carotid artery. Although various insertion angles have been proposed for posterior C1 lateral mass screw, no clear consensus has been reached on the ideal medial angle of the C1 lateral mass. The C1 lateral masses were evaluated using computed tomographic scans and Mimics software in 70 patients. The effective width and effective screw length of posterior C1 lateral mass screws were measured at different medial angulations relative to the midline sagittal plane. The height (H) for screw entry point on the posterior surface of C1 lateral mass and the distance (D) between screw entry point and the intersection of the midline sagittal plane and the posterior arch of the atlas were also measured. The mean height (H) for screw entry on the posterior surface of the lateral mass was 4.25 mm, the mean distance (D) between screw entry point and the intersection of the midsagittal plane and the posterior arch of the atlas was 27.62 mm. The optimal medial angle was 20.86° with a corresponding effective width of 10.56 mm and effective screw length of 21.87 mm. This study helps to define the specific anatomy related to C1 posterior lateral mass screw placement in an effort to facilitate instrumentation. However, variation is seen in lateral mass anatomy, and this study must be combined with customized surgical planning that includes advanced imaging for safe and effective instrumentation. 1.

The height for screw index (HSI) predicts the development of C2 nerve dysfunction associated with C1 lateral mass screw fixation for atlantoaxial instability

To propose a new measure, the height for screw index (HSI), as a predictor of C2 nerve dysfunction in patients who have received posterior C1 lateral mass screw (C1LMS) fixation for atlantoaxial instability and to examine whether the HSI scores correlated with the development of C2 nerve dysfunction through retrospective analysis of 104 C1LMS inserted in 52 patients with atlantoaxial instability. The medical records of patients who underwent C1LMS fixation were retrospectively reviewed. C1LMS, 3.5mm in diameter, was inserted for atlantoaxial stabilization. The sagittal plane of the planned C1LMS trajectory was reconstructed from CT images. The HSI was defined as the difference in height between C2 ganglion and its corresponding foramen. C2 nerve function was assessed using a validated visual analog scale questionnaire. Each foramen receiving C1LMS was considered as a single unit and patients were categorized to group 1, HSI ≥4.0mm; group 2, HSI <4.0mm. The mean HSI score was 4.7±0.8mm (range 3.1-6.5mm) with 85 (81.7%) units in group 1, and 19 (18.3%) units in group 2. Fourteen (13.5%, 14/104) units developed C2 nerve dysfunction. C2 nerve dysfunction was reported in 4 units in group 1, and 10 units in group 2, respectively. The percentage of C2 nerve dysfunction was significantly higher in group 2 than that in group 1 (P<0.001, Pearson Chi-square test). The HSI score correlates with the development of C2 nerve dysfunction in patients receiving C1LMS fixation for atlantoaxial instability and may be a useful predictor of C2 nerve dysfunction.

Vertebral Artery Pseudoaneurysm Resulting in Embolic Stroke as a Complication of Posterior C1 Lateral Mass Screw Fixation: A Case Report.

Current literature supports posterior screw instrumentation of the C1 lateral mass as a reliable procedure for treating many occipitocervical and atlantoaxial pathologies with a low incidence of vertebral artery and neurologic injury and a high accuracy rate for screw placement1-6. The rate of vertebral artery injury from Cl lateral mass screw fixation is unknown1,2. Bransford et al. reported no neurologic or vascular complications in a large series, despite cases of suboptimal screw placement2. However, the variable and unique C1 anatomy can make precise instrumentation challenging with the rare potential for vascular and neurologic injury. Iatrogenic vertebral artery injury can have serious consequences, including excessive acute bleeding, arteriovenous fistula, pseudoaneurysm, occlusion, narrowing, or dissection. These defects may remain asymptomatic or lead to massive bleeding, transient ischemic attack, stroke, or death, occurring at variable time intervals up to several years after surgery1,7,8. Vertebral artery occlusion or vertebrobasilar thromboembolic events typically result in brainstem or cerebellar dysfunction7. To the best of our knowledge, this is the first report of a vertebral artery pseudoaneurysm as a complication of posterior C1 lateral mass fixation that resulted in delayed embolic stroke. The patient’s family was informed that data concerning the case would be submitted for publication, and they provided consent. An eighty-two year-old man with a history of a type-II odontoid fracture, which had been treated with a posterior cervical C1-C2 fusion with lateral mass and pedicular fixation 3.5 years ago, presented to our institution after a fall. There had been no reported intraoperative difficulties during the initial surgery. The patient had been neurologically intact both preoperatively and postoperatively. An immediate postoperative computed tomography (CT) scan had demonstrated that the left C1 lateral mass screw had violated the …

Comparative Results Between C1 pedicle screw and C1 lateral mass screw

Objective To compare the clinical outcomes of C1 pedicle screw with C1 lateral mass screw.Methods From Jan 2006 to Jan 2010,60 cases with atlantoaxial instability were randomly divided into two groups:32 cases underwent posterior C1 pedicle screw fixation (the pedicle group) and 28 cases underwent posterior C1 lateral mass screw fixation (the lateral mass group).Patients were followed up at regular intervals.The blood loss,the time of the operation,the JOA Score,VAS Score,and the bone fusion rate were recorded.Results All cases were followed up for an average of 46.6 months (range,12 to 60 months).Bone fusion were achieved 6 month after operations.There were no loose or breakage of screw-rod.Atlantoaxial re-instability was not found in the series.At the last followed up time,the JOA score and VAS score of pedicle group had respectively improved from 7.1±2.8 and 3.0±1.2 preoperatively to 13.3±2.1 and 1.8±0.9 postoperatively; The JOA score and VAS score of lateral mass group had respectively improved from 7.3±2.4 and 3.2±1.0 preoperatively to 13.0±2.6 and 1.9±1.0 postoperatively.There was no difference in JOA Score,VAS Score,and the bone fusion rate between two groups.There were significant difference in blood loss,the time of the operation.Fracture of posterior arch were observed in 2 cases in the pedicle group,and in the lateral mass group,pain and numbness of cervic-occipital region were observed in 3 cases after operation.Conclusion C1 pedicle screw fixation is less invasive and safe technique.Lateral mass screw fixation is a wise option for atlantoaxial instability. Key words: Atlas; Spinal fusion; Internal fixators; Treatment outcome

Posterior Osteosynthesis of the Atlas for Nonconsolidated Jefferson Fractures

Case report and surgical technique. To describe a new technique to treat atlas burst fractures by selectively reconstructing the atlas from a posterior approach. The two surgical techniques reported until now for stabilizing atlas burst fractures are associated with some drawbacks. Posterior C0-C2 or C1-C2 fixations significantly reduce head rotation, while the transoral C1 lateral masses osteosynthesis can be associated with oropharyngeal and neurological complications. We propose a new surgical technique for the treatment of unstable Jefferson fractures aimed at avoiding these problems. A 25-year-old man presented with a Jefferson type III atlas fracture after a traffic accident. The fracture failed to consolidate after 3 months of halo brace immobilization. Surgery consisted in inserting bilateral posterior C1 lateral mass screws interconnected by a transversal rod, thereby creating a second C1 posterior arch under the fractured one. Postoperative course was uneventful. Immediate postoperative stability was confirmed on dynamic X-ray films and head rotation was preserved. Delayed computed tomography scan demonstrated fracture consolidation. The surgical technique described is new and effective for treating atlas burst fractures. This posterior procedure allows mobility preservation, with a low morbidity rate.

Direct Posterior C1 Lateral Mass Screws Compression Reduction and Osteosynthesis in the Treatment of Unstable Jefferson Fractures

Technical case report. To investigate a new concept and surgical technique in the treatment of unstable Jefferson fractures, which preserves the motion of upper cervical spine, avoiding fusion. The management of unstable Jefferson fractures remains controversial. Conservative treatment usually involves a long time of immobilization in halo vest, whereas surgical intervention generally performs fusion, eliminating the range of motion of upper cervical spine. Two patients with unstable Jefferson fractures were surgically treated via direct posterior C1 lateral mass screws compression reduction and osteosynthesis technique, aiming at restoring the C0-C2 height and maintaining the vertical ligamentous tension for C0-C1-C2 complex stability despite the incompetent transverse ligament, achieving physiologic repair instead of traditional fusion. The clinical and radiographic results were documented. The postoperative CT showed that C1 lateral mass screws were well positioned. At 1-year follow-up, plain radiographs, and CT scan revealed no implant failure, good cervical alignment, and bony healing of the fractures; no C1-C2 instability was observed on the flexion-extension radiographs. The patients were completely pain-free, with full range of motion of the cervical spine. The ideal treatment of unstable Jefferson fractures is expected to preserve the function of C0-C1-C2. Unstable Jefferson fractures involve the concomitant failure of the vertical ligamentous tension because of the loss of C0-C2 height. Reduction of the displaced lateral masses to restore the C0-C2 height and maintain the ligamentous tension is the key to the surgery. Direct posterior C1 lateral mass screws compression reduction and osteosynthesis is a valid technique, avoiding fusion of upper cervical spine.

Inferolateral Entry Point for C2 Pedicle Screw Fixation in High Cervical Lesions

The purpose of this retrospective study was to evaluate the efficacy and safety of atlantoaxial stabilization using a new entry point for C2 pedicle screw fixation. Data were collected from 44 patients undergoing posterior C1 lateral mass screw and C2 screw fixation. The 20 cases were approached by the Harms entry point, 21 by the inferolateral point, and three by pars screw. The new inferolateral entry point of the C2 pedicle was located about 3-5 mm medial to the lateral border of the C2 lateral mass and 5-7 mm superior to the inferior border of the C2-3 facet joint. The screw was inserted at an angle 30° to 45° toward the midline in the transverse plane and 40° to 50° cephalad in the sagittal plane. Patients received followed-up with clinical examinations, radiographs and/or CT scans. There were 28 males and 16 females. No neurological deterioration or vertebral artery injuries were observed. Five cases showed malpositioned screws (2.84%), with four of the screws showing cortical breaches of the transverse foramen. There were no clinical consequences for these five patients. One screw in the C1 lateral mass had a medial cortical breach. None of the screws were malpositioned in patients treated using the new entry point. There was a significant relationship between two group (p=0.036). Posterior C1-2 screw fixation can be performed safely using the new inferolateral entry point for C2 pedicle screw fixation for the treatment of high cervical lesions.