C1 Lateral Mass Fixation Research Articles

C2/3 Transfacetal fixation: An underutilized technique of C2 fixation in the management of atlantoaxial dislocation - A technical note with review of literature.

Background:Atlantoaxial Dislocation (AAD) is a complex disorder of craniovertebral junction (CVJ). Many techniques are available to treat AAD but there are some specific conditions where some techniques have advantage over the other.Technical Advantage:C2-3 transfacetal screw with standard C1 lateral mass fixation provides a stronger construct because of four cortices incorporation and divergent course of screws and is biomechanically comparable to other forms of C2 fixation techniques. It is a technically less demanding and time-consuming. It is also a good alternative in cases having significant osteopenia.Conclusion:C2-3 transfacetal screw with standard C1 lateral mass fixation is an effective alternative to routine C1 lateral mass and C2 pedicle/pars screw fixation in cases of atlantoaxial dislocation complicated with high riding or posteriorly placed vertebral artery and thin pedicle of C2 vertebra.

Posterior fusion for fragility type 2 odontoid fractures.

The purpose of this study was to evaluate the outcomes of elderly patients with type 2 odontoid fractures treated with an instrumented posterior fusion. Ninety-three consecutive patients older than 65 years of age in whom a type 2 odontoid fracture had been treated with a variety of C1-2 posterior screw fixation techniques were retrospectively reviewed. The average age was 78 years (range 65-95 years). Thirty-seven patients had an additional fracture, 30 of which involved C1. Three patients had cervical spinal cord dysfunction due to their injury. All patients had comorbidities. The average total hospitalization was 9.6 days (range 2-37 days). There were 3 deaths and 19 major complications, the most common of which was pneumonia. No patient suffered a vertebral artery injury. Imaging studies were obtained in 64 patients at least 12 months postsurgery (mean 19 months). Fusion was assessed by dynamic radiographs in all cases and with a CT scan in 80% of the cases. Four of the 64 patients did not achieve fusion (6.25% overall). All patients in whom fusion failed had undergone C1 lateral mass fixation and C2 pars (1/29, 3.4%) or laminar (3/9, 33.3%) fixation. Instrumented posterior cervical fusions may be performed in elderly patients with acceptable morbidity and mortality. The fusion rate is excellent except when bilateral C2 translaminar screws are used for axis fixation.

The internal carotid artery and the atlas: anatomical relationship and implications for C1 lateral mass fixation.

The internal carotid artery (ICA) is potentially at risk during posterior fixation of C1. In this study, we performed a CT-based anatomical analysis of the relationship between the internal carotid artery and the lateral mass of the atlas. We analysed 30 CT angiography of the cervical spine, and we measured on both sides the distance of the carotid artery from the midline, distance of the ICA from the anterior cortex of C1 and from the ideal C1 screw entry point. We measured the angle between the sagittal plane passing through the entry point and the tangent line of the vessel. Separated statistical analysis between left and right sides, between male and female patients, and differentiation by age were also performed. Sixty ICAs were studied. The mean distance of the ICA from the midline was 23.3 ± 4.3mm, with a minimum of 15mm. The distance between the ICA and the anterior cortical layer of C1 was 4.8 ± 2.7mm, with a minimum of 1.1mm. The distance between the screw entry point and the arterial wall was 22.6 ± 2.8mm, with a minimum of 17.5mm. The mean angle was 10.4°, with a minimum of 11°. Although rare, intraoperative lesion of the ICA is reported and the spine surgeon must be aware of this risk. Careful preoperative planning is mandatory and the position of the ICA in relation to C1 must be assessed. The anatomical parameters presented in this paper can be useful to reduce the risk of ICA injury.

Transposterior Arch Lateral Mass Screw for C1 Fixation: Application of a 3.5-mm-Diameter Screw in the Vertebral Artery Groove with a Height of ≤3.5 mm

To explore the feasibility and effectiveness of C1 lateral mass fixation via the posterior arch using pedicle screws of 3.5-mm diameter in patients whose atlas in the vertebral artery groove (C1 pedicle) was ≤3.5 mm in height. A total of 14 patients who underwent transposterior arch lateral mass screw fixation between 2014 and 2017 due to atlantoaxial instability were retrospectively studied. The height of the atlas pedicle was ≤3.5 mm on one or both sides. The position of the screw and damage of the screw trajectory were assessed using the postoperative 3-dimensional computed tomography. The patients were regularly followed up to observe the fracture union and bone graft fusion. In total, 27 atlas pedicle heights were ≤3.5 mm and 22 screws were successfully inserted without any neurovascular complications. However, the pedicle wall was found to have a certain degree of damage with damaged superior/inferior wall in 4 of 6 pedicles respectively. Clinical symptoms were relieved to varying degrees, and patients demonstrated bony fusion during the postoperative follow-up. Pedicle screws of 3.5-mm diameter could be fixed with a high success rate using the viscoelasticity and expansivity of the bone tissue even if the atlas pedicles were ≤3.5 mm in height. Although the screws had a certain probability of breaking the superior/inferior wall, they provided sufficient stability and enabled fracture or bone graft healing. Extraverted atlas pedicle screws should be considered in some cases.

Quantitative Assessment of the Anatomical Footprint of the C1 Pedicle Relative to the Lateral Mass: A Guide for C1 Lateral Mass Fixation.

Study Design:Anatomic study.Objectives:To determine the relationship of the anatomical footprint of the C1 pedicle relative to the lateral mass (LM).Methods:Anatomic measurements were made on fresh frozen human cadaveric C1 specimens: pedicle width/height, LM width/height (minimum/maximum), LM depth, distance between LM’s medial aspect and pedicle’s medial border, distance between LM’s lateral aspect to pedicle’s lateral border, distance between pedicle’s inferior aspect and LM’s inferior border, distance between arch’s midline and pedicle’s medial border. The percentage of LM medial to the pedicle and the distance from the center of the LM to the pedicle’s medial wall were calculated.Results:A total of 42 LM were analyzed. The C1 pedicle’s lateral aspect was nearly confluent with the LM’s lateral border. Average pedicle width was 9.0 ± 1.1 mm, and average pedicle height was 5.0 ± 1.1 mm. Average LM width and depth were 17.0 ± 1.6 and 17.2 ± 1.6 mm, respectively. There was 6.9 ± 1.5 mm of bone medial to the medial C1 pedicle, which constituted 41% ± 9% of the LM’s width. The distance from C1 arch’s midline to the medial pedicle was 13.5 ± 2.0 mm. The LM’s center was 1.6 ± 1 mm lateral to the medial pedicle wall. There was on average 3.5 ± 0.6 mm of the LM inferior to the pedicle inferior border.Conclusions:The center of the lateral mass is 1.6 ± 1 mm lateral to the medial wall of the C1 pedicle and approximately 15 mm from the midline. There is 6.9 ± 1.5 mm of bone medial to the medial C1 pedicle. Thus, the medial aspect of C1 pedicle may be used as an anatomic reference for locating the center of the C1 LM for screw fixation.

CT-based morphometric analysis of C1 laminar dimensions: C1 translaminar screw fixation is a feasible technique for salvage of atlantoaxial fusions.

Background:Translaminar screw fixation has become an alternative in the fixation of the axial and subaxial cervical spine. We report utilization of this approach in the atlas as a salvage technique for atlantoaxial stabilization when C1 lateral mass screws are precluded. To assess the feasibility of translaminar fixation at the atlas, we have characterized the dimensions of the C1 lamina in the general adult population using computed tomography (CT)-based morphometry.Methods:A 46-year-old male with symptomatic atlantoaxial instability secondary to os odontoideum underwent bilateral C1 and C2 translaminar screw/rod fixation as C1 lateral mass fixation was precluded by an anomalous vertebral artery. The follow-up evaluation 2½ years postoperatively revealed an asymptomatic patient without recurrent neck/shoulder pain or clinical signs of instability. To better assess the feasibility of utilizing this approach in the general population, we retrospectively analyzed 502 consecutive cervical CT scans performed over a 3-month period in patients aged over 18 years at a single institution. Measurements of C1 bicortical diameter, bilateral laminar length, height, and angulation were performed. Laminar and screw dimensions were compared to assess instrumentation feasibility.Results:Review of CT imaging found that 75.9% of C1 lamina had a sufficient bicortical diameter, and 63.7% of C1 lamina had sufficient height to accept bilateral translaminar screw placement.Conclusions:CT-based measurement of atlas morphology in the general population revealed that a majority of C1 lamina had sufficient dimensions to accept translaminar screw placement. Although these screws appear to be a feasible alternative when lateral mass screws are precluded, further research is required to determine if they provide comparable fixation strength versus traditional instrumentation methods.

Anatomic Feasibility of Posterior Cervical Pedicle Screw Placement in Children: Computerized Tomographic Analysis of Children Under 10 Years Old

ObjectiveTo evaluate the anatomical feasibility of 3.5 mm screw into the cervical spine in the pediatric population and to establish useful guidelines for their placement.MethodsA total of 37 cervical spine computerized tomography scans (24 boys and 13 girls) were included in this study. All patients were younger than 10 years of age at the time of evaluation for the period of 2007-2011.ResultsFor the C1 screw placement, entry point height (EPH) was the most restrictive factor (47.3% patients were larger than 3.5 mm). All C2 lamina had a height larger than 3.5 mm and 68.8% (51/74) of C2 lamina had a width thicker than 3.5 mm. For C2 pedicle width, 55.4% (41/74) of cases were larger than 3.5 mm, while 58.1% (43/74) of pedicle heights were larger than 3.5 mm. For pedicle width of subaxial spine, 75.7% (C3), 73% (C4), 82.4% (C5), 89.2% (C6), and 98.1% (C7, 1/54) were greater than 3.5 mm. Mean lamina width of subaxial cervical spine was 3.1 (C3), 2.7 (C4), 2.9 (C5), 3.8 (C6), and 4.0 mm (C7), respectively. Only 34.6% (127/370) of subaxial (C3-7) lamina thickness were greater than 3.5 mm. Mean length of lateral mass for the lateral mass screw placement was 9.28 (C3), 9.08 (C4), 8.81 (C5), 8.98 (C6), and 10.38 mm (C7).ConclusionC1 lateral mass fixation could be limited by the morphometrics of lateral mass height. C2 trans-lamina approach is preferable to C2 pedicle screw fixation. In subaxial spines, pedicle screw placement was preferable to trans-lamina screw placement, except at C7.

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 …

C1 Lateral Mass Fixation

Abstract OBJECTIVE We review our experience and technique for C1 lateral mass screw fixation. We compare the results of 3 different constructs incorporating C1 lateral mass screws: occipitocervical (OC) constructs, C1–C2 constructs, and C1 to mid/low cervical constructs. METHODS We performed a retrospective chart review of 42 consecutive patients who underwent C1 lateral mass fixation by 2 of the authors (PVM and DC). The patient population consisted of 24 men and 18 women with a mean age of 64 years. Twenty-two patients had C1–C2 constructs. Twelve patients had constructs that started at C1 and extended to the mid/low cervical spine (one extended to T1). Eight patients underwent OC fusions incorporating C1 screws (2 of which were OC-thoracic constructs). All constructs were combined either with a C2 pars screw (38 patients), C2 translaminar screw (1 patient), or C3 lateral mass screw (3 patients). No C2 pedicle screws were used. Fusion was assessed using flexion-extension x-rays in all patients and computed tomographic scans in selected cases. Clinical outcomes were assessed with preoperative and postoperative visual analog scale neck pain scores and Nurick grading. The nuances of the surgical technique are reviewed, and a surgical video is included. RESULTS Two patients (5%) were lost to follow-up. The mean follow-up for the remaining patients was 2 years. During the follow-up period, there were 4 deaths (none of which were related to the surgery). For patients with follow-up, the visual analog scale neck pain score improved a mean of 3 points after surgery (P < .001). For patients with myelopathy, the Nurick score improved by a mean of 1 grade after surgery (P < .001). The postoperative complication rate was 12%. The complication rate was 38% in OC constructs, 17% in C1 to mid/low cervical constructs, and 0% for C1–C2 construct cases. Patients with OC constructs had the statistically highest rate of complications (P < .001). Patients with C1 to mid/low cervical constructs had more complications than those with C1–C2 constructs (P < .001). Of the 42 cases, there were 3 pseudoarthroses (1 in an OC case, 1 in a C1 to midcervical construct, and 1 in a C1–C2 construct). OC constructs had the highest risk of pseudoarthrosis (13%) (P < .001). CONCLUSION Patients treated with C1 lateral mass fixation constructs have a high fusion rate, reduced neck pain, and improved neurologic function. Constructs using C1 lateral mass screws do not need to incorporate C2 pedicle screws. Constructs incorporating C1 lateral mass screws are effective when combined with C2 pars screws, C2 translaminar screws, and C3 lateral mass screws. Constructs using C1 screws are associated with a higher complication rate and a higher pseudoarthrosis rate if extended cranially to the occiput or if extended caudally below C2.

Freehand C1 lateral mass screw fixation technique: our experience

Background Although C1 lateral mass fixation technique is frequently performed in upper cervical instabilities, it requires the guidance of fluoroscopic imaging. The fluoroscopy guidance is time-consuming and has the risks of accumulative radiation. Biplane fluoroscopy is also difficult in upper cervical pathologic conditions because of the use of cranial fixations. This study aimed to demonstrate that unicortical C1 lateral mass screws could be placed safely and rapidly without fluoroscopy guidance. Methods Between 2002 and 2008, 32 C1 lateral mass screws were inserted in 17 consecutive patients with various pathologic conditions involving either atlantoaxial or occipitocervical instability. Results C1 screw lengths ranged from 18 to 32 mm. The atlantoaxial fixation was performed in 13 patients, and C1 lateral mass screws were added to the occipitocervical construct in 3 patients, to the posterior cervical construct in 2 patients, and to the cervicothoracic construct in 1 patient. In 2 patients, because C1 lateral mass screws could not be inserted unilaterally, C1 pedicle screw analogs were inserted. There were no screw malpositions or neurovascular complications related to screw insertion. Operation time and intraoperative bleeding of the isolated atlantoaxial fixations were retrospectively evaluated. The mean follow-up was 32.3 months (range, 7-59 months). No screw loosening or construct failure was observed within this period. Postoperatively, 4 patients complained of hypoesthesia, whereas one patient had superficial wound infection. Conclusion C1 lateral mass screws may be used safely and rapidly in upper cervical instabilities without intraoperative fluoroscopy guidance and the use of the spinal navigation systems. Preoperative planning and determining the ideal screw insertion point, the ideal trajections, and the lengths of the screws are the most important points.

C1 Lateral Mass Anatomy

Cadaveric specimens were measured to determine appropriate placement for C1 lateral mass screws. Instrumentation guidelines were developed and used to instrument a series of cadaveric specimens. Clinical experience with C1 lateral mass fixation was reviewed to evaluate results. Postoperative computed tomographic (CT) scans were reviewed to evaluate screw placement. The cadaveric study measured the dimensions of the atlas and determined ideal trajectory for screw placement. This technique was applied clinically, and 50 cases were retrospectively reviewed for fixation difficulties, neurologic or vascular injuries, and perioperative complications. Postoperative CT scans were reviewed when available. Halo application, posterior wiring, and C1 to C2 transarticular screws have been used to stabilize the upper cervical spine. Each technique has disadvantages, and C1 lateral mass fixation recently has gained popularity as a potential alternative. Recent anatomic studies have documented the dimensions of the C1 lateral mass and its ability to accommodate screw fixation. Small clinical series have documented early success with this technique. Fifteen specimens were stripped of soft tissue and measured by using calipers and CT scans. Guidelines were formulated for C1 lateral mass screw fixation. Additional specimens with intact soft tissue were instrumented without difficulty. A clinical series was reviewed to evaluate for complications related to this technique. Postoperative CT scans were reviewed to evaluate screw placement. The C1 lateral mass safely accommodated screw fixation. Trajectory of 10 degrees medial and 22 degrees cephalad was preferred. The technique was safely applied in a series of 50 patients. Postoperative CT scans showed the ability of the surgeon to achieve the intended goals for starting point and safe trajectory. C1 lateral mass fixation is a safe alternative for upper cervical fixation with several potential advantages versus other techniques, but further clinical evaluation is warranted.

C1 Pedicle Screws Versus C1 Lateral Mass Screws

In vitro biomechanical study. To compare the pullout strengths and the biomechanical stabilities afforded by C1 lateral mass screws and C1 pedicle screws using bicortical and unicortical fixation techniques. Posterior screw fixation techniques in the atlas including C1 lateral mass screw and C1 pedicle screw. The shortcomings of C1 lateral mass screw technique and potential risks of bicortical fixation method were recently described; C1 pedicle screw technique with unicortical fixation might overcome these anatomic and clinical drawbacks. However, it is unknown whether the biomechanical characteristics of unicortical C1 pedicle screw are comparable with that of bicortical C1 lateral mass screw. METHODS.: Bicortical or unicortical C1 pedicle screws and C1 lateral mass screws were inserted into 12 adult fresh human C1 specimens. Pullout strength was evaluated using a material testing machine. The construct's stability of bicortical C1 lateral mass screws or unicortical C1 pedicle screws incorporating unicortical C2 pedicle screws was compared with bilateral transarticular screws using another 6 fresh cervical cadaver spines. Pullout strength and biomechanical stability differences were compared statistically. Bicortical C1 pedicle screws provided the biggest pullout strength (1757.0 +/- 318.7 N) of all 4 methods, whereas unicortical C1 lateral mass screws provided the weakest(794.5 +/- 314.8 N). However, there were no statistically significant differences between bicortical C1 lateral mass screws (1243.8 +/- 350.0 N) and unicortical C1 pedicle screws (1192.5 +/- 172.6 N). Furthermore, there was no statistically significant difference of biomechanical construct stability between unicortical C1 pedicle screw-rod constructs and bicortical C1 lateral mass screw-rod constructs. C1 pedicle screws are stiffer than C1 lateral mass screws. Unicortical C1 pedicle screw provided the same pullout resistance and three-dimensional stability as bicortical C1 lateral mass fixation. Although lateral mass screw placement into C1 requires bicortical purchase, pedicle screw insertion into the atlas only requires unicortical fixation.

Protection of the C1 posterior arch in atlantal lateral mass fixation: technical case report

Screw fixation of the C1 lateral mass is a relatively new technique designed to allow for C1/C2 fixation in scenarios where transarticular screw fixation is not safe or possible. In order to place the screw at the base of the C1 arch, it has been recommended to drill at the junction of the C1 posterior arch and the lateral mass of C1, to accommodate the screw head. This may, however, weaken the C1 arch, making it prone to fracture. In this new technique, we describe a modification to the current technique to allow placement of this screw without compromising the C1 arch. A case of atlantoaxial instability secondary to os odontoideum is described. C1 lateral mass fixation is achieved by selecting a screw 10 mm longer than required and placing the screw 10 mm above the bony entry point, for easier placement of the rod and avoidance of drilling at the base of the C1 arch. Adequate and safe C1/C2 fixation was achieved. Sublaminar wiring was performed around the C1 arch with no weakening or fracture of the arch. We believe that in order to place reasonable C1 lateral mass screws, it is inadvisable to drill the base of the junction between the C1 posterior arch and lateral mass as this may lead to arch weakening and failure. Easier instrumentation can be performed and the integrity of the C1 arch maintained using this alternate technique.

The use of C1 lateral mass fixation in the cervical spine

The use of C1 lateral mass fixation in the cervical spine