C1 Lateral Mass Screw Placement Research Articles

Accuracy and clinical characteristics of robot-assisted cervical spine surgery: a systematic review and meta-analysis.

To evaluate the accuracy and feasibility of robot-assisted cervical screw placement and factors that may affect the accuracy. A comprehensive search was made on PubMed, Embase, Cochrane Library, Web of Science, CNKI, and Wanfang Med for the selection of potential eligible literature. The outcomes were evaluated in terms of the relative risk (RR) or standardized mean difference (MD) and corresponding 95% confidence interval (CI). Subgroup analyses of the accuracy of screw placement at different cervical segments and with different screw placement approaches were performed. A comparison was made between robotic navigation and conventional freehand cervical screw placement. Six comparative cohort studies and five case series studies with 337 patients and 1342 cervical screws were included in this study. The perfect accuracy was 86% (95% CI, 82-89%) and the clinically acceptable rate was 98% (95% CI, 95-99%) in robot-assisted cervical screw placement. The perfect accuracy of robot-assisted C1 lateral mass screw placement was the highest (96%), followed by C6-7 pedicle screw placement (93%) and C2 pedicle screw placement (86%), and the lowest was C3-5 pedicle screw placement (75%). The open approach had a higher perfect accuracy than the percutaneous/intermuscular approach (91% vs 83%). Compared with conventional freehand cervical screw placement, robot-assisted cervical screw placement had a higher accuracy, a lower incidence of perioperative complications, and less intraoperative blood loss. With good collaboration between the operator and the robot, robot-assisted cervical screw placement is accurate and feasible. Robot-assisted cervical screw placement has a promising prospect.

Lateral mass screw placement in the atlas: description of a novel surgical technique, radiographic parameters, and review of the literature.

Numerous techniques of C1 lateral mass screw placement have been described. We sought to delineate the radiographic angle of safety medially and laterally and describe a novel surgical technique of C1 lateral mass screw placement. We sought to (I) determine the angle of safety medially and laterally of the C1 lateral mass; (II) assess the size available of the lateral mass in the AP and coronal planes; (III) describe novel technique of insertion of a C1 lateral mass screw utilizing navigation and a novel start point. We retrospectively reviewed cervical computed tomography (CT) images of normal adults. Radiographic measurements were then obtained using these images including the angle (degrees) of safety medially and lateral of the C1 lateral mass bilaterally, as well as the length and width (mm) of the C1 lateral masses. A novel surgical technique was used by identifying the confluence of the medial aspect of the posterior arch and the lateral mass. This confluence is then marked out as the C1 screw start point. Under navigation guidance, lateral mass screws were placed with 0 degrees of medial-lateral angulation from posterior to anterior. Forty-five patients with a mean age of 52.6±25.6 years (33% female) were included. The mean medial and lateral angle of safety of the C1 lateral mass bilaterally was 23±3.8 degrees and 32±5 degrees, respectively. Average length and width of the lateral mass was 17.7 and 13.3 mm respectively. This study describes the radiographic window of safety medially and laterally for safe and reproducible placement of C1 lateral mass screws. Further, a novel technique using a medial start point and navigation guidance with 0 degrees of angulation in the coronal plane is described. Further research is required to assess outcomes of patients utilizing this method as well as biomechanical studies to assess this construct strength compared to others that are frequently used.

A Computed Tomographic Study to Document Anatomical Variations of First Cervical Vertebra: Prevalence, Classification and Possible Clinical Implications

Background - First cervical vertebra has different anatomical features as compared to other cervical vertebrae. It holds globe of skull and lacks body and spine. It is composed of 2 lateral masses linked by anterior and posterior arches. Posterior atlanto-occipital membrane is attached to posterior arch. Lateral edge of this membrane sometimes ossifies thus converting groove into canal. Consequently, neurovascular groove gets converted into a bony ring “ponticulus posticus”. It is considered as potential cause of neck pain and headache. Knowledge of this variation is important during procedures like instrumentation of atlas including C1 lateral mass screw placement which requires mobilization of C2 nerve root and screw insertion inferior to bony arch of atlas directly into lateral mass. In patients with ponticulus posticus, if not identified pre-operatively may give impression of wide bony arch for screw placement, which may result in vertebral artery injury due to a breach of this variation. Congenital defects of atlantal arch a developmental failure of chondrogenesis is a rare anomaly. These defects are a benign variation discovered incidentally. Detection of these anomalies is clinically important as they can cause acute neurologic deficits, which is associated with neck extension. Currarino et al proposed classification of posterior arch anomalies Type A Failure of posterior midline fusion of the 2 hemi arches. Type B Unilateral cleft. Type C Bilateral cleft with persistent dorsal part of arch. Type D Absence of posterior arch with persistent posterior tubercle. Type E Absence of entire posterior arch Objective Objectives this study is to find the prevalence of Ponticulus posticus Congenital anomalies of atlantal arch and classify them Material and Method- 250 computerized tomography (CT) head and neck in axial and sagittal sections from Picture Archiving and Communication System (PACS) of Dr RMLIMS, Lucknow was studied as CT is the best method to study the bony landmarks and any anomaly. Prevalence of variations was calculated. Data was analyzed statistically using SPSS version 21 by Chi-square test. Result- Prevalence of ponticulus posticus was 32.4%. Males had higher prevalence (20.4%) than females (12%). Incomplete ponticulus posticus (24.4%) was more than complete variant (8%). There was predominance of left sided ponticulus posticus(12% vs 8.4%) Deficient posterior arch was found in 9(3.6%) cases. 6 were of type A 3 were of type B. Conclusion- This study will help in determining cause of neurological deficit in patients due to presence of above variations. Significance Accurate evaluation of anatomic landmarks in patient with migraine or neck ache is important because changes in anatomy of atlas may be index pointing towards underlying disease process like vertebrobasilar insufficiency. Asymmetrical deviations of atlas in form, size, shape, and contour are often multiple and confusing. Therefore, they must not only be studied with care and precision and meticulously recorded. In our future project we plan to carry out computed tomographic study to find association of these variations in patients with migraine and cervical pain.

How to Transect the C2 Root for C1 Lateral Mass Screw Placement: Case Series and Review of an Underappreciated Variable in Outcome

The techniques for atlantoaxial arthrodesis have been modified over the years, and placing C1 lateral mass screws is a modern approach. C2 neuropathy is a complication of concern; however, sacrifice of the C2 nerve is an accepted and often favored adjunct. The impact of the technique for cutting the C2 nerve is not adequately addressed in the literature. The aim of this study was to evaluate the clinical outcomes from a series of roots sacrificed during C1-2 fusion with attention to the C2 transection method. Clinical data were collected from trauma patients who underwent C1 screw fixation for atlantoaxial fusion. Chart review was performed and outcome assessed through telephone surveys to patients who were at least 6 months postoperative. Quality of life, C2 nerve function, neck pain, and head pain were assessed. Sixty-six roots were divided in 35 patients. There were no cases of occipital neuralgia at routine 3-month follow-up. Delayed telephone surveys were completed in 17 patients and exposed 4 cases of severe head/neck pain but none consistent with occipital neuralgia. C2 neuralgia is rare when sharply dividing the C2 root with the aid of bipolar electrocautery at the midportion of the ganglion where it overlies the C1-2 joint. A literature review suggests the impact of the root sacrifice method is an underappreciated modifiable factor in outcome. In future reports, description of the root transection technique is imperative and trials comparing ganglionectomy versus transection proximal to the ganglion or through the ganglion should be considered.

Morphometric Measurements of the C1 Lateral Mass with Congenital Occipitalization of the Atlas

Unfamiliarity with the morphometry of the assimilated C1 lateral mass (C1LM) could make screw placement dangerous. In the present study, we defined the morphometric dimensions of the occipitalized C1LM to provide surgeons with valuable information for preoperative planning. Thin-slice computed tomography scanning data from 131 patients with occipitalization of the atlas (OA) and 50 control cases were imported into Mimics software for analysis. The widths and heights of the C1LM were fully measured in the different planes. The ideal inward angulation and the safe maximum cephalic angulation of C1 screw trajectory were evaluated. Except for the medial height, all the widths and heights of C1LM were significantly shorter in the OA group than those in the control group. The ideal inward angle (α) was significantly larger in the OA group (23.8° ± 8.3°) than that (15.3° ± 3.8°) in the control group; the corresponding screw length was also significantly longer in the OA group (20.9 ± 2.9 mm). The safe maximum cephalic angles (β) of the screw trajectory did not reach a significant difference between the 2 groups. All the widths and heights were shorter in the females than those in the males. The α angle also did not reach a significant difference between the sexes; however, the β angles in the males (35.9° ± 10.4°) was significantly larger than that in the females (32.0° ± 9.4°). Although the hypoplastic C1LM brings limitations to screw insertion to some extent, it is still broad enough to accommodate a screw safely in both female and male patients. Considering the irregularity of the C1LM in patients with OA, the preoperative imaging assessment is critical, and C1LM screw placement should be performed individually.

Steinmann Pins for C1 Lateral Mass Screw Placement During Atlantoaxial Stabilization.

The authors describe a modified technique for placement of the C1 lateral mass screw using a Steinmann pin as a guide. This technique minimizes dissection and provides atlantoaxial stabilization during arthrodesis. In our technique, a nonthreaded 1.6-mm spade-tip Steinmann pin is placed into the lateral mass of C1 to serve as a guide over which a powered drill is used for screw insertion. Perioperative data were collected for consecutive patients who underwent a C1-2 arthrodesis that involved the modified technique between March 2010 and July 2016. Data included blood loss, operative times, and C2 nerve root injury. The data for 93 patients were reviewed. Most (91.4%) patients presented with a fracture from an acute trauma. A mean of 1.97 levels was fused in these patients, with a mean blood loss of 76 mL and a mean operative time of 144 minutes. The overall morbidity and mortality rate was 10.7%. The morbidity rate of 7.5% included 30-day postoperative complications of respiratory failure and dysphasia. There were no postoperative vertebral artery injuries, hardware failures, or instances of occipital neuralgia. The use of Steinmann pins to guide the placement of C1 lateral mass screws is safe and effective in C1-2 arthrodesis. Limiting dissection minimizes blood loss and injury, maintains efficient operative time, and assists in accurate placement of the screws. Furthermore, with less manipulation and retraction of the C2 nerve root, postoperative occipital neuralgia and the need for C2 root transection are avoided.

Does Transection of the C2 Nerve Roots During C1 Lateral Mass Screw Placement for Atlantoaxial Fixation Result in a Superior Outcome?: A Systematic Review of the Literature and Meta-analysis.

Systematic review and meta-analysis. To evaluate the clinical and functional outcomes of transection of the C2 roots during C1 lateral mass screw placement for atlantoaxial fixation. Transection of the C2 nerve roots has been recommended during atlantoaxial fixation to facilitate C1 lateral mass screw placement and possibly reduce postoperative occipital neuralgia, although this practice remains controversial. We searched MEDLINE, EMBASE, Web of Science, and the Cochrane Library for studies evaluating the outcomes of C1-2 fixation involving sacrifice of the C2 roots. We calculated transformed proportions with 95% confidence intervals (CI) for the outcomes of occipital neuralgia, numbness, bony fusion, and procedural morbidity. For studies comparing C2 transection with nerve sparing surgery, we performed meta-analyses for the outcomes of occipital neuralgia, occipital numbness, blood loss, and operative time. Eight observational studies (N = 393) met eligibility criteria. The rate of postoperative occipital neuralgia among included studies was 0% to 25%; occipital numbness, 6.7% to100%; bony fusion, 96.7% to 100%; and procedural morbidity, 0% to 14.3%. Among comparative studies, C2 transection was associated with a higher rate of occipital numbness [odds ratio (OR) 178.6 (95% CI 26.6 to 1198.4)], lower blood loss [mean difference (MD) -195.3 mL (95% CI -317.7 to -72.8 mL)] and shorter operative times [MD -57.5 mins (95% CI -76.9 to -38.2 mins)] than when the C2 roots were spared. We found no difference in rates of occipital neuralgia [OR 1.44 (95% CI 0.45 to 4.68)]. Transection of the C2 nerve roots appears to be a viable, safe option when undertaking placement of C1 lateral mass screws. The procedure is associated with reduced operative duration and blood loss, increased rate of occipital numbness, and no change in the rate of occipital neuralgia. However, given the relatively low quality of evidence, prospective, controlled studies to evaluate this strategy are recommended. N /A.

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.

C2 and Greater Occipital Nerve: The Anatomic and Functional Implications in Spinal Surgery.

IntroductionPosterior C1-C2 fusion is a highly successful treatment for atlantoaxial instability and other pathologies of the cervical spine, with fusion rates approaching 95%-100%. However, poor visualization of the lateral masses of C1 secondary to the course of the C2 nerve root along with blood loss from the venous plexus and compression of the C2 nerve from lateral mass screws are technical obstacles that can arise during surgery. Thus, sacrifice of the C2 nerve root has long since been debated in fusions involving the C1 and C2 vertebral bodies. MethodsCadaveric dissections on four adult specimens were performed. Both intradural and extradural courses of C2 were studied in detail. The tentative site of C2 nerve root compression during placement of C1 lateral mass screws was studied in detail. Both the indication as well as the ease of C2 neurectomy were studied in relation to postoperative compression and entrapment.ResultsFour-six dorsal rootlets of C2 nerve were observed while studying the intradural course. The extradural course was studied with respect to the lateral mass of C1. The greater occipital nerve (GON) course was fairly consistent in all specimens. Transection of C2 around its ganglion would allow for proper C1 lateral mass screw placement as the course of C2 nerve interferes with proper placement of instrumentation.ConclusionC2 nerve root transection is associated with occipital numbness but this often has no effect on health-related quality of life (HRQOL). The C2 nerve root preservation is often associated with entrapment neuropathy or occipital neuralgia, which greatly affects HRQOL. The C2 nerve root transection helps in better visualization, aids in optimal placement of C1 lateral mass screws, minimizes estimated blood loss and improves surgical outcome with successful fusion.

Is C1 lateral mass screw placement safe for the Chinese, Indians, and Malays? An analysis of 180 computed tomography scans.

C1 lateral mass (C1LM) screw is a common procedure in spine surgery. However, related studies are lacking in Asia. We aim to determine the safety of C1LM screw for the Chinese, Indians, and Malays. Three-dimensional computed tomographies of 180 subjects (60 from each ethnic) were analyzed. The length and angulations of C1LM screw and the location of internal carotid artery (ICA) in relation to C1LM were assessed and classified according to the classification by Murakami et al. The incidence of ponticulus posticus (PP) was determined and the differences among the population of these three ethnics were recorded. The average base length was 8.5 ± 1.4 mm. The lengths within the lateral mass were between 14.7 ± 1.6 mm and 21.7 ± 2.3 mm. The prevalence of PP was 8.3%. 55.3% (199) of ICA were located in zone 0, 38.3% (138) in zone 1-1, 6.4% (23) in zone 1-2, and none in zone 1-3 and zone 2. The average angulation from the entry point to the ICA was 8.5° ± 6.4° laterally. The mean distance of ICA from C1 anterior cortex was 3.7 ± 1.7 mm (range: 0.6∼11.3). There was no difference in distribution of ICA in zone 1 among the three population (Chinese-47%, Indians-61%, and Malays-53%; p > 0.05). No ICA is located medial to the entry point of C1LM screw. If bicortical purchase of C1LM screw is needed, screw protrusion of less than 3 mm or medially angulated is safe for ICA. The incidence of PP is 8.3% with higher prevalence among the Indian population.

Detethering of the C2 Nerve Root and Avoidance of Transection and Injury During C1 Screw Placement: A Cadaveric Feasibility Study

Regional neurovascular structures must be avoided during invasive spine hardware placement. During C1 lateral mass screw placement, the C2 nerve root is put in harm's way. Therefore the current anatomic study was performed to identify techniques that might avoid such neural injury. On 10 cadaveric sides, dissection was carried down to the craniocervical junction. The C2 nerve root was identified, and its distal branches were traced out into the surrounding posterior cervical musculature. Once dissected, the nerve was displaced inferiorly away from the lateral mass of C1. On all sides, the C2 nerve root could be easily detethered from surrounding tissues. On all sides, this allowed lateral mass screw placement without compression of the nerve. On the basis of our cadaveric study, the C2 nerve root can be detethered enough at the level of the posterior lateral mass of C1 to avoid its injury during screw placement into this area.

C2 nerve dysfunction associated with C1 lateral mass screw fixation.

The C1 lateral mass screw technique is widely used for atlantoaxial fixation. However, C2 nerve dysfunction may occur as a complication of this procedure, compromising the quality of life of affected patients. This is a review of the topic of C2 nerve dysfunction associated with C1 lateral mass screw fixation and related research developments. The C2 nerve root is located in the space bordered superiorly by the posterior arch of C1 , inferiorly by the C2 lamina, anteriorly by the lateral atlantoaxial joint capsule, and posteriorly by the anterior edge of the ligamentum flavum. Some surgeons suggest cutting the C2 nerve root during C1 lateral mass screw placement, whereas others prefer to preserve it. The incidence, clinical manifestations, causes, management, and prevention of C2 nerve dysfunction associated with C(1) lateral mass screw fixation are reviewed. Sacrifice of the C2 nerve root carries a high risk of postoperative numbness, whereas postoperative nerve dysfunction can occur when it has been preserved. Many surgeons have been working hard on minimizing the risk of postoperative C2 nerve dysfunction associated with C1 lateral mass screw fixation.

Ideal screw entry point and optimal trajectory for anterior C1 lateral mass screw: an anatomical study

To explore the ideal screw entry point and optimal trajectory for anterior C1 lateral mass screw internal fixation, and provide an anatomical basis for the technique of anterior C1 lateral mass screw placement. A radiographic analysis of the anatomy of the C1 lateral mass using Computed tomography, CT scan was performed in cervical spine of 56 healthy Chinese adults (28 males, 28 females; mean age, 36.5 years; age range, 18-55 years), by using the Mimics software to reconstruct the 3-D morphology of C1 lateral mass and measuring the inside, middle and outside effective height of the C1 lateral mass in front and back. Measuring the C1 lateral mass safe width with different extraversion angles range from 0° to 30° with a uniform interval of 5°, to find out the ideal extraversion angle. Measuring the range of sagittal angle, to find out the ideal sagittal angle. The inside (H1), middle (H3) and outside (H5) effective height of the C1 lateral mass in front is 6.67 mm, 12.09 mm, and 17.51 mm, the inside (H2), middle (H4) and outside(H6) effective height of the C1 lateral mass in back is 8.17 mm, 13.20 mm, and 18.22 mm. When the extraversion angle choose 0°, 5°, 10°, 15°, 20°, 25°, 30°, and δ, the relative results of safe width (SW) of lateral mass were 4.73 mm, 5.36 mm, 5.90 mm, 6.33 mm, 6.44 mm, 5.70 mm, 4.38 mm, 6.95 mm averagely. The mean distance along the atlas anterior surface between the anterior tubercle and the screw entry point was 12.80 mm, the mean distance from the inferior border of the lateral mass to the screw entry point was 6.87 mm. The range of sagittal angle is 24.22° (-17.74°∼6.48°) . The ideal extraversion angle was 21.14°. The mean distance along the atlas anterior surface between the anterior tubercle and the screw entry point was 12.80 mm. The mean distance from the inferior border of the lateral mass to the screw entry point was 6.87 mm. The ideal sagittal angle is -5.63°. These measurements may facilitate anterior C1 lateral mass screw fixation decreasing the risk of injury to the spinal cord, vertebral artery, and internal carotid artery theoretically. Delineating the individual anatomy in each case with CT scan before surgery is recommended.

C1 lateral mass screw placement via the posterior arch: a technique comparison and anatomic analysis

Background contextInstrumentation of C1 is becoming increasingly common. Starting points initially described for C1 lateral mass screws at the lateral mass/posterior arch junction are technically challenging. Recently, a number of techniques have evolved advocating varying starting points and trajectories. Despite being technically easier, there are new safety concerns. Insufficient evidence exists for optimal C1 lateral mass screw placement with starting points in the posterior arch. PurposeTo determine anatomic variability of the C1 lateral mass and posterior ring and to compare safety and feasibility of C1 lateral mass screw placement techniques via the posterior arch. Study designDescriptive anatomy for surgical technique. MethodsOne hundred thin-cut cervical spine computed tomography scans were acquired and formatted for virtual surgery. Four different described techniques were used for virtual placement of C1 lateral mass screws. Success was defined as avoidance of critical structures including the transverse foramen, vertebral groove, and spinal dura. Anatomic variability of the C1 vertebra and safe zones for screw placement were also clarified. ResultsOverall screw placement success for the four techniques was 50% (Resnick), 92% (Tan et al.), 58% (Ma et al.), and 85% (Christensen et al.). Average posterior arch height was 6.7±2.1 mm, and vertebral groove height 4.9±1.1 mm was the most limiting dimension to safe screw placement. A safe zone for screw placement was found in 100% of cases (200 screws), 17.0±1.1 mm from midline and a width of 12.6±1.7 mm. Posterior tubercle morphology was variable. ConclusionsC1 lateral mass screws could be virtually placed bilaterally in each of 100 clinical cases without violating critical structures. However, none of the previously described approaches worked in every case because of significant anatomic variability. The vertical starting point was particularly critical, and vertebral groove height was the most limiting variable. Although a reliable safe zone could be found in every case, preoperative planning is essential to avoid critical structures.

Subarachnoid Hemorrhage and Acute Hydrocephalus as a Complication of C1 Lateral Mass Screws

Case report. To present a previously unreported complication of subarachnoid hemorrhage and hydrocephalus after C1 lateral mass screw insertion. To inform spine specialists of this potential postoperative complication. Damage to the carotid artery, vertebral artery, hypoglossal nerve and dural tears are all recognized complications. Acute hydrocephalus as a result of subarachnoid hemorrhage is not previously reported. A 63-year-old female with a traumatic C1 ring and C2 peg fracture underwent C1-C2 fixation. During insertion of the C1 lateral mass screws there was significant hemorrhage from the C1-C2 venous plexus. Three days postoperatively, she developed headache, confusion, and became drowsy. Computed tomographic scan of the brain revealed hydrocephalus and intraventricular blood that was managed with an external ventricular drain. The case of acute hydrocephalus due to intraventricular hemorrhage from C1 lateral mass screw placement has not previously been reported. Surgeons performing the procedure should consider the diagnosis if patients display signs of raised intracranial pressure postoperatively. N/A.

Isocentric C-arm 3D navigation versus conventional C-arm fluoroscopy for placement of C1 lateral mass and C2 pedicle screws in treatment of atlantoaxial instability

Objective To compare the isocentric C-arm 3-dimensional （lso-C 3D） navigation versus conventional C-arm fluoroscopy in terms of accuracy of placing CI lateral mass and C2 pedicle （C1LM-C2P） screws in the treatment of atlantoaxial instability. Methods Thirty patients with atlantoaxial instability were treated with fixation with CI I,M-C2P screws in our hospital from June 2006 to June 201 I. They were 16 men and 14 women, aged frnm 39 to 52 years （average, 45.6 years）. The Iso-C 3D navigation group had 14 patients and there were 16 patients in the conventional fluoroscopy group. The 2 groups were comparable in general clinical data （ P 〉 0.05） . The operation time, radiation time, intraoperative blood loss, insertion accuracy and Japanese Orthopaedic Association （JOA） score were recorded and compared between the 2 groups. Results There were no significant differences between the 2 groups in the mean operation time （132. 1 ±6.4 minutes versus 143.2 ±8.2 minutes） （ t = 1. 761, P =0. 093） . The mean radiation time for the lso-C 3D navigation group （46.8 ± 1.4 seconds） was significantly shorter than for the conventional fluo- roscopy group （65.2±2.9 seeomts）, the mean blood loss for the navigation group （305.6 ±50.8 mL） was significantly less than for the fluoroscopy group （472.4± 56. 1 mL）, the percentage of screws of grade 0 forthe navigation group （94. 6% ） was significantly higher than for the fluoroscopy group （82.8%） （ P 〈 0. 05 ） . The mean follow-up of 12.4 months revealed fracture union on cervical X-ray films 6 months post- operation. There were no significant differences between the 2 groups in the mean JOA score 6 months post- operation （15.2± 0. 2 points versus 15.3 ± 0. 3 points）, but there were significant differences between the preoperative and postoperative scores in the 2 groups （ P 〈 0.05）. Conclusion In the treatment of at- lantoaxial instability with fixation with C1LM-C2P screws, compared with conventional C-ann fluoroscopy, Iso-C 3D navigation can significantly improve the accuracy of screw placement and reduce intraoperative flu- oroscopic time and blood loss. Key words: Atlas; Axis; Surgery, computer-assisted; Bone nail

Routine sectioning of the C2 nerve root and ganglion for C1 lateral mass screw placement in children: surgical and functional outcomes

Adult studies have shown that sectioning the C2 nerve root and ganglion may facilitate placement of C1 lateral mass screws and lead to decreased operative time and blood loss. We report the functional outcomes and complications following routine sectioning of the C2 nerve root and ganglion, which have not been reported in pediatric patients. Fifteen consecutive pediatric patients underwent C1 lateral mass screw insertion and bilateral C2 nerve root and ganglion sectioning. Clinical and radiographic assessments were performed at follow-up. Numbness in the C2 distribution and/or occipital neuralgia, operative times, estimated blood loss (EBL), length of stay (LOS), and complications were recorded. Average follow-up time was 35.7months. Overall mean operative time was 250.5min, LOS was 8.46days, and EBL was 337cc. When considering only atlantoaxial fusions, mean operative time was 180.7min and EBL was 97.1cc. There were no intraoperative complications, and no patient reported new onset occipital neuralgia or numbness in the C2 distribution that would interfere with daily living. Of the patients, 93% achieved Lenke fusion grade A; one achieved Lenke fusion grade B. Routine C2 nerve root sectioning and ganglionectomy enhanced surgical exposure of the C1 lateral mass and C1-2 facet joint, potentially maximizing fusion rate and minimizing intraoperative complications. This technique may yield favorable operative times, EBL, and LOS in children undergoing C1 lateral mass screw insertion without negatively affecting functional outcome.

Feasibility and limitations of C1 lateral mass screw placement in patients of atlas assimilation

BackgroundC1 lateral mass is a common place for screw fixation in normal anatomy; whereas there is no research about whether screw placement is suitable in patients of C1 assimilation (C1A). ObjectiveTo study the feasibility and limitations of C1 lateral mass screw placement in patients with C1A. Patients and methodsFrom April 2008 to March 2009, C1 lateral mass of 17 C1A patients with atlantoaxial instability (AAI) or dislocation (AAD) was observed and measured using CT reconstruction; and factors determining C1 lateral mass screw placement were studied before and during the operation. ResultsA screw of 3.5mm in diameter could be virtually inserted in 31 C1 lateral masses of total 17 C1A patients with maximal length of the screw 18.1±2.7mm; but the entry point of screw had to be modified in the posterior part of inferior facet of C1 instead of posterior middle wall of C1 lateral mass. Clinically, abnormal course of vertebral artery in 6 of 30 (20%) and abundance of venous plexi prevented the proper exposure of C1 lateral mass and screw placement. Hypoglossal canal also had potential risk of injury during screw placement. ConclusionIn patients of C1A, when C1 lateral mass screw placement is programmed, factors limit its use should be well studied, and CT angiography is essential.

C1 lateral mass screw placement with intentional sacrifice of the C2 ganglion: functional outcomes and morbidity in elderly patients

Placement of C1 lateral mass screws may be facilitated by intentional C2 root sacrifice. Functional outcomes and morbidity following intentional sacrifice of the C2 root have not been reported in the literature. The objective is to find out if intentional C2 nerve root sacrifice affects functional outcomes and operative morbidity in patients undergoing posterior cervical fusion with C1 lateral mass screws. The study is a case report. Twenty-two consecutive elderly patients (10 males, 12 females with an average age of 77 years) with C1-2 instability were treated with posterior cervical fusion using C1 lateral mass screw placement. Five patients had preservation of the bilateral C2 nerve roots (PRES group) and 18 patients had intentional sacrifice of the bilateral C2 nerve root (SAC group). Operative times, blood loss, hospital length of stay, and complications were recorded for each patient. Functional outcomes, pain, and satisfaction scores were compared between the two groups at the time of ultimate follow-up. Average follow-up time was 19.3 months (range 6-66). The SAC group demonstrated significantly decreased operative time (109.4 vs. 187 min) and a trend towards decreased blood loss (344 vs. 1,030 mL). At ultimate follow-up both groups experienced similar mild disability with no significant difference in NDI scores, analog pain, and satisfaction scores. No patient had C2 root dysesthesia, swallowing, or speech difficulty. In this small case series, intentional sacrifice of the bilateral C2 nerve root ganglion resulted in less operative time and decreased blood loss in elderly patents undergoing C1-2 posterior fusion with the Harms technique. Functional outcome, pain and satisfaction scores were not adversely affected when this technique was used in elderly patients.

IMPORTANCE OF THE C1 ANTERIOR TUBERCLE DEPTH AND LATERAL MASS GEOMETRY WHEN PLACING C1 LATERAL MASS SCREWS

We measured the variability in the size of the anterior tubercle of C1 and the optimal depth and angle of placement of C1 lateral mass screws using axial and sagittal reconstructed computed tomographic scans to determine the utility of these parameters for preoperative planning and intraoperative guidance. One hundred consecutive cervical spine computed tomographic scans were reviewed (mean patient age, 44.6 years; age range, 7-96 years). The size of the anterior tubercle of C1, bilateral depths of optimal screw placement in the axial and sagittal planes, and optimal angles of placement in the axial and sagittal planes were measured in a standardized manner using the measuring tool included in our radiology server software. These measurements were correlated with age and sex. The mean depth of the C1 tubercle was 6.9 mm (range, 2.7-11.2 mm; standard deviation, 1.7 mm). The depth of the C1 tubercle tended to increase with age, but the relationship was not significant. The optimal screw depth in the sagittal plane was significantly greater than in the axial plane (right 2.09 versus 1.93 cm; left 2.07 versus 1.91 cm). The depth of the right lateral mass increased significantly with age. No other relationships reached significance. The depth of the anterior tubercle of C1 varies considerably and should be studied carefully before using lateral fluoroscopy of this structure to guide depth of C1 lateral mass screw placement. Optimal angles and depths of placement of C1 lateral mass screws vary widely and should be examined preoperatively to plan appropriate depth and trajectory.